16 Biomechanical Factors

The 16 Biomechanical Factors in the Application of Resistance Exercise for the Purpose of Optimal Muscle Loading and Development

(aka “Brignolean Principles of Biomechanics”)

by Doug Brignole
March 2021

Careful analysis of the many resistance exercises that have been traditionally used in the pursuit of “fitness” or “bodybuilding”, viewed through the lens of biomechanics, reveals that many of them are not as good as we’ve been lead to believe. In fact, the value of an exercise can be assessed using biomechanical, physiological and neurological factors in three categories:

A.   Efficiency: How mechanically efficient an exercise is—referring to the amount of load a muscle receives versus the amount of weight that is required in order to deliver that amount of muscle load. This is based on physics….“energy cost / effort – vs – muscle load / benefit”.

B.  Productivity: How efficacious an exercise is—referring to physiological factors that include range of motion; how precisely the exercise mimics the target muscle’s ideal anatomical motion; whether the exercise’s “resistance curve” matches the target muscle’s “strength curve”; whether the target muscle is positioned in the line of force (aligned with the direction of resistance); whether or not various neurological conflicts are occurring; etc.

C.  Safety: How safe the exercise is—referring to whether or not the exercise requires an unnatural joint motion or an excessive amount of joint rotation; whether or not the spine is excessively / unnecessarily loaded; whether or not the exercise requires excessive participation from weaker non-target muscles; whether there is a “mechanical disadvantage” (double magnification) occurring at a vulnerable moment in the range of motion, etc.

This does not suggest that exercises which fail to fully comply with the 16 factors have no value. They may still produce some degree of muscle development. It’s not “all-or-nothing”. Exercises vary in their degree of efficiency, productivity and safety. An exercise that is compromised to some degree, may still be reasonably good—although not “as good” as it could be. It may be less productive, less efficient, or less safe—as compared with an exercise which fully complies with all the factors. This is not a matter of opinion. It’s quantifiable, and can be easily demonstrated. Each exercise can be rated using this set of biomechanical factors as a checklist.

Many of the beliefs regarding “traditional” exercises have been based on dogma and emotional bias, rather than on physics, biomechanics or logic. Sociological factors, economic factors (i.e., commercialization), miscalculation and misinterpretation have exacerbated the confusion. These misguided beliefs include the following:

  1. “Compound” exercises are always better than “isolation” exercises. This is false. Compound exercise “can” be good for certain applications, but they are generally not better than isolation exercises for muscle development.
  2. The amount of weight lifted during an exercise accurately reflects the amount of load a muscle receives. This is also false.
  3. An exercise used by a person with an outstanding physique is “proof” of the efficacy of that exercise. False.
  4. Exercises shown or recommended in commercial fitness publications are “probably good”, and the belief that commercial fitness magazines are “scientific journals”—dedicated to consumer education, rather than profit. Neither is true.
  5. Trainers and physical therapists are all well-informed. In fact, many trainers and physical therapists are themselves misled by the commercialized fitness industry.

The human musculoskeletal system is essentially a collection of pulleys (muscles), levers (bones / limbs) and pivots (joints). Therefore, as with all things mechanical, the laws of physics apply during all resistance exercises.

Using physics (“classical mechanics”), the approximate amount of muscle load versus the amount of weight being lifted (as a percentage) can be calculated.

A muscle only recognizes the amount of force it is required to produce. It does not “know” how much weight is actually being lifted. This is because a muscle cannot pull directly on a weight. Rather, a muscle pulls on the bone (the limb) which is holding the weight. The length of that limb, the angle of that limb relative to the direction of resistance, and the angle of a “secondary” limb (e.g., a forearm) which is attached to the “primary” limb (e.g., an upper arm bone), all influence the amount of load that is delivered to the corresponding muscle, in conformance with the laws of physics.

A muscle could be loaded with 90 pounds of resistance—manifested as 90% of 100 pounds being lifted, or as 30% of 300 pounds being lifted. The difference depends on the “moment arm” (a physics terms referring to lever magnification), which is determined by the length of the limb involved, as well as the angle of that limb relative to the direction of resistance.

In addition, the direction of anatomical motion and the direction of resistance (relative to the position of the target muscle) also play critical roles in determining how efficacious an exercise is—as well as safe it is.

Further still, there are several physiological and neurological factors that play a role in resistance exercise. Sometimes theses factors interfere with optimal muscle engagement, so it is prudent to know how to determine which exercises cause those conflicts. Only then, can informed exercise-selection decisions be made.

For these reasons, it is important to understand the factors which optimize or compromise the benefits and risks of every resistance exercise.

Resistance exercise is governed by this set of 16 principles, which allow a person to logically evaluate each resistance exercise. An exercise with higher compliance of these principles has a higher value—in terms of muscular development benefit, energy cost, and safety. An exercise with lower compliance of these factors has a lower value.

The 16 Biomechanical Factors

1.  Ideal Directions of Anatomical Motion

The ideal direction of anatomical / musculoskeletal motion is one that moves the target muscle’s insertion directly toward that muscle’s origin, upon concentric contraction of that muscle. Then, upon eccentric contraction of that muscle, the insertion of that muscle is moved directly away from that muscle’s origin. This determines the ideal trajectory of the limb being operated by the target muscle. A muscle can participate in other motions—along with other participating muscles—but in diminishing percentages.

Performing the precise anatomical motion that a muscle is meant to produce (i.e., pulling its corresponding limb directly toward its origin), is generally more productive (for that particular muscle) than performing an anatomical motion that departs from that precise motion. A motion that is “similar” (close) to the precise motion of the target muscle, but not precisely that muscle’s primary action, would naturally require more participation from other muscles, and less from the target muscle.

When an exercise (an anatomical motion) precisely mimics that of the target muscle, the effort of that motion is not “shared” (as much) with other muscles, so the target muscle’s required force is not diluted.

In addition, the range of motion of the target muscle is likely to be less than full-range, if the motion is not precise. This is because the target muscle’s insertion is not able to move as close to its origin (upon concentric contraction), nor as far from its origin (upon eccentric contraction), as the target muscle’s precise function would allow.

The degree to which an anatomical motion (i.e., during an exercise) differs from that which directly moves the operating limb toward the target muscle’s origin, is matched by a commensurate reduction of that muscle’s participation. The more the anatomical motion differs from a target muscle’s precise motion, the less that muscle participates in that motion.

An example of an improper direction of anatomical motion is an “Incline Press”—intended for the Pectorals—regardless of whether it’s performed with dumbbells, a barbell or a machine.

During an Incline Press exercise, the arms (i.e., the Pectoral insertion on the humerus) are moved in a direction that is above (“superior” to) the shoulder joint—essentially toward the neck or the chin. However, there are no Pectoral origins above the shoulder joint, nor above the clavicles—certainly none on the neck or chin. All of the Pectoral origins are located either at the same level as the shoulder joint, or below (“inferior” to) the shoulder joint.

