How Isometrics can Promote Tendon Health and Performance

By Coach Sam Elsner

Let’s start off with what an isometric contraction and tendon is. An isometric contraction is when the tension within the muscle equals the amount of force an external load imposes upon it. In layman’s terms, there is no lengthening or shortening of the muscle. An example of an isometric contraction is clenching your fist as hard as you can and holding it for a certain amount of time. A tendon is a tough band of white fibrous connective tissue that connects a muscle to a bone. This band of connective tissue is made up of collagen, which is also found in ligaments, skin, nails and hair. One thing to note about tendons, there is a compliant end (towards the muscle) and a stiff end (towards the bone). A tendon can be trained to be more compliant of stiffer. The graph below shows how compliant a healthy tendon is and how stiff a tendon is after 5 weeks of being immobilized. 

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Tendon stiffness is important for athletes, having stiff tendons are great for elite performance because a stiffer tendon allows for better force application. If a tendon’s stiffness exceeds the isometric strength of the muscle, the movement must change, or the muscle is forced to undergo potentially lengthening, which can lead to muscle pulls or tears. Tendons act as a shock absorber because a tendon must lengthen so the muscles can contract isometrically. 

Tendons adapt differently to external loads compared to muscles. Tendons adapt best to duration (time) rather than reps and weight. the collagen fibers within the tendon. The sliding of collagen fibers breaks the crosslinks that each fiber has with one another which then decreases the stiffness of the tendon and improves its health. When a tendon is loaded rapidly, then the collagen fibers move together as a sheet which increases the crosslinks between collagen fibers. The more crosslinks, the stiffer the tendon becomes. The ideal range of time that a tendon adapts best is 5-10 minutes. If a tendon is loaded longer than 10 minutes, it will not adapt. For a tendon to be ready to adapt again, 6 hours of rest must happen.

There are two types of isometric contractions that can improve the health and performance of tendons and those types are: yielding and overcoming isometrics. Yielding isometrics are basically holding a position while being loaded or unloaded. These are usually called as Long-Duration Isometrics because this type can be held for longer durations. These are ideal for improving the health of tendons. Overcoming isometrics are the intent to overcome an external force. An example of this is by pushing against an immovable object like a wall or pins on a rack. This type improves the performance of a tendon because an athlete can exert much more force in a quicker period. Both types of isometrics can improve the strength of the muscle at any joint angle, so if you are weak at the bottom of a squat, them do a wall sit for 5-10 minutes everyday or push up against pins at the bottom of the squat. 

Isometrics also can reduce tendon pain in those that are experiencing tendinitis (inflammation of the tendon) or tendinopathy (tendon pain and dysfunction). In a study conducted by Dr. Ebonie Rio and her colleagues, athletes that performed an isometric single-leg decline squat reduced their pain from 7/10 on a pain scale to a 0.17/10 and that reduction of pain was sustained for 45 minutes. 

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There are a few nutritional methods that can improve the health of tendons. Consuming 500 mg of Vitamin C before each training session can increases the synthetization and secretion of procollagen which is a precursor to collagen. Also, ingesting 15 grams of gelatin helps improve the collagen fibers within tendons because gelatin includes the amino acids glycine, lysine, proline, hydroxylysine and hydroxyproline, which are the amino acids collagen is made of. The more collagen that can be synthesized within the tendon, the healthier the tendon will be. The recipe below is made by Dr. Keith Baar, who is a professor at University of California-Davis who specializes in tendon physiology. 

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Recommendations for improving tendon health and performance are:

  • Perform 1-3 sessions that include yielding isometrics that last 5-10 minutes each exercise within the session. Allow 6 hours of rest in-between sessions.  
  • 30-60 minutes before training, consume 15 grams of gelatin and 500 mg of Vitamin C
  • Incorporate overcoming isometrics into training sessions. 3-5 sets of 5-10 second duration reps to improve the performance of tendons. 



Coach Sam Elsner

CrossFit Sabertooth


Baar, K. (2017). Minimizing Injury and Maximizing Return to Play: Lessons from Engineered Ligaments. Sports Medicine47(S1), 5–11. doi: 10.1007/s40279-017-0719-x

Rio, E., Kidgell, D., Purdam, C., Gaida, J., Moseley, G. L., Pearce, A. J., & Cook, J. (2015). Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. British Journal of Sports Medicine49(19), 1277–1283. doi: 10.1136/bjsports-2014-094386

Close, G. L., Sale, C., Baar, K., & Bermon, S. (2019). Nutrition for the Prevention and Treatment of Injuries in Track and Field Athletes. International Journal of Sport Nutrition and Exercise Metabolism29(2), 189–197. doi: 10.1123/ijsnem.2018-0290

Dietz, C., & Peterson, B. (2012). Triphasic training: a systematic approach to elite speed and explosive strength performance. Hudson, WI: Bye Dietz Sport Enterprise. 

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