The Organization of Multisegmental Pulls Made by Standing Humans: II. Submaximal Pulls

Previously, an autonomous oscillator model with three parameters was derived that describes the relationship between anterior-posterior center of mass motions and pulling force for near-maximal, bimanual pulls made by standing subjects (Michaels, Lee, & Pai, 1993). The present study evaluated the extent to which a full range of pulling forces could be fit by the model and how the model's three parameters changed with intended pulling force. How much variation in force each parameter could contribute was determined by simulating the model. Qualitative and quantitative analyses of pulls made by 6 well-practiced subjects at 5%, 10%, 20%, 40%, 60%, 80%, and 95% of their maximum pulling force revealed that the model holds well, except for the least forceful pulls of some subjects. Two parameters appeared to be controlled; one, related to the position of the center of pressure, varied most among less forceful pulls; the second, related to the position of the center of mass at the time of handle-force onset, varied most among more forceful pulls. How these parameters might be set is discussed.