S5.1-3 Sunday, Jan. 5 09:00 Partitioning the Metabolic Cost of Human Running: A Task-by-Task Approach ARELLANO, C.J.*; KRAM, R; Brown University firstname.lastname@example.org
Humans are very tractable and thus an ideal “model system” that allows us to better understand locomotion energetics. In this talk, we review our current understanding of the biomechanical basis for the metabolic cost of running. Running can be modeled as a simple spring-mass system whereby the leg acts a linear spring, storing and returning mechanical energy during stance. However, if running can be modeled as a simple spring-mass system, why does running incur a metabolic cost at all? C.R. Taylor and colleagues (1980) proposed the ‘cost of generating force’ hypothesis, which was based on the idea that muscles transform metabolic energy into force, not necessarily mechanical work. Kram and Taylor (1990) then demonstrated that the rate of metabolic energy was proportional to body weight and inversely proportional to the time of foot-ground contact for a variety of animals ranging in size and running speed. Kram and colleagues then adopted a task-by-task approach to study human running and found that the metabolic cost can be partitioned into body weight support (65-75%), propulsion (37-40%), and leg swing (7-10%). In our recent human running experiments, we have continued to refine this task-by-task approach, demonstrating that lateral balance exacts a modest cost of only 2%. In contrast, arm swing reduces the cost by 3%, thereby acting as a mechanism that saves metabolic energy during running. Summing all these biomechanical tasks, the lower and upper bounds for the metabolic cost of running are paradoxically 111% and 126%, respectively. To end this talk, we will discuss the interactive nature of these biomechanical tasks to try to explain this overestimation. We also discuss future experiments aimed at exploring in-vivo measurements that will allow us to characterize muscle-tendon function related to these biomechanical tasks.