Arm-cranking muscle power and arm isometric muscle strength are independent predictors of all-cause mortality in men

Abstract

Poor muscle strength is associated with mortality, presumably due to low muscle mass. Notably, muscle power declines more rapidly than muscle strength with increasing age, which may be related to more complex central nervous system movement control. We examined arm-cranking power against four workloads and isometric strength measured in the upper extremities of 993 men longitudinally tested over a 25-yr period. Muscle mass was estimated by using 24-h creatinine excretion; physical activity was assessed by self-reported questionnaire. Muscle power and strength were modeled by time by using mixed-effects models, which developed regression equations for each individual. The first derivative of these equations estimated rate of change in strength or power at each evaluation. Survival analyses, using the counting method, examined the impact of strength, power, and their rates of change on all-cause mortality while adjusting for age. Arm-cranking power [relative risk ( rr) = 0.984 per 100 kg·m·min-1, P < 0.001] was a stronger predictor of mortality than was arm strength ( rr = 0.986 per 10 kg, P = not significant), whereas rate of power change ( rr = 0.989 per 100 kg·min-1·yr-1) and rate of arm strength change ( rr = 0.888 per 10 kg/yr) were risks independent of the power or strength levels. The impacts of power and strength were partially independent of muscle mass and physical activity. The risk of mortality was similar across the four power workloads ( rr = 0.93-0.96 per 100 kg·m·min-1), whereas the lowest load generated less than one-half the power as the higher loads. Arm-cranking power is a risk factor for mortality, independent of muscle strength, physical activity, and muscle mass. The impact is found with loads that do not generate maximal power, suggesting an important role for motor coordination and speed of movement.