Positive, site-specific associations between bone mineral status, fitness, and time spent at high-impact activities in 16- to 18-year-old boys F. Ginty * , K.L. Rennie, L. Mills, S. Stear, S. Jones, A. Prentice MRC Human Nutrition Research, Elsie Widdowson Laboratory, Cambridge, CB1 9NL, United Kingdom Received 11 May 2004; revised 20 August 2004; accepted 5 October 2004 Available online 24 November 2004 Abstract The incidence of hip and forearm fracture in elderly men in the United Kingdom is a public health issue, but there is limited knowledge on lifestyle factors affecting male bone health. The aim of this cross-sectional study was to evaluate the relationships between whole body and regional bone mineral status and self-reported participation time in no-, low-, moderate-, and high-impact activities and fitness measurements in 16- to 18-year-old boys. One hundred twenty-eight boys underwent absorptiometry (DXA) measurements (Hologic QDR 1000W) of bone mineral content (BMC), bone area (BA), and bone mineral density (BMD) at the whole body, hip, spine, and forearm. They also completed the EPIC (European Prospective Investigation of Cancer) physical activity questionnaire, which allowed categorization of activities according to impact and aerobic intensity. Fitness and strength were assessed in each subject using estimated VO 2 max, grip strength, and back strength. Significant positive relationships were found between BMC, BA, and BMD and the fitness and strength measurements and participation time in high-impact sports at most skeletal sites. The relationships were further examined after adjustment of BMC for height, weight, and bone area, thereby minimizing the influence of body and bone size on these relationships. VO 2 max was a significant positive determinant of size- adjusted BMC at the whole body, the ultradistal and one-third radius, and all the hip sites, except the trochanter. Size-adjusted BMC at the forearm sites and trochanter was significantly positively associated with grip strength. Size-adjusted BMC at the whole body and all the hip sites was significantly positively associated with time spent at high-impact activities. Differences in size-adjusted BMC across thirds of time spent at high-impact activities were also examined. Boys in the highest third of high-impact activity had significantly greater size-adjusted whole body BMC and total hip BMC compared to subjects in the lowest third [+3.4 (1.2)% for whole body and +8.5 (2.2)% for hip, both P = 0.001]. Boys in the highest third of high-impact activity spent most activity time jogging, playing tennis, football and rugby, basketball, and exercising with weights. Back strength and lean mass were significantly greater in subjects in the highest third compared to those in the middle ( P = 0.02) and lowest third ( P = 0.03). No significant differences were found between subjects in each third of high-impact activity for potential confounders including TV viewing, calcium intake, body fat, and height. These findings indicate that participation of male adolescents in a range of high-impact activities for 1 h or more a day is associated with greater bone size and mineral content, especially at the hip. D 2004 Elsevier Inc. All rights reserved. Keywords: Male; Adolescents; Bone mineral status; Physical activity; Fitness; Strength Introduction Osteoporosis and its associated fractures is a significant contributory factor to morbidity and mortality in the elderly. Recent data from the European Prospective Osteoporosis Study (EPOS) of men and women aged 50–79 years confirm that the incidence of limb fracture is a major public health issue and will become a greater burden as the proportion of elderly rises [1]. In the United Kingdom, the lifetime risk of an osteoporotic fracture of hip, spine, or distal forearm for a man is 1 in 12, and 30% of all fractures occur in men [2]. Furthermore, the effects of hip fracture on morbidity have been reported to be greater in men than women [3]. 8756-3282/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.bone.2004.10.001 * Corresponding author. MRC Human Nutrition Research, Elsie Widdowson Laboratory, Fulbourn Road, Cambridge, CB1 9NL, United Kingdom. E-mail address: fiona.ginty@mrc-hnr.cam.ac.uk (F. Ginty). Bone 36 (2005) 101 – 110 www.elsevier.com/locate/bone