THE 3-D MOTION OF THE CENTER OF GRAVITY OF THE HUMAN-BODY DURING LEVEL WALKING - II - LOWER-LIMB AMPUTEES

Objective. To analyse the motion of the centre of gravity (CG) of the body during gait in unilateral lower limb amputees with good kinematic patterns. Design. Three transtibial (below-knee, BK) and four transfe moral (above-knee, AK) amputees were required to perform successive wa lks over a 2.4 m long force plate, at freely chosen cadence and speed. Background. In previous studies it has been shown that in unilateral lower limb amputee gait, the motion of the CG can be more asymmetric t han might be suspected from kinematic analysis. Methods. The mechanica l energy changes of the CG due to its motion in the vertical, forward and lateral direction were measured. Gait speed ranged 0.75-1.32 m s(- 1) in the different subjects. This allowed calculation of (a) the posi tive work done by muscles to maintain the motion of the CG with respec t to the ground ('external' work, W-ext) and (b) the amount of the pen dulum-like, energy-saving transfer between gravitational potential ene rgy and kinetic energy of the CG during each step (percent recovery, R ). Step length and vertical displacement of the CG were also measured. Results. The recorded variables were kept within the normal limits, c alculated in a previous work, when an average was made of the steps pe rformed on the prosthetic (P) and on the normal (N) limb. Asymmetries were found, however, between the P and the N step. In BK amputees, the P step R was 5% greater and W-ext was 21% lower than in the N step; i n AK amputees, in the P step R was 54% greater and W-ext was 66% lower than in the N step. Asymmetries were also found in the relative magni tude of the external work provided by each lower limb during the singl e stance as compared with the double stance: a marked deficit of work occurred at the P to N transition.