This study evaluated factors that contribute to the increased energy cost of locomotion in youth. The subjects were 321 8-18-year-old youth, similar dispersed by age and sex. Oxygen uptake (VO2) was measured during rest (REE), running at 8 km · h−1 and cycling at 16 km · h−1, using a COSMED K4b2 metabolic system. Developmental stage was obtained via questionnaire. Stature, body mass, and skinfolds (triceps & subscapular) were measured. Both sexes had similar absolute VO2 (mL · min−1) at rest (p = 0.065) and running (p = 0.084), but the males had a higher VO2 during cycling (p = 0.046). There were no sex differences in relative VO2 (mL · kg−1 · min−1) at rest (p = 0.083); however, the males had a higher VO2 than the females during cycling and running (p £ 0.002). Multiple regression, tested for collinearity, found that absolute VO2 during cycling and running was mostly related to fat-free mass (p = 0.0001). Similar analyses for relative VO2 (mL · kg−1 · min−1) during cycling found that fat-free mass, sex, and skinfolds were significant contributors (p ‡ 0.003). During running the relative VO2 was related to skinfolds, fat-free mass, and resting energy expenditure (p < 0.05). Neither age nor developmental stage was a significant contributor. The results indicate that the VO2 of locomotion is most closely associated with fat-free mass. Thus, to compare youth of varying age or pubertal developmental status, fat-free mass should be taken into consideration.
Robert G. McMurray, Joanne S. Harrell, Shrikant I. Bangdiwala, Shibing Deng and Chris Baggett
Peter A. Hosick, Robert G. McMurray, A.C. Hackney, Claudio L. Battaglini, Terry P. Combs and Joanne S. Harrell
Reports suggest children with high aerobic fitness (VO2max; mL/kg/min) have healthier profiles of TNF-α and IL-6; however, research has not accounted for differences in adiposity between high-fit and low-fit individuals. Thus, this study examined differences in inflammatory markers of obese and normal weight children of different fitness levels, using two different VO2max units: per unit of fat free mass (VO2FFM) or total body mass (VO2kg). Children (n = 124; ages 8–12) were divided into four matched groups; normal weight high-fit (NH), normal weight low-fit (NL), obese high-fit (OH), and obese low-fit (OL). Height, weight, skinfolds, body mass index (BMI), and predicted VO2max were measured and a morning, fasting blood sample taken. IL-6 was elevated in the NL and OL groups compared with the NH group, as well as the OL group compared with the OH group. No differences were found in TNF-α. The relationship between IL-6 or TNF-α and the two units of predicted VO2max did not differ suggesting that either VO2FFM or VO2kg can be used to describe aerobic power when studying inflammation and exercise in youth. The relationship between IL-6 or TNF-α and predicted VO2max, whether expressed per mass or per fat-free mass was similar, suggesting that both can be used to describe aerobic power when studying inflammation and exercise in youth. Given the polar design of this study, this relationship should be confirmed including overweight subjects.
Denise M. Roche, Sarah Edmunds, Tim Cable, Mo Didi and Gareth Stratton
No studies to date have evaluated the relationship between exercise and microvascular function in youth with type 1 diabetes mellitus (T1DM). Twenty-nine complication free children and adolescents with T1DM were assessed for skin microvascular reactivity, aerobic fitness (VO2peak) and physical activity. VO2peak but not physical activity was significantly and independently associated with maximal hyperemia of the skin microcirculation (p < .01). No significant associations were found between venoarte-riolar reflex (VAR) vasoconstriction and VO2peak or physical activity. Aerobic fitness may be an important indicator or mediator of effective microvascular endothelial function in youth with T1DM.
K. Fiona Iredale and Myra A. Nimmo
Thirty-three men (age 26–55 years) who did not exercise regularly were exercised to exhaustion using an incremental treadmill protocol. Blood lactate concentration was measured to identify lactate threshold (LT, oxygen consumption at which blood lactate concentration begins to systematically increase). The correlation coefficient for LT (ml · kg−1 · min−1) with age was not significant, but when LT was expressed as a percentage of peak oxygen consumption (VO2 peak), the correlation was r = +.69 (p < .01). This was despite a lack of significant correlation between age and VO2 peak (r = −.33). The correlation between reserve capacity (the difference between VO2 peak and LT) and age was r = −.73 (p < .01 ), and reserve capacity decreased at a rate of 3.1 ml · kg−1 · min−1 per decade. It was concluded that the percentage of VO2 peak at which LT occurs increases progressively with age, with a resultant decrease in reserve capacity.
