Effects of a calcium supplement on bone mineral density in male cyclists.

AIM: The purpose of this study was to maintain or improve bone density in male road cyclists through provision of calcium and vitamin D3 supplementation ingested before cycling. METHODS: Participants were male cyclists (N=17), with a mean (±SD) age of 42.7 (9.4) years. Measurements of lumbar spine and hip areal bone mineral density (aBMD) were performed at the start and end of a cycling season. Cyclists were randomized into the calcium supplement (CAL) or the control group (CON) group based on lumbar spine T-scores. The CAL group was instructed to consume 1600 mg calcium and 1000 IU vitamin D3 prior to cycling for the 5-month period. RESULTS: Femoral trochanter aBMD significantly decreased during the 5 month cycling season. There was no difference in aBMD between CAL and CON groups. CONCLUSION: Negative effects of competitive cycling on aBMD in hip structures can be observed within 5 months. Calcium and vitamin D3 ingested prior to cycling does not ameliorate this effect. This proof of concept paper provides evidence that more work is needed to find mechanisms to protect cyclists from destructive bone loss in hip structures.

Validity and reliability of the BOD POD® S/T tracking system.

BOD POD(®) self-testing (S/T) body composition tracking system is a practical assessment tool designed for use in the health and fitness industries. Relative to its parent counterpart, the BOD POD(®) S/T has received little research attention. The primary purpose was to determine the validity of the BOD POD(®) S/T against hydrostatic weighing and 7-site skinfolds. Secondary aim was to determine the within-day and between-day reliability of the BOD POD(®) S/T. After a period of equipment and testing accommodation, volunteer's (N=50) body composition (%BF) via 7-site skinfolds, BOD POD(®) S/T, and hydrostatic weighing were obtained on the second and third visits. BOD POD(®) S/T significantly overestimated %BF when compared to hydrostatic weighing and 7-site skinfolds. There was no statistical difference between 7-site skinfolds and hydrostatic weighing values. BOD POD(®) S/T reliability within-day and between-days were high. While the BOD POD(®) S/T body composition tracking system is deemed reliable both within-day and between-days, it did significantly overestimate %BF in comparison to hydrostatic weighing and skinfolds. Future research should be aimed at deriving a correction factor for this body composition assessment tool.

The influence of respiratory muscle training upon intermittent exercise performance.

The purpose of this study was to determine the effect of respiratory muscle training (RMT) on intermittent exercise performance, respiratory muscle strength (PI (max)), respiratory muscle fatigue (RMF), and dyspnea in soccer athletes. Collegiate soccer athletes (20 male, 7 female) were randomly divided into either a RMT or control condition during off-season conditioning. The RMT group performed a 30RM protocol (10 times weekly) for 5 weeks using a commercially-available training device, while the controls received no RMT. Performance was evaluated utilizing Level 1 of the Yo-Yo Intermittent Recovery Test (IRT) and dyspnea was assessed during and immediately following the IRT. RMF was quantified within 2 minutes (RMF2) and 10 minutes (RMF10) after completing the IRT. Following training, the RMT group significantly increased IRT performance by 216.6 +/- 231.0 meters (p = .008) while the 49.2 +/- 75.1 meter increase observed in the controls was not significant. PI (max) in the RMT group increased from 138.1 +/- 19.6 to 165.3 +/- 23.5 cmH (2)O (p < .001), with no significant change observed in the controls. RMT did not significantly affect RMF or dyspnea. In conclusion, RMT improved intermittent exercise performance in these soccer athletes. The mechanisms by which RMT improves performance warrant further study.

Interrelationships among thigh muscle co-contraction, quadriceps muscle strength and the aerobic demand of walking in children with cerebral palsy.

The purpose of this study was to quantify interrelationships among thigh muscle co-contraction, quadriceps muscle strength, and the aerobic demand of walking in 13 children with spastic hemiplegic cerebral palsy (CP). During Session 1, subjects were familiarized with testing procedures, given five minutes of treadmill walking practice, and completed quadriceps muscle strength testing. In Session 2, subjects performed three 5-min walking bouts on the treadmill at 0.67 m x s(-1) to further accommodate to treadmill ambulation. During Session 3, resting VO2 was measured and subjects walked at 0.67, 0.89, and 1.12 m x s(-1) for five minutes while oxygen uptake (VO2) and thigh muscle co-contraction data were collected. Results demonstrated that no significant relationship existed between net VO2 and measures of thigh muscle co-contraction or quadriceps muscle strength. In addition, thigh muscle co-contraction was not shown to be associated with quadriceps muscle strength. Collectively, thigh muscle co-contraction and quadriceps muscle strength explained 13. 5%, 6.2%, and 2.2% of the variance in VO2 at 0.67, 0.89, and 1.12 m x s(-1), respectively. Viewed in concert, these results suggest that the walking energy expenditure of children with spastic hemiplegic CP is not influenced by the level of thigh muscle co-contraction or quadriceps muscle strength.

