Tracking of muscular strength and power from youth to young adulthood: Longitudinal findings from the Childhood Determinants of Adult Health Study

Objectives: Low muscular fitness levels have previously been reported as an independent risk factor for chronic disease outcomes. Muscular fitness tracking, the ability to maintain levels measured at one point in time to another point in time, was assessed from youth to adulthood to provide insight into whether early identification of low muscular fitness in youth is possible.

Design: Prospective longitudinal study.

Methods: Study including 623 participants who had muscular fitness measures in 1985 (aged 9, 12 or 15 years) and again 20 years later in young adulthood. Measures of muscular fitness were strength (right and left grip, leg, shoulder extension and flexion measured by dynamometer, and a combined strength score) and power (standing long jump distance).

Results: Strength and power were relatively stable between youth and adulthood; the strongest tracking correlations were observed for the combined strength score (r = 0.47, p ≤ 0.001), right grip strength (r = 0.43, p ≤ 0.001) and standing long jump (r = 0.43, p ≤ 0.001). Youth in the lowest third of muscular fitness had an increased risk of remaining in the lowest third of muscular fitness in adulthood (strength: relative risk (RR = 4.70, 95% confidence interval (CI) (3.19, 6.92); power: RR = 4.06 (2.79, 5.90)).

Conclusions: Youth with low muscular fitness are at increased risk of maintaining a low muscular fitness level into adulthood. These findings warrant investigation into the long term effects of early interventions that focus on improving low muscular fitness levels in youth which could potentially improve adult muscular fitness and reduce future chronic disease outcomes.