Small muscle mass aerobic exercise in health and disease: Unique insights into muscle vascular and metabolic control and performance

Abstract Studies of small muscle mass exercise (SMME) have revealed that the peripheral O 2 transport–utilization cascade is a dynamically regulated system in which perfusive and diffusive components can be selectively amplified, redistributed and mechanically limited depending on contraction pattern, recruitment strategy and intramuscular pressure development. By relatively unbridling skeletal muscle from systemic circulatory restraint, SMME can expose both the maximal capacity and the intrinsic mechanical vulnerabilities of convective and microvascular O 2 delivery () in humans. The evidence reviewed herein demonstrates that kinetics in young healthy individuals, performing cycling or SMME, are not limited by per se. With mass‐specific blood flows and diffusive conductance being markedly elevated during SMME, intramuscular metabolic regulation remains the dominant determinant of kinetics, while alterations in ‐to‐ matching primarily shape fatigue development, metabolite accumulation and force economy rather than the speed of the kinetics. SMME alters not only the pattern of muscle recruitment but also the balance between and in a muscle‐specific manner, uncoupling activation from deoxygenation in selected muscles. Above critical power, mechanical impedance to both conduit and microvascular blood flow can emerge, linking peripheral perfusion directly to metabolic instability and exercise intolerance. By isolating active muscle mass, SMME reveals whether a mitochondrial and microvascular metabolic reserve exists at peak exercise, and whether this reserve can be restored, or at least improved, through focused training. From a translational perspective, SMME provides a uniquely powerful framework to both diagnose and therapeutically target peripheral limitations in patients whose exercise intolerance is traditionally ascribed to central or ventilatory constraints.