Metabolic accommodation of young children to treadmill walking.

Few data exist concerning the reproducibility of stable oxygen uptake (VO(2)) values during level treadmill walking in young able-bodied children. To address this issue, 41 able-bodied 6-year-olds (19 boys, 22 girls, X height=117.2+/-4.7 cm, X body mass=21.8+/-2.5 kg) were tested on two occasions. In session 1, subjects were familiarized with the laboratory environment and performed 5 min of level treadmill walking at 1.34 m s(-1). During session 2, each child completed 30 min (three 10-min trials) of level treadmill walking at 1.34 m s(-1). For each 10-min trial, mean VO(2) was determined by averaging VO(2) values obtained from analysis of two 2-min expired gas samples. While the mean VO(2) for trial 1 was higher than values recorded for trials 2 and 3, effect sizes corresponding to these differences were low (

Perceived stress and blood pressure in early adolescent children.

The objective of this investigation was to determine the individual contributions of perceived daily, major, and total stressors to blood pressure in early adolescent children. Toward this goal, cardiovascular risk factors were assessed in 74 6th-grade students. Height and body weight, measured in standard fashion, were used to calculate body mass index (BMI). Waist and hip circumferences and triceps and calf skinfolds were taken to determine the distribution and percentage of body fat, respectively. Seated resting blood pressure was obtained using a mercury sphygmomanometer. The dietary sodium-to-potassium ratio was calculated from a food intake questionnaire. Family history of hypertension was self-reported by participant's parents, and physical activity and perceived stress levels were determined by questionnaire. When added to the hierarchical regression models, the perceived stress variables did not significantly predict any additional variance in systolic or diastolic blood pressure in this early adolescent sample. Additionally, bivariate correlations between the stress variables and blood pressure were nonsignificant. The nonpsychological hypertension risk factors accounted for 25%-35% of the total variance in systolic and diastolic blood pressure. Further, regression analyses revealed that with the exception of BMI and the sodium-to-potassium ratio, no other risk factors were independent predictors of systolic or diastolic blood pressure. Further identification and understanding of environmental precursors of childhood hypertension is recommended.

Stability of running economy in young children.

Few studies have been conducted documenting the length of time required for young children to achieve stable measures of running economy. Hence the purpose of this study was to quantify within- and between-day stability in running economy among young children. To address this issue, 30 6-year olds (16 girls, 14 boys) completed three test sessions within a 2 wk period. During Sessions 1 and 2 subjects performed three 5 min level treadmill runs at 2.23 m x sec(-1). During Session 2 expired air was collected during the last 2 min of each 5 min run (R1, R2, R3) and analyzed to determine VO2. In Session 3 subjects completed a single 5 min run (R4) at 2.23 m x sec(-1) and VO2 was measured during the last 2 min of running. Data analysis revealed no significant difference (p>0.05) in absolute or relative VO2 across trials. The average coefficient of variation for both absolute and relative VO2 among runs completed in Session 2 was 2.17 %, and the mean coefficient of variation for VO2 between R4 and the average VO2 of R1, R2, and R3 was 2.51 % and 2.35% for absolute and relative VO2, respectively. Moreover intraclass correlation coefficients for absolute and relative VO2 across all runs were 0.99 and 0.96, respectively. Viewed in concert, these results suggest that following 15 minutes of level treadmill running practice, stable within- and between-day measures of running economy can be obtained in young, prepubescent children.

Influence of positive life events on blood pressure in adolescents.

It has been reported that adults suffering from refractory essential hypertension experience significantly fewer positive life events than healthy peers. However, the influence of positive life events on blood pressure (BP) in adolescents has been largely ignored. Therefore, we examined the relationship between self-reported positive life events and BP in 69 sixth graders with a mean age of 11.7 years. Positive life events were assessed with the Adolescent Perceived Events Scale and resting blood pressure was measured with a mercurial sphygmomanometer. Correlational analyses showed an inverse relationship between positive life events and diastolic BP, suggesting that adolescents experiencing more positive life events were more likely to have lower diastolic BP's. Hierarchical regression analyses revealed that physical activity level, dietary sodium-to-potassium ratio, parental history of hypertension, and measures of body composition predicted 24.6% of the variance in systolic BP and 34.6% of the variance in diastolic BP. Moreover, positive life events predicted an additional 4.3% of the variance in diastolic BP when statistically controlling these established risk factors for hypertension. These results suggest that increased perceptions of positive life events may act as a buffer to elevated BP in adolescents.