Breathing pattern during exercise in untrained children

Cardio-Respiratory and Muscle Oxygenation Responses to Submaximal and Maximal Exercise in Normobaric Hypoxia: Comparison between Children and Adults

As differential physiological responses to hypoxic exercise between adults and children remain poorly understood, we aimed to comprehensively characterise cardiorespiratory and muscle oxygenation responses to submaximal and maximal exercise in normobaric hypoxia between the two groups. Following familiarisation, fifteen children (Age = 9 ± 1 years) and fifteen adults (Age = 22 ± 2 years) completed two graded cycling exercise sessions to exhaustion in a randomized and single-blind manner in normoxia (NOR; FiO2 = 20.9) and normobaric hypoxia (HYP; FiO2 = 13.0) exercises conditions. Age-specific workload increments were 25 W·3 min−1 for children and 40 W·3 min−1 for adults. Gas exchange and vastus lateralis oxygenation parameters were measured continuously via metabolic cart and near-infrared spectroscopy, respectively. Hypoxia provoked significant decreases in maximal power output PMAX (children = 29%; adults 16% (F = 39.3; p < 0.01)) and power output at the gas exchange threshold (children = 10%; adults:18% (F = 8.08; p = 0.01)) in both groups. Comparable changes were noted in most respiratory and gas exchange parameters at similar power outputs between groups. Children, however, demonstrated, lower PETCO2 throughout the test at similar power outputs and during the maintenance of V˙CO2 at the maximal power output. These data indicate that, while most cardiorespiratory responses to acute hypoxic exercise are comparable between children and adults, there exist age-related differential responses in select respiratory and muscle oxygenation parameters.

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.

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).

Prepubescents' ventilatory responses to exercise with reference to sex and body size

STUDY OBJECTIVES

To examine the ventilatory responses of prepubescent children to submaximal and peak exercise using appropriate allometric modeling to control for differences in body size.

DESIGN

Cross-sectional study of a representative sample of children.

SETTING

Middle schools (8 to 11 years) in Exeter, UK.

PARTICIPANTS

We studied 101 boys and 76 girls aged 11.1 (0.4) years and classified Tanner stage 1 for pubic hair (no true pubic hair).

MEASUREMENTS

At rest: stature, mass, sum of skinfolds, hemoglobin concentration, FVC, and FEV1. During treadmill exercise at 7, 8, 9, and 10 km/h, and at peak exercise: oxygen uptake (VO2), minute ventilation (VE), tidal volume (VT), and respiratory frequency (Rf).

RESULTS

At peak exercise, boys' VO2, VE, and VT were significantly (p<0.01) higher than girls' values and remained so even when the influence of body size was controlled using allometric principles. There were no significant (p>0.05) sex differences in Rf or the ratios VT/FVC or VE/VO2. When data were compared at the same relative exercise intensity (ie, 70 to 75% or 80 to 85% peak VO2), no significant (p>0.05) sex differences in Rf, VT/FVC, or VE/VO2 were detected. Boys' higher (p<0.001) VO2 values were reflected by their higher VE which remained higher than values for girls at both submaximal levels even when the influence of body size was covaried out.

CONCLUSIONS

Prepubescent boys demonstrate higher peak VO2 than girls and this is supported by a higher VE and VT, even when the influence of body size is accounted for using allometry. Other ventilatory responses to both peak exercise and exercise at the same relative intensity are remarkably similar in both boys and girls.

Ventilatory responses to imagined exercise

We studied whether the ventilatory responses to imagined exercise are influenced by automatic processes. Twentynine athletes produced mental images of a sport event with successive focus on the environment, the preparation, and the exercise. Mean breathing frequency increased from 15 to 22 breaths/min. Five participants reported having voluntarily controlled breathing, two of them during preparation. Twenty participants reported that their breathing pattern changed during the experiment: 11 participants were unable to correctly report on the direction of changes in frequency, and 13 incorrectly reported changes in amplitude. This finding suggests that these changes were not voluntary in most participants and may therefore reveal automatic forebrain influences on exercise hyperpnea. However, these changes may also reflect nonspecific processes (e.g., arousal) different from those occurring during actual exercise.

