Adaptive control for backward quadrupedal walking. IV. Hindlimb kinetics during stance and swing

Abstract

1. Hindlimb step-cycle kinetics of forward (FWD) and backward (BWD) walking in adult cats were assessed. The hindlimb was modeled as a linked system of rigid bodies and inverse-dynamics techniques were used to calculate hip, knee, and ankle joint kinetics. For swing, net torque at each joint was divided into three components: gravitational, motion dependent, and a generalized muscle torque. For stance, vertical and horizontal components of the ground-reaction force applied at a point on the paw (center of pressure) were added to the torque calculations. Muscle torque profiles were matched to electromyograms (EMGs) recorded from hindlimb muscles. 2. Torque profiles for BWD swing were the approximate time reversal of those for FWD swing. At each joint, the net torque during swing was small because the mean motion-dependent and muscle torque components counteracted each other. At the hip a flexor muscle torque persisted except for a brief extensor muscle torque late in FWD swing and at the onset of BWD swing. At the knee the muscle torque was relatively negligible except for a peak flexor muscle torque late in FWD swing and early in BWD swing. At the ankle there was a midswing transition from a flexor to an extensor muscle torque during FWD swing and the reverse was true for BWD swing. 3. The vertical ground-reaction force was greater for the forelimbs than the hindlimbs during FWD stance; the reverse was true for BWD stance. Thus the hindlimbs bore a greater percentage (66%) of body weight than the forelimbs during BWD stance, and the forelimbs bore a greater percentage (59%) during FWD stance. For most of FWD stance, the hindlimb exerted a small propulsive ground-reaction force, but for BWD stance the hindlimb first exerted a braking force and then a propulsive force, with the transition occurring after midstance (59% of stance). 4. At the hip the ground-reaction force vector was oriented anteriorly and then posteriorly to the estimated joint center with a midstance transition during FWD stance. The muscle torque and joint power patterns showed similar transitions, changing from extensor and power generation to flexor and power absorption, respectively. For most of BWD stance the ground-reaction force vector was oriented anteriorly to the joint center and was counter-balanced by a large extensor muscle torque; nonetheless, power was absorbed because the hip flexed.(ABSTRACT TRUNCATED AT 400 WORDS)

Motoneuronal and muscle synergies involved in cat hindlimb control during fictive and real locomotion: a comparison study

“…For example, during cat backward walking, RF and sartorius anterior (hip flexors, knee extensors) are activated prior to stance and maintain activity for most of stance (Buford and Smith 1990;Pratt et al 1996), a pattern that was not observed in forward level walking or fictive locomotion in our study (Fig. 3) but is consistent with the required hip flexor and knee extensor moments during this task (Perell et al 1993).…”

Effects of Reinnervation of the Biarticular Shoulder-Elbow Muscles on Joint Kinematics and Electromyographic Patterns of the Feline Forelimb during Downslope Walking

“…Because the shoulder was flexing and the elbow was extending in the face of a shoulder extensor and elbow flexor contraction, it is likely that power was absorbed as these muscles undergo a lengthening (eccentric) contraction. Similar conditions exist in the hip for the iliopsoas and rectus femoris during downslope walking ] and backward walking [Perell et al, 1993]. These data suggest that the ClB and the Bi muscles retard the forward pitch of the animal due to the effects of gravity and momentum from moving down the walkway.…”

Motor control of locomotor hindlimb posture in the American alligator(Alligator mississippiensis)

“…One possible explanation for these patterns in mammals is that crouched posture demands greater motor recruitment because it requires muscles to contract at lengths that are not optimal for force production (Trank et al, 1996). However, crouching might also lead to more intense bursts of motor activity in mammals because, in mammals, crouched posture increases the flexor moments of the ground reaction force about joints (Biewener, 1989(Biewener, , 1990, requiring extensor muscles to exert greater forces to keep the joints in equilibrium (Perell et al, 1993;Trank et al, 1996;Grasso et al, 2000). Because humans and cats have fairly small feet relative to the length of their hindlimb, when they use an upright limb posture they align the limb with the ground reaction force, decreasing its moment arms about the joints and, thereby, decreasing joint flexor moments and the extensor muscle forces needed to counter them in order to prevent the limb from collapsing (Biewener, 1989(Biewener, , 1990.…”