Mechanical output and iEMG of isokinetic plantar flexion in 40-64-year-old subjects.

Peak torque (PT), contractional work (CW) and mean power of isokinetic plantar flexions were measured in unselected, clinically healthy subjects, randomly chosen from the official census lists of Umeå, in three age groups: 40-44, 50-54 and 60-64 years. Simultaneous recordings of integrated electromyograms (iEMG) were obtained by surface electrodes from all three heads of the m. triceps surae. PT and CW decreased exponentially with increasing velocity of angular motion and at 60 degrees X s-1 (r2 = 0.79 and 0.63, respectively) were adequately determined by crural circumference, age and sex. The muscular output declined with increasing age. Both output and iEMG showed an approximate 3:2 male:female ratio. Therefore, the ratio CW/iEMG was age, but not sex-dependent at any given velocity of angular motion. Independently of this age, the iEMGs were inversely proportional to velocity of angular motion, while iEMG/manoeuvre time was constant indicating that torque/velocity and work/velocity exponential relationships are mainly determined by muscular properties. Based on the literature it is suggested that the dependence of the measured parameters on age and sex is determined by muscular properties, rather than by the central nervous system. Moreover, the CW/iEMG ratio appears to provide a comprehensive picture of excitation and mechanical output of the muscle group studied and may therefore be a useful measure.