Overweight were younger, heavier, shorter, and had higher BMIs and percent fat (P < 0.01, ). Overweight, older women had similar lean mass as normal weight, but carried an additional 13.2 kg of fat mass. Overweight women had significantly lower overall SPPB scores with 17% slower habitual gait speed and 15% slower chair rise time (all P < 0.05). Additionally, fat mass was negatively correlated with chair rise time (r = 0.55, P = 0.005) and maximal gait speed (r = −0.65, P = 0.003) but the correlation with habitual gait speed did not reach statistical significance (r = −0.28, P = 0.109).
When strength relative to body mass was assessed, overweight, older women demonstrated 17% lower KE maximal torque, 20% lower KF maximal torque, and 43% lower PF maximal torque than normal weight (, P < 0.05). Strength relative to body mass was correlated to fat mass for the KE (r = −0.63, P = 0.001), KF (r = −0.48, P = 0.014), and PF (r = −0.55, P = 0.005) but not for DF (r = −0.31, P = 0.087). When absolute strength was compared, the groups had equivalent maximal torques for the KE, KF, and DF but overweight still showed 30% lower maximal PF torque (36.4 ± 15.4 vs. 51.6 ± 13.5 Nm, P = 0.018). Similarly, normalizing strength to fat-free mass attenuated the difference in performance between groups for each joint action (). Relative to body weight, overweight had 42% lower KE RTD, 39% lower KF RTD, and 50% lower PF RTD than normal weight (, P < 0.05). The differences between overweight and normal weight groups persisted even when maximal RTD was expressed in absolute terms (KE RTD, 407 ± 205 vs. 565 ± 131 Nm s−1; KF RTD, 222 ± 93 vs. 292 ± 63 Nm s−1; PF RTD, 159 ± 83 vs. 252 ± 85 Nm s−1 respectively, all P < 0.05) and when normalized to fat-free mass (). The onset EMG measured during the first 500 ms of the isometric contraction was not different between normal and overweight groups for either the KE (96 ± 30 vs. 80 ± 24 %peak EMG at MVC, P = 0.195) or PF (100 ± 29 vs. 98 ± 44 %peak EMG at MVC, P = 0.935), respectively.
Figure 2 Comparison of maximal torque relative to body mass (A) maximal rate of torque development relative to body mass (B) maximal torque relative to fat-free mass (FFM) (C) and maximal rate of torque development relative to fat-free mass (D) between those with (more ...)
At the standard walking speed of 0.83 m s−1 there were no differences between groups for any gait or muscle activation variable and therefore only the results of the maximal speed trial are reported next. During weight acceptance at the maximal speed, KE peak EMG was 52 ± 23% peak EMG at MVC in overweight and 32 ± 9% peak EMG at MVC in normal weight (P = 0.029, ). The difference in KE peak EMG during push-off between overweight (17 ± 12%) and normal weight (8 ± 5%) approached statistical significance (P = 0.057). Similarly, PF peak EMG was higher in overweight during weight acceptance (52 ± 32% vs. 27 ± 13%, P = 0.031) but not during push-off (42 ± 21% vs. 46 ± 25%, P = 0.736). Correlational analysis demonstrated that there was a positive linear relationship between BMI and PF peak EMG during weight acceptance (r = 0.59, P = 0.003) but the correlation between BMI and muscle activation did not reach statistical significance for the KE during weight acceptance (r = 0.20, P = 0.20), KE during push-off (r = 0.33, P = 0.075), or PF during push-off (r = 0.17, P = 0.24).
When walking at maximal speed, overweight experienced higher absolute vGRFs during weight acceptance (846 ± 146 vs. 730 ± 74 N, P = 0.035) and push-off (757 ± 159 vs. 613 ± 58 N, P = 0.009) than did normal weight (). This relationship between BMI and supportive force was reversed when the peak vGRF was expressed relative to body weight () with overweight having an 11% lower peak force during weight acceptance (, P = 0.006). The push-off rate relative to weight was 18% lower in overweight (P = 0.026). At maximal speed, overweight demonstrated 8% slower stride rates, 12% shorter strides, 13% longer foot-ground contact times, and 21% longer double-limb support times (, P < 0.05). With the exception of stride length (P = 0.067), the differences in these gait parameters remained when height was used as a covariate.
Comparison of kinetic, temporal, and spatial gait parameters between normal and overweight groups at self-selected, maximal walking speed.
demonstrates that maximal walking speeds were strongly associated with peak vGRFs and shows that KE strength was moderately correlated to the maximal walking speed. When examining the relationship between body composition and walking performance, lean body mass was not associated with maximal speed () whereas fat mass was inversely correlated to speed ().
Figure 3 Pearson product moment correlations associating self-selected, maximal walking speed with maximal vertical ground reaction force (A), maximal knee extensor torque (B), lean body mass (C) and body fat mass (D). Closed circles represent those with normal (more ...)