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The pulmonary oxygen uptake (pVO₂) kinetic response at the onset of exercise provides a noninvasive window into the metabolic activity of the muscle and a valuable means of increasing our understanding of developmental muscle metabolism. However, to date only limited research has been devoted to investigating the pVO₂ kinetic response during exercise in children and adolescents. From the rigorous studies that have been conducted, both age- and sex-related differences have been identified. Specifically, children display a faster exponential rise in the phase II pVO₂ kinetics, which are purported to reflect the rise in muscle O₂ consumption, during moderate, heavy and very heavy intensity exercise compared with adults. Furthermore, for heavy and very heavy exercise, the O₂ cost of exercise is higher for the exponential phase and the magnitude of the pVO₂ slow component is smaller in young children. Sex-related differences have been identified during heavy, but not moderate exercise, with prepubertal boys displaying a faster exponential phase II pVO₂ kinetic response and a smaller pVO₂ slow component compared with prepubertal girls. The mechanisms underlying these differences are currently poorly understood, and form the basis for future research in this area. However, it is hypothesized that an age-related modulation of the muscle phosphate feedback controllers to signal an increased rate of oxidative phosphorylation and/or altered muscle fiber type recruitment strategies have the potential to play an important role. Overall, the data support the view that at the onset of exercise children have an enhanced potential for oxidative metabolism in the myocyte compared with adults.

Sprinting is an important physical capacity and the development of sprint ability can take place throughout the athlete’s growth. The purpose of this study therefore was to determine if the kinematics and kinetics associated with maximum sprint velocity differs in male youth participants of different maturity status (pre, mid- and postpeak height velocity (PHV)) and if maximum sprint velocity is determined by age, maturity or individual body size measurement. Participants (n = 74) sprinted over 30 meters on a nonmotorized treadmill and the fastest four consecutive steps were analyzed. Pre-PHV participants were found to differ significantly (p < .05) to mid- and post-PHV participants in speed, step length, step frequency, vertical and horizontal force, and horizontal power (~8-78%). However, only relative vertical force and speed differed significantly between mid and post-PHV groups. The greatest average percent change in kinetics and kinematics was observed from pre- to mid-PHV (37.8%) compared with mid- to post- PHV groups (11.6%). When maturity offset was entered as a covariate, there was no significant difference in velocity between the three groups. However, all groups were significantly different from each other when age was chosen as the covariate. The two best predictors of maximal velocity within each maturity group were power and horizontal force (R ² = 97−99%) indicating the importance of horizontal force application while sprinting. Finally, maturity explained 83% of maximal velocity across all groups.

Peak oxygen consumption and anaerobic threshold are both decreased in patients with a Fontan-type circulation. This study wanted to evaluate oxygen uptake kinetics at the onset and at the end of of a steady-state low-level exercise. The delay in cardiorespiratory response was evaluated by calculating the oxygen deficit at the onset of exercise and the recovery half-time at the end. Twelve patients with Fontan circulation (aged 11.4 − SD 5.1 year; 5.2 − 1.9 year after surgery) and 26 normal controls of comparable age (11.3 − 2.2 year) were submitted to a constant-load exercise test of six minutes on a treadmill (speed 5 km/h, inclination 4%). Gas exchange was measured using a breath-by-breath technique. The normalized oxygen deficit was calculated by subtracting the oxygen uptake (VO₂) values measured at the onset of exercise from the steady-state VO₂ obtained at the end of exercise. These differences were cumulated and expressed as a percentage of the cumulated oxygen cost for the 6 min exercise test. The half-time recovery time was defined as the time to reach 50% of the end exercise VO₂ value. The normalized oxygen deficit was significantly higher in Fontan-patients compared to the control group (10.2 − 4.6% vs. 6.1 − 1.3%; p < .001). Also the recovery half-time was significantly higher in the patient group compared to the control group (74.2 − 25.6 s vs. 51.2 − 10.8 s; p < .05). A blunted heart rate response was present in the patients during the first two minutes of exercise, indicating that a slowed cardiac output response could explain the decreased oxygen kinetics in Fontan-patients.

The influence of training status on pulmonary VO₂ recovery kinetics, and its interaction with maturity, has not been investigated in young girls. Sixteen prepubertal (Pre: trained (T, 11.4 ± 0.7 years), 8 untrained (UT, 11.5 ± 0.6 years)) and 8 pubertal (Pub: 8T, 14.2 ± 0.7 years; 8 UT, 14.5 ± 1.3 years) girls completed repeat transitions from heavy intensity exercise to a baseline of unloaded exercise, on both an upper and lower body ergometer. The VO2 recovery time constant was significantly shorter in the trained prepubertal and pubertal girls during both cycle (Pre: T, 26 ± 4 vs. UT, 32 ± 6; Pub: T, 28 ± 2 vs. UT, 35 ± 7 s; both p < .05) and upper body exercise (Pre: T, 26 ± 4 vs. UT, 35 ± 6; Pub: T, 30 ± 4 vs. UT, 42 ± 3 s; both p < .05). No interaction was evident between training status and maturity. These results demonstrate the sensitivity of VO₂ recovery kinetics to training in young girls and challenge the notion of a “maturational threshold” in the influence of training status on the physiological responses to exercise and recovery.

Physical activities involving impact loading are important for improving bone strength and mineral density in children. There is little research quantifying impact loads associated with various high-impact activities. Purpose: Examine the magnitude of peak ground reaction forces (pGRF) across different jumping activities in children. Methods: Eight children between 8 and 12 years (9.63 [1.49] y; 1.42 [0.08] m; 33.69 [4.81] kg), performed 5 trials of a broad jump, countermovement jump, jumping jack, leap jump, and drop jump on a force plate. The pGRF were determined during the landing phase of each activity and expressed in units of body weight (BW). A repeated-measures analysis of variance was employed to assess differences in pGRF across activities. Results: Drop jump exhibited the greatest pGRF (3.09 [0.46] BW) in comparison with the vertical jumping jack (2.56 [0.21] BW; P < .001) and countermovement jump (2.45 [0.22] BW; P = .001), as well as the horizontal broad jump (2.25 [0.2] BW; P = .003), and leap jump (2.01 [0.1] BW; P = .002). Conclusion: Peak loads between 2 and 3.1 BW were exhibited across each jump activity, which is moderate compared with magnitudes in most jump interventions seeking to improve bone health. All conditions except drop jump exhibited loading <3 BW, suggesting these activities may not produce sufficient loads to improve bone outcomes.

The primary objective of this study was to investigate the influence of segmental mass and body composition on the upper extremity biomechanics of overweight youth participating in baseball activities. The study used a regression framework to investigate the relationship between whole body, throwing arm segmental mass and body composition measures to kinetic variables about the shoulder and elbow. The multivariate regression results indicated a strong positive significant relationship between each of the mass variables to that of the moment variables about the shoulder and elbow. Participants who had a greater percentage of fat mass produced greater injury correlated moments about the shoulder and elbow.