The role of muscle mechano and metaboreflexes in the control of ventilation: breathless with (over) excitement?

Mechanically and metabolically sensitive thin fibre (group III and IV) muscle afferents are activated during exercise, causing reflex cardiovascular responses that are essential to normal cardiovascular control. Impaired exercise performance in some disease states can be linked to abnormal muscle mechanoreflex and muscle metaboreflex activity. A role for this same afferent feedback in contributing to the hyperpnoea of exercise and the dyspnoea experienced by some patient groups on exercise has recently received increased attention. Evidence is summarised here that supports a role for muscle mechanoreflex and muscle metaboreflex involvement in the human ventilatory response to exercise and also their synergistic interaction with the central chemoreflex during muscular activity. The effects of local muscle training induced attenuation of the human muscle metaboreflex on this synergistic interaction and associated decrease in ventilation is discussed.