Isometrics, Timed Static Contractions, and Static Holds
by Andrew M. Baye
The term isometrics refers to exercise protocols primarily involving isometric muscular contraction, during which no shortening or lengthening of the muscle occurs. Traditional isometric protocols typically involved the sudden application of a maximal contraction lasting 10-15 seconds. Current isometric training protocols are far safer and produce a much deeper level of muscular inroad since they involve a more controlled application of force over a longer duration. Of these, the most popular are Ken Hutchins' Timed Static Contraction (TSC) protocol and Mike Mentzer's Static Hold (SH) protocol.
Isometrics are very useful in certain situations. If a subject is unable to perform a particular exercise dynamically due to an injury or joint deformities or if they experience pain or irritation in certain portions of the range of movement, TSC performed in a position where the subject does not experience any pain or irritation is an extremely effective alternative.
Subjects suffering from neck problems that may be exacerbated by various dynamic exercises for the upper body can often perform them using TSC with little or no irritation to the neck.
Since very little skill or motor control is necessary, many subjects possessing too poor a level of motor ability to perform dynamic exercise in a slow and controlled manner can safely perform TSC or SH.
When properly performed, isometrics are capable of producing a deep level of muscular inroad using less of one's recovery energy and resources. This is due to the effects of intramuscular friction.
For example, suppose your biceps are capable of producing a maximal force input of 1000 lbs. Suppose also that the distance from the axes of your elbows to the middle of your palms is 10 inches (very short, but it works well for this example), and your biceps tendons are inserted exactly one inch from the axes. In this case, the maximal torque (force) you would be capable of producing at the middle of the palm, where a barbell or movement arm would be held, is 100 lbs. (1000 x 1" = 100 x 10" = 1000 inch/lbs. torque).
If you wanted to inroad your biceps strength levels by 20%, you would need to perform an exercise using a level of resistance which would require 80% of their maximal force input, or 800 lbs. Muscular failure would be achieved when the biceps strength level was reduced to slightly below 80%, a 20% inroad. During an isometric exercise such as a SH, this would require holding an 80 lb barbell or 80 lbs. of resistance on a machine until failure occurs. The average force input per unit of time (F/T), or force per second (F/sec.) of the exercise would remain a relatively constant 800 lbs. until the point of failure. The rate at which the muscle is fatigued or inroaded is related to the F/T. The more force the muscles are producing, the faster they are fatigued.
Due to the effects of intramuscular friction, dynamic exercise is not quite as efficient. More time, and thus more of one's recovery energy and resources are required to achieve the same degree of inroad. Assuming intramuscular friction at the start of an exercise to be approximately 20%, a muscular force input of 800 lbs. would result in a muscular force output of only 640 lbs. (800 - 20% friction = 640) would result in a torque of 64 lbs. at 10 inches (640 x 1" = 64 x 10" = 640 inch/lbs. torque). To achieve a 20% inroad during the dynamic version of the above exercise, one would have to work to failure using 64 lbs. of resistance (intramuscular friction increases over the course of an exercise, but for the sake of this example we will ignore this, as well as all real and virtual cam effects and assume a constant force output and resistance over the full range of motion).
While the muscles would still be producing the same amount of force during the positive of this dynamic exercise as they would for the duration of the above mentioned SH (approximately 800 lbs.), during the negative muscular force input would be significantly lower, thus the average F/T would be lower. Intramuscular friction reduces the amount of muscular force input required during the negative portion of an exercise.
The muscular force input required to perform the negative of the exercise in this example would be only 512 lbs. (640 - 20% friction = 512). Using a protocol with equal speed during the positive and negative such as 10/10, the average muscular force input would be only 656 lbs. F/sec. ([800 + 512] / 2 = 656). Assuming 20% intramuscular friction the average F/T produced during dynamic protocols of equal positive and negative speed is 18% lower than that of isometric protocols such as SH (800 - 18% = 656).
It is also important to consider that with the exception of MedX, SuperSlow Systems, and Nautilus 2ST equipment, the majority of selectorized resistance machines currently being produced possess unacceptably high levels of friction, as well as grossly inaccurate resistance curves and poor or incorrect tracking of muscle/joint function. This apparatus friction reduces the efficiency of dynamic exercise even further.
Adding another 20% apparatus friction to the above example, the average F/T during the dynamic exercise would be reduced to only 544 lbs. F/sec., which would be 32% less efficient than performing a SH or TSC.
Despite these major design flaws TSC and SH can provide an effective means of exercise using such inferior equipment since neither friction nor resistance curves are significant factors during isometric exercise.
