JBMR

LETTER TO THE EDITOR

The Effect of Vigorous Physical Activity and Body Composition on Cortical Bone Mass in Adolescence Adrian Sayers, Kevin Deere, and Jon H Tobias Musculoskeletal Research Unit, University of Bristol, Learning and Research Southmead Hospital, Westbury on Trym, Bristol, United Kingdom

To the Editor

W

e would like to thank Tan and colleages for their very extensive thought-provoking systematic review narrative synthesis on the influence of physical activity (PA) bone strength in children adolescents.(1)The authors conclude that there is still much to learn about how bone mass and bone structure responds to PA during skeletal growth development. However we would like to highlight how our research based on the Avon Longitudinal Study of Parents shed Children (ALSPAC) has helped to shed light on some of the issues they discuss, including the contribution of muscle strength to PA effects on bone development, and the importance of PA magnitude/ intensity. Though representing by far the largest cohort study to examine relationships between PA bone development, and despite meeting the inclusion criteria for the review, for some reason relevant publications from this cohort were not included in this systematic review For example, in terms of teasing out independent effects of PA on bone from those via muscle, in 2011 we explored the association in 1748 adolescent (aged 15.5 years) boys and girls between PA as assessed by accelerometry, body composition as measured by dual-energy X-ray absorptiometry (DXA), and cortical bone mass and geometry as measured by pQCT.(2) Using a path analysis approach, we decomposed the effect of vigorous PA via total body fat mass, total body lean mass, and cortical bone mass pathways, observing that the pathway between PA and cortical bone via muscle mass was 37% as strong as the direct PA pathway. Furthermore, our findings revealed the important role of fat mass, which was not discussed by Tan and colleagues; fat mass is inversely related to PA, positively related to both bone and muscle mass, and was found to contribute independently to the overall relationship between PA and bone development.(2) A further important question is how accurately measures of muscle mass, as conventionally used in studies of bone development, reflect the role of muscle function. We recently found interesting relationships between peak lower limb muscle strength as assessed by jumping mechanography and pQCT measures, albeit in an adult population(3); it would be intriguing to establish whether equivalent interrelationships between PA, muscle, and bone development are observed using these functional measures of muscle function compared with muscle mass as measured by DXA in adolescence. Despite the prediction from animal studies that relationships between PA and bone development are likely to be strongly

influenced by PA magnitude/intensity, Tan and colleagues cite findings from previous cross-sectional studies that this only makes a “meager” contribution to overall strength. However, this conclusion is based on results from questionnaire studies, which are notoriously inaccurate at quantifying PA. In ALSPAC, as well as using accelerometry to provide an objective measure of moderate to vigorous PA as used conventionally, we adapted this approach to record rare, high-impact events, when the participants were 2 years older (aged 17.7 years). Interestingly, we found that the positive relationship between hip bone mineral density could be entirely explained by the number of (albeit rare) impacts >4.2 g (equivalent to running 10 km/hr).(4) In studying equivalent relationships with pQCT parameters, we found that the number of impacts beyond the 4.2-g threshold was positively related to periosteal circumference, particularly in boys and obese individuals.(5) We, therefore, disagree with the suggestion by Tan and colleagues that cross-sectional studies only provide limited evidence as to the importance of PA magnitude/intensity in influencing bone development either directly or indirectly via body composition across childhood and adolescence.

Acknowledgment AS is funded by an MRC Fellowship (MR/L01226X/1).

References 1. Tan VP, Macdonald HM, Kim S, Nettlefold L, Gabel L, Ashe MC, McKay HA. Influence of physical activity on bone strength in children and adolescents: a systematic review and narrative synthesis. J Bone Miner Res. 2014; 29(10):2161–2181. 2. Sayers A, Mattocks C, Deere K, Ness A, Riddoch C, Tobias JH. Habitual levels of vigorous, but not moderate or light, physical activity is positively related to cortical bone mass in adolescents. J Clin Endocrinol Metab. 2011; 96(5):E793–E802. 3. Hardcastle SA, Gregson CL, Rittweger J, Crabtree N, Ward K, Tobias JH. Jump power and force have distinct associations with cortical bone parameters: findings from a population enriched by individuals with high bone mass. J Clin Endocrinol Metab. 2013; 99:266–275. 4. Deere K, Sayers A, Rittweger J, Tobias J. Habitual levels of high, but not moderate or low, impact activity are positively related to hip BMD and geometry: results from a population-based study of adolescents. J Bone Miner Res. 2012; 27(9):1887–1895. 5. Deere K, Sayers A, Rittweger J, Tobias JH. A cross-sectional study of the relationship between cortical bone and high-impact activity in young adult males and females. J Clin Endocrinol Metab. 2012; 97(10):3734–3743.

This article was published online on February 16, 2015. The Letter to the Editor was inadvertently published before the Reply. This notice is included in the online and print versions to indicate that both have been corrected February 20, 2015. Journal of Bone and Mineral Research, Vol. 30, No. 3, March 2015, p 584 DOI: 10.1002/jbmr.2400 © 2014 American Society for Bone and Mineral Research

584

The effect of vigorous physical activity and body composition on cortical bone mass in adolescence.

The effect of vigorous physical activity and body composition on cortical bone mass in adolescence. - PDF Download Free
44KB Sizes 4 Downloads 9 Views