The influence of height, body mass, daily physical activity (DPA), and dietary calcium intake (DCI) on bone mineral density (BMD) and content (BMC) was evaluated in 33 four-year-old girls. Results indicated that body mass was significantly correlated with and predictive of BMD and BMC at all sites except the femoral neck BMD. DPA and height also explained a significant proportion of the variance in femoral neck BMD and BMC of the lumbar spine and total body. DCI was not related to or predictive of BMD or BMC at any bone site. These findings highlight the importance of engaging in daily weight-bearing physical activity to promote bone health in young girls.
Kristin S. Ondrak and Don W. Morgan
Kristin S. Ondrak and Robert G. McMurray
Researchers have investigated the energy expenditure of tennis practice and match play in adults but not youth.
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).
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.
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.
Mitch D. VanBruggen, Anthony C. Hackney, Robert G. McMurray, and Kristin S. Ondrak
The effect of exercise intensity on the tracking of serum and salivary cortisol responses was examined in 12 endurance-trained males (maximal oxygen uptake [VO2max] = 58.2 ± 6.4 mL/kg/min).
Subjects rested for 30 min (control) and exercised on a cycle ergometer for 30 min at 40% (low), 60% (moderate), and 80% (high intensity) of VO2max on separate days. Serum and saliva samples were collected pretrial, immediately posttrial, and 30 min into the recovery period from each trial.
Cortisol responses increased significantly for both serum (40.4%; P = .001) and saliva (170.6%; P = .007) only in response to high-intensity exercise. Peak saliva cortisol occurred at 30 min of recovery, whereas peak serum was at the immediate posttrial sampling time point. The association between serum and saliva cortisol across all trials was examined using concordance correlation (R c) analysis, which accounts for repeated measures. The overall correlation between serum and saliva cortisol levels in all matched samples was significant (R c = 0.728; P = .001). The scatter plot revealed that salivary cortisol responses tracked closely to those of serum at lower concentrations, but not as well at higher concentrations.
Findings suggest salivary measurements of cortisol closely mirror those in the serum and that peak salivary concentrations do not occur until at least 30 min into the recovery from intense exercise.