The most obvious disadvantage to isometric training protocols is that they do not provide stretching, and will do nothing to maintain or improve one's flexibility. This problem is easily solved by performing separate stretching exercises for the muscles trained isometrically.
Due to the greater blood pressure (BP) elevation associated with isometric exercise, especially during exercises requiring a grip, extreme caution is necessary in administering it to subjects with high BP or conditions that may be exacerbated by significant BP elevation. Proper breathing is absolutely essential to minimize BP elevation. Val Salva (forcefully holding the breath as to create an increase in intra-abdominal pressure) during isometrics is extremely dangerous and must be avoided.
Isometric exercise protocols may produce strength increases specific to the position or joint angle trained, and not over the full range of motion (ROM). This depends upon several factors, which will be discussed in more detail under the Compound Movements section below.
Timed Static Contraction
During TSC, the subject contracts against an effectively immobile source of resistance such as a movement arm that has been locked into a fixed position or is held motionless by an instructor or training partner. This is different than SH where the subject holds and attempts to resist the negative movement of a barbell or machine's movement arm.
TSC is best performed on MedX exercise machines whose movement arms can be locked into position at any point over the ROM. This is also possible using selectorized machines with conventional weight stacks that allow an adequate amount of resistance to be pinned with the movement arm in the desired position, preventing further positive movement. When using machines that do not provide a means of locking the movement arm into position it can be held motionless by an instructor or training partner. TSC can also be performed using manual resistance for many exercises. TSC is safer than SH since the use of a fixed rather than moveable resistance requires no inter or intrapersonal transfer of a movement arm or barbell.
Starting with a minimal effort, the subject gradually increases the amount of force he is applying until he's contracting about half as hard as he believes he can, and continues to contract against the resistance at this level of effort for approximately one minute. After one minute he gradually increases the intensity of contraction to what he perceives to be almost a maximal effort. After another 30 seconds he gradually increases the intensity of contraction to a maximal effort which is sustained for the last 30 seconds of the exercise. After this the subject should very gradually reduce the intensity of contraction over the period of a couple of seconds, rather than suddenly let off. It is just as important to gradually reduce the intensity of contraction as it is to apply it in a gradual and controlled manner.
The procedural sequence for TSC is as follows:
Gradual increase of contraction from 0% to perceived 50% effort: ~5 seconds
Contraction against resistance at perceived 50% effort: 60 seconds
Contraction against resistance at perceived near maximal effort: 30 seconds
Contraction against resistance at maximal effort: 30 seconds
Gradual decrease of contraction from maximal to 0% effort: ~ 5 seconds
Although TSC may sound easy, when properly performed it is extremely intense and capable of producing an extremely deep level of muscular inroad.
A particular disadvantage of TSC is that unless it is performed on MedX testing equipment, there is no objective or accurate means of measuring exercise performance or progress. Since the subject is contracting against a fixed object rather than resisting the pull of gravity on a barbell or the back pressure of a machine's movement arm there is no way to quantify resistance.
During a SH, a barbell or the movement arm of a machine is carefully transferred from the instructor or training partner to the subject in either the fully contracted position or end-point of a simple exercise, or in the mid-range of a compound movement. The subject then contracts against the resistance, attempting to hold it motionless as long as possible. After the muscles are inroaded to the point where it is impossible to prevent the downward movement of the resistance, the subject continues to contract against the resistance, performing the negative as slowly as possible.
Due to the effects of intramuscular friction on muscular force output significantly more resistance is required for the performance of SH than is necessary for dynamic, full-range exercise. Most subjects require approximately 20% more resistance for SH. This will vary somewhat between individuals and muscle groups, and when using barbells or equipment with incorrect resistance curves the increase in resistance necessary depends on the position or joint angle at which the exercise is performed.
The procedural sequence for SH is as follows:
The instructor or training partner assists in raising the resistance to the desired position, or in the case of bodyweight exercises such as chins or dips, using a step the subject lifts himself into the starting position with his legs.
Inter or intrapersonal transfer of resistance.
The resistance is held motionless until muscular failure occurs, which is defined here as the point at which the muscles no longer possess adequate strength to prevent negative movement of the resistance.
The resistance is then lowered slowly under strict control.
SH requires considerably more caution than TSC due to the requirement for a relatively high amount of resistance and the need for inter or intrapersonal transfer of resistance in many exercises. SH may not be appropriate for some subjects who can not tolerate dynamic exercise due to injuries or joint deformities, in which case TSC should be used.
The major advantage of SH over TSC is that it allows for measurement of exercise performance and progress in terms of resistance x TUL. If a subject performs a SH for the prescribed TUL before muscular failure occurs, the resistance should be increased the following workout.
