Kinematic Coordination in Human Gait: Relation to Mechanical Energy Cost

Abstract

Twenty-four subjects walked at different, freely chosen speeds (V) ranging from 0.4 to 2.6 m s-1, while the motion and the ground reaction forces were recorded in three-dimensional space. We considered the time course of the changes of the angles of elevation of the trunk, pelvis, thigh, shank, and foot in the sagittal plane. These angles specify the orientation of each segment with respect to the vertical and to the direction of forward progression. The changes of the trunk and pelvis angles are of limited amplitude and reflect the dynamics of both right and left lower limbs. The changes of the thigh, shank, and foot elevation are ample, and they are coupled tightly among each other. When these angles are plotted one versus the others, they describe regular loops constrained on a plane. The plane of angular covariation rotates, slightly but systematically, along the long axis of the gait loop with increasing V. The rotation, quantified by the change of the direction cosine of the normal to the plane with the thigh axis (u3t), is related to a progressive phase shift between the foot elevation and the shank elevation with increasing V. As a next step in the analysis, we computed the mass-specific mean absolute power (Pu) to obtain a global estimate of the rate at which mechanical work is performed during the gait cycle. When plotted on logarithmic coordinates, Pu increases linearly with V. The slope of this relationship varies considerably across subjects, spanning a threefold range. We found that, at any given V > 1 m s-1, the value of the plane orientation (u3t) is correlated with the corresponding value of the net mechanical power (Pu). On the average, the progressive rotation of the plane with increasing V is associated with a reduction of the increment of Pu that would occur if u3t remained constant at the value characteristic of low V. The specific orientation of the plane at any given speed is not the same in all subjects, but there is an orderly shift of the plane orientation that correlates with the net power expended by each subject. In general, smaller values of u3t tend to be associated with smaller values of Pu and vice versa. We conclude that the parametric tuning of the plane of angular covariation is a reliable predictor of the mechanical energy expenditure of each subject and could be used by the nervous system for limiting the overall energy expenditure.

Development of a kinematic coordination pattern in toddler locomotion: planar covariation

“…Gait cycle paths progress in time in the counterclockwise direction, heel strike and toe-off phases corresponding roughly to the top and bottom of the loops, respectively (see also Fig. 1C) nation, because it reflects the phase relationship between the different segments (Bianchi et al 1998b). As seen in Fig.…”

“…3E-J). It has previously been shown that the first two harmonics of a Fourier series expansion account together for >99% of the experimental variance of the thigh, shank, and foot angles in normal adult locomotion (Bianchi et al 1998b). Figure 4 illustrates the evolution of the intersegmental coordination in one child, from her very first steps at the (Fig.…”

“…A mature pattern of coordination is characterized by a quasi-elliptic loop lying close to a plane (Bianchi et al 1998b;Borghese et al 1996;Lacquaniti et al 1999). The pattern of a 12-year-old child is plotted in Fig.…”

“…When the elevation angles of the thigh, shank, and foot (α t , α s and α f ) are plotted one versus the others, they describe a regular loop constrained close to a plane in adults (Bianchi et al 1998b;Borghese et al 1996). This is not an inevitable mechanical consequence of a system of linked segments that are cross-coupled by passive inertial and visco-elastic forces.…”

“…When the elevation angles of the thigh, shank, and foot are plotted one versus the others, they describe a regular gait loop which lies close to a plane. The plane orientation and the shape of the loop reflect the phase relationship between the different segments and therefore the timing of intersegmental coordination (Bianchi et al 1998b), on which postural stability with respect to gravity and dynamic equilibrium for forward progression depend. The plane orientation shifts in a predictable way with increasing speed of walking (Bianchi et al 1998b) and with the walking posture adopted (Grasso et al 2000).…”