Respiratory muscle function in trained and untrained adolescents during short-term high intensity exercise

The breathing pattern and respiratory muscle function were investigated in ten trained and ten untrained adolescents (aged 15-16 years) while undergoing an incremental intensity exercise test on a cycle ergometer up to 80% maximal oxygen consumption (VO2max), maintained to exhaustion. Before and after exercise, maximal inspiratory (PImax) and expiratory (PEmax) pressures were measured at residual volume and total lung capacity, respectively. During exercise, the breathing pattern [tidal volume (VT), respiratory frequency (fR), ventilation] and the relative contribution of ribcage and abdomen to VT were assessed using inductance plethysmography. Electromyographic activities of transversus abdominis (EMGtr) and diaphragm (EMGdi) muscles were recorded and analysed during exercise. There was a difference in the change in the pattern of breathing between the trained and the untrained group; fR increased significantly (P < 0.05) at 40% VO2max for the untrained group. Before exercise there was no difference in the maximal respiratory pressures. Up to 60% and 80% VO2max, transversus abdominis and diaphragm muscle activity increased significantly in the trained adolescents. However in this group, no evidence of respiratory muscle fatigue appeared: PImax, PEmax and the frequency spectrum of EMGtr and EMGdi were not altered by exercise up to exhaustion. In the untrained group, who had high ventilatory responses, expiratory muscle function was unchanged at the end of the exercise, but signs of inspiratory muscle fatigue appeared in that PImax was significantly decreased after exercise.

Evaluation of breath-by-breath measurement of respiratory gas exchange in pediatric exercise testing

In adults, breath-by-breath analysis has been used for measuring respiratory gas exchange during exercise. The present study evaluates the validity and reproducibility of this method in children. In 21 patients with various types of congenital heart disease, steady state exercise testing was performed on a motor-driven treadmill. Based on simultaneous measurements of VO2, VCO2, VE and R, comparisons were made between the breath-by-breath and Douglas bag methods. No significant differences were found between both methods for any of the variables. In seven other patients the reproducibility of cardiorespiratory variables during exercise was assessed. No significant difference was found for the cardiorespiratory variables during any of the tests and the coefficients of variation were comparable to data obtained in adults. It is concluded that the breath-by-breath method for measuring respiratory values can be applied in children with an acceptable degree of validity and reproducibility.

Influence of anthropometric characteristics on changes in maximal exercise ventilation and breathing pattern during growth in boys

The aim of this study was to investigate the effect of growth on ventilation and breathing pattern during maximal exercise oxygen consumption (VO2max) and their relationships with anthropometric characteristics. Seventy six untrained schoolboys, aged 10.5-15.5 years, participated in this study. Anthropometric measurements made included body mass, height, armspan, lean body mass, and body surface area. During an incremental exercise test, maximal ventilation (VEmax), tidal volume (VTmax), breathing frequency (fmax), inspiratory and expiratory times (tImax and tEmax), total duration of respiratory cycle (tTOTmax), mean inspiratory flow (VT/tImax), and inspiration fraction (tI/tTOTmax) were measured at VO2max. A power function was calculated between anthropometric characteristics and ventilatory variables to determine the allometric constants. The results showed firstly, that VEmax, VTmax, tImax, tEmax, tTOTmax, and VT/tImax increased with age and anthropometric characteristics (P less than 0.001), fmax decreased (P less than 0.001), and tI/tTOTmax remained constant during growth; secondly that lean body mass explained the greatest percentage of variance of VEmax (62.1%), VTmax (76.8%), and VT/tImax (70.6%), while anthropometric characteristics explained a slight percentage of variance of fmax and timing; and thirdly that VEmax, VTmax, and VT/tImax normalized by lean body mass did not change significantly with age. We concluded that at VO2max there were marked changes in ventilation and breathing pattern with growth. The changes in VEmax, VTmax, and VT/tImax were strongly related to the changes in lean body mass.