Biomechanics of lower limb raising from the supine position

Aim. This study analyses the kinematics of the lower limb raising movement from the supine position and the electromyography activity of the muscles involved. Methods. Twenty healthy right hand subjects performed the right lower limb raising from the supine position, starting from the clinical bed plane and up to a 70° inclination of the thigh over the horizontal plane, while the knee was kept flexed at 120° by a soft splint. The same exercise was executed with no resistance and with 2 kg and 8 kg respectively applied to the ankle. The kinematics was recorded utilising an optoelectronic system, whereas the electromyography activity was recorded by a surface electromyography (EMG) applied to the following muscles: right rectus femoris, left biceps femoris, rectus abominalis from both sides and dorsal major from both sides. Results. In all the cases the pelvis performed a backwards rotation retroversion. The highest increase of EMG activation was recorded on the right rectus femoris as well as on the left biceps femoris; the increase was lower in the right rectus abdominis and in the right dorsal major, whereas it was minimum in the left rectus abdominis and in the left dorsal major. A great variability in the activation times was reported in the various muscles of the different subjects, regardless of the trials. The only muscle anticipating the right rectus femoris activation was the left biceps femoris. Conclusions. The research has shown how the simple movement under study is more complex than what is usually described by the text books, both in regard to the kinematics and to muscles' actions. Even the individual variability in utilising the agonist and stabilisation muscles can be of relevance for a more rational utilisation of the physical exercise in motor re-education.