Physical Growth and Maximal Work Capacity in Preadolescent Boys at High-altitude

Maximal exercise tests were given to 67 boys of European ancestry and between the ages of 8.8 and 13.1 years in La Paz, Bolivia (mean altitude of 3600m). Thirty-four of the boys were born at high altitude while the remaining 33 were born at low altitude. The boys born at high altitude were significantly fatter than the low-altitude born boys after controlling for age and had larger chest circumferences after controlling for stature. Otherwise the samples were morphologically similar. Also, the statures and weights of the boys in both groups were similar to those of normal U.S. boys, suggesting that their growth may not have been affected by hypoxia to any great extent. Although most measures of maximal work performance, including maximal aerobic power (V02max), did not differ significantly between the samples, maximal work output was significantly greater in the high- altitude born boys than in the low-altitude born boys. Length of residence at high altitude and maximal work output were positively related in the low-altitude born boys but no other relationships were found between maximal work performance and length of exposure to hypobaric hypoxia. The considerable individual variability in the responses of these boys to maximal exercise may have masked these relationships, however, and longitudinal studies may be needed to reveal developmental adaptations to hypoxia

Submaximal Work Performance of Native and Migrant Preadolescent Boys at High Altitude

Fifty-five preadolescent boys of European ancestry were given submaximal exercise tests in La Paz, Bolivia (mean altitude of 3600 m). Twenty-nine of the boys were born at high-altitude (HAB) and 26 were born at low-altitude (LAB). V02 and relative work intensity (V02W02max) were significantly lower in HAB boys than in LAB boys, suggesting that the HAB boys were better adapted to hypobaric hypoxia than the LAB boys. After controlling for relative work intensity, there were no significant differences between the groups in their physiological responses to sub­maximal exercise, suggesting that the greater V02 of the LAB boys was not due to a less efficient oxygen transport system. Also, interindividual variability was considerably greater in LAB than HAB boys for many measures, including V02. This may reflect considerable individual differences in the development of adaptive responses to hypobaric hypoxia among LAB boys

Effects of Drop Height on Drop Jump Performance

Background: Drop jumps (DJ) are commonly implemented in plyometric training programs in an attempt to enhance jump performance. However, it is unknown how different drop heights (DH) affect reactive strength index (RSI), jump height (JH) and ground contact time (GCT). Objectives: The purpose of this study was to assess the effect of various DHs on RSI, JH, and GCT. Methods: Twenty volunteers with a history of plyometric training (Males = 13, Females = 7; age: 22.80 ± 2.69 yr, height: 175.65 ± 11.81 cm, mass: 78.32 ± 13.50 kg) performed DJs from 30 cm (DJ30), 45 cm (DJ45), 60 cm (DJ60), 76 cm (DJ76), and 91 cm (DJ91) and a countermovement jump (0 cm). A 16-camera Vicon system was used to track reflective markers to calculate JH; a Kistler force plate was used to record GCT. RSI was calculated by dividing JH by GCT. RSI and GCT were compared using a 2x5 (sex x DH) mixed factor repeated measures ANOVA, while JH was compared using a 2x6 (sex x DH) repeated measures ANOVA. Results: There were no interactions, but there was a main effect for sex for both JH (M>F) and GCT (F>M). JH demonstrated no main effect for DH: DJ30 (0.49 ± 0.11 m), DJ45 (0.50 ± 0.11 m), DJ60 (0.49 ± 0.12 m), DJ76 (0.50 ± 0.11 m), and DJ91 (0.48 ± 0.12 m). However, GCT showed a main effect where DJ30 (0.36 ± 0.10 s), DJ45 (0.36 ± 0.12 s), and DJ60 (0.37 ± 0.10 s) were not significantly different but were less than DJ76 (0.40 ± 0.12 s) and DJ91 (0.42 ± 0.12 s). Conclusions: Increasing DH beyond 60 cm increased GCT but did not affect JH, resulting in decreased RSI. Therefore, practitioners designing plyometric training programs that implement DJs may utilize DHs up to 60 cm, thereby minimizing GCT without compromising JH