Defining the metabolic and neuromuscular mechanisms of skeletal muscle adaptation to reduced physical activity and subsequent recovery throughout adult lifespan

Physical inactivity is the 4th leading cause of death in the world. People with the highest prolonged sedentary time have greater chance of developing health problems such as cardiovascular disease and Type 2 diabetes, and a greater risk of dying younger. High levels of sedentary time are particularly harmful for older adults as they complete less physical activity than other age groups. Up to 20% of individuals aged over 65 are significantly debilitated due to losses in muscle mass and function (sarcopenia). Sarcopenia is associated with increased falling risk and disability.

The mechanisms driving sarcopenia remain poorly understood, however a key risk factor is known to be low physical activity. Among older adults, the reduction in muscle function is much more marked than would be predicted by the loss of muscle mass, suggesting there is likely a neuromuscular component contributing to the loss of strength and power that accompanies ageing and unloading. Preliminary data from our labs has demonstrated significant skeletal muscle dysfunction in young adults, following a step count reduction model. We propose that implementing this model with older adults will be a major step in revealing the mechanistic drivers of sarcopenia, for which novel and effective countermeasures and interventions can then be developed.

The overarching research aim is to determine the key metabolic and neuromuscular response of younger and older adults to reduced physical activity, and to subsequent re-training and recovery.

Key techniques that will be used within this research are: functional assessments, muscle quality assessment, incorporating isometric force measurement and muscle mass determination (B-mode ultrasound and DXA); muscle tone (tensiomyography); voluntary activation and excitation (peripheral nerve stimulation and surface electromyography); motor unit firing rates, number and size (intramuscular electromyography).