Interpersonal Resistance Transfer
It is extremely important that interpersonal transfer of resistance be performed properly. When handing the bar or movement arm to the subject it is important not to suddenly let go, abruptly loading the subject, as this may cause injury. When the bar or movement arm is in the desired position and the subject indicates that he is ready the instructor or training partner should inform the subject that he is going to begin to transfer the resistance. Keeping the bar or movement arm perfectly motionless, the training partner should very gradually reduce the amount of force he is applying as the subject gradually increases the amount of force he is applying.
For example, suppose the subject is going to perform a SH on the MedX leg extension with 400 pounds. Once he was properly aligned and positioned in the machine, both he and his training partner would gradually begin to lift the movement arm into the fully contracted position. Pretend that each one applies 50% of the force required to move the arm into and hold it in the finished position. Rather than suddenly letting go of the weight at this point, violently loading the subject and requiring him to instantly double the force of contraction, the transfer should be gradual.
Once the subject indicates that he is ready and the training partner has informed the subject that he is about to begin the transfer, the training partner should very gradually reduce the amount of force he is applying to the movement arm as the subject increases the force he is applying by an equal amount, attempting to hold it perfectly still. The ratio of force being applied between the training partner and subject would gradually change from 50/50 to 40/60 to 30/70 etc., until the subject was producing 100% of the force necessary to hold the weight. At the point where the training partner has completely transferred the weight to the subject, he should indicate that he has done so.
Free weight exercises requiring interpersonal transfer should be performed using a barbell rather than dumbbells, as this allows both the subject and the training partner better control over the weight and is therefore much safer.
Intrapersonal Resistance Transfer
During intrapersonal transfer, rather than the transfer of resistance being between the instructor or training partner and the subject, the subject is transferring the resistance from one of his muscle groups to another. For example, when performing static or negative only chins on the Nautilus Multi Exercise, the subject would set the machine's carriage so that while standing on the top step the chinning bar is level with the top of his chest. He would then gradually raise his feet off of the step transferring his bodyweight from his legs to his arms and torso. This can also be performed with a regular chinning bar using a stepladder or tall chair.
Muscular Force Output, or Usable Strength
There are several factors that affect the variation in usable strength or muscular force output in different positions or joint angles over a particular muscle's ROM. These factors include the changes in leverage resulting from the changing angles of the muscle's tendon insertions, force produced by stored energy due to stretching and compression of tissues, changes in friction, and to a very minor degree the interdigitation of myofibrils occurring near the fully contracted position. However, while usable strength or muscular force output is position dependent due to these factors, muscular force input, the actual force produced by the contraction of the muscle, is not.
Muscular Force Input, or Actual Strength
Muscular force input, the pulling force of the contracting muscle, is determined by the resistance the muscle is working against, the number and size of myofibrils in the muscle, neurological efficiency, and volitional control, and has no significant relationship to joint position. An intense muscular contraction of sufficient TUL will produce a deep level of inroad and effective growth stimulation in any position.
None of the major factors responsible for variation in muscular force output between different joint angles or positions are trainable. You can't change the geometry of your skeletal system. The only factor that is trainable, the actual strength or force producing capacity of the muscle, has no relationship to position. Muscular stimulation is related to the intensity of exercise, which is determined by the resistance used and muscular effort and has no meaningful relationship to the position or range over which the muscle is exercised. No matter what position or range of motion used to exercise a particular muscle, if you stimulate increases in the strength of that muscle muscular force output will increase proportionally in all positions or joint angles.
The Myth of the Position of Full Muscular Contraction
Arthur Jones, the founder of Nautilus, has often stated that the only position in which one is capable of contracting and thus stimulating all of the fibers in a particular muscle is the position of full muscular contraction. This is incorrect for several reasons. First, unless a person is a genetic freak possessing a neurological efficiency of 100%, they will never simultaneously contract all of the fibers in a given muscle regardless of position. A maximal contraction does not mean every single fiber in a muscle is involved, it means that one has recruited all of the motor units or groups of muscle fibers one is capable of and they are firing at the highest possible rate. It has been assumed that average neurological efficiency is between 20-30%. Second, there is a difference between a motor unit firing, or attempting to contract, and actually being in the fully contracted position. Maximal fiber recruitment is not dependent upon maximal muscle shortening.
