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LB03 - THE RESPONSE OF CORTICAL BONE TO HIGH IMPACT ACTIVITY IS ATTENUATED IN GIRLS: FINDINGS FROM A CROSS-SECTIONAL PQCT STUDY IN ADOLESCENTS

K. Deere1, A. Sayers1, J. Rittweger2, J. Tobias1,*
1School of Clinical Sciences, University of Bristol, Bristol, United Kingdom, 2Division of Space Physiology, Institute of Aerospace Medicine, Cologne, Germany

Abstract:
Background: The factors which govern skeletal responses to physical activity remain poorly understood, conceivably because accelerometers measuring physical activity are calibrated against energy expenditure rather than mechanical strain. We investigated whether a more precise understanding of these factors, including gender and fat mass, can be gained based on measurement of exposure to defined levels of impact using a Newtest device (Newtest Oy, Finland).

Methods: Participants attending the ALSPAC research clinic underwent total body DXA and pQCT of the mid-tibia, and were subsequently invited to wear a Newtest accelerometer for seven days. Accelerometer results were partitioned into low (0.5-2.1g), medium (2.1-4.1g) and high (>4.1g) impact activity.

Results: 675 participants (272 boys) had valid accelerometer recordings and information on pQCT data and other covariates (mean age=17.7 years). In our fully adjusted model (for age, height, fat mass and lean mass), moderate impact activity was positively related to periosteal circumference (PC) in boys but negatively related in girls [0.039 (95%CI -0.013, 0.090.p=0.14) and -0.023 (-0.023, 0.017.p=0.26) respectively. p=0.03 for gender interaction, coefficient= SD change per doubling in activity]. High impact activity showed a stronger positive association with PC in boys but no association was seen in girls [0.054 (0.007, 0.100. p=0.024) and 0.007(-0.028, 0.041. p=0.707) respectively]. In further analyses additionally stratified by fat mass, an independent interaction was observed, such that the positive relationship between high impact activity and PC was greatest in those with highest fat mass [high impact versus PC in boys: 0.01 (-0.064, 0.085. p=0.783), 0.045 (-0.040, 0.131 .p=0.298), 0.098 (0.012, 0.185. p=0.027); high impact versus PC in girls: -0.041 (-0.101, 0.020, p=0.187), -0.028 (-0.077, 0.022.p=0.271), 0.082 (0.015, 0.148. p=0.017) (p=0.01 for fat mass interaction); lower, middle and upper fat-tertiles respectively].

Conclusions: Female gender and low body fat are associated with reduced periosteal expansion in response to high impact activity, via independent pathways. Our results suggest that skeletal response to high impacts is particularly impaired in girls with low body weight, which may partly explain the excess of stress fractures observed in this group after undergoing strenuous exercise.

Disclosure of Interest: None Declared

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