Because I often recommend isometric protocols like timed static contractions and static holds as an alternate to dynamic exercise when it is not possible or practical I get a lot of questions about their effectiveness compared to dynamic exercise and whether strength gained from isometrics is specific to the positions trained or transfers to the full range of motion. Isometric training has been proven to be an effective way to improve muscular strength and size, however studies on specificity of strength gains to the position trained have had mixed results; some show strength improvements only within about fifteen to twenty degrees of the joint position trained while others show full-range strength increases, and some, like the studies conducted by MedX at the University of Florida in the 90’s, showed different people responded differently, with most having position specific strength increases and a few improving strength over a full range of motion.
I suspect a large part of the specificity in test results is due to both some exercises involving significant variation in the relative contribution of the muscles involved over the range of motion and lack of skill in dynamic exercise performance in subjects only training with isometrics.
For example, if a muscle is significantly involved in only one part of the range of motion of an exercise if that exercise is performed isometrically in a position where that muscle has little or no involvement the strength in the part of the range of motion where it is involved will not increase proportionally. This assumes no other exercises are being performed which involves the muscle in question, which is usually the case in studies where subjects only perform and are tested on one or two exercises. If the whole body is being trained isometrically using exercises for all major muscle groups, these relative weak spots in the range of motion of dynamic exercises would be eliminated.
This is more of an issue with compound exercises than simple ones, since more muscles are involved and the actions of many of the muscles which move the shoulders and hips are position dependent. For example, when your shoulders are flexed (elbows in front of body) the lats extend your shoulders, and when your shoulders are extended (elbows behind the body) the lats flex the shoulders. This means the lats are significantly involved at the beginning of both a compound row and a parallel bar dip, but have little or no involvement once the elbows pass the body (depending on body position the lats can extend, flex, depress, retract, adduct, or internally rotate the shoulders, and assist in trunk flexion, lateral flexion, rotation, and extension).
Regardless of the joint position or portion of the range of motion trained, if a muscle is contracting with a high intensity of effort all of the motor units in that muscle will be involved and stimulated to increase in strength and size. If the strength of that muscle increases, it will be able to produce more force at any length, from a full stretch to full contraction. So, if isometrics result in position specific strength increases in some exercises because of significant variation in the contribution of the different muscles involved over the range of motion, the solution is simply to perform enough variety of exercise for all the major muscle groups to be worked effectively.
Also, since skill is highly specific and has a strong influence on test performance, subjects who have only trained isometrically will be at a disadvantage in dynamic tests compared to subjects who have trained dynamically.
In my own experience using timed static contractions and static holds in my workouts and with clients, there has been no indication that strength gains are limited to the position trained. While working with Ken Hutchins a few years ago we had many clients performing ninety second timed static contractions on equipment specially designed for the purpose, which measured and displayed force input on a monitor which could be positioned in front of the user. This was most frequently done with compound row, pullover, close underhand-grip pulldown, lateral raise, leg extension, leg curl, hip adduction, hip abduction, neck extension, and neck flexion. Occasionally, clients who normally performed these exercises isometrically would perform them dynamically (if they were capable – some only performed timed static contraction due to physical limitations). When they did, there was no indication their strength did not improve over the entire range of motion of the exercise. If strength gains were specific to the position trained they would have consistently failed in portions of the range of motion where strength did not increase proportionally, but this did not happen. When using equipment with relatively well-balanced resistance curves, or when performing free weight exercises in a manner resulting in well-balanced resistance curves, momentary muscular failure should occur at random points over the range of motion, and this was the case with everyone.
So, in addition to being effective for improving muscular strength and size in general isometric protocols like timed static contractions and static holds will improve full range strength as long as you aren’t neglecting to work any muscle groups.
Since some people still get these two mixed up I’m going to finish by explaining the difference between timed static contractions and static holds.
Timed static contractions are isometric contractions performed against an immovable object for a predetermined duration. These can be performed using machines with handles, pads, or pedals that can be locked or pinned into position using more weight than you can lift, using a barbell too heavy for you to lift in a power rack, or using a variety of straps, pads, and other objects which can be contracted against without moving. With most equipment these should be performed at the mid-range position, halfway between the start and end of the range of motion.
Static holds are isometric contractions performed against a movable object, which you hold motionless for as long as you can. These can be performed with any equipment dynamic exercises can be performed with. With most equipment static holds should also be performed in the mid-range position, however when performing some compound pulling exercises or when using properly designed machines to perform simple exercises static holds should be performed at the end point. The duration of the hold should be recorded using a stopwatch or the second hand on a clock, starting when the weight is lifted or handed to you at the hold position, and ending when you are unable to prevent the weight from moving downward. When it is no longer possible to prevent downward movement of the weight attempt to lower it as slowly as possible.
The advantage of timed static contractions is that it can be performed with a greater variety of equipment and common objects, and they are very safe since there is no risk of dropping a weight and if you experience any pain or joint discomfort you can unload immediately without having to worry about setting down or re-racking a weight. The disadvantage is performance can not be measured objectively without equipment with force-measuring devices, most of which is prohibitively expensive. An inexpensive workaround for this is to use a high capacity digital spring scale, which can be attached to a chain with a bar, handles, or belt at one end and the other securely attached to an immobile object.
The advantage of static holds is performance can be more easily measured, using weight and time under load. The disadvantage is some exercises are difficult to perform on some types of equipment unless you have one or more strong partners to help you lift the weight to the hold position. Extreme caution should be used when performing static holds on exercises which start in a stretched position so that you do not drop into the stretch when you are no longer able to hold the weight.
The following is an example of a basic full-body workout using timed static contractions (TSC) or static holds (SH):
- Squat (TSC using hip-squat belt or SH in mid-range position) or Wall Sit
- Chin Up (SH in mid-range position)
- Dip (SH in mid-range position) or Chest Press (TSC or SH in mid-range position inside a power rack)
- Row (SH in mid-range position)
- Shoulder Press (TSC or SH in mid-range position inside a power rack)
- Stiff Leg Deadlift (TSC or SH in mid-range position inside a power rack)
- Crunch (TSC or SH bar crunch at end point inside a power rack)
- Heel Raise (TSC using hip-squat belt or SH in mid-range position)
- Neck Extension (TSC in neutral position using head pad or other cushioned surface on floor or bench)
- Neck Flexion (TSC in neutral position using head pad or other cushioned surface on floor or bench)
Still have questions about timed static contractions or static holds? Post them in the comments below.