Collective Weakness Is Associated With Time to Mortality in Americans

Abstract

McGrath, R, McGrath, BM, Jurivich, D, Knutson, P, Mastrud, M, Singh, B, and Tomkinson, GR. Collective weakness is associated with time to mortality in Americans. J Strength Cond Res XX(X): 000–000, 2024—Using new weakness cutpoints individually may help estimate time to mortality, but their collective use could improve value. We sought to determine the associations of (a) each absolute and body size normalized cut point and (b) collective weakness on time to mortality in Americans. The analytic sample included 14,178 subjects aged ≥50 years from the 2006–2018 waves of the Health and Retirement Study. Date of death was confirmed from the National Death Index. Handgrip dynamometry measured handgrip strength (HGS). Men were categorized as weak if their HGS was <35.5 kg (absolute), <0.45 kg·kg−1 (body mass normalized), or <1.05 kg·kg−1·m−2 (body mass index [BMI] normalized). Women were classified as weak if their HGS was <20.0 kg, <0.337 kg·kg−1, or <0.79 kg·kg−1·m−2. Collective weakness categorized persons as below 1, 2, or all 3 cutpoints. Cox proportional hazard regression models were used for analyses. Subject values below each absolute and normalized cutpoint for the 3 weakness parameters had a higher hazard ratio for early all-cause mortality: 1.45 (95% confidence interval [CI]: 1.36–1.55) for absolute weakness, 1.39 (CI: 1.30–1.49) for BMI normalized weakness, and 1.33 (CI: 1.24–1.43) for body mass normalized weakness. Those below 1, 2, or all 3 weakness cut points had a 1.37 (CI: 1.26–1.50), 1.47 (CI: 1.35–1.61), and 1.69 (CI: 1.55–1.84) higher hazard for mortality, respectively. Weakness determined by a composite measure of absolute and body size adjusted strength capacity provides robust prediction of time to mortality, thus potentially informing sports medicine and health practitioner discussions about the importance of muscle strength during aging.