Descending motor drive does not interact with muscle metaboreflex for ventilation regulation during rhythmic exercise...

The muscle metaboreflex effect on pulmonary ventilation (V̇_E) regulation is more apparent during rhythmic exercise than rest, possibly because this reflex interacts with other mechanisms regulating V̇_E during voluntary contractions, such as central command. Therefore, we tested whether one part of central command, the descending component of motor execution (i.e., descending motor drive), and the muscle metaboreflex interact synergistically to regulate V̇_E. Thirteen healthy adults (9 men) completed four experiments in random order under isocapnia. The muscle metaboreflex was activated by rhythmic handgrip exercise at 60% maximal voluntary contraction (MVC) force with the dominant hand. Then, the muscle metaboreflex remained active during a 4-min recovery period via postexercise circulatory occlusion (PECO), or it was inactivated, maintaining free blood flow to the dominant upper limb. During the last 2 min of the handgrip exercise recovery, participants either performed rhythmic voluntary plantar flexion with the dominant leg at 30% MVC torque to generate descending motor drive or the dominant leg's calf muscles were involuntarily activated by electrical stimulation at a similar torque level (i.e., without descending motor drive). V̇_E increased to a similar level during handgrip exercise in all conditions (≈22 L/min, P = 0.364). PECO maintained V̇_E elevated above recovery with free blood flow (≈17 L/min vs. ≈13 L/min, P = 0.009). However, voluntary and involuntary plantar flexion with or without PECO evoked similar V̇_E responses (Δ ≈ 4 L/min, P = 0.311). Therefore, an interaction between descending motor drive and muscle metaboreflex is not ubiquitous for V̇_E regulation during rhythmic exercise.NEW & NOTEWORTHY Voluntary (i.e., with descending motor drive) and involuntary (i.e., no descending motor drive) plantar flexion elicited similar ventilatory responses when postexercise circulatory occlusion was or was not used in an upper limb. These results indicate that the descending motor drive component of the central command and the muscle metaboreflex do not interact to regulate pulmonary ventilation during rhythmic exercise, which suggests that a supposed interaction between central command-muscle metaboreflex is more complex than previously thought.