Fig 1.
Experimental settings for measuring hip flexion torque.
The pad (A) that measures the vertical force generated by hip flexion is linked to the force transducer (B).
Fig 2.
Definition of onset of muscle activation.
The determined time difference between the onset of activation of rectus femoris and vastus intermedius during isometric hip flexion at maximal effort. Arrows indicate the onset of muscle activation. Horizontal dashed lines represent the threshold for determining the onset of muscle activation. RF, rectus femoris; VI, vastus intermedius.
Fig 3.
Torque and electromyographic amplitude.
Rectified electromyographic signals from the four quadriceps femoris muscles and torque exerted during isometric knee extension and hip flexion with maximal effort at a hip joint angle of 130°. VI, vastus intermedius; VL, vastus lateralis; VM, vastus medialis; RF, rectus femoris.
Fig 4.
Neuromuscular activation of the four quadriceps femoris muscles at three hip joint angles.
The results for each muscle at each hip joint angle were normalized to root mean square amplitude of the signal during maximal voluntary isometric contraction of the knee extensors at a hip joint angle of 90°. *, P < 0.05 vs. vastus intermedius, vastus lateralis and vastus medialis; †, P < 0.05 vs. vastus medialis.
Fig 5.
Time difference between onset of vastus intermedius and rectus femoris activation.
Time lag is the duration from the onset of rectus femoris activity to the onset of vastus intermedius activity during isometric hip flexion and knee extension at maximal effort. *, P < 0.05 vs. knee extension.