This paper reviews some of the statistical methods available for controlling for body size differences in the interpretation of developmental changes in exercise performance. For cross-sectional data analysis simple per body mass ratio scaling continues to be widely used, but is frequently ineffective as the computed ratio remains correlated with body mass. Linear regression techniques may distinguish group differences more appropriately but, as illustrated, only allometric (log-linear regression) scaling appropriately removes body size differences while accommodating the heteroscedasticity common in exercise performance data. The analysis and interpretation of longitudinal data within an allometric framework is complex. More established methods such as ontogenetic allometry allow insights into individual size-function relationships but are unable to describe adequately population effects or changes in the magnitude of the response. The recently developed multilevel regression modeling technique represents a flexible and sensitive solution to such problems allowing both individual and group responses to be modeled concurrently.
Joanne R. Welsman and Neil Armstrong
Neil Armstrong and Joanne R. Welsman
Over 60 years ago, Robinson published the first investigation of boys’ aerobic fitness; almost 50 years ago, Åstrand conducted his pioneering studies of both sexes. Twenty four percent of the papers published during the first 10 years of Pediatric Exercise Science (1989-98) involved the determination of peak V̇O2. Yet, the interpretation of aerobic fitness during childhood and adolescence is still shrouded with controversy. In this paper we review peak V̇O2 in relation to age, growth, maturation, and sex. We describe the increase in peak V̇O2 with age, challenge the traditional interpretation of peak V̇O2 during growth, demonstrate the independent contribution of maturation to peak V̇O2, and address the progressive divergence of boys’ and girls’ peak V̇O2, during childhood and adolescence.
Saul R. Bloxham, Joanne R. Welsman and Neil Armstrong
This study examined ergometer-specific relationships between short-term power and peak oxygen uptake (peak VO2) in children. Boys (n = 28) and girls (n = 28) age 11-12 years completed two incremental tests to exhaustion on a cycle ergometer and motorized treadmill for the determination of peak VO2. In addition, they completed two 30 s “all-out” sprint tests, one on a cycle ergometer and one on a nonmotorized treadmill for the assessment of peak power (PP) and mean power (MP). Relationships between peak VO2 and shortterm power measures were examined by sex for cycle- and treadmill-derived data using simple per-body-mass ratios and sample-specific allometric exponents to control for body size differences. From correlational analyses on scaled data, sex differences in responses were shown. In boys, PP and MP were unrelated to peak VO2 for cycle-derived measures but significantly related (r = 0.58 PP; r = 0.69 MP) for treadmill values. PP and MP were significantly related to peak VO2 for both modes of exercise in girls (r = .41−.68). In all but one case, correlation coefficients based on mass-related data were higher than those based on allometrically adjusted data.
Melitta A. McNarry, Joanne R. Welsman and Andrew M. Jones
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.
Joanne R. Welsman, Neil Armstrong and Brian J. Kirby
This study was designed to investigate the influence of sexual maturity on peak V̇O2 and blood lactate responses to exercise using serum testosterone levels as an objective measure of maturity. Testosterone levels were determined in venous blood samples obtained from 12- to 16-year-old males (n = 50). Peak V̇O2 and percentage of peak V̇O2 at blood lactate levels of 2.5 and 4.0 mmol·L−1 were determined during incremental treadmill running. Standard multiple regression revealed that body mass, age, and height explained 74% of the variance in peak V̇O2 scores. The addition of serum testosterone to the equation failed to produce a significant increase in the explained variance. Correlation coefficients between testosterone and the lactate variables were not significant (p > .05). These findings do not support the hypothesis that hormonal changes per se during sexual maturation play an important role in the development of peak V̇O2 and blood lactate responses to exercise.
Neil Armstrong, Joanne R. Welsman and Brian J. Kirby
The influence of sexual maturation on the Wingate anaerobic test performance of 100 boys and 100 girls, ages 12.2 ±0.4 years, was examined using Tanner’s indices of pubic hair and, in boys, salivary testosterone as measures of maturation. No sex differences (p > .05) in either peak power (PP) or mean power (MP) were revealed. Significant main effects (p < .01) for maturation were detected for both PP and MP expressed in W, W · kg−1, or with body mass controlled using allometric principles. Testosterone did not increase the variance in PP or MP explained by body mass alone (p > .05). No sex or maturational effects were observed for postexercise blood lactate (p > .05). Testosterone was not (p > .05) correlated with blood lactate. Thus, sexual maturation exerts an influence on PP and MP independent of body mass, but maturational effects on postexercise blood lactate remain to be proven in this age group.
