An isometric contraction is a static form of exercise in which a muscle contracts to produce force without an appreciable change in muscle length and without visible joint movement1 We learn these basic concepts in school and are told to provide these types of interventions during the early phases of rehabilitation, but do we truly understand the benefit of these seemingly simple exercises?
Eccentrics versus Isometrics
While eccentric exercise is the mainstay of most rehabilitation programs for tendinopathies, some patients find them painful to complete and difficult to perform.2 In these cases, patient compliance suffers due to increased pain, leading to underwhelming outcomes.3
Conversely, the impact of isometric contraction on pressure pain thresholds (PPTs) yields promising results. When asymptomatic volunteers held a quadriceps isometric contraction at 21% MVIC until exhaustion (maximum of 5-minute duration), patients demonstrated a significant increase in PPT at the start of contraction. PPT continued to increase until the middle of the contraction period and stayed increased for up to 5 minutes post-intervention.4
Reduced Perceived Pain
In a similar study, PPTs were determined after 14 healthy women completed 2 sets of submaximal (40-50% MVIC) isometric exercise consisting of squeezing a dynamometer for 2 minutes with their dominant hand.5 This trial demonstrated a positive contralateral and ipsilateral hypoalgesic effect with elevated PPTs and a reduction in self-perceived pain rating for both hands following isometric exercise. While this provides a good foundation of support, it does not provide information regarding isometric exercise’s effect on individuals with a painful condition
To answer this question, Rio and associates performed a randomized cross-over study to investigate the hypoalgesic impact of a single bout of isometric contractions on individuals with patellar tendinopathy.6 Those in the intervention group performed 5 sets of 45 second isometric quadriceps contractions (70% MVIC) with a 2 minute rest break between each set. Those in the control group performed 4 sets of 8 repetitions (100% 8-repition maximum) of an isotonic leg extension exercise with a 4 second eccentric phase and 3 second concentric phase.
At the conclusion of the study, isometric contractions reduced pain during single-leg decline squat from 7.0 to 0.17 on an 11-point scale and increased MVIC by 18%. Both values were maintained for 45 minutes post-intervention. Also, cortical inhibition increased from 27.5% to 54.9%, which may factor into the underlying mechanism of this hypoalgesia.7
Further supporting the hypoalgesic properties of isometric contractions, Rio and colleagues once again added to the depth of literature in this area. They used a within-session randomized controlled trial to compare isometric leg extension at 60 degrees of knee flexion to isotonic leg extension in volleyball or basketball players with patellar tendinopathy. At the conclusion of the study, those randomized to the isometric knee extension group demonstrated significantly greater immediate analgesia throughout the 4 weeks trial.8
Back to the Basics
Isometrics are not simply an introductory exercise for patients following a post-operative procedure (i.e. quad sets following ACL reconstruction). Their hypoalgesic effects are far more impactful then most of us recognize. Although we are not sure why isometrics are efficacious in these tendinopathies, they give us an intervention that is successful. Clinicians often get too caught up in complex and intricate treatment philosophies when in reality all we have to do is go back to the basics!
1. Kisner, Carolyn, and Lynn Allen. Colby. Therapeutic Exercise: Foundations and Techniques. 5th ed. Philadelphia: F.A. Davis, 2007. Print.
2. Alfredson H, Pietila T, Jonsson P, et al. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med 1998;26:360–6.
3. Visnes H, Hoksrud A, Cook J, et al. No effect of eccentric training on jumper’s knee in volleyball players during the competitive season: a randomized clinical trial. Clin J Sport Med 2005;15:227–34.
4. Kosek E, Ekholm J. Modulation of pressure pain thresholds during and following isometric contraction. Pain 1995;61:481–6.
5. Koltyn KF, Umeda M. Contralateral attenuation of pain after short-duration submaximal isometric exercise. J Pain 2007;8:887–92.
6. Rio E, Kidgell D, Purdam C, et al. Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. British Journal of Sports Medicine. 2015;49(19):1277-1283. doi:10.1136/bjsports-2014-094386.
7. Rio E, Kidgell D, Moseley GL, et al. Tendon neuroplastic training: changing the way we think about tendon rehabilitation: a narrative review. British Journal of Sports.
8. Rio E, van Ark M, Docking S, Moseley GL, Dawson K, Gaida J, van den Akker-Scheek I, Zwerver J, Cook J. Isometric Contractions Are More Analgesic Than Isotonic Contractions for Patellar Tendon Pain: An In-Season Randomized Clinical Trial. Clinical Journal of Sport Medicine. 2016.