Moving the arms directly toward the origin of the highest Pectoral fibers on the sternum (i.e., the sternal fibers), as well as toward those on the clavicles (i.e., the clavicular fibers), would move the arms in a direction that is typically used during a Supine (flat bench) Press—in a direction that is perpendicular to the torso. In other words, a Supine (flat bench) Dumbbell Press is an “upper chest” exercise. An Incline Press is not a sensible exercise for the pectorals, because it does not move the arms directly toward any pectoral fiber origins.

Moving the arms in an “incline” direction (above the shoulders) would only make sense if the arms were attached to the torso midway between the highest and the lowest part of the Pectorals—but they are not. The arms are attached to the torso at the highest part of the Pectorals. All the Pectoral fiber origins are situated below the shoulder joint and clavicles.

2.  Utilizing Optimal Range of Motion

The ideal range of motion for an exercise targeting a particular target muscle, is one that utilizes all—or most—of that muscle’s motion capacity. This would cause complete, or mostly complete, muscle contraction (shortening), as well as complete, or mostly complete, muscle elongation (lengthening / stretching). Performing an exercise with mostly full range of motion has been shown to be significantly more productive than performing an exercise with partial range of motion. This was proven true even when more weight is used during the partial range of motion, and and less weight with full range of motion.

         2B.  A resistance exercise that incorporates no skeletal motion (aka “static exercise”) utilizes isometric muscle contraction. Isometric contraction produces no skeletal motion, and results in no muscle shortening nor elongation. Rather, the muscle is simply required to hold a particular joint / skeletal position, against resistance.

Isometric muscle contraction has been demonstrated to be significantly less productive than dynamic muscle contraction (with joint motion / with muscle elongation and shortening), for the goal of strength development through a muscle’s entire range of motion, and also for visible muscle hypertrophy.

Given that “partial range of motion” is less productive than “full range of motion”, it stands to reason that “no range of motion” would be even less productive than “partial range of motion”. An ideal exercise, therefore, is one that utilizes dynamic muscle contraction (full, or mostly full, range motion)—avoiding “partial range of motion” as well as “no range of motion.”

3.  Avoiding Neurological Conflict of Interest

“Reciprocal inhibition” is a mechanism whereby the Central Nervous System (CNS) reduces or completely inhibits the innervation of an antagonist muscle when the agonist muscle is activated. An example of this is that triceps innervation is inhibited (shut off) off when the biceps is loaded and engaged. This prevents the triceps from interfering with the activation of the biceps (i.e., the biceps is the agonist and the triceps is the antagonist, in this case). Reciprocal inhibition thus allows a body to be coordinated—to not interfere with itself when performing physical tasks.

However, in some cases during some compound exercises, a muscle which we intend to target (i.e., an agonist), is forced to be the antagonist of another muscle, which we are also intending to target. When this happens, that muscle—the one you intend to target—is forced to relax, despite your intentions. This results in compromised benefit and wasted effort.

Specifically, this happens when one of the participating muscles is “bi-articulate” (crosses two joints, and serves two functions) and you are performing a multi-joint (two function) exercise—one of which opposes the other. Examples of this are Barbell Squats, Leg Press or any other exercise that combines simultaneous knee extension and hip extension. Gluteus activation (hip extension) shuts off the hip flexors, one of which is part of the Quadriceps (i.e., the Rectus femoris).

Given that Squats and Leg Presses are typically performed with the intention of optimally stimulating the Quadriceps, it is counterproductive to cause a significant portion of the Quadriceps to de-activate, by simultaneously activating the Gluteus.

In addition to the de-activation of the Rectus femoris, Squats and Leg Presses also trigger the de-activation of the Hamstrings, caused by the activation of the Quadriceps. The Hamstrings (i.e., knee flexors) are the antagonist of the Quadriceps (i.e., knee extensors), so they receive a “relaxation synapse” from the Central Nervous System when the Quadriceps are activated. This prevents interference of the Quadriceps, but compromises hip extension.

The Hamstrings is a bi-articulate muscle. It flexes (bends) the knee joint, and has the secondary function of assisting in hip extension because it also crosses the hip joint. Thus, when the Hamstrings are “inhibited” as a result of Quadriceps activation, they are unable participate in hip extension.

For this reason, the knee extensors (Quadriceps, including the Rectus femoris) would be activated more effectively without the simultaneous activation of the hip extensors, and hip extension would be activated more effectively without the simultaneous activation of the Quadriceps. Isolating each of these two joint functions would avoid the neurological interference caused by combining the two joint functions simultaneously.

This does not mean that Squats have no value. It simply means that muscle development of the Quadriceps and of the hip extensors—achieved by way of  Squats—is less than optimal, as compared with isolation exercises. Squats (and other compound leg movements) DO have proprioceptive value, which is useful in sports and activities that involve movements similar to Squats.

4.  Ensuring Sufficient Length of the “Active” Muscle

Muscles that are bi-articular (i.e., muscles which cross two joints, instead of only one joint) are subject to having their length increased or decreased, based on the position / angle of their “non-primary” (secondary) joint.

For example, the biceps crosses the elbow joint and the shoulder joint. The primary joint is the elbow, because the primary function of the biceps is elbow flexion. Its non-primary joint is the shoulder, because the shoulder joint is moved primarily by the pecs and/or deltoids.

However, the length of the biceps is influenced by the position (the angle) of the shoulder joint. If the shoulder joint is positioned such that the arm is extended posteriorly, the biceps is elongated—the insertion of the biceps is moved farther away from its origin.

If the shoulder joint is positioned such that the arm is held directly in front of you, or up alongside your head, the biceps is shortened—the biceps’ insertion is moved closer to its origin.

Because skeletal muscles contract as a result of actin filaments sliding together, there is an optimal length at which a muscle has its greatest contractile force potential. Generally speaking, a muscle is stronger when it is elongated and it is weaker when it is shortened. A muscle has the least strength potential when it’s over-shortened.

This is known as “active insufficiency”. It’s referred to as the “active” muscle because it’s the muscle doing the work, and it experiences compromised strength when it has “insufficient” length.

For this reason, a bi-articulate muscle (e.g., primarily the biceps and hamstrings) should ideally be exercised without the over-shortening that is caused by the position of the secondary joint, causing its origin to be brought too close to its insertion. Ideally, a bi-articulate target muscle should have its non-primary joint positioned such that it allows the target muscle to have sufficient length, thereby allowing optimal strength potential during the exercise.

5.  Avoiding Excessive Stretch of the Antagonist Muscle

As described above, muscles that are bi-articular (i.e., muscles which cross two joints, instead of only one joint) are subject to having their length increased or decreased, based on the angle of their “non-primary” joint.

In the above example, the issue was the over-shortening of the bi-articular active muscle (the muscle doing the work). However, a bi-articular muscle can also be over-stretched when it is the “passive” muscle—positioned opposite the “active” (agonist) muscle.

This is called “passive insufficiency”. It is referred to as “passive” because it is the muscle that is NOT actively working, and it is “insufficient” because its excessive stretching prevents the active muscle from being able to complete its range of motion with full force.

One example of this occurs when hip flexion is performed with a straight knee. 

