Examining The Association Between Muscular Fatigue Index And Physical Function In Middle-aged Women

Abstract

PURPOSE: To examine the independent contribution of muscle fatigue to physical function (PF) performance in middle-aged women. METHODS: In this cross-sectional study, 104 middle-aged women (52.93 ± 6.10 years; BMI =26.38 ± 5.10 kg/m2) were assessed for muscle fatigue performance using a 25-repetition fatiguing knee flexion and extension task at 180 degrees per second. Muscle fatigue index (MFI) was calculated as the decline in peak torque from the first three repetitions to the last three repetitions. PF was objectively measured via the transfer task, 8-foot-up-and-go, 30-second chair stands, 6-minute-walk-test, and the lift-and-carry. A lower-extremity PF composite score also was calculated. Moderate to vigorous physical activity (MVPA) was measured using accelerometry and physical activity logs, while whole body and regional composition were measured using Dual Energy X-ray Absorptiometry. Muscle strength was assessed using isokinetic dynamometry for isometric knee flexion and extension at 60 degrees, and isokinetic knee flexion and extension at 60 degrees per second and 180 degrees per second, and muscle quality (MQ) was calculated as muscle strength normalized for thigh lean mass. The data were analyzed using bivariate correlation and hierarchical linear regression, with a p-value of less than 0.05 used to establish significance. RESULTS: When controlling for age, percent body fat, muscle quality, and MVPA per day, MFI was significantly associated with transfer task performance (r = .260, p < 0.05), and higher MFI was associated with slower transfer task time. While MFI contributed to 3.5% of the variance in transfer task performance (p = 0.024), percent body fat contributed to 19.4% of the variance (p = 0.001). Percent body fat was most highly associated with all measures of PF. CONCLUSIONS: The strength of the association between MFI and PF performance decreased when other independent variables (percent body fat, MVPA, MQ) were considered. Therefore, muscle fatigue may be a less important target for intervention in this population, while reducing percent body fat may be most influential in improving physical functional performance in middle-aged women.