Linda Schücker, Christian Knopf, Bernd Strauss and Norbert Hagemann
The aim of this study was to examine differentiated effects of internally focused attention in endurance sports. Thirty-two active runners ran 24 min on a treadmill at a fixed speed of moderate intensity. For each 6-min block, participants had to direct their attention on different internal aspects (movement execution, breathing, or feeling of the body) or received no instructions. Oxygen consumption (VO2) was measured continuously to determine running economy. Results revealed that the different internal focus instructions had differentiated effects on VO2: A focus on breathing as well as a focus on the running movement led to higher VO2 than a focus on feeling of the body which showed similar VO2 as the control condition. We conclude that an internal focus of attention is solely detrimental to performance when directed to highly automated processes (e.g., breathing or movement). However, an internal focus on how the body feels during exercise does not disrupt movement efficiency.
Kenneth H. Pitetti and Bo Fernhall
The purpose of this study was to evaluate the relationship between aerobic capacity (VO2peak) and leg strength of male (n = 17) and female (n = 12) youths (age = 14.2 ± 2.1 years) with mild to moderate mental retardation. Aerobic capacity was determined by a treadmill test (GXT) and isokinetic knee flexion and extension strength (peak torque, peak force, average force) was determined by isokinetic dynamometry. Results indicate that significant positive relationships (p < .05) exist between VO2peak (ml · min−1 · kg−1) and isokinetic leg strength expressed relative to body weight. The results indicate that leg strength is a contributor to aerobic fitness in youths with mental retardation. Additionally, when considering the low levels of both strength and VO2peak, leg strength may be a limiting factor of VO2peak in these youths, or the relationship may be explained by the concept of metabolic nonspecialization.
Joanne R. Williams and Neil Armstrong
A total of 100 boys and 91 girls, ages 11 to 16 years, completed a discontinuous treadmill test to voluntary exhaustion to determine the oxygen uptake/blood lactate relationship. Maturational stage was assessed in 72 boys and 47 girls using Tanner’s indices. Mean blood lactate at peak VO2 was significantly higher in the girls compared to the boys (6.1 vs. 5.8 mmol•l-1, P<0.01). Lactate at peak VO2 and percent peak VO2 at 4.0 mmol•l-1 were not significantly correlated with chronological age (p>0.05) in either sex, although a relationship was obtained between chronological age and percent peak VO2 at 2.5 mmol•l-“1 for boys (r= ‒0.226, p<.05) and girls (r= ‒0.272, p0.05). Analysis of variance revealed no significant changes (p>0.05) in any of the lactate variables examined with progression through the Tanner stages of maturity.
Hye-Ryun Hong, Jin-Kyung Cho, Ji-Young Lee, Jin-Koo Park and Hyun-Sik Kang
The present study investigated the relationships among metabolic risk factors, major lifestyle factors, and serum cytokines in a sample of Korean children. In a cross-sectional design, we studied a total of 275 children (130 boys and 145 girls) aged 12–13 years. Measured variables included anthropometrics, blood pressures (BP), VO2max, physical activity (PA), dietary intakes, lipids, glucose, and insulin. We explored the extent to which dietary intakes, VO2max, PA, and serum cytokines explained variance in a clustered risk score, which is a sum of Z scores for waist circumference, BP, TG, HDLC, and HOMA-IR, using a stepwise linear regression by blocks. VO2max, vigorous PA (VPA), and leptin were independent predictors for the clustered risk score while adjusting for age and Tanner stage. Our findings suggest that the clustered risk score is associated not only with low levels of VO2max and VPA, but also with elevated serum leptin in Korean children.
Thomas Rowland, Gregory Kline, Donna Goff, Leslie Martel and Lisa Ferrone
Little is known regarding the physiological determinants of maximal oxygen uptake (VO2max) in children. A group of 39 healthy sixth-grade boys (mean age, 12.2 years) underwent maximal cycle testing with determination of cardiovascular factors using Doppler echocardiography as well as standard gas exchange variables. Maximal stroke index was related to VO2max/kg (r=0.52, p < .05), but no relationship was observed between VO2max/kg and either maximal heart rate or calculated maximal arteriovenous oxygen difference. Values of maximal stroke index were closely related to those at rest (r = 0.67). These findings suggest that factors influencing resting stroke volume are primarily responsible for inter-individual differences in VO2max per kg in healthy, non-athletically-trained boys.
Kathleen M. Shuleva, Gary R. Hunter, Donna J. Hester and Donna L. Dunaway
This study compared submaximal and maximal oxygen uptake (V̇O2 max) in children ages 3–4 and 5–6 years. Methods appropriate for this age group were developed to elicit maximal performance on the exercise tests. Subjects (N = 22) performed progressive treadmill walking tests. The criteria used to determine whether V̇O2 max was reached were a plateauing of oxygen uptake, HR > 195, and an R > 1.00. The V̇O2 max for the 3- and 4-year-olds (44.5 ml•kg−1•min−1) was not significantly different from that of the 5- and 6-year-olds (44.1 ml•kg−1•min−1). At submaximal levels, 5- and 6-year-olds had significantly lower relative oxygen uptake, indicating better economy in walking. A large proportion of children met testing criteria for V̇O2 max. Test-retest results indicated that the tests were reliable.