Abstract des Autors

9 healthy men (25 to 35 yrs) performed sustained maximal voluntary contractions (MVC) of foot plantar and dorsal, and finger flexor muscles. Contractions lasted 10 min and were followed by short test contractions at 30 MVC during recovery. 2 positions of the working extremity high or low were established by different body postures (supine or sitting). Under these conditions, studies of force, integrated electromyogram (iEMG), blood pressure, and heart rate showed 1) force decreased throughout the first few minutes of maximal contraction but reached a near steady-state value after 5 to 6 min. 2) force decay and steady-state level depended on muscle group and body position. When sitting (low leg), muscles with a high incidence of slow twitch fibres (plantar flexors) showed a slower force decay and a higher relative steady-state force than fast dorsal flexor muscles. When supine (high leg), plantar and dorsal flexor muscles reached about the same low level of relative steady-state force. Changes in iEMG, blood pressure, and heart rate did not differ in the two positions. 3) during recovery, plantar flexor muscles showed higher iEMG values as well as higher values of blood pressure and heart rate when supine than when sitting. Recovery of dorsal flexor muscles was little affected by body posture. 4) force development and recovery of predominantly fast finger flexor muscles were almost independent of arm position. It was concluded that muscle fibre composition was the main factor in determining muscle endurance.