Biomechanical analysis of 'heavy-load eccentric calf muscle' exercise used in the rehabilitation of achilles tendinosis
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Objective The objective of this dissertation was to firstly review studies examining the effect of a specific eccentric calf muscle exercise prescribed to achilles tendinosis subjects, and secondly to conduct a pilot study to examine the muscle activity of the triceps surae during the same eccentric exercise programme. Background Achilles tendinosis is a common achilles tendon disorder, often difficult to treat conservatively. Recently, an eccentric based exercise coined ‘heavy-load eccentric calf muscle’ training has been shown to return over 60% of achilles tendinosis sufferers back to activity with reduced pain. The mechanism behind these good results is still unknown, and there are aspects of the exercise that are not clear or standardised. The exercise is based on performing exclusively eccentric loading on the affected achilles-calf muscle complex. It is considered painful to perform, yet is repeated in 3 sets of 15 repetitions twice per day in two variations, first with knee straight, and the second with knee bent. The knee bent variation is reported to maximally facilitate muscle activity of the soleus. No studies have yet provided evidence that this selective activation occurs. Method A critical review of literature examining the use and effect of heavy-load eccentric calf muscle training in achilles tendinosis sufferers was undertaken. A table was produced to display and summarise the reviewed literature, thereby allowing comparison of their methods and findings. As a result of the critical review a pilot study was undertaken examining muscle activity of the triceps surae during heavy-load eccentric calf muscle training. Specifically, surface electromyography was used to quantify activity of the soleus and medial gastrocnemius in 23 healthy adult volunteers. Results The critical review highlighted several issues regarding subject selection, variability in the performance of exercise, pain experienced during exercise, and variation in reported results. Electromyography data from the pilot study show there was no significant difference in triceps surae muscle activity when comparing bent and straight knee techniques. Conclusion The eccentric exercise programme developed by Alfredson, Pietila, Jonsson, & Lorentzon (1998) appears to be effective in treating achilles tendinosis. The critical review highlights variation within the execution of the programme, and a lack of clarity with regard to the pain commonly experienced during the exercise. Addressing these issues may assist our understanding of the exercise. With regard to the pilot study, the findings do not support the conjecture that the soleus muscle is maximally activated when performing bent knee eccentric loading as suggested by Alfredson, Pietila, Jonsson, & Lorentzon (1998). As the current study was limited to subjects with no history of achilles injury, further research using the same methodology will be of interest in those diagnosed with achilles tendinosis.