Calf Muscle Activation Strategies in Healthy and Injured Achilles Tendon Conditions

Achilles tendon transmits triceps surae muscle force to the foot and is one of the strongest tendons in human body. Despite its strength, it is not immune to injuries leading to disruption of normal calf muscle activation strategies and leg function.

The objective of this series of studies was to investigate 1) plantarflexor muscle use during submaximal isometric plantarflexion contractions, 2) electrical and metabolic activity patterns of superficial and deep ankle plantarflexors in Achilles tendinopathy and Achilles tendon rupture, and 3) effects of eccentric calf myotendon rehabilitation on skeletal myotendon glucose uptake and myoelectric activity patterns of ankle plantarflexors. Isometric plantarflexion force, surface electromyography and positron emission tomography measurements were performed on 19 - 35 year old subjects and both longitudinal and cross-sectional study designs were used. Myoelectric activity and myotendon glucose uptake during submaximal isometric plantarflexion were quantified at baseline, and after eccentric rehabilitation in Achilles tendon injury patients. Results indicated that in healthy individuals the triceps surae accounted for 70% and 80% of cumulative myoelectric and metabolic activities respectively. Additionally, although muscle glucose uptake was similar to healthy controls, myoelectric activity of soleus was greater in the symptomatic leg of the Achilles tendinopathy patients. Similarly, Achilles tendon glucose uptake in both legs of the tendinopathy patients was higher than that of healthy controls. The significant reduction in the maximal plantarflexion force caused by Achilles tendinopathy was eliminated by 12 weeks of heavy-load eccentric rehabilitation. Furthermore, the rehabilitation caused a greater glucose uptake in both soleus and lateral gastrocnemius of the symptomatic leg, while medial gastrocnemius and flexor hallucis longus had higher uptake in the asymptomatic leg. Conversely, the Achilles tendon glucose uptake was not affected by eccentric rehabilitation. Regarding electro-myography, significant rise in the activity of lateral gastrocnemius was evident after the rehabilitation. Eccentric rehabilitation was also effective in reducing self-reported severity of Achilles tendinopathy. In the Achilles tendon rupture patient, all plantarflexors and Achilles tendon displayed substantially higher glucose uptake than in the control subject followed by considerable reduction due to eccentric rehabilitation.


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City (for University):
University of Jyväskylä