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 (-0.6% per year; P < 0.001), middle-aged men and women (-1.1% to -1.4% per year; P < 0.001), and older men and women (-2.2% to -2.4% 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/T₀ , that is, the linear slope of the T-V relationship relative to maximal torque, exhibited a significant decline over time (-0.10%T₀ ·rad·s^-1 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 (-5.26 vs. -5.05 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.

Keywords: Aging; Force-velocity; Knee extension; Sarcopenia; Torque; Torque-velocity.

Figure 1

Analysis of the torque‐velocity (A and C) and power velocity (B and D) relationships in two participants (subject 1: A and B; subject 2: C and D). A hybrid equation was applied to measured data after excluding those data that fulfilled the following criteria: Maximum isometric torque values lower than any of the registered dynamic torque values (in A); dynamic trials showing a lower torque value for a corresponding velocity compared with a faster contraction (in A); and dynamic trials showing a lower power for a corresponding velocity compared with both a slower and a faster contraction (in B and D).

Figure 2

Individual longitudinal annual percentage changes in the study outcomes as a function of baseline age in women and men. Longitudinal changes were calculated as the difference between follow‐up and baseline values divided by follow‐up time in years, and then relative to baseline levels. The dotted lines represent no change (i.e., zero) whereas the solid lines were calculated using regression analyses (2nd order polynomials) to represent the continuum of longitudinal percentage changes as a function of baseline age. ∆, change in a respective outcome; T₀, estimated maximum isometric torque; V₀, estimated maximum unloaded contraction velocity; S/T₀, slope of the linear part of the torque‐velocity relationship; a/T₀, curvature of the hyperbolic part of the torque‐velocity relationship; P_max, maximum muscle power; T_opt, optimal torque; V_opt, optimal velocity; BMI, body mass index.

Figure 3

Longitudinal changes observed after the 10‐year follow‐up in the torque‐velocity relationship in young women and men, middle‐aged women and men, and older women and men. The dotted lines represent standard error of the estimate values, and the solid lines represent the hybrid equation used for modelling the torque‐velocity relationship.

Figure 4

Longitudinal changes observed after the 10‐year follow‐up in the power‐velocity relationship in young women and men, middle‐aged women and men, and older women and men. The dotted lines represent standard error of the estimate values, and the solid lines represent the hybrid equation used for modelling the torque‐velocity relationship that resulted in the power‐velocity relationship.