Flexing the hip while keeping the knee straight would maximally stretch the hamstrings. This typically prevents the hip from flexing as much (with as much ROM) as it could if the knee were bent.

In the image above-left, you can see how a person would need to compensate for this “conflict of interest” by rounding the spine. Doing so lessens the degree of hamstrings stretch, although the remaining hamstring stretch would still limit the degree of hip flexion that is possible.

Also, there appears to be a degree of inhibited innervation of the hip flexors, caused by the CNS trying to prevent the over-stretching of the hamstrings. The solution, in this case, is to simply bend the knee as you flex the hip. Adding resistance (an ankle weight) to compensate for the shorter lever length (“moment arm” of the leg, from hip joint to foot) is an option.

Another example of “passive insufficiency” is the excessive stretching of the hamstrings which sometimes occurs during Seated Leg Extensions, if the hip joint is excessively flexed. This would occur if the person is seated very upright (perhaps even leaning forward in the seat), as the knees are extended.

Note: The degree to which Passive Insufficiency is triggered depends on each person’s degree of flexibility. People who are very flexible will experience less Passive Insufficiency, while people with limited flexibility will experience more Passive Insufficiency.

The solution, in this case, is to modify the Leg Extension exercise such that the hip angle is less bent (i.e., less “flexed”). Leaning farther back (reclining) on the Leg Extension machine seat, lessens the degree of hip flexion, which lessens the degree of hamstrings stretch that occurs when the knees are fully extended.

6.  Favoring Unilateral Loading

There is a significant difference between using a barbell, versus using dumbbells, in terms of muscle loading. Independent loading (using dumbbells or cables) is far more advantageous than using a single instrument (barbells or machines that use a single device / carriage for both limbs).

Independent limb loading produces greater coordination demand—as compared with using a barbell or a single instrument for both (right side / left side) limbs—and also requires distinctly different exercise mechanics.

For example, a Flat Bench Barbell Press prohibits you from being able to “pull” the hands and arms medially—toward the midline of the body. When using a barbell, your fixed hand position on the bar requires a more linear diagonal (slightly outward) “push”—which engages the triceps more by way of “friction force” (although arguably not enough to qualify as a “great” triceps exercise), and engages the pectorals less. It also compromises the pectorals’ range of motion, because you are unable to complete the final 30 degrees of the pectoral’s range of motion.

In addition, independent limb loading (using dumbbells or cables) triggers “cross education”, which causes an added strength and coordination benefit to cross over to the contralateral muscle, by the separate loading and activation of the ipsilateral muscle. Typically, the percentage of crossover benefit to the contralateral muscle ranges between 7% and 34% of the ipsilateral muscle benefit*.

*The Cross-Education Phenomenon: Brain and Beyond: 2017, Ashlee M. Hendy and Severine Lamon

Therefore, whenever it’s practical to do so, using unilateral muscle loading is ideal.

7.  Favoring Unilateral Muscle Activation, When Possible

“Bilateral exercise” is the term typically used when referring to muscle activation using both limbs with a single instrument, like a barbell. However, it’s also often used when referring to independently loaded (right side/left side) simultaneous muscle activation.

As explained in principle 6 above, separately loading each side is “better” than using a single instrument, even when both independently loaded sides are activated simultaneously. However, better still is activating only one side at a time, as compared with activating both (independently loaded) sides simultaneously.

The reason for this is due to a trait known as “bilateral deficit”, which causes each side to be a little bit weaker when working “bilaterally” (simultaneously), as compared when working “unilaterally”—one side at a time.

For example, performing Standing Dumbbell Curls with a pair of  25 pound dumbbells—engaging the left and right biceps simultaneously—is more difficult than performing Alternating Dumbbell Curls*—engaging only one biceps at a time (even though using the same weight).

The degree of strength reduction—apparently due to reduced muscle innervation as well as other execution factors—averaged up to 11.2%, according to one study*. The degree of strength reduction depends on various factors, including individual genetics, the particular muscle group being activated, and the age of the participant. Whatever the exact percentage, it seems there is always some degree of strength reduction that occurs when engaging contralateral muscles (left side and right side) simultaneously.

*Bilateral Deficit in Explosive Force Production Is Not Caused By Changes in Agonist Neural Drive: 2013 — Matthew W. Buckthorpe, Matthew T.G. Pain and Jonathan P. Folland

The broad recommendation, therefore, is to favor unilateral resistance exercise (one contralateral limb at a time) whenever it is practical to do so. This can be accomplished by alternating repetitions (i.e., left side, right side, left side, right side, etc.) or performing all the repetitions of one set with the right limb, followed by all the repetitions of that set with the left limb. This would allow each side’s working muscle to operate without compromise in strength capacity.

There is an exception to this recommendation, however.

In some situations, it is not practical to perform an exercise unilaterally—using only one limb at a time. For example, performing a heavy Flat Bench Dumbbell Press using one arm at a time, would result in significant instability, causing the person to be pulled off the bench toward the side that is more laterally weighted.

This type of exercise (Flat Bench Dumbbell Press) requires “counter-balancing”, in order to maintain stability. Any effort to compensate for the instability caused by performing a One Arm Flat Bench Dumbbell Press (i.e., using a lighter weight or lowering the arm closer to the side / closer to the midline of the body) would result in more diminished muscle loading than would be caused by the bilateral deficit triggered by engaging both arms simultaneously.

8.  Avoiding Limitation from Weaker Peripherally Recruited Muscles

Sometimes, when attempting to target a particular muscle, another muscle that is engaged in assisting or maintaining posture (i.e., but is not the target muscle) will fatigue/fail first—causing the set to end before the target muscle has been effectively challenged.

One example of this is the inevitable over-participation of the Anterior deltoids, during Parallel Bar Dips. Due to the mechanics of the exercise, the Anterior deltoids are loaded more than the pectorals and more than the triceps—despite the Anterior deltoids not being the priority muscle of the exercise. The Anterior deltoids are also weaker (have less strength capacity) than either the pectorals or the triceps. The result of this that they fail first, before the target muscles have been  fully challenged. In addition, the Anterior deltoids incur a significant injury risk due to being overloaded and over-stretched.

Another example is Deadlifts. The Erector spinae has less strength capacity than do the hip extension muscles (gluteus, adductors and hamstrings), and they are arguably challenged more than the hip extension muscles due to the length of the torso, as compared to the length of the femurs. As a result, the Erector spinae fatigues / fails before the gluteus / hip extensors are maximally challenged.

Another example is Bent Over Barbell Rows. The Erector spinae is loaded more than the Latissimus or the Middle Trapezius, and fatigues / fails before the target muscles are maximally challenged.

An ideal exercise, therefore, is one that minimizes the excessive simultaneous participation of weaker, non-target muscles (“peripheral recruitment”) because it limits the maximum engagement of the target muscle. Avoiding peripheral recruitment also decreases the risk of injuring the weaker, non-target muscle(s).

This is a common problem associated with “compound exercises”. Because they engage various muscles simultaneously—and each to the degree dictated by the physics of the exercise, not per the prioritization of the person doing the exercise—the weaker muscle fails first, despite it not being the target muscle.

