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[RC] Exercise during growth - Ridecamp Guest

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Authors S IulianoBurns, J Stone, JL Hopper, E Seeman
Title   Diet and exercise during growth have site-specific skeletal effects: a 
co-twin control study
Full source     Osteoporosis International, 2005, Vol 16, Iss 10, pp 1225-1232

Exercise and improved nutrition offer safe, low-cost and widely applicable 
approaches to potentially reduce the burden of fractures. We conducted a 
cross-sectional study of 30 monozygotic and 26 dizygotic male twin pairs, aged 
7-20 years to test the following hypotheses: (1) Associations between bone mass 
and dimensions and exercise are greater than between bone mass and dimensions 
and protein or calcium intakes; (2) exercise or nutrient intake are associated 
with appendicular bone mass before puberty and axial bone mass during and after 
puberty. Total body and posteroanterior (PA) lumbar spine bone mineral content 
(BMC) and mid-femoral shaft dimensions were measured using dual energy X-ray 
absorptometry (DEXA). Relationships between within-pair differences in nutrient 
intake (determined by weighed-food diaries) or exercise duration (determined by 
questionnaire) and within-pair differences in BMC and bone dimensions were 
tested using linear regression analysis. In multivariate analyses, within-pair 
differences in exercise duration were associated with within-pair differences 
in total body, leg and spine BMC, and cortical thickness. Every-hour-per-week 
difference in exercise was associated with a 31-g (1.2%) difference in total 
body BMC, a 10-g (1.4%) difference in leg BMC, a 0.5-g difference in spine BMC 
and a 0.1-mm difference in cortical thickness ( p < 0.01- p < 0.1). A 1-g 
difference in protein intake was associated with a 0.8-g (0.4%) difference in 
arm BMC ( p < 0.05). These relationships were present in peri-pubertal and 
post-pubertal pairs but not in pre-pubertal pairs. Exercise during growth 
appears to have greater skeletal benefits than variations in protein or calcium 
intakes, with the site-specific effects evident in more mature twins.


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