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

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 ((V) over dot(E)) showed a similar time course and a large correlation with (V) over dotCO(2) in all the tests. Nevertheless, (V) over dotCO(2) was associated more with (V) over dot(E) than with V-T because V-T seems to adjust continuously on the basis of f(R) levels to match (V) over dot(E) with (V) over dotCO(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.

Differentiating between respiratory frequency (fR) and tidal volume (VT) may improve our understanding of exercise hyperpnoea because fR and VT seem to be regulated by different inputs. We designed a series of exercise manipulations to improve our understanding of how fR and VT 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, VT or the amount of muscle activation. However, fR dissociates from RPE during moderate exercise. Both VT and minute ventilation (_VE) showed a similar time course and a large correlation with _VCO2in all the tests. Nevertheless, _V CO2 was associated more with _V E than with VT because VT seems to adjust continuously on the basis of fR levels to match _VE with _V CO2. The present findings provide novel insight into the differential control of fR and VT – 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.