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Robert G. McMurray and Peter A. Hosick

The study evaluated the interactions of puberty and obesity on substrate oxidation of overweight girls (n = 38) and boys (N = 35; BMI > 85th percentile) matched for gender, age, and puberty (pre/pubertal) with normal weight girls and boys. Metabolic rates (VO2) were obtained during rest and at 4, 5.6 and 8 k/h. Carbohydrate oxidation rates (mg/kgFFM/min) adjusted for % predicted VO2max, were higher for prepubertal OW children than pubertal children (p < .03). Fat oxidation rates were higher for NW prepubertal boys compared with other boys. Results indicate that OW children, regardless of gender or pubertal status, increase their carbohydrate oxidation rate to compensate for higher than normal metabolic rates. The effects of obesity on the substrate use is marginally related to puberty.

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Kristin S. Ondrak and Robert G. McMurray

Background:

Researchers have investigated the energy expenditure of tennis practice and match play in adults but not youth.

Methods:

VO2 was recorded for 36 youth, ages 9 to 18, during 10-minute bouts of tennis practice and match play. A GLM was used to compare VO2 between practice and match play and among age groups (9–12 years, 13–15 years, and 16–18 years); also to compare the difference in adult and child-derived MET values (ΔMET).

Results:

VO2 was higher for tennis match play vs. practice (P < .05) and there was a trend for 16 to 18 year olds having lower VO2 than 9 to 12 year olds (P = .055). ΔMET did not differ between settings but varied by age group (P = .004); it was highest in 9- to 12-year-olds and lowest in 16- to 18-year-olds.

Conclusions:

Youth expend more energy while playing a tennis match than practice, regardless of age. Child-derived MET values equaled those of adults once youth reached ages 16 to 18.

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Victoria L. Bowden and Robert G. McMurray

The purpose of this study was to determine if there is a difference between the way in which aerobically trained and untrained women metabolize fats and carbohydrates at rest in response to either a high-fat or high-carbohydrate meal. Subjects, 6 per group, were fed a high CHO meal (2068 kJ, 76% CHO. 23% fat, 5% protein) and a high fat meal (2093 kJ, 21% CHO, 72% fat, 8% protein) in counterbalanced order. Resting metabolic rate (RMR) was measured every half-hour for 5 hours. RMR was similar between groups. Training status had no overall effect on postprandial metabolic rate or total energy expenditure. The high fat meal resulted in no significant differences in RMR or respiratory exchange ratio (RER) between groups. However, after ingesting a high CHO meal, trained subjects had a peak in metabolism at minute 60, not evident in the untrained subjects. In addition, postprandial RER from minutes 120-300 were lower and fat use was greater after the high CHO meal for the trained subjects. These results suggest that aerobically trained women have an accelerated CHO uptake and overall lower CHO oxidation following the ingestion of a high CHO meal.

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Dawn M. Maffucci and Robert G. McMurray

The purpose of this study was to compare the effect a 6-hr versus 3-hr prefeeding regimen on exercise performance. The subjects were 8 active women (21.4 ± 0.9 years, 60.4±2.4 kg, 19.9 ± 1.3% body fat. and 165.6±2.1 cm). All women completed 2 exercise trials (separated by 3—6d) on a treadmill where they ran at moderate intensity for 30 min with 30-s sprints at 5-min intervals, followed directly by increasing incrementally the grade until volitional fatigue was achieved. The exercise trials were performed 3 hr and 6 hr after consuming 40 ± 3 kJ/kg meal. Time to exhaustion was 0.75 min shorter (p = .0001) for the 6-H trials compared to the 3-H trials. There were no significant differences in submaximal or peak oxygen uptake, heart rate, or rating of perceived exertion (p > .05). The 6-H trials compared to the 3-H trials resulted in .05 lower RERs (p = .0002), and a 2 mmol lower blood lactate at exhaustion (p = .012). Blood glucose levels and cortisol responses to exercise were similar between trials (p > .05). However, both resting and post exercise insulin levels were lower during 6-H trials. It was concluded that performance of moderate- to high-intensity exercise lasting 35—40 min is improved by consuming a moderately-high carbohydrate. low fat, low protein meal 3-hr before exercise compared to a similar meal consumed 6 hr prior to exercise. Thus, athletes should not skip meals before competition or training sessions.

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Daniela A. Rubin, Robert G. McMurray, and Joanne S. Harrell

Differences in insulin concentrations between normal weight or overweight adolescents (n = 437) were determined depending on their habitual physical activity (PA) and aerobic power (pVO2max). Tertiles were computed for PA (survey) and pVO2max (submaximal predicted cycle test). Independent of their weight, adolescents in the upper 2 tertiles for vigorous PA had lower insulin concentrations than those in the bottom tertile (p < .05). Adolescents in the top tertile for pVO2max expressed per kg fat-free mass also had lower insulin concentrations than those in the medium and bottom tertiles (p = .002). In youth, vigorous physical activity and aerobic power are associated with fasting insulin independent of weight status.

