A comparison of the associations between bone health and three different intensities of accelerometer-derived habitual physical activity in children and adolescents: a systematic review

Abstract

Positive associations have been identified between bone outcomes and accelerometer-derived moderate (MPA) and vigorous (VPA) physical activity (PA) in youth; however, it remains unclear which intensity is most beneficial. This systematic review aimed to summarise accelerometer-derived methods used to estimate habitual PA in children and adolescents and determine whether the magnitude of association was consistently stronger for a particular intensity (MPA/MVPA/VPA). Observational studies assessing associations between accelerometer-derived MPA and/or MVPA and VPA with bone outcomes in children and adolescents (≤ 18 years) were identified in MEDLINE, EMBASE, Web of Science, SPORTDiscus and the Cochrane Central Register of Controlled Trials. Thirty articles were included (total n = 20,613 (10,077 males), 4-18 years). Chi-square tests determined whether the proportion of significant associations and strongest within-study associations differed significantly between intensities. Results demonstrated that accelerometer methods were highly variable between studies. Of the 570 associations analysed, 186 were significant (p < 0.05). The proportion of within-study strongest associations differed by PA intensity (3 × 2 χ² = 86.6, p < 0.001) and was significantly higher for VPA (39%) compared to MVPA (5%; 2 × 2 χ² = 55.3, p < 0.001) and MPA (9%, 2 × 2 χ² = 49.1, p < 0.001). Results indicated a greater benefit of VPA over MPA/MVPA; however, variability in accelerometer-derived methods used prevents the precise bone-benefitting amount of VPA from being identified. Long epochs and numerous intensity cut-point definitions mean that bone-relevant PA has likely been missed or misclassified in this population. Future research should explore the use of shorter epochs (1 s) and identify bone-specific activity intensities, rather than using pre-defined activity classifications more relevant to cardiovascular health.

Keywords: Accelerometry; Bone; Children; Physical activity.

Fig. 1

Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) flow diagram of the study selection process. PA physical activity, MPA moderate physical activity, MVPA moderate-to-vigorous physical activity, VPA vigorous physical activity

Fig. 2

Overall significant counts (stage 1) and ‘strongest within-study association’ counts (stage 2) expressed as a proportion of the total number of counts available for each intensity (total counts are the number of counts available, regardless of statistical significance; MPA, moderate physical activity; MVPA, moderate-to-vigorous physical activity; VPA, vigorous physical activity). In stage 1, votes were counted based on whether each intensity was statistically significant (p < 0.05; 1 = yes). In stage 2, out of the significant intensities within a study, only the intensity with the largest effect size (association) received a vote (only 1 count available out of the 2/3 intensities). Votes were counted for all analyses for each outcome included in a study (e.g. for the whole sample, boys and girls). When the value of association was the same for two intensities, votes were counted if significant in stage 1, but a stage 2 vote was not cast. When negative associations were observed, their significance was noted but again, no stage 2 vote was cast. p-values (vs VPA) represent the Bonferroni-adjusted p-values from the 2 × 2 chi-square tests for ‘MPA vs VPA’ and ‘MVPA vs VPA’ when the omnibus 3 × 2 chi-square test indicated that there was a significant difference between at least two of the three intensities. Significance was set at the 5% level