Mechanical-ventilatory responses to peak and ventilation-matched upper- versus lower-body exercise in normal subjects.

NEW FINDINGS: What is the central question of this study? To what extent are the mechanical-ventilatory responses to upper-body exercise influenced by task-specific locomotor mechanics? What is the main finding and its importance? When compared to lower-body exercise performed at similar ventilations, upper-body exercise was characterised by tidal volume constraint, dynamic lung hyperinflation and an increased propensity towards neuromechanical uncoupling of the respiratory system. Importantly, these responses were independent of respiratory dysfunction and flow limitation. Thus, the mechanical-ventilatory responses to upper-body exercise are attributable, in part, to task-specific locomotor mechanics (i.e., non-respiratory loading of the thorax). ABSTRACT: Aim : To determine the extent to which the mechanical-ventilatory responses to upper-body exercise are influenced by task-specific locomotor mechanics. METHODS: Eight healthy men (mean ± SD, age = 24 ± 5 y; mass = 74 ± 11 kg; stature = 1.79 ± 0.07 m) completed two maximal exercise tests, on separate days, comprising 4-min stepwise increments of 15 W during upper-body exercise (arm-cranking) or 30 W during lower-body exercise (leg-cycling). The tests were repeated at work rates calculated to elicit 20, 40, 60, 80, and 100% of peak ventilation achieved during arm-cranking (V̇E,UBE ). Exercise measures included pulmonary ventilation and gas exchange, oesophageal pressure-derived indices of respiratory mechanics, operating lung volumes, and expiratory flow limitation. RESULTS: Subjects exhibited normal resting pulmonary function. Arm-crank exercise elicited significantly lower peak values for work rate, V̇O2 , V̇CO2 , V̇E , and VT (p < 0.05). At matched ventilations, arm-crank exercise restricted tidal volume expansion relative to leg-cycle exercise at 60% V̇E,UBE (1.74 ± 0.61 vs. 2.27 ± 0.68 L, p < 0.001), 80% V̇E,UBE (2.07 ± 0.70 vs. 2.52 ± 0.67 L, p < 0.001) and 100% V̇E,UBE (1.97 ± 0.85 vs. 2.55 ± 0.72 L, p = 0.002). Despite minimal evidence of expiratory flow limitation, ERV was significantly higher during arm-crank versus leg-cycle exercise at 100% V̇E,UBE (39 ± 8 vs. 29 ± 8% VC, p = 0.002). At any given ventilation, arm-cranking elicited greater inspiratory effort (oesophageal pressure) relative to thoracic displacement (tidal volume). CONCLUSIONS: Arm-crank exercise is sufficient to provoke respiratory-mechanical derangements (restricted tidal volume expansion, dynamic hyperinflation, neuromechanical uncoupling) in subjects with normal pulmonary function and expiratory flow reserve. These responses are likely attributable to task-specific locomotor mechanics (i.e., non-respiratory loading of the thorax). This article is protected by copyright. All rights reserved.