49.1 Thursday, Jan. 5 What are walking and running, and why? Modeling optimization tested against gravity manipulation BERTRAM, JEA*; HASANEINI, SJ; University of Calgary email@example.com
Simulated reduced gravity studies indicate a fundamental difference between human walking and running. The metabolic cost of running decreases directly with decrease in gravity and kinematic patterns change substantially and systematically. In contrast, only relatively minor changes occur in walking when gravity is changed. Although numerous hypotheses have been put forward to explain these differences, no clear evidence of the root of these differences exists. Here we test the gait predictions of a simple but comprehensive model of bipedal locomotion under varying gravity levels. The model is able to predict optimum actuation patterns, mechanical cost and the resultant movement patterns that provide the most effective locomotion under the circumstances encountered. We then evaluate the response of human subjects to the same locomotion conditions and find that their response parallels that of the model’s predictions. Since the behavior of the model can be analyzed in detail, we can conclude that these gaits are optimized largely for the trade-off between momentum loss resulting from strut-like contact of the supporting limb and the cost of leg work required to limit those losses. The decreased cost of running in reduced gravity is largely due to the low cost of the non-contact ‘flight’ phase of this gait. The cost of walking is largely determined by momentum loss, a function of mass and velocity that is little influenced by gravity level. There appears no reason why the results found for human locomotion mechanics would not apply to the fundamentals of quadrupedal gait as well.