9.  Avoiding Unnatural Joint Torque and Unnecessary Spinal Loading

The human musculoskeletal system evolved over millennia to accommodate routinely necessary anatomical motions. As such, an ideal exercise would mimic those natural motions, thereby allowing joints to move without strain—as they were meant to move. However, many traditional exercises do not mimic “natural” anatomical motions.

A “natural” motion could be defined as one that our early ancestors “needed” to do routinely, with a degree of force. It could also be defined as one that does not have a significant tendency to cause orthopedic stress, or one which can be easily performed by the vast majority of people, without joint discomfort.

An exercise performed for the purpose of muscular development does not require that a joint to be moved beyond its mobility limits, nor causes the intervertebral discs of the spine to be excessively compressed or distorted (overly flexed / extended).

One example of “unnatural joint torque / joint distortion” is the excessive external rotation of the humerus, as well as impingement of the Supraspinatus tendon and Subacromial bursa, that occurs during Overhead Pressing movements.

The Glenohumeral joint (i.e., the shoulder joint, which is compromised of the humeral head and the glenoid cavity in which it sits) has mobility limits. The maximum degree of external humeral rotation when the arm is “abducted” (away from the side of the body) is usually between 70 degrees and 80 degrees (i.e., 90 degrees would result in a perfectly vertical forearm, when the elbow is bent and the humerus is perpendicular to the torso). The exact limits of an individual’s shoulder mobility depends on their genetics, as well as their age and possibly also past injury. However, an Overhead Press essentially requires 90 degrees of external humeral rotation. It requires that the forearm be vertical.

A person whose limit of external humeral rotation is 80 degrees, would be unable to rotate his humerus externally enough to allow his forearm to be perfectly vertical (90 degrees) when the humerus is abducted (arm held perpendicular to the torso). A 70 degree or 80 degree angle (of the forearm) would result in a slight forward tilt to the forearm, which would cause an internal rotational force on the humerus. This would load the Infraspinatus (the primary external humeral rotator), in an effort to prevent the weighted forearm from rotating (“falling”) farther forward.

The Infraspinatus originates on the inner edge of the scapula (“C” below), and its fibers radiate laterally—across the scapula—and wraps around the humeral head. When the arm is down alongside the torso, the Infraspinatus is able to externally rotate the humeral head efficiently because the direction of the humeral rotation is toward the origins of the Infraspinatus. However, when the arm is perpendicular to the torso, the sagittal rotation of the humerus is NOT toward the origins of the Infraspinatus (…it is toward “B”, below) and thus requires significantly more force. This tremendously increased force requirement, during a typical Overhead Press movement, can easily injure the Infraspinatus.

Additionally, Overhead Pressing tends to cause impingement (pinching) of the Supraspinatus tendon, and also of the Subacromial Bursa (below). This occurs when the humerus is pushed upward, against the Acromion process of the scapula, which is being pressed down by the weight being lifted. The tendon and the bursa are caught (squeezed) in between the upward rising humerus and the downward pressed scapula.

Depending on the circumstances (i.e., the frequency of Overhead Pressing, the amount of weight used, individual genetic factors, etc.), this could lead to “Impingement Syndrome”, which is inflammation or rupture of the Supraspinatus tendon and/or of the Subacromial Bursa.

It’s important to note that an overhead pressing movement does not improve the mechanics of the Lateral deltoids, nor of the Anterior deltoids. There is no developmental advantage in loading the shoulder muscles while the humerus is severely externally rotated. In other words, there is no “bonus” in exchange for the injury risk which occurs during Overhead Pressing.

In fact, having the humerus externally rotated compromises the mechanics of the Lateral and Anterior deltoids, by rotating the Lateral deltoid out of alignment with direction of resistance (i.e., the straight downward pull of gravity). Therefore, in addition to incurring an increased injury risk, a person doing an Overhead Press also experiences a compromised benefit.

The Lateral deltoids and the Anterior deltoids can each be worked much more productively and more safely, using isolation exercises that precisely mimic the motion each is designed to produce, without any rotational torque of the shoulder joint.


An example of unnecessary spinal loading is heavy Barbell Squats.

Barbell Squats are typically performed for the purpose of developing the Quadriceps and the Gluteus maximus.

The primary function of the Quadriceps is extension of the knee joint, and the primary function of the Gluteus is extension of the hip joint. Barbell Squats involve simultaneous hip extension (Gluteus contraction) and knee extension (Quadriceps contraction). However, there is no added benefit to either of these two muscle groups by their simultaneous participation.

More importantly, Barbell Squats involve several mechanical compromises, if one’s goal is muscular development. This includes the reduction of the “moment arm” of the quadriceps lever (i.e., the lower leg), and of the gluteus lever (i.e., the femur). This reduces the magnification of the load to each of these two muscle groups (i.e., reduces the percentage of load to the quadriceps and to the gluteus), thus requiring that more weight be added to the bar in order to compensate for the reduced magnification.

This reduction in the percentage of quadriceps and gluteus load compels the user to add more weight to the barbell, in order to compensate for the compromised* mechanics of the exercise.

Note: “Compromised”, in this context, refers to the diminished percentage of muscle loading. However, if the objective is to lift the heaviest possible weight, this diminished percentage of muscle load may be perceived as being “more efficient”, because it “allows” more weight to be lifted. This also means that it “requires” more weight be lifted, in order to optimally load the participating muscles.

Adding weight onto the barbell does increase the net amount of resistance to the quadriceps, but at the same inefficient percentage. More importantly, increasing the weight of the barbell increases spinal compression, which can be very risky.

The wiser method of increasing load to the Quadriceps would be to use an exercise with more efficient mechanics—one that allows the lower leg lever to interact more perpendicular with the direction of resistance (e.g., a “Sissy Squat” or Leg Extensions). This would deliver a higher percentage of load to the Quadriceps, which results in more Quadriceps resistance even though a lighter weight may be used. As a bonus, there would be much less (if any) spinal compression at all.

The amount of load directed at the Gluteus is also compromised, during Barbell Squats. The femur—which is the operating lever of the Gluteus maximus—has its length (its “momentum arm”) reduced because the lower leg (acting as the “secondary lever” of the Gluteus) doubles back under the femur. Thus, the Gluteus is loaded with a “lever” that is approximately 9 inches long, instead of its full length (average 18 inch). The user then compensates for this reduction in the magnification of the load to the Gluteus by adding more weight onto the barbell, further compressing the spine.

The reductions in the load percentages that the Quadriceps and the Gluteus receive, during Barbell Squats, require that a heavier weight be used—in order to adequately load the Quadriceps and the Gluteus.

However, it’s this same “reduced magnification” that allows a heavier weight to be moved. This is why Barbell Squat are popular—because it creates the impression (the mistaken belief) that the person is “very strong”, and also that the participating muscles are loaded “more”, as compared with exercises that do not “allow” as much weight to be moved. Ironically, this thinking is backward. Exercises that do not allow you to move “heavy” weight are the ones that utilize “better” mechanics (cause more magnification of the resistance), allowing you to achieve maximum muscle load with less skeletal strain.

