Ventilatory responses to static handgrip exercise

Previous research indicates that fatiguing static exercise causes hyperventilation and a decrease of end-tidal CO₂ partial PET(CO₂). The objectives of this study were 1) to examine the changes in pattern of breathing during static exercise, and 2) to define the isocapnic ventilatory response. Six healthy males were studied once a week at one of three levels of static handgrip exercise: 15, 25, or 30% maximum voluntary contraction (MVC) was sustained for 5 min while holding PET(CO₂) constant or allowing it to run free. During 25 and 30% MVC, we observed 1) progressive increases in mean tidal volume (VT), inspiratory ventilation (V̇(I), V(T)/T(I), heart rate (HR), and arterial BP, 2) increased breath-to-breath variability of V(T), 3) no significant changes in respiratory frequency (f), and 4) progressive decreases in PET(CO₂). Keeping PET(CO₂) constant at preexercise levels did not change the pattern or magnitude of the ventilatory response to exercise. The time course and magnitude of the subjects' perceived effort resembled the time course and magnitude of the ventilatory response. The variability of V(T) during the response to static exercise suggests an element of control instability. The identical ventilatory responses during hypocapnic and isocapnic conditions may result from the slow response of the central chemoreceptors; an overriding influence of muscle afferents; and/or increased central command arising with fatigue.