Respiratory frequency and tidal volume during exercise: differential control and unbalanced interdependence

Abstract

Differentiating between respiratory frequency (f_R ) and tidal volume (V_T ) may improve our understanding of exercise hyperpnoea because f_R and V_T seem to be regulated by different inputs. We designed a series of exercise manipulations to improve our understanding of how f_R and V_T are regulated during exercise. Twelve cyclists performed an incremental test and three randomized experimental sessions in separate visits. In two of the three experimental visits, participants performed a moderate-intensity sinusoidal test followed, after recovery, by a moderate-to-severe-intensity sinusoidal test. These two visits differed in the period of the sinusoid (2 min vs. 8 min). In the third experimental visit, participants performed a trapezoidal test where the workload was self-paced in order to match a predefined trapezoidal template of rating of perceived exertion (RPE). The results collectively reveal that f_R changes more with RPE than with workload, gas exchange, V_T or the amount of muscle activation. However, f_R dissociates from RPE during moderate exercise. Both V_T and minute ventilation ( ${\dot{V}}_E$ ) showed a similar time course and a large correlation with $\dot{V}{\text{CO}}_2$ in all the tests. Nevertheless, $\dot{V}{\text{CO}}_2$ was associated more with ${\dot{V}}_E$ than with V_T because V_T seems to adjust continuously on the basis of f_R levels to match ${\dot{V}}_E$ with $\dot{V}{\text{CO}}_2$ . The present findings provide novel insight into the differential control of f_R and V_T - and their unbalanced interdependence - during exercise. The emerging conceptual framework is expected to guide future research on the mechanisms underlying the long-debated issue of exercise hyperpnoea.

Keywords: Breathing control; exercise hyperpnoea; perceived exertion; sinusoidal exercise; ventilatory pattern.