Electromyographic analysis of an eccentric calf muscle exercise in persons with and without Achilles tendinopathy

Objectives: To compare surface electromyographic (EMG) activity of the gastrocnemius and soleus muscles between persons with and without Achilles tendinopathy (AT) during an eccentric muscle exercise in different knee joint positions.

Design: Repeated measures design.

Setting: Research laboratory.

Participants: Participants (n = 18) diagnosed with AT and 18 control subjects were recruited.

Main outcome measures: Gastrocnemius and soleus muscle activity was examined by surface (EMG) during extended and flexed knee joint conditions while performing the eccentric training technique. The EMG data were expressed as a percentage of a maximum voluntary contraction (MVC).

Results: EMG activity was notably higher (mean difference: 10%, effect size: 0.59) in those subjects with AT. Irrespective of the presence of AT, there was a significant interaction effect between muscle and joint position. The gastrocnemius muscle was significantly more active in the extended knee condition and soleus muscle activity was unchanged across joint positions.

Conclusions: The results indicated that the presence of AT influenced calf muscle activity levels during performance of the eccentric exercise. There were differences in muscle activity during the extended and flexed knee conditions. This result does support performing Alfredson, Pietila, Jonsson, and Lorentzon (1998) eccentric exercise in an extended knee position but the specific effects of the knee flexed position on the Achilles tendon during eccentric exercise have yet to be determined, particularly in those with AT.