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

Abstract

Plantarflexor muscle endurance was measured during concentric–eccentric muscle contractions at 90◦/sec over 20 repetitions using a Humac Norm Isokinetic dynamometer. Testing utilised an 80◦ knee flexed position as this significantly inhibits Gastrocnemius thereby testing the function of Soleus, which is the endurance muscle. Previous work has already shown that Soleus is most affected by tendinopathy. Total work done was used to measure endurance capacity as it has been shown to be the most reliable measure. Results: Participants with tendinopathy had a mean total work done of 1313NM on the symptomatic side and 1490NM on the non-symptomatic side, whilst controls had a mean of 1900NM. This data clearly shows that those with tendinopathy have a lower endurance than healthy age, sex and activity matched controls. Independent t tests show a clear statistical difference between the symptomatic leg and healthy controls (p= 0.001) and between the non-symptomatic leg and healthy controls (p= 0.006). There was a significant difference between symptomatic and non-symptomatic legs in participants with disease (p= 0.009). Conclusion(s): Runners with Achilles tendinopathy have less Plantarflexor endurance capacity compared to those without tendinopathy. These differences are bilateral andmay be associated with central nervous system changes or may be pre-existing weakness. Further research needs to ascertain whether these differences are pre-existing and lead to tendinopathy or are a direct result of tendinopathy. Future prospective risk factor studies need to incorporate Plantarflexor endurance in addition to strength parameters so that a more comprehensive understanding of neuromuscular factors can be developed. Implications: Endurance is affected by tendinopathy and as such conservative management (Physiotherapy) needs to fully resolve these deficits. This research highlights that the contralateral limb should not be used as a “normal” measure of endurance and that further studies need to use healthy control data.