The Quadriceps and the Gluteus can each be loaded and stimulated more effectively using isolation exercises—a knee extension exercise for the Quadriceps and a hip extension exercise for the Gluteus. This would also eliminate the need toplace a heavy barbell on one’s spine, thus avoiding needless spinal compression.

It’s never beneficial to load the spine with very heavy downward compression. The spine can tolerate a fairly heavy amount of load, and it does benefit (i.e., improved bone density) from some degree of load. But the spine receives plenty of “weight bearing” stimulation from other resistance exercises like heavy vertical Shrugs, (using dumbbells, cables, barbell, etc.), as well as carrying weights from the rack to a bench, and back again. But very heavy and frequent downward compression of the spine drastically increases the risk of spinal injury. Thus, it is prudent to minimize it whenever possible.

10.  Favoring an Optimal “Moment Arm”by Avoiding Secondary Limb Reduction of the Target Muscle’s Primary Lever

An ideal exercise, meant for a particular target muscle, is one that does not cause the “moment arm” of a target muscle’s primary lever to be reduced by a secondary lever. This was referenced above in the discussion regarding Barbell Squats.

Another example of this sometimes occurs during Supine Dumbbell Press— performed for the Pectorals.

During a Supine Dumbbell Press—typically performed as an exercise for the Pectorals—the humerus (upper arm bone) is the primary lever because it is the limb onto which the Pectorals are directly attached. However, the dumbbells are not held by the humerus—there is no “hand” at the end of the humerus, with which a weight can be held. Rather, the weight is held by the hand at the distal end of the forearms. Therefore, the forearm becomes the secondary lever because it is attached to the primary lever, but is not directly connected to the Pectorals. For this reason, the forearm’s position—its angle relative to gravity—influences the load experienced by the Pectorals.

Tilting the forearm laterally (away from the midline of the body)—represented in the center image below—has the effect of increasing the moment of arm of the humerus—essentially lengthening it. This causes an increase in the magnification of the load on the Pectorals. Tilting the forearm medially (toward the midline of the body)—represented in the right image below— has the effect of reducing the moment arm of the humerus—essentially shortening it. This causes a reduction the magnification of the load on the Pectorals.

Therefore, tilting the forearm “inward” (medially) reduces the “efficiency” of Pectoral loading. It would thus require that more weight be used, in order to equal the same amount of Pectoral load that could be achieved using less weight, without the inward tilt of the forearm—without the moment arm reduction.

Reducing the moment arm magnification by 20% would require a 20% increase in the amount of weight being used, in order to equal the same amount of Pectoral load. That would result in 20% more effort, with no additional Pectoral benefit. Many people naively tilt their forearms inward when doing a Supine Dumbbell Press so they can use more weight—assuming that using more weight translates directly to greater Pectoral loading. This is misguided.

Note: Tilting the forearms medially—inward, toward the midline of the body—away from the vertical / neutral position (represented in the left image above), would cause a degree of engagement of the Triceps. This would theoretically benefit the Triceps to a small degree, but it would not necessarily constitute a “good” Triceps exercise, as compared with other better Triceps exercises.

It is more efficient to use an exercise, or to use exercise form, that allows the target muscle’s operating limb to use its full “effective” length—without moment arm reduction. This would optimize the loading of the target muscle. “Efficiency”, in this context, refers to the ratio of “muscle loading” as a percentage of the “amount of weight being used” (cost vs benefit). More muscle loading with less “cost” (less weight used) is more efficient. More weight used (“cost”) without more muscle loading is inefficient.

11.  Favoring an Optimal “Moment Arm” of the Target Muscle Limb by Ensuring a Perpendicular Direction of Resistance

When loading a particular target muscle, the ideal direction of resistance “should” cause the limb operated by that muscle to encounter a point at which it is perpendicular to the direction of resistance, somewhere in that muscle’s range of motion—preferably during the early phase.

A limb that is perpendicular to the direction of resistance loads its operating muscle with 100% of the available resistance. Conversely, a limb that is parallel to the direction of resistance loads its operating muscle with 0% of the available resistance. A limb that is between parallel and perpendicular with the direction of resistance, loads its operating muscle with a commensurate percentage of the available resistance, between 0% and 100%.

If an exercise does not allow the limb operated by the target muscle to reach a point at which it is perpendicular with resistance, the amount of load encountered by that muscle will only be a fraction of the “available resistance” (i.e., the “available resistance” is the weight being used, plus the magnification caused by the length of the limb).

The reduced percentage of muscle loading—caused by a muscle’s operating limb not encountering a perpendicular angle with resistance—would require that more weight be used in order to compensate for the percentage reduction.

Using more weight in order to compensate for using an inefficient limb angle results in wasted effort because the same amount of muscle load could be achieved using a lighter weight, if a “better” (more efficient) exercise / limb angle were used—i.e., an exercise that uses a direction of resistance that is more perpendicular with the operating limb.

As a reminder, a muscle only recognizes the amount force it’s required to produce, which is determined by the amount of resistance it encounters. Lifting a heavier weight, which is then reduced in the percentage of resistance it delivers to the muscle (due to the inefficient mechanics of the exercise), may not load the target muscle any more than would an exercise with “better mechanics”, using a lighter weight.

This was demonstrated in the discussion above, in regards to Barbell Squats. Another example of an inefficient muscle loading occurs during Parallel Bar Dips, (shown below) when the intention is to load the Triceps.

The forearm is the operating limb (i.e., the lever) of the Triceps. Notice—in the image above—the angle of the forearm. The angle is approximately 10 degrees from the vertical / neutral position. This results in a very short “moment arm” (i.e., the distance between the elbow (pivot), and the hand (point of the “load” application), using lines that run parallel with the direction of resistance.

Compare that with the angle of the forearm in the photo above, showing me in the almost fully descended position of a Supine Dumbbell Triceps Extension. Notice the width of the “moment arm” (the distance between the two white lines), and how much more distance that is, compared to that of the Parallel Bar Dips (both with the elbow fully bent / “descended” position). In the image above, the forearm is fully perpendicular with resistance, which provides maximally efficiency loading of the triceps.

The Supine Dumbbell Triceps Extension is much more efficient than are Parallel Bar Dips, in terms of loading the Triceps with the greatest percentage of the load and the least wasted effort. This same physics principle is in play during all resistance exercises—the width of the “moment arm” determines how much resistance a muscle encounters, as a percentage of the amount of weight being moved.

12.  Avoiding Exercises that include a Base or Apex at Mid-Range of Motion

An ideal exercise, meant for a particular target muscle, is one that does not cause the operating limb of the target muscle to encounter an Apex or a Base, in the middle of that muscle’s range of motion.

The Apex is characterized as the “highest point” in the upper half of the arc around a pivot (the joint); it is the point that is farthest away from the origin of the resistance (gravity). The Base is characterized as the “lowest point” in the lower half of that arc; it is the point that is closest to the origin of the resistance. The Apex and the Base represent points of zero resistance, because that is where a lever (i.e., a limb) is parallel with the direction of resistance (gravity), resulting in that limb having a zero moment arm.

