Profiling skeletal muscle loss during leg immobilisation and a reduced energy diet

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The nature of training and competition in the majority of popular sports dictates that debilitating injury is not uncommon when individuals engage in high musculoskeletal loading patterns and/or high impact collisions. A consequence of such injuries is that repair and remodelling of tissues and joints often requires significant periods of limb immobilisation. During immobilisation a reduction in the normal mechanical loading of skeletal muscle results in muscle wasting (atrophy). A challenge for individuals during periods of reduced physical activity (e.g. bed rest) or immobilisation is the management of body composition. The muscle unloading interaction with dietary intake has the capacity to modulate the effects of immobilisation on mechanisms regulating skeletal muscle mass. We (Areta et al. 2014) and others (Pasiakos et al. 2013) have shown that reduced total energy intake (30-40% below energy balance requirements) decreases muscle protein synthesis and results in a loss of fat mass but also muscle mass. However, higher protein intakes (>1.6 g/kg) during energy deficit may attenuate losses in lean mass (Pasiakos et al. 2013), despite an increased expression of genes associated with muscle protein breakdown (Carbone et al. 2013). How these dietary-muscle protein interactions change during periods of immobilisation is unknown. Decreased energy expenditure from cessation of physical activity with immobilisation necessitates restriction of energy intake to prevent undesirable gains in fat mass. However, whether implementing an energy deficit, despite higher protein intakes, exacerbates muscle wasting experienced during muscle unloading is unknown. Importantly, the effect of an energy deficit on the magnitude of muscle loss and the associated underlying molecular profile during immobilisation is currently unknown. The aim of this study is to determine changes in inducible gene/protein expression and skeletal muscle mass in the acute (3 d) and early (14 d) immobilisation period while under a moderate (30%) energy restriction with sufficient protein intake (1.4-1.5 g/kg). We will compare the effect of this energy deficit on muscle mass with immobilised participants in energy balance, a study previously completed in our laboratory. We hypothesize that 14 d of limb immobilisation with energy deficit will result in greater losses of total body fat, immobilised limb mass and gene expression for protein breakdown compared to immobilised limbs in energy balance.

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