Samantha G. Fawkner, Neil Armstrong, David J. Childs and Joanne R. Welsman
The purpose of this study was to assess the reliability of the ventilatory threshold using visual analysis (TVent) and a computerised v-slope method (TV - slope) with children. Twenty-two children completed 2 ramp incremental cycling tests to voluntary exhaustion. Oxygen uptake (V̇O2) at TVent was derived independently by two observers using plots of V̇E/V̇CO2, V̇E/V̇O2, PETO2 and PETCO2, V̇E and RER as a function of time. V̇O2 at TV - slope was determined by both observers using linear regression analysis of the plot of V̇CO2 against V̇O2. A TV – slope was determined for each test, although a TVent could not be found by one of the observers in 7 of the 44 tests. Inter-observer reliability was slightly better for TV - slope, and both methods had similar test-retest coefficients of repeatability (0.19 and 0.22 L • min−1, TVent and TV - slope, respectively). Although TV slope may be the method of choice, investigators should consider the 95% limits of agreement when interpreting their data.
Amândio M.C. Santos, Joanne R. Welsman, Mark B.A. De Ste Croix and Neil Armstrong
Age- and sex-related differences in optimal peak power (PPopt) and associated measures determined using a force-velocity (F-V) cycling test were examined in pre teenage, teenage and adult males and females. Absolute PPopt increased significantly with age in both males and females. With body mass controlled for using allometric scaling significant age related increases remained, an effect masked in the females when PPopt was expressed as W • kg−1. Sex differences in PPopt were minimal in the preteens but males demonstrated higher PPopt than females in both teenage and adult groups. These patterns of change with age and sex broadly reflect those obtained for Wingate Anaerobic Test determined PP but the use of a single non-optimized braking force underestimates the magnitude of any differences observed.
Mark B.A. De Ste Croix, Neil Armstrong and Joanne R. Welsman
The purpose of this study was to examine the reliability of repeated isokinetic knee extension and flexion in young children and to examine sex differences in 30 untrained subjects (16 boys and 14 girls) aged 12.2 ± 0.3 years. Total work and the percentage decline in average torque and work were recorded during 50 repetitions. Intra-class correlation coefficients indicated a strong positive correlation between test 1 and 2 for all parameters ranging from 0.36–0.95. Coefficient of variation data ranged from ± 0% to ± 5.4%. Repeatability coefficients and limits of agreement indicated that the extensors were more reliable than the flexors for both torque and work. There were no significant sex differences in any of the parameters measured. This study suggests that repeated isokinetic muscle actions of the knee, as a function of muscle endurance, can be reliably assessed in young people.
Brynmor C. Breese, Craig A. Williams, Alan R. Barker, Joanne R. Welsman, Samantha G. Fawkner and Neil Armstrong
This study examined longitudinal changes in the pulmonary oxygen uptake (pV̇O2) kinetic response to heavy-intensity exercise in 14–16 yr old boys. Fourteen healthy boys (age 14.1 ± 0.2 yr) completed exercise testing on two occasions with a 2-yr interval. Each participant completed a minimum of three ‘step’ exercise transitions, from unloaded pedalling to a constant work rate corresponding to 40% of the difference between the pV̇O2 at the gas exchange threshold and peak pV̇O2 (Δ). Over the 2-yr period a significant increase in the phase II time constant (25 ± 5 vs. 30 ± 5 s; p = .002, ω 2 = 0.34), the relative amplitude of the pV̇O2 slow component (9 ± 5 vs. 13 ± 4%; p = .036, ω 2 = 0.14) and the pV̇O2 gain at end-exercise (11.6 ± 0.6 vs. 12.4 ± 0.7 mL·min−1·W−1; p < .001, ω 2 = 0.42) were observed. These data indicate that the control of oxidative phosphorylation in response to heavy-intensity cycling exercise is age-dependent in teenage boys.