Pain and function are the primary outcomes assessed in physical therapy research. Restricting our patient assessment to those variables impairs our ability to gauge the success of treatment and carry over to moderate and high-intensity physical activity. Furthermore, most patients need improvements in strength, power, endurance, muscle mass, and tissue integrity (e.g., tendon stiffness). For example, Achilles tendinopathies often present with degeneration and weakening of the tendon. Strictly measuring pain and function does not mean the tendon has adapted. If our goal is to improve the integrity of the tendon, what type of training should be prioritized? This controlled trial (PMID: 36538166) compared high-loading tendon exercises with standard exercise therapy (Alfredson’s eccentric exercise protocol) or passive therapy (i.e., no mechanical loading).
The trial included 44 males (15 in the Alfredson group, 15 in the High-load group, and 14 in the passive group) between the ages of 20 and 55 years old with chronic (>3 months) Achilles tendinopathy. The trial lasted 12 weeks and included a 6-month follow-up. The passive group was asked to adhere to a maximum of 12 passive therapeutic and manual treatment sessions while refraining from any explicit plantar flexor strengthening during the trial period.
The Alfredson protocol is eccentric single-leg heel lowering on the edge of a stair (the un-involved limb is used to return to the starting position). The participants completed two sessions per day consisting of 3 sets of 15 reps with knees extended and 3 sets of 15 reps with knees bent. The optimal load progression was the addition of 5kg per week (usually through a backpack).
The high-load group completed a resisted plantar flexion in long sitting with the knee fully extended. They completed five sets of four repetitions at 90% max isometric voluntary contraction (MVIC). The contraction last 3 seconds followed by 3 seconds of rest between reps. Rest breaks between sets were 1 minute. The training session was completed 4 times per week for 12 weeks. The load progressed by ~ 5% of the individual training load each week. For both training groups, load progression occurred when the pain level was <6/10 and the individual rating of perceived exertion (RPE) was <3/10. Load reduction was recommended when either the pain level was > 5/10 or the RPE was > 5/10.
At the end of the trial, the high-load group experienced significant improvements in strength, mean tendon cross-sectional area, and tendon stiffness and a reduction in maximum tendon strain. The Alfredson group experienced no changes across the board. The passive group experienced a decrease in tendon stiffness. All three groups experienced significant improvements in pain and function at post-assessment and follow-up.
The last finding is key. If we restrict our assessment to pain and function, the protocol does not matter. If we aim to improve strength and tendon adaptation, which will improve performance and resilience, we need to train at appropriate intensities.