Figure 2. Simultaneous force and surface electromyography (SEMG) recordings during quadriceps maximal volitional contraction (QMVC) tests: the lines on the top channel represent the 3 consecutive volitional contraction forces; SEMG signals from vastus lateralis muscle (VL-M), rectus femoris muscle (RF-M) and vastus medialis muscle (VM-M) were shown in channel 2, 3 and 4, respectively; the number below the X axis represents the time (minute: second).

QMVC was about 25(Figure 2A) 40 kg in a male normal subject (Figure 2B).