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

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