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

https://doi.org/10.1016/j.jsams.2017.03.021Get rights and content

Abstract

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.

Introduction

Muscular fitness is a unique fitness phenotype that incorporates strength, power and endurance.1 Observational studies have shown low levels of muscular fitness to be associated with increased disability, morbidity, and mortality2, 3, 4 independent of cardiorespiratory fitness and measures of adiposity. In a recent analysis of almost 140,000 individuals from 17 countries of varying incomes (median age: 50 years old) in the Prospective Urban Rural Epidemiology study, muscular strength was shown to be as strong a predictor of all-cause and cardiovascular mortality as systolic blood pressure.5 Consequently, the early identification and possible intervention of individuals with low muscular fitness may improve long-term health outcomes.

Because many chronic disease risk factors are established in childhood and adolescence (herein termed youth), studies have been undertaken to examine the extent to which risk factors measured in youth predict the same measure collected years later in adulthood. These tracking studies attempt to determine the stability of a risk factor over time. Risk factors that track sufficiently provide a means for early identification and possible intervention among those where the risk factor is present. Evidence for tracking of muscular fitness phenotypes is sparse, with most previous research examining tracking of muscular fitness phenotypes throughout youth alone.6, 7, 8 However, longitudinal evidence that muscular fitness phenotypes track between youth and adulthood is limited.9, 10, 11

Using data from the Childhood Determinants of Adult Health (CDAH) Study, a 20-year prospective cohort beginning in youth, we aimed to determine the extent to which muscular fitness phenotypes of strength and power track from youth to adulthood.

Section snippets

Methods

In 1985, a representative sample of 2726 Australian school youth aged 9, 12 and 15 years participating in the Australian Schools Health and Fitness Survey (ASHFS) had field measures of muscular fitness as well as other health-related risk factors collected. Details on the ASHFS sampling strategy have been published elsewhere.12 In 2004–2006, the CDAH study conducted 34 follow-up clinics across Australia where participants from the 1985 ASHFS were invited to attend as young adults aged 26–36

Results

Pertinent baseline and follow-up characteristics of the 623 participants are presented in Table 1. Mean (SD) length to follow-up was 19.9 (0.6) years, ranging from 18.7 to 21.0 years. Compared with females, males had on average more muscular phenotypes in youth and adulthood.

On average participants had a higher combined strength score, a greater distance in the standing long jump test and had a greater proportion of people in high socioeconomic position compared to non-participants (Table S1).

Discussion

The results of this tracking analysis showed that muscular fitness phenotypes tracked moderately between youth and young adulthood. Youth who were older at the baseline measurement tended to track the most, and females tracked more strongly in upper body strength measures, whereas males tracked stronger in the lower body strength and power measures. Furthermore, youth power and strength were shown to predict adult levels, with those in the lowest third in youth approximately four times more

Conclusion

In conclusion, our findings show that measures of strength and power track from youth to adulthood. These data suggest that strength and power levels in youth form, in part, the basis for strength and power levels in adulthood and that those with low muscular fitness in youth are at increased risk of maintaining this level into adulthood. Given that low levels of muscular fitness in adulthood are an independent risk factor for several chronic diseases, our data warrant further investigation

Practical implications

  • Levels of muscular fitness track from youth to adulthood, whereby youth muscular fitness levels are predictive of adult muscular fitness levels.

  • Muscular fitness levels have the potential to be used as a screening tool to identify those at increased risk of maintaining low levels of muscular fitness over time. While 50–60% of participants maintained a low muscular fitness level between the two time-points, there was some suggestion that muscular fitness levels measured later in youth might be a

Acknowledgements

We acknowledge the contribution of CDAH staff and volunteers to this study. Especially, we acknowledge the ongoing commitment of CDAH participants to the study. The baseline survey was supported by grants from the Commonwealth Departments of Sport, Recreation and Tourism, and Health; The National Heart Foundation; and the Commonwealth Schools Commission. The follow-up study was funded by grants from the National Health and Medical Research Council, the National Heart Foundation, the Tasmanian

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