Heavy isometric exercises are a popular treatment option for tendon pain. The work by Ebonie Rio on the patellar tendon demonstrated that heavy isometric exercise had an analgesic effect. The exercise protocol was a 5 set, 45 second 70% maximal voluntary isometric contraction (MVIC) with 2 minute rest break between sets. This resulted in a significant reduction in patellar tendon pain immediately and 45 minutes after the isometric muscle contraction.

Because of these results, heavy isometric contractions have been recommended to reduce the pain of tendinopathy in several other body regions, such as the rotator cuff and achilles tendon.

However, a recent study by Seth O’Neil replicated the patellar tendon study to see whether heavy isometric exercises had the same analgesic effect for Achilles tendinopathy. The study on heavy isometric exercises for Achilles tendinopathy found that isometric exercises did not have an analgesic effect as they do for patellar tendinopathy. The average group pain rating increased by 1 point after isometric. Those who experienced more severe Achilles tendon pain before isometric contractions had a larger increase in pain rating while those with less pain had a small reduction in pain.  

The results of the study on Achilles tendinopathy suggests that tendinopathy in different regions of the body may respond differently to load. Isotonic loading programs such as a heavy, slow resistance or an eccentric loading program have been shown to be effective in the treatment of Achilles tendinopathy. Whereas patellar tendinopathy appears to respond well to heavy isometric exercises.

It also appears that the response to isometrics might vary among different individuals. While of questionable clinical significance, some of the individuals from the Achilles tendinopathy study did report a small reduction in pain following isometric exercise. The reason why these individuals better tolerated isometric exercises remains unclear. It could be that these individuals had a less irritated Achilles tendinopathy presentation and would have benefited from any loading program.

Overall, isometric exercises do not appear to be detrimental to those with Achilles tendinopathy. Isometric exercises can be used as a beginning exercise in the rehab program to introduce load, although they do not seem to have the same effects as they do with patellar tendinopathy. It may be that Achilles tendinopathy responds better to heavy isotonic exercises than heavy isometric exercises.

References:

• Beyer, Rikke, et al. “Heavy Slow Resistance Versus Eccentric Training as Treatment for Achilles Tendinopathy.” The American Journal of Sports Medicine, vol. 43, no. 7, 2015, pp. 1704–1711.
• O’Neill, S., et al. “Acute Sensory and Motor Response to 45-s Heavy Isometric Holds for the Plantar Flexors in Patients with Achilles Tendinopathy.” Knee Surgery, Sports Traumatology, Arthroscopy, 2018.
• Rio, Ebonie, et al. “Isometric Exercise Induces Analgesia and Reduces Inhibition in Patellar Tendinopathy.” British Journal of Sports Medicine, vol. 49, no. 19, 2015, pp. 1277–1283.