Preferred Walking Speed and Cost of Transport are similar for Obese and Normal Weight Women

Abstract

1739 Normal weight individuals prefer to walk at the speed (1.4 m/s) that minimizes the amount of metabolic energy consumed per unit distance or cost of transport (COT). Previous research suggests that obese individuals prefer to walk at a slower speed and have lower aerobic capacities (VO2max). The COT vs. speed relationship has not been measured for obese individuals. Thus, the strategy used by obese individuals in choosing preferred speed is not clear. We hypothesized that obese individuals would choose to walk at a slower than normal speed in order to reduce the relative effort (% of VO2max), rather than choosing the speed that minimizes COT. PURPOSE: To compare the preferred walking speed, metabolic cost of walking versus speed relationships, and the relative aerobic effort at the preferred walking speed for obese vs. normal individuals. METHODS: Twenty adult female volunteers, 10 obese, BMI = 34.1 ± 3.2 kg/m2 and 10 normal weight, BMI = 20.4 ± 2.2 kg/m2 (mean ± S.D.) participated in this study. We measured preferred walking speed on a 50 m section of level sidewalk (mean of 5 trials). To determine the metabolic energy and COT vs. speed relationships, we measured VO2 and VCO2 while subjects walked on a level treadmill at 6 speeds (0.5, 0 .75, 1.0, 1.25, 1.5, and 1.75 m/s; 5-minute trials, with a 5-minute rest period between trials). To obtain VO2max, we used a modified Balke treadmill protocol. We used repeated measure ANOVAs to determine statistical significance. RESULTS: Contrary to previous reports, preferred walking speeds were not different between the obese (1.40 m/s) and normal weight (1.47 m/s) groups (p = 0.20). Although the obese subjects had somewhat greater metabolic rates (W/kg) at all speeds, the speeds corresponding to minimum COT were only slightly different, 1.23 m/s for obese and 1.33 m/s for normal weight subjects (p = 0.027). The average VO2max of the obese subjects was 33% less than the normal weight subjects (25.8 ml/kg/min vs. 38.7 ml/kg/min, p = 0.0001). Thus, at the preferred walking speed, the obese subjects used a significantly greater percentage of VO2max (51% vs. 36%, p = 0.001). CONCLUSION: Obese and normal weight individuals use a similar strategy of minimizing metabolic energy cost per distance in choosing preferred walking speed, even though this strategy requires a greater relative aerobic effort, i.e. rate of energy expenditure. The authors acknowledge the financial support by NIH grants AR44688 and M01-RR00051