Motor time of the rectus femoris under loading of different weights

Motor time (MT) of the rectus femoris was measured for seven normal subjects during rapid extension of the knee joint at 60 degrees flexion in the sitting position with and without external loads on the leg. MT prolonged linearly with external load from 0 to 4 kg. Tangent of this linearity, the rate of tension development (RTD), was significantly different from one another of the subjects and was not related to MT without external load. RTD is a relevant index to assess an efficiency of rapid force generation of a muscle.