An exercise that causes a person’s limb to encounter a Base or an Apex in the middle of the target muscle’s range of motion is counterproductive because it deprives that muscle of having an opposing resistance throughout its full range of motion.

In fact, a muscle is strongest (i.e., has its greatest strength potential) during the first third of its range of motion. Therefore, that is where a muscle “should” encounter the most resistance provided by an exercise’s resistance curve. Thus, having a muscle encounter a neutral (zero resistance) position (i.e., an Apex or Base) somewhere near the middle or first third of its range of motion is the worst (most unfortunate) “place” for it to occur.

It also means that the target muscle has no resistance at all, during part (either the first half or the second half) of its range of motion.

It is acceptable if the Apex or Base occurs at the very end of the range of motion (the muscle’s most contracted position). It is also sometimes acceptable if it occurs at the very beginning of the range of motion (the muscle’s most elongated position). However, having the Apex or Base occur midway in the target muscle’s range of motion significantly compromises the exercise.

In addition to the target muscle being deprived of resistance where it would most benefit from it, and having zero resistance for the second half of its range of motion, this situation also results in the target muscle experiencing excessive resistance elsewhere in the range of motion, where its strength potential has most diminished and can least handle it.

In the image below-left (showing a Dumbbell Triceps Kickback), you can see that the forearm reaches the Base (i.e., the vertical position) when the elbow is at a 90 degree bend. This vertical forearm position results in the Triceps experiencing zero resistance, despite the Triceps being at its strongest phase of the range of motion.

When the elbow is extended (above-right), the forearm reaches the horizontal position, which delivers the most resistance to the triceps because the tricep’s operating lever is perpendicular to gravity. However, that is the point where the triceps has the least strength potential.

         11-B. Crossing over to the other side of the Apex or Base in the middle of an exercise’s range of motion results in an additional problem (image below). It causes a transference of the load to the antagonist muscle (the muscle which operates that same joint but in the opposite direction, the biceps in this case). This would result in the target muscle (the triceps, in this case) being neurologically disengaged, due to reciprocal inhibition. Given that the objective of an exercise is to optimize stimulation of the target muscle, it is obviously counterproductive for that muscle to be neurologically de-activated in the middle of its range of motion.

13.  Ensuring “Opposite Position Loading” by Utilizing a Direction of Resistance that is Opposite the Target Muscle Origin

The ideal position for a target muscle, during an exercise intended for that muscle, is to position its origin directly opposite to the direction of resistance—aligned with (on the same plane as) the anatomical motion, and also with the origin and insertion of that muscle.

For example, if the direction of resistance is “7:30” (using a clock analogy, below), the ideal position for the target muscle’s origin would be at the “1:30” position. If the target muscle is situated at positions “near” that 1:30 location (e.g., 12:00 or 3:00), it will LESS loaded than whichever other muscle is located at the 1:30 position—even though that muscle may not be prioritized by you.

The Lying Side Dumbbell Raise—shown below—is a good example of this. The trajectory of the this person’s arm is from North to South (as per the compass). The direction in which resistance (gravity) is pulling his arm, in this scenario, is from South to North. This is perfect, given the intention of “working” the Lateral Deltoid. Notice also that the origin of his Lateral Deltoid (the larger red dot) is positioned directly “South”—opposite the direction of resistance.

Notice also that the direction of resistance and the direction of anatomical motion are aligned with (on the same plane as) the origin and insertion of the target muscle—the Lateral Deltoid. This is perfect alignment.

This allows the Lateral Deltoid to be the primary recipient of the load, without the load being diluted by misalignment. If the alignment is not correct, the participation of the target muscle is reduced, and the engagement of other (nearby) non-target muscles is increased.

Whichever muscle is positioned directly opposite the direction of resistance (i.e., the “line of force”) will be the most loaded, whether that is your intention or not.

         13-B.  In addition to optimally loading the target muscle, proper alignment also ensures the least amount of joint torque, and the least amount of injury risk to weaker non-target muscles which could be strained as a result of that joint torque

An example of this is demonstrated below—Supine Dumbbell Press performed with an improper trajectory (i.e., anatomical motion not aligned with the direction of resistance).

Notice that the trajectory of the arms is at an angle tilting slightly to the left of vertical (from this view), and the direction of resistance is completely vertical (i.e., gravity). In essence, resistance is pulling in a 6:00 direction, but the direction of arm movement is toward an 11:00 trajectory. The trajectory should be in a 12:00 direction for proper alignment.

The result of this misalignment is that the pectoral load is slightly diluted. That  load shifts to the deltoids, because they are then tasked with preventing the arms from “falling” farther toward the feet (when the arms are extended). However, this added deltoid loaded does not constitute a good strategy for improved deltoid development.

In addition, the Infraspinatus (i.e., the primary external rotator of the humerus) is strained when in the descended position—when the elbows are bent—because the infraspinatus is then tasked with preventing further inward rotation of the humerus.

Proper alignment, in this case, would require a straight upward (vertical) trajectory, on the same plane as the direction of resistance, which also ensures that the pectoral origins and insertions are on that same plane. Thus, the load to the pectorals is not diluted, the deltoids are not unnecessarily engaged, and the Infraspinatus is not at risk of being strained.

14.  Favoring Exercises that Provide “Early Phase Loading” of the Target Muscle

An ideal exercise intended to target a particular muscle is one that provides more resistance during the early part of that muscle’s range of motion—known as “early phase loading”—and less resistance in the latter part of that muscle’s range of motion.

Skeletal muscles are generally “stronger” (i.e., have more strength potential) when they are elongated, and they are “weaker” (i.e., have less strength potential) when they are shortened (contracted). This is known as the natural “strength curve” of a muscle. A muscle tends to have more “recoil” when it is at a greater length, because its actin filaments are more “spread out”. A muscle tends to lose strength potential when it contracts because its actin filaments slide over each other—essentially colliding—thereby compromising the muscle’s ability produce optimal contractile force.

Therefore, it is most efficacious—most productive—to utilize exercises that provide more resistance during the “early phase” of the range of motion, and less resistance during the late phase of the range of motion.

Generally speaking, exercises that allow the limb operated by the target muscle to have the greatest possible “moment arm” (to reach a mostly perpendicular angle with the direction of resistance)—during the EARLY part of that muscle’s range of motion—are more productive.

Ideally, the resistance would then diminish during the latter part of the range of motion. This would occur by having the muscle’s operating limb approach an angle that has a fairly short “moment arm” (more parallel with the direction of resistance, rather than perpendicular to it) as the limb approaches the completion of that muscle’s range of motion.

The exercise below is a good example of this. The image below-left shows the early phase of the Supine Dumbbell Triceps Extensions. The forearm (the operating lever of the Triceps) is mostly perpendicular with gravity (i.e., the “moment arm” / greatest distance between the elbow and the weight, using vertical lines) when the Triceps is elongated and is therefore in its strongest position. This is good.

