Eccentric rehabilitation for runners with Achilles tendinopathy improves endurance capacity of the plantarflexors

Background: Our previous work has highlighted that runners with Achilles tendinopathy have lowered Plantarflexor endurance capacity compared to healthy controls. It is currently unknown how common tendinopathy rehabilitation protocols alter this deficit in endurance capacity. Purpose: To determine how an eccentric rehabilitation protocol alters Plantarflexor endurance capacity in participants with Achilles tendinopathy. Methods: 20 endurance runners with Achilles tendinopathy were recruited and underwent an eccentric rehabilitation program based on Alfredson's regime. Achilles tendinopathy was diagnosed on clinical and ultrasonographic examination. Inclusion criteria were – symptoms for 3 months or more. Participants were excluded if they had insertional tendinopathy, bilateral tendinopathy or a clinical history and/or ultrasound diagnosis suggestive of partial rupture. A control group of 24 healthy endurance runners was used from a previous study. These participants were age, sex, leg and activity matched to the Achilles tendinopathy group. Plantarflexor muscle endurance was measured during concentric and eccentric muscle contractions at 90°/sec over 20 repetitions using a Humac Norm Isokinetic dynamometer. This testing protocol has been shown to be reliable. Endurance can be measured using “total work done”, “fatigue index” or “endurance ratio”, but previous work has identified that “total work done” measured in Newton Metres (NM) is the most reliable measure. Participants with Achilles tendinopathy were tested at baseline and after 12 weeks of an eccentric exercise regime whilst the control group were only tested at one time point. Results: At baseline participants with tendinopathy had a mean total work done of 1168 NM on the symptomatic side and 1350 NM on the non-symptomatic side, whilst healthy controls had a mean of 1900 NM. After completion of the intervention protocol the symptomatic leg increased to 1618 NM whilst the non-symptomatic leg increased to 1763 NM. The intervention significantly increased endurance capacity of the symptomatic and non-symptomatic legs (p ≥ 0.001). Baseline testing comparing those with Achilles tendinopathy to healthy controls showed a clear difference between the groups (p ≥ 0.001 for symptomatic and non-symptomatic sides) whilst after rehabilitation there is no statistical difference on the symptomatic or non-symptomatic leg (p = 0.103 and p = 0.332). Conclusion(s): This was the first study to determine how an eccentric exercise regime for the Plantarflexors affects endurance capacity in those with Achilles tendinopathy. This study highlighted significant differences in endurance capacity prior to the intervention, these deficits were resolved after the completion of an eccentric regime. This study also highlights that eccentric rehabilitation regimes alter endurance capacity in both legs despite only being performed on one leg. Implications: Eccentric exercise protocols appear to correct endurance capacity of those with tendinopathy, further studies need to determine if this is critical to good clinical outcomes.