Background Observational studies do not always find positive associations between physical activity and muscle strength despite intervention studies consistently showing that resistance exercise improves muscle strength in older adults. In previous analyses of the MRC National Survey of Health and Development (NSHD), the 1946 British birth cohort, there was no evidence of an association between leisure time physical activity (LTPA) across adulthood and grip strength at age 53 years. This new study tested the hypothesis that cumulative benefits of physical activity across adulthood on grip strength will have emerged by age 60–64 years.
Methods Data from the MRC NSHD were used to investigate the associations between self-reported participation in LTPA at ages 36, 43, 53 and 60–64 years and grip strength at 60-64. Linear regression models were constructed to examine the effect of activity at each age separately and as a cumulative score, including adjustment for potential confounders (gender, height, weight, smoking status, limiting disability, educational attainment and occupational class). Formal testing of two different life course hypotheses, the sensitive period and accumulation models, was also performed.
Results There were complete longitudinal data available for 778 men and 867 women. Being more active at ages 36, 53 (men only) and 60–64 was associated with stronger grip at 60-64 in models adjusted for gender only. These findings attenuated after adjustment for confounders but associations with LTPA at 53 and 60–64 remained, with for example those who were most active at 60–64 having 1.73 kg ([95% CI 0.61, 2.85], p < 0.01) stronger grip than those who were inactive. There was also evidence of a cumulative effect of LTPA across mid-life; compared to the third of participants who reported the least LTPA participation across the four time points, those in the top third had on average 2.11 kg ([0.88, 3.35], p < 0.01) stronger grip after adjustment for confounders. Consistent with this, in comparison to a fully saturated model, an accumulation model best fit the data.
Conclusion Increased levels of physical activity across adulthood were associated with stronger grip at age 60–64, in both men and women. As these associations have emerged since age 53 years it suggests that LTPA across adulthood may prevent decline in grip strength in early old age. Given the negative health outcomes associated with weaker grip at similar ages, the findings from this observational study provide additional evidence in support of guidelines which recommend that physical activity should be maintained across adult life.
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