Age as a moderator of the secular trend for grip strength in Canada and the United States

Purpose: To determine whether grip strength changed on average over recent decades at each of two age levels (children and adolescents versus adults) in Canada and the US. Methods: For each sex, weighted least squares regression analyses were performed on mean grip strength values as reported in studies conducted from the 1960s onwards. Results: Grip strength did not change significantly as a function of year tested in children and adolescents, whereas it declined as a negatively accelerated function of year tested in adults. Conclusion: The results are contrary to what might be expected given that body weight has increased in both countries in recent decades and given that grip strength has been found to be positively correlated with body weight. It is suggested that there was a concurrent change in a factor that operated to counteract the effect of increased body weight on grip strength, a prime candidate being a decrease in levels of serum vitamin D. It is also suggested that the secular decline in adult grip strength can be explained by a factor that affects muscular function but which has a long latency period, a prime candidate here being obesity history.