Question: In the comments on my previous Q&A on training to momentary muscular failure on timed static contractions, someone asked what I thought about performing isometrics in several different points in the range of motion (ROM) of an exercise. His reason for asking is that some studies, including research performed by MedX, have shown strength gains from isometric exercise to be specific to the position trained for most people.
Answer: If your goal is to improve your general muscular strength and size you do not need to perform isometrics in more than one position. While some studies on isometrics suggest strength gains are position specific the effect appears to be due to neural adaptations rather than to changes in the muscle that would affect general strength or appearance, and other studies show strength gains are not specific to the position trained.
If your goal is to lift more weight in a specific exercise for competition there may be benefit to taking advantage of the neural effect and alternating between performing the exercise dynamically and performing it isometrically at the weakest position or “sticking point”. This is not going to transfer to greater improvements in strength in similar joint angles in different movements, however.
If general strength gains were specific to the positions trained isometrically during exercise (as opposed to exercise specific neural adaptations) it would mean a person’s strength curves would change over time to match the resistance curves of the exercises they perform. If this happened the sticking points in those exercises would eventually be eliminated, but this doesn’t happen; no matter how long you perform the barbell squat or bench press in your workouts the bottom of the ROM of those exercises will always be more difficult than the top.
It would also mean someone who only performs an exercise isometrically for a long time may become weaker in other portions of the ROM and have difficulty in them if they attempt the exercise dynamically. However, this does not happen either. I have trained many people using TSC protocol on the RenEx isometric machines which measured and displayed their force input. On occasion I would have people perform some of their exercises dynamically instead of using TSC, increasing their weight for the dynamic exercise proportional to their isometric strength increases. Contrary to what would be expected if the strength gains were specific to the position trained during TSC, their strength curves did not appear to be effected.
For most exercises I recommend performing isometrics at or below the mid-range position. Avoid performing any kind of isometrics at or near the end point of compound pushing movements and avoid performing static holds in positions where the targeted muscles are stretched.
- Graves, J., Pollock, M., Jones, A., Colvin, A., & Leggett, S. (1989). Specificity of limited range of motion variable resistance training. Medicine And Science In Sports And Exercise, 21(1), 84-89.
- Knapik JA. Mawdsley RH. Ramos MU: Angular Specificity and Test Mode Specificity of Isometric and lsokinetic Strength Training. Journal Of Orthopaedic & Sports Physical Therapy 5:58-65.1983
- Kitai, T., & Sale, D. (1989). Specificity of joint angle in isometric training. European Journal Of Applied Physiology And Occupational Physiology, 58(7), 744-748. doi:10.1007/bf00637386
- Jackson, A. (1985). Strength Development: Using Functional Isometrics in an Isotonic Strength Training Program. Research Quarterly For Exercise And Sport, 56(3), 234-37.