Exercise-induced breathing patterns of youth are related to age and intensity

The influences of sex, age, exercise intensity, and end-tidal CO(2) on the inspiratory drive ([V(T) kg(-1)] x T(i)(-1)) and respiratory timing (T(i) x T(tot)(-1)) components of ventilation were examined in 295 youth (138 females, 157 males); similarly distributed 8-18 years of age. Ventilatory and metabolic measures were collected breath-by-breath at rest and during a slow walk (4.0 km h(-1)), fast walk (5.6 km h(-1)) and run (8.0 km h(-1)). Regression modeling for drive (age, sex, and P(ET)CO(2)) found that sex was significant (R (2) < 0.017; P < 0.05) for rest and running, but not walking. Compared to rest, drive increased by 120% for the slow walk, 217% for the fast walk and 258% for the run (P < 0.0001). Drive decreased with age (P < 0.0001): rest = 0.41 ml kg(-1) s(-1) year(-1); slow walk = 0.90 ml kg(-1) s(-1) year(-1); fast walk = 1.30 ml kg(-1) s(-1) year(-1); and run = 1.47 ml kg(-1) s(-1) year(-1). In the regression models for timing, sex provided approximately 1% of the variance during the run, but was not significant during rest or walking. Timing increased with exercise intensity by approximately 0.02 units (P < 0.001), but decreased by approximately 0.002 units year(-1) with age for all conditions (P < 0.003). Changes in drive and timing were marginally related to end-tidal CO(2) (exercise R(2) < 0.063 for all models). These results suggest that in the control of inspiratory drive and timing during exercise in youth, sex is of minor importance but there are age-related changes which are marginally associated with CO(2).