Building physiological reserve in immobilisation: does nutritional supplementation work?

Bostock, Emma Louise (2015) Building physiological reserve in immobilisation: does nutritional supplementation work? Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Introduction: Disuse models, such as limb immobilisation, result in profound changes in skeletal muscle morphology and function. Exercise prescription would be the recommended intervention to prevent immobilisation-induced atrophy and declines in maximal voluntary strength. Nutritional supplementation may stand as a viable intervention to combat muscle atrophy with disuse, when exercise is an unpractical therapeutic option. Aims: To (1) investigate the multifactorial effects of short-term upper limb sling immobilisation and (2) determine whether three potential protein-sparing modulators (essential amino acids (EAA), omega-3 (-3) and vitamin D) would attenuate the anticipated deleterious effects of immobilisation. Methods: Measures of muscle and sub-cutaneous adipose thickness (Brightness mode ultrasonography), body composition (dual-energy x-ray absorptiometry), arm girth (anthropometry), isometric and isokinetic elbow torque (dynamometry), co-contraction (electromyography (EMG)), muscle fatigability (dynamometry and EMG), arterial blood flow (Doppler ultrasound) and endocrine profile (enzyme-linked immunosorbent assay and colorimetry), were taken before and after arm immobilisation in a mixed sex population. Supplementation of EAA (n = 9 vs. placebo n = 7) during three weeks of immobilisation, -3 (n = 8) or vitamin D (n = 8) during two weeks of immobilisation (placebo n = 8) and EAA for two weeks pre-immobilisation (n = 5 vs. placebo n = 5). Main findings: Immobilisation resulted in decreases in muscle thickness, arm girth, lean mass, isometric and isokinetic elbow torque, and an increase in sub-cutaneous adipose thickness. Muscle fatigability, resting arterial blood flow, EMG co-contraction and endocrine profile were unchanged. At the current dosage -3 supplementation only attenuated the increase in sub-cutaneous adipose thickness. Despite some trends, neither -3 nor vitamin D supplementation attenuated any other parameters. EAA supplementation during immobilisation impacted positively on the immobilisation-induced changes in the structural and functional characteristic of the remaining muscle. EAA supplementation before immobilisation did not attenuate the immobilisation-induced changes in muscle structure and function. Conclusion: Although EAA supplementation only showed some benefit to muscle size and function with immobilisation, it was confirmed that the sling immobilisation model used in the thesis, is a suitable model for observing the effects of relatively short-term immobilisation. The findings of the thesis are relevant to both sporting (e.g. off-season detraining modulation) as well as clinical (e.g. injury/illness induced short-term immobilisation/bed rest) populations. This relatively short-term sling immobilisation provides a model to be used to assess other supplements and treatments in future studies. The modest effect of supplementation suggests further research into either: a) more at risk populations (e.g. injury or ageing); b) larger doses of these supplements.