Characteristics of repeated isokinetic plantar flexions in middle-aged and elderly subjects with special regard to muscular work.

Contractional work (CW), mean power (CP) and peak torque (PT) were recorded for each of up to 200 full range-of-motion (RoM) repetitive isokinetic (60 degrees X s-1) maximum effort plantar flexions. Subjects were 88 unselected clinically healthy males and females aged 40-44, 50-54 and 60-64 years with similar distributions of age and sex. Simultaneous recordings of integrated electromyograms (iEMGs) were obtained from the three heads of the m. triceps surae. Within approximately 50 contractions CW had decreased 36-21% for the different groups (by age and sex). The corresponding decreases for PT and CP were 28-14% and 25-13%, respectively. During the remaining part of the experiment only minor changes occurred. For CW but not for PT and CP reductions were negatively related to age while no sex differences were evident. Decreases in CW were significantly smaller in subjects physically active during leisure time than in those relatively inactive. Decreases in active range-of-motion provide an explanation for greater reductions in CW than in PT and CP. The iEMGs of the mm. gastrocnemii decreased significantly more than that of the m. soleus. Close associations between CW and iEMG were evident. Hence the chosen expression of output/input balance: CW/iEMG was nearly constant throughout the experiments. Results indicate that measurements of contractional work throughout the range-of-motion may provide more differentiated information on mechanical output during supposedly fatiguing dynamic manoeuvres than can recordings of maximum strength.