Adam Baxter-Jones. 1. 1College of Kinesiology .... (Ward et al., 2005) In conclusion, there are site and sex specific differences in the development of forearm ...
Chapter 51
Is gymnastics exposure associated with skeletal benefits in the forearm in young children? Stefan A Jackowski 1, Marta C Erlandson 1,2,3, Rita GruodyteRaciene 1,4, Saija A Kontulainen1Adam Baxter-Jones1 1
College of Kinesiology, University of Saskatchewan, Canada; 2University Health Network, Osteoporosis and Women’s Health, Canada; 3Department of Medicine, University of Toronto, Canada; 4Lithuanian Sports University, Lithuania
51.1 INTRODUCTION The amount of bone gained during childhood and adolescence impacts greatly on lifetime skeletal health and it is well accepted that physical activity during growth increases bone acquisition. Gymnastics training results in unique high mechanical loading to the skeleton and therefore, provides an excellent model for assessing the effects of weight-bearing physical activity on bone development (Daly et al., 1999). Young recreational gymnasts experience loads up to 3-10 times that of body weight on their feet and hands. Previous studies in young adolescent competitive female gymnasts have shown that they have 8-23% areal bone mineral density (aBMD, cm/g2), at the total body, lumbar spine and hip (Laing et al., 2002; Faulkner et al., 2003; Erlandson et al., 2011a). It is often presumed that higher the aBMD or BMC translates to greater bone strength but when estimating whole bone strength (resistance to fracture) it is important to assess bone size and geometry in addition to parameters charactering bone mass and areal density (Kontulainen et al., 2007). Therefore, it is important to assess the geometrical indices of bone and not simply aBMD or BMC. Peripheral quantitative computed tomography (pQCT) is a novel technology that is able to measure bone cross sectional properties in three dimensions. It has been recently observed that early recreational and precompetitive gymnastic participation may confer 6-25% greater adjusted bone strength, as assessed by pQCT, at the distal radius compared to individuals not involved in gymnastic training (Erlandson et al, 2011b). What remain unsubstantiated are the long term effects of early recreational gymnastics on the development of childhood bone strength. Therefore, the primary purpose of this study was to investigate whether gymnastics exposure was associated with estimated bone strength development derived from pQCT at the distal radius in young males and females.
297
51.2 METHODS Participants were drawn from the University of Saskatchewan’s Young Recreational Gymnast Study. This cohort consists of 178 children recruited into a mix-longitudinal study examining the influence of early life gymnastic participation on bone development (2006-2012; Erlandson et al, 2011a). pQCT scan were implemented into the study in 2008 and by 2012, there were 3 years of pQCT data collected in children between 4 and 10 years of age. The gymnasts consisted of individuals who were participating in recreation and/or precompetitive gymnastics programs at one of three competitive gymnastics clubs in Saskatoon. The non-gymnastic controls were individuals recruited from other local recreational sport programs and camps (soccer, T-ball, basketball and karate). Participants were excluded from the current study if they had any condition that prevented them from performing exercise safely, had any condition known to affect bone development, or did not have valid distal radius scan at two or more assessment occasions. This resulted in the inclusion of 126 participants (58 Males, 68) consisting of 75 gymnasts (35 males, 40 females) and 51 non gymnasts (23 males, 28 females). Consent was obtained from all parents and/or guardians and verbal assent was obtained from all children. All procedures and protocols were approved by the Biomedical Research Ethics Board at the University of Saskatchewan. Height was recorded without shoes to the nearest 0.1cm using a wall mounted stadiometer. Weight was measures on a calibrated digital scale to the nearest 0.5 kg. Cross sectional slices of the left radius and tibia were measure by pQCT (XCT, Stratec Medizintechnik GmbH, Pforzheim, Germany). For this present study only data from the radius are presented. The radius was scanned at the distal and shaft sites represented by the 4% and 65% of the limb length proximal to the wrist, respectively. All scan were performed using a voxel size of 0.4mm at a speed of 20mm/s. All scans were analyzed using Stratec software, Version 6.0. Scans obtained from the distal radius and tibia 4% site were analyzed for total cross sectional bone area (ToA, mm2), bone density (ToD, mg/cm3), and bone content (ToC, mg/mm). All images at the 4% distal sites were analyzed using contour mode 1, 280 mg/cm3 to separate bone from surrounding soft tissue. Peel mode 2 with the inner threshold of 480 mg/cm3 was used to separate trabecular bone. Additionally, at the distal radius bone strength index (BSI) was calculated (ToA x ToD2) as a measure of estimate compressive strength. Images at the 65% radius site were analyzed using contour mode 1, 480mg/cm3 to separate bone from the surrounding soft tissue. Separation Mode 4 with inner and outer thresholds of 480 mg/cm3 was used to determine the cortical bone cross-sectional area (CoA, mm2), density (CoD, mg/cm3), content (CoC, mg/mm), and polar stress strain index (SSIp, mm3). Forearm
298
muscle area was measured and analyzed according to the manufacturer’s recommendations, using Contour Mode 1 with a threshold of 40 mg/cm3 and muscle filter C02 at the 65% sites. Physical activity was assessed annually using the Netherlands Physical Activity Questionnaire (NPAQ). The NPAQ ranks individuals based on parental reports of their child’s current activity preferences and everyday activity choices. The questionnaire response ranges from 7 (low level physical activity) to 35 (high level physical activity). All variables were assessed for normality and violations were adjusted using logarithmic transformations. Multilevel random effects models were constructed to assess association in the development of pQCT estimated bone strength measures between individuals exposed and not exposed to gymnastics whilst controlling for age, radius length, weight, physical activity, muscle area, sex and hours of training. A total of 8 independent multilevel random effects models were constructed using MLwiN version 2.26 (Centre for Multilevel Modelling, University of Bristol, UK). Significance was accepted if the estimate mean coefficient was greater than twice the standard error of the estimates (SEE, ie. p