In the image above-right, the forearm is closer to the neutral position (nearly zero “moment arm”), so the triceps encounters much less resistance precisely when its strength potential has diminished. This is also good. The resistance curve of this exercise matches the strength curve of the muscle.

Conversely, in the image below-left, you can see that the early phase of this triceps exercise causes the forearm to be in the neutral position (zero “moment arm”) precisely when the Triceps is in its strongest phase. Then, when the elbow is extended (below-right), the forearm enters a more perpendicular angle with gravity (i.e., maximum “moment arm”), causing the triceps to encounter the most resistance when it is at its weakest position. This is not good.

The resistance curve of Triceps Kickback is the opposite of the strength curve of the triceps—provides less resistance where the triceps is stronger, and more resistance where the triceps is weaker.

         14-B.  When attempting to match the resistance curve of an exercise, with the strength curve of a muscle, all the various types of resistance—and their respective characteristics—must be considered. It’s important to identify precisely where, in an exercise’s range of motion, the resistance is most and least.

The types of resistance that are commonly used in resistance exercise include the following:

*  “Free Weight Gravity” (dumbbells, etc.)

*   Cable Resistance

*   Cam Resistance

*   “Sled Resistance” (weighted carriage moving along guide rods)

*   Elastic Band Resistance

*   “Ground Reaction Force” (sometimes mistakenly referred to as “friction force”)

 *   A composite direction of resistance created by combining two or more disparate directions of resistance simultaneously

Each of these produce a different resistance curve—some “good” and some “not so good” (more productive / less productive).

Note: The characteristics of each of these resistance types are fully explained in “The Physics of Resistance Exercise”

The objective is to match the point of maximum resistance in the ROM of an exercise, with the “early phase” of the target muscle’s range of motion.

         14-C.  There is a caveat—an exception—to the above rule. It’s generally true that a target muscle should be loaded more in the “early phase” of its range of motion, however “mechanical loading” (i.e., by way of having the operating limb interact perpendicularly with the direction of resistance) is NOT the only way that occurs.

The amount of force required of a muscle is also influenced by the angle at which that muscle pulls on its operating limb. In flexion and adduction muscles (i.e., muscles that reduce a joint angle, as opposed to muscles that increase a joint angle), the angle from which the muscle is able to pull on its corresponding limb—therefore the amount of muscle force required—is variable.

“Mechanical disadvantage” is the term used to describe when a muscle must pull on its operating limb (bone) from a mostly parallel angle. “Mechanical advantage” is the term used to describe when a muscle is able to pull on its operating limb (bone) from a mostly perpendicular angle.

In the image below-left, notice that the biceps tendon is pulling on the forearm bone from a mostly parallel angle, because the elbow is nearly straight. That is a mechanical DISadvantage, and it requires significantly more biceps force (all other factors being equal) than would be required when the biceps is able to pull on the forearm bone from a more perpendicular angle, shown in the image below-right.

Muscles that flex or adduct their corresponding joint are generally at greater risk of injury when the joint angle is at “mechanical disadvantage” (e.g., image above-left), and that coincides with a significant “mechanical load” (the corresponding limb is perpendicular with  the direction of resistance, or sufficiently so given the amount of weight being used). This would constitute “double magnification” of the resistance being used—and may exceed the capacity of the muscle or its tendon, resulting in rupture.

Therefore, when attempting to “early phase load” an exercise, it’s important to consider any mechanical disadvantage that occurs in flexion muscles*, as part of the loading. In other words, use less mechanical loading when the flexion muscle pulls from a parallel angle on its limb. Then, increase mechanical loading  (“perpendicular-ness” of limb to direction of resistance) when the muscle is able to pull more perpendicularly on its limb.

* The primary flexion muscles of the body are the Biceps brachii, the Hamstrings, and the hip flexors. The primary adduction muscles are the Pectorals, the Latissimus and the femoral adductors. Not coincidentally, these are the muscles which are often injured.

Muscles that extend a joint—like the triceps shown below—always operate with a “mechanical disadvantage”. Thus, extension muscles have a more consistent force requirement throughout their entire range of motion (all other factors being equal), as compared with flexion muscles. Extension muscles have adapted to that, and are thus less vulnerable to injury.

15.  Ensuring Stability During a Resistance Exercise

An ideal exercise, intended to optimally improve muscular development, is one that is stable. A resistance exercise that is performed while unstable—on a wobbly foundation, on one leg, on a Swiss Ball, or on an uneven surface—compromises the ability of the person to produce maximum force with the participating muscles.

Instability forces the person to use a lesser weight in order to prevent falling. It also compromises ideal exercise form, distracts from one’s ability to concentrate on precise anatomical motion, increases the risk of injury and often interrupts completion of the set because balance was lost. As such, instability interferes with the optimal loading and contraction of target muscles.

Separate from the fact that unstable exercises compromise optimal muscle development, it is worth asking whether unstable exercises are worth doing at all.

Unstable exercises are often promoted as a method by which a person can improve their “balance”, while simultaneously improving their strength and overall fitness. This is often euphemistically referred to as “functional training”, but it’s misleading.

The suggestion that unstable exercise is “functional”, implies that stable exercise has no functional benefit, which indirectly implies that it’s purely cosmetic. In fact, when a muscle is challenged with resistance—it causes it to become stronger, in addition to improving its visible development. A stronger muscle is certainly more functional than a weaker muscle, and its improved strength is applicable in a wide variety of functional applications.

Perhaps more importantly, there is a significant difference between “balance” and “coordination”.

A person’s sense of balance is technically regarded as their “equilibrium”. It is a person’s innate ability to sense the position of their body in space—to sense whether they are centered over their feet, to sense if they are moving or standing still, to sense whether they are vertical or horizontal, etc. It relies on one’s equilibrium sensors—primarily in the inner ear, but also in various joints throughout the body, the hands and feet, as well as one’s vision.

A problem with equilibrium must be addressed by an Ear, Nose and Throat Specialist (aka “otolaryngologist”)—not by a Personal Trainer or Strength Coach.

Exercises that are typically marketed as “balance exercises” are actually proprioception (skill) exercises. Learning how to “not fall” while on an unstable foundation is a specific skill, and is only useful if a person is preparing for similar situations in their day to day life, or a particular sport.

For example, the skill of coordinating oneself on a wobble board is useful when surfing (on a surfboard) or when skate-boarding (on a skateboard). It is not useful when standing on solid ground because the skill of “coordinating / adjusting to a moving foundation” is not required when standing on solid ground.

As people age, they often lose athleticism and coordination. They lose their ability to step sideways and backwards (which is required if their body leans too far to the side or too far back), because they have limited themselves to walking only straight forward for decades. In addition, they have typically allowed their legs to become weak from inactivity.

Leg weakness (1), combined with the loss of familiarity of side-stepping and back-stepping (2), and possibly also the onset of neuropathy (3) (i.e., the loss of sensation in the extremities, caused by nerve damage) increases the likelihood of falling. However, this type of coordination loss is NOT remedied by standing on a wobble board, while attempting to simultaneously perform Dumbbell Curls.

