Temporal trends in muscular fitness of English 10-year-olds 1998-2014: an allometric approach

Objectives To identify temporal trends in muscular fitness of English children using allometric scaling for height and weight to adjust for the influence of body size. Design Repeated cross-sectional study. Methods We measured; height, weight, standing broad-jump, handgrip, sit-ups and bent-arm hang in 10-year-old boys and girls from Chelmsford, England in: 2014 (n = 306), 2008 (n = 304) and 1998 (n = 310). Physical activity was (PAQ-C) was assessed in 2008 and 2014. Muscular fitness was allometrically scaled for height and weight. We assessed temporal trends using General Linear Models (fixed factors: wave and sex) and reported effect sizes using partial eta squared (ηP²). We compared percentage change per year 1998-2008 with 2008-2014. Results Ten-year-olds in 2014 were taller and heavier than in 2008 and 1998 but there were no differences in BMI. Compared with 2008, physical activity was lower in boys (ηP² = 0.012) and girls (ηP² = 0.27) assessed in 2014. There were significant main effects of wave for handgrip (ηP² = 0.060), sit-ups (ηP² = 0.120) and bent-arm hang (ηP² = 0.204). Pairwise comparisons showed muscular fitness of both sexes was significantly lower in 2014 than in 1998. From 2008 to 2014 percent change per year in handgrip (1.6%) and sit-ups (3.9%) were greater than for the preceding decade (handgrip 0.6%, sit-ups 2.6%). Conclusions Downward temporal trends in muscular fitness appear independent of secular changes in body size. We found a decrease in self-reported physical activity concurrent with the accelerated declines in fitness from 2008 to 2014. These findings suggest the declines in children are not engaging in physical activities which support development of muscular fitness.