Exercise performance after ventilatory work

Although increased ventilation is one of the most readily observed physiological responses to exercise, it is uncertain how severely this hyperpnea stresses the ventilatory muscles. As one approach to this question, we compared short-term maximal running performance in nine subjects with and without prior ventilatory work designed to reduce ventilatory muscle endurance. This work consisted of 150 min of sustained maximum ventilation performed isocapnically while the subjects were seated. Both the level of sustained expired minute ventilation and the O2 uptake associated with it slowly declined with time during this 150-min period. On the average, subjects were able to maintain two-thirds of their 12-s maximum voluntary ventilation (MVV) during this long-term breathing test. The test had no effect on subsequently measured vital capacity, forced expiratory volume in 1 s, or the MVV. However, in short-term maximal running, at constant speed upgrades increased 1% each minute until volitional exhaustion, performance after prior breathing work was reduced as compared with control (6.5 vs. 7.6 min; P less than 0.01). Subjects ceased work at significantly lower ventilation (117 vs. 124 1.min-1 BTPS; P less than 0.05) and heart rate (179 vs. 187 beats.min-1; P less than 0.01) and reached significantly lower peak O2 uptake (3.07 vs. 3.24 1.min-1 STPD; P less than 0.05) during maximal running after ventilatory work. We conclude that reduced ventilatory muscle endurance alone is sufficient to decrease short-term maximal running performance.