Can we really say getting stronger makes your tendon feel better? No current evidence of a relationship between change in Achilles tendinopathy pain or disability and changes in Triceps Surae structure or function when completing rehabilitation: a systematic review
- It is unclear whether current Achilles tendinopathy exercise protocols improve muscular strength or function.
- Research has consistently shown that structural adaptation during tendinopathy rehabilitation is not needed to demonstrate improved pain and function.
- Improvement in clinical symptoms following exercise rehabilitation for mid portion Achilles tendinopathy is likely due to a complex interaction of factors including biopsychosocial mechanisms.
BACKGROUND & OBJECTIVE
The Achilles Tendon is the largest and strongest tendon in the body. It is routinely subjected to loads up to 6 to 12 times bodyweight. The triceps surae muscle group and tendon play a large role in athletic movements, propulsion, and rapid force production by storing and releasing high amounts of energy. The presence of Achilles Tendinopathy (AT) has been thought to be associated with significant deficits in strength and power production (1).
Despite loading protocols becoming the standard care for AT, the mechanisms of improvement in clinical symptoms for AT are not well understood. It is thought that improvements in Triceps Surae structure and function may act as a stress shield to the Achilles tendon contributing to improvements in symptoms of mid-portion AT (2).
The authors of this paper sought to answer two questions:
Are changes in muscle structure/function related to changes in Achilles tendon pain/disability during exercise rehabilitation?
How effective are rehabilitation protocols for improving triceps surae structure and function?
Although the method of improvement is not well understood, loading protocols remain an appropriate entry point for mid portion AT rehabilitation.
The authors narrowed down their systematic review to 17 total studies, representing 25 total cohorts with 432 participants (age range 20 to 55). All studies provided some measure of muscle structure and function and focused on mid portion AT. Individual studies had a large variation in measurement methods ranging from using ultrasound to measure muscle CSA to using dynamometry or heel raise tests to measure performance. The authors were unable to perform a meta-analysis due to the large heterogeneity in study design.
All studies reported significant within-group improvement in either pain or disability following exercise rehabilitation. No studies reported the relationship between changes in pain and disability and changes in muscle structure and function when completing exercise rehabilitation. 3 studies measured plantarflexion force output with isometric dynamometry. 6 studies used isokinetic dynamometry, 6 studies assess heel-raise capacity, 2 studies assessed jump capacity, and 2 studies used ultrasound to assess gastrocnemius fascicle length, pennation angle, CSA, and Achilles tendon tissue elasticity.
The results of the review are unable to support a strong relationship between improvements in muscle structure/function and tendon pain/disability given no studies have currently investigated this outcome.
This systematic review is limited by the lack of data available from completed trials, the large heterogeneity of studies relating to AT, the low study quality of included trials, and the potential influence of measurement error. All cohorts had a sample size of 50 or fewer and a high risk of small study bias. Despite their ranking in the hierarchy of evidence, all systematic reviews are inherently limited by the quality of the studies available to them.
The process of pain perception is largely controlled by higher level brain processing, and thus can change quickly. Pain has been shown to decrease significantly following a single bout of isometric loading. In cases of persistent pain, the analgesic effect of load has been shown to decrease over time. A peak effect is shown at 12 weeks with diminishing returns from the 3 to 6 months post treatment initiation (3).
Although the method of improvement is not well understood, loading protocols remain an appropriate entry point for mid portion AT rehabilitation (4). The question of whether it is the act of strengthening, or the result of strength that is improving pain remains unanswered.
Many of the trials currently referenced for AT loading are underpowered, not well documented, and underdosed in their exercise prescription. A 2019 systematic review including 7 studies on mid portion AT showed heavy eccentric calf training to be superior to traditional physiotherapy, however it was unable to show it to be superior to other alternative exercise interventions (5). Moreover, a recent 12-week trial was unable to distinguish outcome differences between the addition of heel lift orthoses versus an eccentric exercise protocol (6).
The results of this study should not deter clinicians from utilizing a strengthening protocol. Individuals have been shown to exhibit strength deficits for greater than 1 year following the resolution of symptomatic AT, highlighting the importance of emphasizing strength throughout the rehabilitation process (7). The area of research investigating functional performance and structural adaptations during tendinopathy rehabilitation is its infantile stages. Future studies are warranted to better understand the capacity for strengthening adaptations in the presence of tendinopathy.
Murphy M, Travers M, Chivers P, Debenham J, Docking S, Rio E, Gibson W, Ardern C (2023) Can we really say getting stronger makes your tendon feel better? No current evidence of a relationship between change in Achilles tendinopathy pain or disability and changes in Triceps Surae structure or function when completing rehabilitation: A systematic review. Journal of science and medicine in sport. Published online ahead of print.
- Alfredson H, Pietila T, Jonsson P, Lorentzon R. (1998). Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med.
- O'Neill, S., Watson, P. J., & Barry, S. (2015). Why are eccentric exercises effective for achilles tendinopathy? International journal of sports physical therapy.
- Stevens, M., & Tan, C. W. (2014). Effectiveness of the Alfredson protocol compared with a lower repetition-volume protocol for midportion Achilles tendinopathy: a randomized controlled trial. The Journal of orthopaedic and sports physical therapy.
- Murphy Myles, Travers Mervyn, et al. (2018) Rate of Improvement of Pain and Function in Mid-Portion Achilles Tendinopathy with Loading Protocols: A Systematic Review and Longitudinal Meta-Analysis. Sports Med.
- Murphy, M. C., Travers, M. J., Chivers, P., Debenham, J. R., Docking, S. I., Rio, E. K., & Gibson, W. (2019). Efficacy of heavy eccentric calf training for treating mid-portion Achilles tendinopathy: a systematic review and meta-analysis. British journal of sports medicine.
- Rabusin, C. L., Menz, H. B., McClelland, J. A., Evans, A. M., Malliaras, P., Docking, S. I., Landorf, K. B., Gerrard, J. M., & Munteanu, S. E. (2021). Efficacy of heel lifts versus calf muscle eccentric exercise for mid-portion Achilles tendinopathy (HEALTHY): a randomised trial. British journal of sports medicine.
- McAuliffe S, Tabuena A, McCreesh K, O'Keefe M, Hurley M, Comyns T, Purtill H, O'Neill S, O'Sullivan K. (2019) Altered Strength Profile in Achilles Tendinopathy: A Systematic Review and Meta-Analysis. Journal of Athletic Training