Influence of upper-body exercise on the fatigability of human respiratory muscles

PURPOSE: Diaphragm and abdominal muscles are susceptible to contractile fatigue in response to high-intensity, whole-body exercise. This study assessed whether the ventilatory and mechanical loads imposed by high-intensity, upper-body exercise would be sufficient to elicit respiratory muscle fatigue. METHODS: Seven healthy men (mean±SD: age 24±4 y; peak O2 uptake [V[Combining Dot Above]O2 peak] 31.9±5.3 ml/kg/min) performed asynchronous arm-crank exercise to exhaustion at work rates equivalent to 30% (heavy) and 60% (severe) of the difference between gas-exchange threshold and V[Combining Dot Above]O2 peak. Contractile fatigue of the diaphragm and abdominal muscles was assessed by measuring pre- to post-exercise changes in potentiated transdiaphragmatic and gastric twitch pressures (Pdi,tw and Pga,tw) evoked by supramaximal magnetic stimulation of the cervical and thoracic nerves, respectively. RESULTS: Exercise time was 24.5±5.8 min for heavy exercise and 9.8±1.8 min for severe exercise. Ventilation over the final minute of heavy exercise was 73±20 L/min (39±11% maximum voluntary ventilation [MVV]) and 99±19 L/min (53±11% MVV) for severe exercise. Mean Pdi,tw did not differ pre- to post-exercise at either intensity (p>0.05). Immediately (5-15 min) after severe exercise, mean Pga,tw was significantly lower than pre-exercise values (41±13 vs. 53±15 cmH2O, p<0.05), with the difference no longer significant after 25-35 min. Abdominal muscle fatigue (defined as ≥15% reduction in Pga,tw) occurred in 1/7 subjects after heavy exercise and 5/7 subjects after severe exercise. CONCLUSIONS: High-intensity, upper-body exercise elicits significant abdominal, but not diaphragm, muscle fatigue in healthy men. The increased magnitude and prevalence of fatigue during severe-intensity exercise is likely due to additional (non-respiratory) loading of the thorax.This is an open access article distributed under the Creative Commons Attribution License 4.0 (CCBY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 American College of Sports Medicine