Plantarflexor strength and endurance deficits associated with mid-portion Achilles tendinopathy: The role of soleus.

Objectives: Determine how the strength and endurance of the plantar flexors are affected by Achilles tendinopathy and whether one muscle is more affected than another.

Design: Case control study.

Setting: University Laboratory.

Participants: 39 Runners with mid-portion Achilles tendinopathy and 38 healthy runners participated in this study.

Main Outcome Measures: Isokinetic dynamometry was completed bilaterally in two knee positions on all subjects to assess the torque and endurance capacity of the plantar flexors.

Results: Subjects with Achilles tendinopathy were statistically weaker (by 26.1Nm Concentric 90°/sec, 14,8Nm Concentric 225°/sec and 55.5Nm Eccentric 90°/sec for knee extended testing and 17.3Nm, 10.1Nm and 52.3Nm for the flexed knee respectively) than healthy controls at all isokinetic test speeds and contraction modes irrespective of knee position (p value = <0.001). The endurance capacity of the plantar flexors was significantly reduced (Total work done 613.5Nm less) in subjects with Achilles tendinopathy when compared to the healthy controls (p value = <0.001).

Conclusions: Achilles tendinopathy is associated with large deficits in plantar flexor torque and endurance. The deficits are bilateral in nature and appear to be explained by a greater loss of the soleus force generating capacity rather than the gastrocnemius.