1.  Leg weakness is best improved with simple resistance exercises for the quadriceps (knee extension), the gluteus (hip extension), the hamstrings (knee flexion), the hip flexors and the calves (ankle extension), performed regularly (e.g., two or three times per week).

2.  The coordination of stepping sideways and backward is improved by doing precisely that, on a regular basis. Simple drills can be done whereby a person quickly steps forward four steps, and then backward four steps—repeating that for a count of 20. Likewise, drills can be done whereby a person quickly shuffles sideways, to the left for two or three steps, then to the right two or three steps—repeating that for a count of 20.

Note: This could be done while holding hands with a trainer or therapist—for comfort and security—if necessary.

3.  Neuropathy cannot be significantly improved by way of exercise, although the exercises described above would increase circulation to the legs and feet, which may help a bit. Serious neuropathy is best addressed by a neurologist.

If an older person finds himself in a situation where he needs to prevent himself from falling—because he was bumped sideways in crowded room, or was pushed backward—he needs to instinctively reposition his feet. He needs to take a large step or two, to the side or backward, to get his feet under the weight of his torso. If the instinct to reposition the feet (in order to accommodate a bodyweight shift) has been “forgotten”, the person will fall.

For this reason, macro skills (side stepping and back stepping) are far more productive for gaining the type of coordination (athleticism) that is necessary to prevent falling during day to day activities, as compared with micro skills (standing on one leg, or standing on a “BosuBall”).

Dancing, playing tennis or practicing agility exercises (side stepping and back stepping) are excellent ways of improving coordination in older adults.

16.  Favoring Exercises that Allow Appropriate Resistance Levels

An ideal resistance exercise allows a person to select and use a resistance level (i.e., weight) that is within that person’s strength capacity (the strength capacity of the target muscle) and allows a reasonable number of repetitions to be performed, using full range of motion.

If only one level of resistance is available for that particular exercise, and that amount of resistance is “too light” (insufficient resistance to be productive) or “too heavy” (excessive resistance limiting the number of repetitions to fewer than 10, requiring maximum effort without sufficient warm-up, and compromising form / range of motion) the exercise is effectively disqualified as being “optimally beneficial”—even if the movement would be considered ideal when using the proper level of resistance.

Bodyweight exercises typically do not allow a person to decrease the amount of resistance, if one’s bodyweight is excessive for that exercise.

For example, “Bodyweight Ab Crunches” (spinal flexion) performed while on a flat surface (e.g., a floor mat) typically provides too much resistance for a person with average Rectus abdominis strength. As such, it would have to be modified— converted to an Incline angle so as to reduce the exercise’s moment arm, thereby reducing the resistance.

As another example, “Push Ups”* — also often provide too much resistance (for an untrained person), thereby preventing the person from performing sufficient repetitions, safely, with full range of motion. It would be similar to a person using the only available barbell on a rack for a Supine Barbell Press—even though it is too heavy for that person’s strength level, and does not allow sufficient repetitions.

Note: Push-Ups also violate Principle 2 (“full range of motion”), Principle 6 (“favoring independent limb loading”) and Principle 8 (“avoiding limitation from weaker, peripherally recruited muscles”).

Yet another example would be a One Arm Cable Side Raise (for the lateral deltoids) if the weights on the pulley machine are too heavy.

Sometimes, even the lightest available weight on a pulley machine is too heavy for a person’s first (warm up) sets. The weight might be acceptable as their heaviest set, after having performed several lighter, progressively more intense sets.

In addition, the incremental sequence of weights (each additional “plate” on the stack) may be greater than would be ideal for a progressive increase of resistance / decrease of repetitions. In this case (using that particular machine), One Arm Cable Side Raise would not be an acceptable exercise—even though it would be considered an excellent exercise, if the appropriate resistance levels (weights) were available.

Generally speaking, an appropriate (ideal) level of resistance would allow as many as 20 full-range-of-motion repetitions, comfortably—as a warm up. The succession of sets would require a weight that allows 15 repetitions with relative comfort—followed by 10 repetitions with a fair amount of effort—followed by 8 repetitions with a greater percentage of maximum effort—possibly followed by 6 repetitions with a very high percentage of maximum effort…all with full range of motion.

This sequence of sets and reps is not absolute among all muscle groups, but it is a reasonably good general guide. Sometimes it is preferable to do 30 repetitions as a first set, or even as many as 50, depending on the muscle group, the particular exercise, and the condition of the person doing the exercise.

An ideal exercise would allow a person the option of selecting resistance levels that are within that person’s capacity to perform repetitions ranging from “high” (between 20 and 50) to “low” (between 4 and 10), with reasonable resistance increases on successive sets, all with full range of motion.


Every resistance exercise—intended for the purpose of achieving optimum muscular development—can be evaluated using the 16 principles above. An exercise that conforms with all of these principles (with the exception of the principles that are not relevant to a particular exercise) would have the highest rating. It would be considered “ideal” (un-compromised) for the purpose of muscular development.

A highly rated exercise would deliver the most amount of muscle load with the least amount of wasted effort. It would also provide the target muscle with optimal stimulation—full range of motion, optimal resistance curve, no dilution of the load due to the target muscle being improperly positioned, no neurological interference and no “physio-mechanical” interference (e.g., a non-target muscle preventing / “competing with” the target muscle from working optimally).

An ideal exercise would also avoid the unnecessary loading of the spine, as well as any unnatural joint distortion, or needless tendon and bursa impingement, or risk of muscle rupture due to neglecting to account for “mechanical disadvantage”.

Examination of all commonly used exercises—using these 16 biomechanical factors—reveals that many exercises which have been regarded as “foundational” or “essential” are actually not so good. It is apparent that they lack efficiency (cost / benefit), or they are compromised in terms of productivity, or they impose an unnecessary injury risk, or a combination of these.

It’s worth noting that these 16 principles are true regardless of a person’s ultimate goal, and regardless of their age, gender or their current condition. This is because physics, ideal musculoskeletal motion, muscle physiology and “musculo-neurology” are universal, regardless of the application—notwithstanding individual injuries a person may have previously incurred, which could make even a “perfect” exercise contraindicated to that individual.

“Sports specific training” would likely require additional strengthening exercises that are unique to the requirements of each individual sport. But that would not negate the value—nor reduce the value—of any exercise deemed “ideal” by these 16 factors, for the purpose of “functional” and “visible” muscle development.


Doug Brignole is a veteran competitive bodybuilder with over 43 years of experience, with decades of independent study and research in the field of biomechanics.

He is a former State, National and International bodybuilding champion, having won his second and final Mr. Universe competition at the age of 59—using these biomechanical principles.

He is the co-author of “Million Dollar Muscle”, a university sociology book that analyzes social behaviors within the fitness industry, and he has written numerous magazine articles over the course of his 43 year career.

Brignole’s latest book—“The Physics of Resistance Exercise”—is endorsed by 10 Ph.D. scholars from a variety of scientific backgrounds, as well as 3 orthopedic surgeons. He is currently co-authoring a university biomechanics book, which will provide a more broad perspective of biomechanical applications.