Effects of an 8-year childhood physical activity intervention on musculoskeletal gains and fracture risk

Abstract

Link to publicationCitation for published version (APA): Cöster, M. E., Rosengren, B. E., Karlsson, C., Dencker, M., & Karlsson, M. K. (2016). Effects of an 8-year childhood physical activity intervention on musculoskeletal gains and fracture risk. Bone, 93, 139-145. AbstractBackground: Physical activity (PA) in childhood is associated with musculoskeletal benefits while the effect on fracture risk is yet to be determined. The aim of this study was to evaluate whether extension of a PA intervention leads to improvement in musculoskeletal traits with an accompanied reduced fracture risk. We hypothesized that the PA program would have beneficial effects in both sexes, but more so in girls since they tend to be less physically active than boys during this time frame. Methods:In one elementary school we increased physical education (PE) from 60 to 200 minutes per school week and followed 65 girls and 93 boys from a mean age of 7 years until a mean age of 15 years. Thirty-nine girls and 37 boys in three other schools continued with 60 minutes of PE per week during the same years and served as controls. We measured bone mineral content (BMC), areal bone mineral density (aBMD), and bone area annually with dual energy X-ray absorptiometry, and leg muscle strength with a computerized dynamometer. In 3 534 children within the same PE program (1 339 in the intervention and 2 195 in the control group) we registered incident fractures during the 8-year study period and estimated annual sex-specific fracture incidence rate ratios (IRRs).Results: Girls in the intervention group annually gained more total body less head aBMD, spine aBMD (p<0.01), femoral neck BMC (p<0.05), lumbar vertebrae size (p<0.05), and knee flexion strength (p<0.05) than girls in the control cohort. In boys we found no group differences. There was an inverse correlation between number of years with extra PE and the annual IRR of sustaining fractures in both girls (r = -0.90 (95% CI -0.98 to -0.51); p<0.001) and boys (r = -0.74 (95% CI -0.94 to -0.02); p<0.05). Conclusion:In this 8-year pediatric school-based moderate exercise intervention program there is an inverse correlation in both sexes between annual IRR and each additional year of extra PA. A sub-cohort of girls in the intervention group had greater gains in bone mass, bone size, and muscle strength, which could possibly explain the inverse correlation between years within the PA program and fracture risk, while in boys the reason for the inverse correlation remains unknown. It should be noted that differences in unreported factors such as skeletal maturity status, diet, and spare time PA could confound our inferences. That is, true causality cannot be stated.

Exercise and Peak Bone Mass

“…In contrast, high PA in adulthood is associated with high BMD [11], superior neuromuscular function [12], low risk of falls [12,13] and low fracture incidence [14][15][16][17]. High PA during growth is also associated with beneficial BMD and high peak bone mass (PBM) [18][19][20][21][22], superior neuromuscular function [18][19][20][21]23] and greater muscle strength [18][19][20][21]23], each of which decreases fracture risk [18,19,24,25]. In fact, the National Osteoporosis Foundation's position statement on peak bone mass development and lifestyle factors concluded in a 2016 systematic review, when grading evidence from A to D, that there is grade A (strong) evidence that PA is a modifiable lifestyle factor that may improve the development of BMD [26].…”

“…In spite of the compelling evidence that PA is beneficial for health [1,2,18,20,[27][28][29], modern society has gradually adopted an increasingly sedentary lifestyle [30].…”

“…PA is associated with a variety of health benefits [1,2,18,20,[26][27][28][29]. The desired approach would therefore be to increase the level of PA in children through intervention strategies.…”

“…The questions raised above have been addressed in the Pediatric Osteoporosis Prevention (POP) study, a population-based prospective controlled PA interventional study in children, with the primary aim of investigating whether daily school-based PA improves musculoskeletal development and reduces fracture risk [18][19][20][21]. The POP cohort included children from four government-funded and community-based elementary schools, all located in the same city area with similar socioeconomic status.…”

“…Other prospective controlled PA intervention studies support this hypothesis, but most include volunteers and are short-term in duration [21,[43][44][45][46][47]. A few long-term studies have been published [18,48,49], but these have not followed children from before to after puberty. All these limitations may obscure inferences, since as much as 25-40% of adult bone mass is acquired during puberty [50], and the pre-and early pubertal periods are the periods with the greatest skeletal response to mechanical load [51].…”