RESUMO
Muscle activity of human ankle extensors during ballistic plantar flexion movement was studied by use of the rubber-strain-gauge method. The muscle power was measured by using the after-loading method. The subjects quickly extended the ankle joint with loads of 20, 40 and 60% of the maximum voluntary contraction (MVC) of ankle extensor muscles.<BR>Maximum muscle power was exerted at about the load of 60% MVC. This result can presumably be attributed to the increase in the recruitment and firing frequency of motor units in gastrocnemius muscle with each load attached to ankle extensors.<BR>Although the amount of muscle power increased consistently with an increase in the calf girth immediately after an onset of load lifting (r=0.8479, p<0.001), the period in which it obtained maximum velocity was not significant. On the other hand, muscle activity immediately after onsets of load lifing are important and girth changes in muscle should be considered as parameter for estimating the power output of human muscles during ballitic contraction.