The EMG results indicated a proximal-to-distal innervation of the muscles. The m. iliopsoas was active during the entire motion while the m. rectus femoris
was activated a little later and the m. vastus lateralis a little later again (Fig. 2). The activity of these 3 muscles was often close to 100'%1I. n the period wherethe angular velocity of the thigh was positive until impact, the activity of the m. iliopsoas averaged 79.4% (65.1-100.9%) while the activity in the m. rectus femoris was 46.3% (32.5-68.7%). The peak value of the m. iliopsoas was 98.3% (80.0-121.1Y0) while
the peak value of the m. rectus femoris was 93.7% (79.1-99.9%). In the same period there was only little activity in the m. biceps femoris (22.6% (5.2-3O.O'Yb))
and the m. gluteus maximus (10.2% (2.1-32.1%)). Just before impact the activity of these two muscles reached their peak values of 40.10/(1( m. biceps femoris)
and 27.lo/o (m. gluteus maximus). The activity of the m. vastus lateralis was 81.7% (64.0-102.1%) in the period of knee extension with a peak value of 101.6% (91.6-1 12.3%).
The method used to collect EMG from the m. iliopsoas
proved to be applicable in the studies of fast
movements. The larger baseline shifts in the signals
collected with the wire electrodes could be removed
using a fourth-order Butterworth high-pass filter with
a cut-off frequency of 20 Hz (Fig. 3).
The maximal potentials of the EMG signals collected
with the wire electrode reached 3.22 mV (2.26-
3.94 mV), while the maximal potentials of the skin
electrodes were between 0.61 mV and 1.97 mV