A motor unit, or group of muscle fibers sharing a common innervation, can be firing at an extremely high rate and producing force, without actually shortening, the same as you can apply a maximal amount of force to an extremely heavy object without actually moving it. A muscle can contract with the same amount of force in the mid-range of a movement as it can when completely shortened (possibly more due to interdigitation of myofibrils in this position), which would indicate that an equal percentage of motor units would be active in both positions. Due to leverage and other factors the muscular force output would be different in those two positions, but the actual force of muscular contraction and thus fiber recruitment would be the same, and that's what counts. There is nothing special about the position of full muscular contraction.
Position Specific vs. Full Range Strength Increases
Based on these arguments it would appear that isometric exercise protocols such as TSC and SH would result in full-range rather than position or range specific strength increases. However, the fact that many exercises involve multiple muscles or groups of muscles whose relative involvement may vary considerably over the full ROM complicates the issue somewhat.
Compound (Multi-Joint or Linear) Movements
Isometric exercise protocols may not produce full range strength gains in some compound movements. Unlike many simple or single joint exercises, during compound exercises significantly more muscles are involved and the relative involvement of those muscles changes continuously from position to position throughout the range of movement. Depending on the degree of change in muscular involvement from position to position, isometric exercise in some positions of a compound movement may provide inadequate loading and stimulation for muscles that are not involved to some minimal necessary degree at that position, but may be involved to a greater degree in other portions of the ROM. As a result, there would be a disproportionately low strength increase in those parts of the ROM.
For example, during the front grip pull down, the chest is involved in shoulder extension during the first 30 to 45 degrees of movement. If a person performs TSC or SH on the front grip pull down in a position past that portion of the ROM involving the chest, the resulting strength increases will not be proportional over the full range of the exercise. They will be lower over the ROM involving the chest.
Realize that in such a situation although strength increases may not be proportional over the full ROM, they would not be limited to the specific position trained either.
In exercises where this is a problem, one should either perform the exercise at a position in which all of the muscular structures involved in the dynamic version of the exercise are meaningfully loaded or address the inadequately loaded muscles with a different exercise.
Weight vs. Resistance
During compound pushing movements such as squats, chest press and overhead press, none of the muscles involved in the exercise are meaningfully loaded near or at the position of full extension due to changes in leverage. In positions at or near full extension the bones are supporting the majority of the load and the muscles encounter a minimal amount of resistance. This lever advantage is the reason a person can perform partial repetitions in these exercises over the portion of the ROM near extension with much more weight than they can use to perform the exercise over the full ROM. It is because the muscles do not encounter a significant amount of resistance in that portion of the ROM.
Weight and resistance are not the same thing. Weight is a scalar quantity, a measure of an object's mass. Resistance is a vector quantity, a type of force, which in the case of exercise is a product of weight and leverage. Depending on leverage, one can have a tremendous amount of weight with very little resistance in some positions, as in the above compound exercises, or a tremendous amount of resistance with very little weight. It is the resistance the muscle encounters during exercise that is important.
SH should be performed in the position of an exercise where the target muscles encounter the greatest resistance, not where the most weight can be handled. This position will vary depending on the equipment used. An exception to this would be cases where these techniques are being used to work around an injury or physical condition which prevents dynamic, full range exercise, in which case the position depends upon the subjects physical limitations.
Simple (Single-Joint or Rotary) Movements
Doug McGuff, M.D. alerted me to a similar situation that occurs during certain simple movements. He explained that the vastus medialus, the most medial of the muscles that make up the quadriceps, is only significantly involved during approximately the last 15 degrees of knee extension. If a person were to perform SH or TSC leg extensions in a position where the knees are flexed greater than 15 degrees this muscle may not be significantly inroaded, and the resulting strength increases would be disproportionately low in approximately the last 15 degrees of extension.
Comparisons of the relative effectiveness of different exercise protocols using a dynamic test to measure changes in strength are grossly inaccurate due to several factors. These include the effects of skill, intramuscular and apparatus friction, body and apparatus torque variation, momentum and problems with positional reference, etc. Performing static testing solves all of these problems. Static testing involves no significant friction, no momentum, no torque variation, skill does not have a considerable effect on the tests, and using MedX testing machines it is now possible to accurately counterbalance bodytorque and factor for torque produced by stored energy.
Since isometric protocols do nothing to maintain or improve flexibility, which is an important factor of functional ability, and may not produce proportional strength increases over a full ROM in certain exercises, I do not recommend them for general use. However, static training protocols are often the only means of safely and effectively addressing muscular structures in individuals with joint debilities or other physical conditions in which dynamic exercise is contraindicated. Because they provide a slightly more efficient means of inroad they may also be useful in dealing with subjects with extremely low tolerance to intense physical stress who require extremely low training volumes. In such cases, I recommend occasionally performing the workout dynamically or supplementing it with stretching for the muscle groups trained statically.