CONTRACTILE PROPERTIES OF HUMAN ANKLE MUSCLES DETERMINED BY A SYSTEMS-ANALYSIS METHOD FOR THE EMG-FORCE RELATIONSHIP

In order to determine painlessly and non-invasively the contractile pr operties of human skeletal muscles, the systems analysis method was ap plied to the relationship between the electromyogram (EMG) of agonist muscles and the isometric force produced by the voluntary contraction of the ankle plantarflexors and dorsiflexors. The subject's task was t o product force impulses at six different ankle positions for both mus cles, The EMG(input)-force(output) relationship was approximated using the linear second-order system, and the contraction time (CT), half-r elaxation time (HRT) and impulse response (IMP) were estimated. CT, HR T and IMP were found to increase as the muscles were stretched. The CT and HRT were longer for the plantarflexors than for the dorsiflexors, except at extremely plantarflexed positions. These results show quali tative agreement with results obtained by supramaximal electrical stim ulation. It is suggested that the method of systems analysis is useful in identifying differences in muscle contractile properties under var ious force-production conditions. Copyright (C) 1996 Elsevier Science Ltd.