The role of exercise and amino acid supplementation in disuse-induced muscle and tendon atrophy and subsequent active recovery

Campbell, Emma-Louise (2017) The role of exercise and amino acid supplementation in disuse-induced muscle and tendon atrophy and subsequent active recovery. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Skeletal muscle atrophy due to disuse is a widespread problem arising from many situations including clinical immobilisation due to injury or disease. As individuals age, the universally observed loss of muscle mass and function known as sarcopenia compounds this problem leading to a significant reduction in locomotor ability and quality of life for sufferers. Recently there has been much work investigating ways to mitigate muscle mass loss in immobilised limbs and to aid in recovery in the post immobilisation phase. Much focus has been placed on recovery protocols based upon either resistance training, nutritional supplementation, or both. In study 1 we report an extensive data set describing in detail skeletal muscle adaptations in structure and function in response to both disuse (ULLS) and retraining. The results indicate that, 1) the loss of muscle force with 3-week unloading in humans is mostly explained by muscle atrophy and a decrease in myosin content and, 2) all the neuromuscular changes induced by this model of disuse can be fully restored after a resistance training intervention of equal duration Study 2 tests the hypothesis that increasing amino acid leucine availability by nutritional supplementation will increase muscle protein synthesis in immobilised muscle and result in mitigating the loss of lean muscle mass. In fact, we found that leucine supplementation alone was not sufficient to maintain muscle mass during 3 weeks of unilateral lower limb suspension. Study 3 examined the effect of leucine supplementation on muscle mass gains during an active recovery training program of muscles previously subjected to ULLS. Despite low participant numbers, the data suggest that leucine supplementation had no effect on the extent to which muscle recovered post ULLS. Study 4 investigates the role of training and immobilization in sarcopenia and discusses the potential of using ultrasound imaging to develop an image based biomarker of sarcopenia. Cross sectional data from both young and old individuals subjected to different loading conditions are analysed in this study. Life-long training appears to slow down the process of sarcopenia whilst periods of disuse due to injury or disease worsen the condition. The change in muscle fibre geometry exhibited in sarcopenia and disuse atrophy could potentially act as a convenient and inexpensive indicator of the onset of sarcopenia.