Page 252 - Handbook of Biomechatronics

248 Georgios A. Bertos and Evangelos G. Papadopoulos

Siegler et al. (1982) performed simulations of the human gait with the aid
of a simple mechanical model consisting of a spring in parallel to a damping
element (Fig. 2C). Gard and Childress (2002) expanded the rocker-based
inverted pendulum model by adding a spring and a damper (Fig. 2D).
Τo design improved lower-limb prostheses, we need to understand
the normal gait and the interaction of the amputees with the prostheses,
so as to be able to improve the prosthetic gait to match the characteristics
of the normal one. Despite many attempts around the world, there is no
complete theory of the gait up to now.
Two of the aspects of normal walking we have investigated are the
stance-phase knee flexion and pelvic obliquity. We believe that both of these
movements provide shock absorption during the early stance phase. Pelvic
obliquity was one of the six determinants of gait believed to decrease the
vertical excursion of the body center of mass (BCOM) in order to conserve
energy (Saunders et al., 1953; Inman et al., 1994, 1981). Using the NUPRL,
it was found that the above statement is not true for normal walking (Gard
and Childress, 1997a). The peak-to-peak vertical displacement of the center
of mass due to pelvic obliquity is not different than the peak-to-peak vertical
displacement of the center of mass without pelvic obliquity (Fig. 3A). The
conclusion was that pelvic obliquity does not decrease the vertical excursion
of the BCOM. Pelvic obliquity is maximum at around the time of contra-
lateral toe-off, being out of phase with the vertical excursion of the BCOM,
suggesting that this movement is important for shock absorption in the early
stance phase, as suggested by Perry (1992) and Sutherland et al. (1994).
Similar to pelvic obliquity, stance-phase knee flexion during the early
stance is one of the six determinants of gait and was believed to lower the
vertical excursion of the BCOM in order to conserve energy (Inman
et al., 1981, 1994; Saunders et al., 1953). Data show that the effect of the
stance-phase knee flexion on the peak-to-peak vertical excursion of the
BCOM is negligible (Gard and Childress, 1997a,b, 1999; Fig. 3B). During
the stance phase, knee flexion is maximized around the time of contralateral
toe-off, and minimized when the knee is nearly fully extended and the trunk
reaches its peak vertical displacement during the gait cycle (Fig. 3B). Like
pelvic obliquity, stance-phase knee flexion is out of phase with the BCOM
vertical displacement due to joint configuration; these results also have been
verified by Quesada and Rash (1998).
Pelvic obliquity and stance-phase knee flexion play a critical role in
shock absorption during the early stance phase of normal walking. Thus,
it might be beneficial for the amputees to incorporate the shock absorption