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Peter A. Hosick, Robert G. McMurray, and Dan M. Cooper

The relationship between peak aerobic fitness (peakVO2) and plasma leptin was assessed in 25 normal (BMI < 85th %tile) and 25 overweight (BMI > 85th %tile) youth, ages 7–17 years. In the overall analysis peakVO2 was related to leptin when expressed in mL/kg/min (R 2 = .516, p < .0001), or as ml/kgFFM/min (R 2 = .127, p = .01). The relationships between peakVO2 and leptin were no longer significant when percent bodyfat was added to the models. In subanalyses by weight groups, peakVO2: leptin relationships were not evident for normal weight, but remained for overweight youth. In conclusion the relationship between aerobic fitness and leptin in youth is dependent upon weight status.

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Barbara E. Ainsworth, Robert G. McMurray, and Susan K. Veazey

The purpose of this study was to determine the accuracy of two submaximal exercise tests, the Sitting-Chair Step Test (Smith & Gilligan. 1983) and the Modified Step Test (Amundsen, DeVahl, & Ellingham, 1989) to predict peak oxygen uptake (VO2 peak) in 28 adults ages 60 to 85 years. VO2 peak was measured by indirect calorimetry during a treadmill maximal graded exercise test (VO2 peak, range 11.6–31.1 ml · kg −l · min−1). In each of the submaximal tests, VO2 was predicted by plotting stage-by-stage submaximal heart rate (HR) and perceived exertion (RPE) data against VO2 for each stage and extrapolating the data to respective age-predicted maximal HR or RPE values. In the Sitting-Chair Step Test (n = 23), no significant differences were observed between measured and predicted VO2 peak values (p > .05). However, predicted VO2 peak values from the HR were 4.3 ml · kg−1 · min−1 higher than VO2 peak values predicted from the RPE data (p < .05). In the Modified Step Test (n = 22), no significant differences were observed between measured and predicted VO2 peak values (p > .05). Predictive accuracy was modest, explaining 49–78% of the variance in VO2 peak. These data suggest that the Sitting-Chair Step Test and the Modified Step Test have moderate validity in predicting VO2 peak in older men and women.

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Daniela A. Rubin, Robert G. McMurray, Joanne S. Harrell, Barbara W. Carlson, and Shrikant Bangdiwala

The purpose of this project was to determine the accuracy in lipids measurement and risk factor classification using Reflotron, Cholestech, and Ektachem DT-60 dry-chemistry analyzers. Plasma and capillary venous blood from fasting subjects (n = 47) were analyzed for total cholesterol (TC), high density lipoprotein (HDL-C), and triglycerides (TG) using these analyzers and a CDC certified laboratory. Accuracy was evaluated by comparing the results of each portable analyzer against the CDC reference method. One-way ANOVAs were performed for TC, HDL-C, and TG between all portable analyzers and the reference method. Chi-square was used for risk classification (2001 NIH Guidelines). Compared to the reference method, the Ektachem and Reflotron provided significantly lower values for TC (p < .05). In addition, the Cholestech and Ektachem values for HDL-C were higher than the CDC (p < .05). The Reflotron and Cholestech provided higher values of TG than the CDC (p < .05). Chi-squares analyses for risk classification were not significant (p > .45) between analyzers. According to these results, the Ektachem and Cholestech analyzers met the current NCEP III guidelines for accuracy in measurement of TC, while only Ektachem met guidelines for TG. All 3 analyzers provided a good overall risk classification; however, values of HDL-C should be only used for screening purposes.

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Robert G. McMurray, Joanne S. Harrell, Shrikant I. Bangdiwala, Shibing Deng, and Chris Baggett

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.

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Adam M. Hyde, Robert G. McMurray, Frank A. Chavoya, and Daniela A. Rubin

Purpose: Prader–Willi syndrome (PWS) is a genetic neurobehavioral disorder presenting hypothalamic dysfunction and adiposity. At rest, PWS exhibits hypoventilation with hypercapnia. We characterized ventilatory responses in children with PWS during exercise. Methods: Participants were children aged 7–12 years with PWS (n = 8) and without PWS with normal weight (NW; n = 9, body mass index ≤ 85th percentile) or obesity (n = 9, body mass index ≥ 95th percentile). Participants completed three 5-minute ambulatory bouts at 3.2, 4.0, and 4.8 km/h. Oxygen uptake, carbon dioxide output, ventilation, breathing frequency, and tidal volume were recorded. Results: PWS had slightly higher oxygen uptake (L/min) at 3.2 km/h [0.65 (0.46–1.01) vs 0.49 (0.34–0.83)] and at 4.8 km/h [0.89 (0.62–1.20) vs 0.63 (0.45–0.97)] than NW. PWS had higher ventilation (L/min) at 3.2 km/h [16.2 (13.0–26.5) vs 11.5 (8.4–17.5)], at 4.0 km/h [16.4 (13.9–27.9) vs 12.7 (10.3–19.5)], and at 4.8 km/h [19.7 (17.4–31.8) vs 15.2 (9.5–21.6)] than NW. PWS had greater breathing frequency (breaths/min) at 3.2 km/h [38 (29–53) vs 29 (22–35)], at 4.0 km/h [39 (29–58) vs 29 (23–39)], and at 4.8 km/h [39 (33–58) vs 32 (23–42)], but similar tidal volume and ventilation/carbon dioxide output to NW. Conclusion: PWS did not show impaired ventilatory responses to exercise. Hyperventilation in PWS may relate to excessive neural stimulation and metabolic cost.