STANDARD MECHANICAL ENERGY ANALYSES DO NOT CORRELATE WITH MUSCLE WORKIN CYCLING

The goal of this study was to assess the utility of experimental metho ds to quantify mechanical energy expenditure (MEE) in human movement. To achieve this goal, a theoretical model of steady-state cycling driv en by individual muscle actuators was used to produce two distinct ped al simulations. The simulations yielded the same pedaling rate and pow er output, but one reduced the MEE by avoiding eccentric muscle contra ctions. Contractile element force and length change in the individual muscles was used to quantify the total positive and negative work prod uced by the muscles. Three methods using external measurements were ap plied to the simulated movement. The three methods to quantify MEE wer e based on: (1) segment kinematic measurements, (2) work done by total joint powers and (3) intercompensated joint powers, i.e. negative wor k from one joint is transferred to an adjacent joint where energy is b eing generated (positive work) via biarticular muscles. The results sh owed that none of the MEE analyses were correlated to the MEE of the i ndividual muscles, with errors reaching 40%. Errors were mainly attrib uted to the inability of the MEE methods to account fbr co-contraction s of antagonistic muscle groups. This phenomenon occurred primarily wh en one muscle generated force during activation while the antagonist g enerated force during deactivation. (C) 1998 Elsevier Science Ltd. All rights reserved.