Influence of sex-specific concurrent changes in age, maturity status, and morphological covariates on the development of peak ventilatory variables in 10-17-year-olds

Differential control of respiratory frequency and tidal volume during exercise

The lack of a testable model explaining how ventilation is regulated in different exercise conditions has been repeatedly acknowledged in the field of exercise physiology. Yet, this issue contrasts with the abundance of insightful findings produced over the last century and calls for the adoption of new integrative perspectives. In this review, we provide a methodological approach supporting the importance of producing a set of evidence by evaluating different studies together-especially those conducted in 'real' exercise conditions-instead of single studies separately. We show how the collective assessment of findings from three domains and three levels of observation support the development of a simple model of ventilatory control which proves to be effective in different exercise protocols, populations and experimental interventions. The main feature of the model is the differential control of respiratory frequency (f_R) and tidal volume (V_T); f_R is primarily modulated by central command (especially during high-intensity exercise) and muscle afferent feedback (especially during moderate exercise) whereas V_T by metabolic inputs. Furthermore, V_T appears to be fine-tuned based on f_R levels to match alveolar ventilation with metabolic requirements in different intensity domains, and even at a breath-by-breath level. This model reconciles the classical neuro-humoral theory with apparently contrasting findings by leveraging on the emerging control properties of the behavioural (i.e. f_R) and metabolic (i.e. V_T) components of minute ventilation. The integrative approach presented is expected to help in the design and interpretation of future studies on the control of f_R and V_T during exercise.

Sex-Related Differences in Oxygen Consumption Recovery After High-Intensity Rowing Exercise During Childhood and Adolescence

PURPOSE

To determine sex-related differences in oxygen consumption (V˙O2) recovery after high-intensity exercise during childhood and adolescence.

METHODS

Forty-two boys and 35 girls (10-17 y) performed a 60-second all-out test on a rowing ergometer. Postexercise V˙O2 recovery was analyzed from (1) the V˙O2 recovery time constant obtained from a biexponential model (τ1V˙O2) and (2) excess postexercise oxygen consumption calculated over a period of 8 minutes (EPOC8) and until τ1V˙O2 was reached (EPOCτ1). Multiplicative allometric modeling was used to assess the concurrent effects of body mass or lean body mass, and age on EPOC8 and EPOCτ1.

RESULTS

EPOC8 increased significantly more in boys from the age of 14 years. However, the sex difference was no longer significant when EPOC8 was analyzed using an allometric model including body mass + age or lean body mass + age. In addition, despite a greater increase in EPOCτ1 in boys from the age of 14 years, τ1V˙O2 was not significantly different between sexes whatever age.

CONCLUSION

While age and lean body mass accounted for the sex-related differences of EPOC during childhood and adolescence, no significant effect of age and sex was observed on the V˙O2 recovery time constant after high-intensity exercise.

Ventilatory responses at submaximal exercise intensities in healthy children and adolescents during the growth spurt period: a semi-longitudinal study

PURPOSE

To identify the changes of ventilation ([Formula: see text]_E), tidal volume (V_T) and respiratory frequency (fr) at different incremental step test intensities during maturation of children and adolescents.

METHODS

A semi-longitudinal study was conducted on 68 healthy untrained boys and girls aged 11-17 years. The subjects were separated into three distinct age groups. [Formula: see text]_E, V_T and fr parameters were evaluated annually during 3 years by modifying incremental step test intensities according to ventilatory threshold (V_Th) level (30, 60 and 90% of [Formula: see text]O_2max). Absolute and relative values of ventilatory responses were analyzed and compared according to age and developmental phase.

RESULTS

(1) Height, weight, lean body mass and vital capacity increased significantly from 11 to 17 years of age. (2) [Formula: see text]O_2max, [Formula: see text]_E, and V_T increased during maturation even when exercise intensity changed, especially from 11 to 15 years of age. On the other hand, fr showed a decreasing trend.

CONCLUSION

Increases of V_T are the main reason for [Formula: see text]_E increases during maturation of children. fr decreased independently of total body mass during maturation. [Formula: see text]_E.kg^-1 was stable despite intensity variations. V_T.kg^-1 increased significantly from 11 to 15 years then stabilized at 17 years. Lean body mass seems to explain the evolution of V_T.kg^-1 during maturation.