Central motor output does not interact with muscle metaboreceptors input for ventilation regulation during dynamic exercise in health humans
Authors: Gomes Felipe S. , Lopes Thiago R. , Bruce Richard M. , Silva Bruno M. 
Published: May 2024

INTRODUCTION: The muscle metaboreflex typically does not contribute to ventilation regulation when activated in isolation at rest via post-exercise circulatory occlusion (PECO), but it might synergistically interact with other mechanisms operating during voluntary exercise. Efferent signals from brain areas involved in the motor control of appendicular skeletal muscles to the medulla (i.e., central command) supposedly contribute to ventilation regulation during voluntary exercise. Therefore, we sought to test the hypothesis that central motor output interacts with muscle metaboreceptor input, generating a greater ventilatory response to PECO during voluntary exercise than electrically-induced involuntary exercise. METHODS: Thirteen healthy adults (4 women, age: 26 ± 5 years) participated in the study. Each participant completed four experiments in random order. Two experiments were accomplished per visit at 30-minute intervals. The interval between visits was at least two and at most seven days. The muscle metaboreflex was activated by rhythmic handgrip exercise with the dominant hand at 60% of the maximal voluntary contraction force with a 2-s duty cycle. Then, the muscle metaboreflex remained active for a 4-minute recovery period via PECO, or it was inactivated via free circulation to the exercised arm. During the last 2-minutes of the handgrip exercise recovery, participants either performed unilateral voluntary plantar flexion with the dominant leg to generate central motor output or the dominant leg’s calf was involuntarily activated by electrical stimulation not to have central motor output. Voluntary and involuntary calf contractions were performed at the same external workload. A rebreathing circuit maintained isocapnia throughout all experiments. A bidirectional turbine measured breath-by-breath airflow. Heart rate was measured via ECG, and arterial pressure by auscultation in a resting arm. RESULTS: Ventilation, heart rate, and arterial pressure increased during handgrip exercise similarly in all experiments. PECO-induced muscle metaboreflex activation maintained ventilation (Δ = 5.4 ± 5.2 l/min, P = 0.003), heart rate (Δ = 6.6 ± 8.0 bpm, P = 0.011) and systolic arterial pressure (Δ = 28.4 ± 14.8 mmHg, P < 0.001) elevated above the control handgrip exercise recovery with free circulation to the exercised arm. The ventilation response to voluntary plantar flexion was greater when PECO was present in the arm than when it was absent (Δ = 8.3 ± 5.6 l/min vs. 4.5 ± 2.7 l/min, P = 0.006), reproducing previous findings. However, the ventilation response to voluntary and involuntary plantar flexion with a PECO background was similar (Δ = 8.3 ± 5.6 l/min vs. 8.2 ± 6.3 l/min, P = 1.000). CONCLUSION: The data do not support that an interaction between central motor output and muscle metaboreceptors input is obligatory to generate a ventilatory response to PECO during voluntary exercise. FINANCIAL SUPPORT: grant 2023/07135-0, São Paulo Research Foundation (FAPESP); Scientific production award from the National Council for Scientific and Technological Development (CNPq; Process: 310110/2019-0). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.