ON THE METABOLIC AND MECHANICAL DEMANDS OF WALKING: THE EFFECTS OF SLIDING FRICTION, LIMB SWING WORK, AND BOUT DURATION.

Researchers have long investigated the metabolic and mechanical demands of locomotion. Discoveries in such field not only have advanced our understanding of the physiology of movement and energy transformations, but have also impacted anthropology, zoology, sports science, and clinical medicine. However, the relation between how much metabolic energy animals use to move and how much mechanical work they produce remains partially understood. In this thesis, I summarize some key concepts and discoveries about the bioenergetics, mechanics, and efficiency of locomotion; I then present three novel studies that examine how the bioenergetics and mechanics of human locomotion are linked. The first study investigates walking in a virtual reality emulator, where participants slide their feet on the surface of a multidirectional treadmill. In this gait, mechanical work is required to overcome sliding friction, and the metabolic cost is hence relevantly greater than normal walking. The second study compares bipedal walking in chimpanzees and humans. Humans walk with less than half the metabolic cost of chimpanzees, and we propose that the difference is due to the lower work needed to swing limbs. In the third study, we quantified how the duration of a walking bout influences its metabolic cost and efficiency. We found that shorter bouts have a greater metabolic cost and lower efficiency than longer ones.