Rook, Karen M; (1996) The storage of elastic energy by the muscle tendon complex: The effects of tendon compliance and muscle strength and the implications for locomotion. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

1) A computer model of a hopping "beast" (a muscle tendon complex) was developed to show how the energetics of hopping maybe affected by changes in the compliance of the tendon and changes in muscle strength. The model shows firstly for a given spring stiffness there is a sharp optimum for the amount of muscle. Secondly for a given mass of "beast", there is an optimum spring stiffness, but it is not a sharp optimum. 2) In men it was found that a 29% reduction in maximum voluntary force per cross sectional area (MVF/CSA) of the adductor pollicis muscle, happens gradually with age. The decline in men begins at about 60 years of age. The time course of the decline is similar to the time course of the decline in free testosterone levels, which is known to decline also at about 60 years of age (McKinlay, 1989). This suggests that in men, reduced testosterone levels might be responsible for the reduced MVF/CSA associated with old age. 3) Quick length release experiments were conducted on mouse soleus muscle to determine its compliance. The compliance of the three components in series add up: the tendon, the aponeurosis and the crossbridges. In order to determine what proportion of the total compliance is due to each component, the timing of the T1 to T2 transition needs to be known. The T1 to T2 transition was found to be faster in mouse soleus muscle than that found by Huxley and Simmons (1971) in frog muscle. It is concluded that 41 % of the compliance of mouse soleus muscle is due to the crossbridges and 59% due to aponeurosis compliance. 4) In ovariectomized and castrated mice it was found that the extensor digitorum longus tendons were approximately 15% more compliant than in aged matched control mice. Indicating that in the absence of oestrogen and testosterone the increase in stiffness of the tendon with age is inhibited.

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