Physical Activity, Exercise Physiology, Movement
Decision-making: cost analysis of step rate preference in treadmill walking
(School of Public Health (UMD) KNES Doctoral Student)
Introduction When gait mechanics are unconstrained, humans tend to walk with relatively minimal metabolic energy expenditure. This tendency suggests the hypothesis that minimal energy expenditure governs decision-making in gait. In this study, we tested the minimum energy hypothesis by investigating step rate preferences in human walking when humans must choose between two different step rates. Methods During a calorimetric test, subjects walked on a treadmill using seven different step rates while O2/CO2 rates were measured. These data were used to predict metabolic cost as a function of step rate. Subjects then performed 10 conditions of treadmill walking while electromyographic (EMG) data from muscles were measured. Each condition was a pair of one-minute trials with randomly assigned step rates. Subjects were asked at the end of each condition which step rate they preferred. We then calculated how often subjects preferred trials with five candidate decision criteria: lower metabolic cost of transport (MetCost), lower metabolic energy per step (StepCost), lower muscular effort (total integrated EMG), step length closer to normal, and step rate closer to normal. Results Subjects preferred the trial with step length closer to their normal length in 88.3±7.5% of the trials, and preferred the trial with step rate closer to their normal rate in 85±7.7% of the trials. Both preference rates were significantly greater (p < 0.001) than the number of trials preferred with lower MetCost (73.3±15%), lower StepCost (66.6±17.5%) or lower EMG (61.7±16%). Discussion The results indicate that subjects prefer gait mechanics with step rates or step lengths closer to their normal gait, even if this choice sometimes incurs a higher metabolic cost or more muscular effort. In addition, the preference for step rates and lengths closer to their normal values was more consistent between subjects than the other tested criteria.
Importance to public health: