Principles, Insights and Potential Pitfalls of the Non-Invasive Determination of Muscle Oxidative Capacity by Near-Infrared Spectroscopy

Skeletal muscle oxidative capacity is highly plastic, strongly associated with whole-body aerobic capacity (16, 18) and state of health. Loss of muscle oxidative capacity is associated with physical inactivity, aging and chronic disease (17), and has been implicated in the pathophysiology of obesity and diabetes (21). Evaluating these changes has traditionally been limited to invasive or costly assessments (biopsy or ³¹P MRS). To address this, Hamaoka and colleagues developed an innovative, non-invasive approach using near-infrared spectroscopy (NIRS) to quantitatively measure muscle oxygen consumption (mV̇O₂; 12) and use this to infer muscle oxidative capacity based on the mV̇O₂ recovery rate constant (k) (23; later modified 26). This technique has been subsequently used to interpret relative differences in oxidative capacity across a wide range of muscles, ages and disease states (Figure 1C). The purpose of this Viewpoint is to open a discussion on the principles, insights and potential pitfalls of using NIRS to measure k and infer muscle oxidative capacity.