Facebook
Twitter
LinkedIn
Email
 |
Checking for direct PDF access through Ovid | |
Excerpt
The cost of generating force (c) has been shown to be constant across speeds during level running because of proportional inverse changes in metabolic power (Em) and time of foot contact (tc) (Taylor, 1994; Browder et al., 1997). According to Taylor (1994), this constant cost occurs because of the use of musculoskeletal springs. The stretch and recoil occurs in the tendons during foot contact with the ground while the muscle develops a constant isometric force, regardless of running speed. To test this hypothesis in humans, Em, c, and tc were investigated in 11 males (M±SD: age(yrs)=23±2; body weight (Wb) (kg)=76±10) during horizontal and graded running at 3 randomly ordered speeds (2.4, 2.9, 3.4 m s-1). Each subject completed each speed at 0% and 4% grade on a motor-driven treadmill. Subjects were videotaped while steady state oxygen uptake data were collected during the last minute of each 4-min stage. C was calculated with the equation, Em / Wb = c(1/tc). Repeated measures ANOVAs with appropriate post hoc tests were calculated to examine the effects of grade on Em, c, and tc (Bonferroni adjustment:.05/3 = p ≤.02). There was a significant main effect of grade for all three variables (Em and c, p =.0001; tc, p =.01). As expected, there was a significant increase in Em (M±SD: 0%=927±155 W; 4%=1077±182 W) and c (M±SD: 0%=0.38±.04 J·N-1; 4%=0.46±.04 J·N-1) with increasing grade for each speed. Unexpectedly, however, tc also increased significantly with increasing grade for each speed (M±SD: 0%=0.31±.03 s; 4%=0.32±.03s). These findings suggest that Taylor's hypothesis may not explain fully the mechanisms underlying the energy costs of running. Future studies should examine the assumptions of Taylor's economic force hypothesis.
