Ten‐year longitudinal changes in muscle power, force, and velocity in young, middle‐aged, and older adults

Abstract

Background Maximum muscle power (P max ) is a biomarker of physical performance in all ages. No longitudinal studies have assessed the effects of aging on P max obtained from the torque-velocity (T-V) relationship, which should be considered the 'gold standard'. This study evaluated the longitudinal changes in the T-V relationship and P max of the knee-extensor muscles in young, middle-aged, and older adults after 10 years of follow-up. Methods Four hundred eighty-nine subjects (311 men and 178 women; aged 19-68 years) were tested at baseline and after a 10-year follow-up. Anthropometric data, daily protein intake, physical activity level (PAL), and knee-extension muscle function (isometric, isokinetic, and isotonic) were evaluated. A novel hybrid equation combining a linear and a hyperbolic (Hill-type) region was used to obtain the T-V relationship and P max of the participants, who were grouped by sex and age (young: 20-40 years; middle-aged: 40-60 years; and old: ≥60 years). Linear mixed-effect models were used to assess effects of time, sex, and age on T-V parameters, P max , and body mass index (BMI). Additional analyses were performed to adjust for changes in daily protein intake and PAL. Results P max decreased in young men (À0.6% per year; P < 0.001), middle-aged men and women (À1.1% to À1.4% per year; P < 0.001), and older men and women (À2.2% to À2.4% per year; P ≤ 0.053). These changes were mainly related to decrements in torque at P max at early age and to decrements in both torque and velocity at P max at older age. BMI increased among young and middle-aged adults (0.2% to 0.5% per year; P < 0.001), which led to greater declines in relative P max in those groups. S/T 0 , that is, the linear slope of the T-V relationship relative to maximal torque, exhibited a significant decline over time (À0.10%T 0 •rad•s À1 per year; P < 0.001), which was significant among middle-aged men and old men and women (all P < 0.05). Annual changes in PAL index were significantly associated to annual changes in P max (P = 0.017), so the overall decline in P max was slightly attenuated in the adjusted model (À5.26 vs. À5.05 W per year; both P < 0.001). Conclusions P max decreased in young, middle-aged, and older adults after a 10-year follow-up. The early declines in P max seemed to coincide with declines in force, whereas the progressive decline at later age was associated with declines in both force and velocity. A progressively blunted ability to produce force, especially at moderate to high movement velocities, should be considered a specific hallmark of aging.

Neural and muscular contributions to the age-related loss in power of the knee extensors in men and women

“…An important limitation in the present study is the rates of power loss with aging are estimated based on cross-sectional data spanning several decades where power output has been shown to be relatively stable (2)(3)(4). Thus, our data most likely underestimates the rate of power loss that occurs after the age of ~40-50 years old.…”

“…Human aging is accompanied by a progressive decline in the neuromuscular system that ultimately leads to decreased physical function and quality of life for older adults. Mechanical power output of limb muscle, the product of force or torque and velocity, has emerged as one of the strongest predictors for the decrements in physical function with aging (1), with the decline in power typically beginning around the fourth to fifth decade of life and accelerating thereafter (2)(3)(4).…”

“…Importantly, the age-related decrements in power output vastly exceed the age-related loss in total muscle mass (2,3,5,6), suggesting other factors, such as a reduced ability of the nervous system to activate the muscle and/or factors disrupting the contractile properties of the muscle, must also be contributing to the age-related loss in power. Despite the importance of limb muscle power output to physical function in older adults, the extent that neural and muscular mechanisms contribute to the accelerated age-related decline in power relative to muscle mass remains poorly understood.…”

“…Identifying the primary mechanisms for the accelerated age-related loss in power relative to muscle mass is particularly important in cohorts that may be most affected by the detrimental effects of losing muscle power, such as older women and very old adults (≥80 yr). For example, young adult women generate less power than men before the decrements that occur from aging (2,3,25,26), which may result in older women being more susceptible to having insufficient power to maintain mobility and perform activities of daily living (2,(27)(28)(29). Both cross-sectional and longitudinal studies have observed that the rates of absolute power loss with aging are greater in men than women, but do not differ between the sexes when expressed relative to muscle mass or as a percent decline (2)(3)(4).…”

“…For example, young adult women generate less power than men before the decrements that occur from aging (2,3,25,26), which may result in older women being more susceptible to having insufficient power to maintain mobility and perform activities of daily living (2,(27)(28)(29). Both cross-sectional and longitudinal studies have observed that the rates of absolute power loss with aging are greater in men than women, but do not differ between the sexes when expressed relative to muscle mass or as a percent decline (2)(3)(4). These findings suggest that the mechanisms for the age-related loss in power may be similar between men and women.…”