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

Differentiating between respiratory frequency (fR) and tidal volume (V T) may improve our understanding of exercise hyperpnoea because fR and V T seem to be regulated by different inputs. We designed a series of exercise manipulations to improve our understanding of how fR 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 fR changes more with RPE than with workload, gas exchange, V T or the amount of muscle activation. However, fR dissociates from RPE during moderate exercise. Both V T and minute ventilation ( V˙E ) showed a similar time course and a large correlation with V˙CO2 in all the tests. Nevertheless, V˙CO2 was associated more with V˙E than with V T because V T seems to adjust continuously on the basis of fR levels to match V˙E with V˙CO2 . The present findings provide novel insight into the differential control of fR 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