Stumbling Corrective Responses During Treadmill‐Elicited Stepping in Human Infants

Abstract

This study examined stumbling corrective (tripping) responses to mechanical disturbances applied to the foot during stepping in healthy human infants, in whom independent walking had not yet developed. During treadmill‐elicited stepping, a foam‐padded baton instrumented with a force transducer was used to deliver light touches to either the dorsum or the side of the foot at various times of the step cycle. Disturbances to the dorsum of the foot during the swing phase resulted in a general enhancement of flexor activity, including a significant facilitation in the tibialis anterior muscle and an increase in knee flexion during swing. There was also an increase in step cycle duration. Stance phase disturbances resulted in a significant inhibitory effect in the quadriceps muscle and after early stance disturbances, a significant prolongation of the stance phase duration. Disturbances applied to the side of the foot during the swing phase of forward stepping did not result in any effect on the kinematic pattern. If the infant was stepping sideways, however, disturbances to the side of the foot resulted in an increase in flexion during the swing phase. The results show that infants have a phase‐dependent reflex response to light touches applied to the foot. Furthermore, the reflex response is location specific and task specific. Thus, much of the sophistication necessary for controlling sensory inputs in walking is present well before the onset of independent walking.

Intracellular Analysis of Reflex Pathways Underlying the Stumbling Corrective Reaction During Fictive Locomotion in the Cat

“…Because the main features of motoneuron activation during these functionally important reflexes seem similar in fictive and real locomotion (Quevedo et al 2005), these results also provide a framework for understanding the synaptic events in motoneurons that result in lifting the foot over an obstacle to avoid tripping in intact preparations. Similarities between the stumbling reaction described here and in humans (Lam et al 2003;Schillings et al 1996;Zehr et al1997) include the increase in ongoing flexor activity, and when using an electrical stimulus train in adults, inhibitory effects in TA as well as a facilitation of ankle extensor EMG (Zehr et al 1997).…”

Single joint perturbation during gait: Preserved compensatory response pattern in spinal cord injured subjects

“…For example, vestibular influences on spinal responses are likely to be less evident in the stable environment provided by the DGO. Further, as the orthosis controls the timing of the gait cycle, perturbations were not associated with phase resetting which has been observed in studies of freely-moving limbs (Pang and Yang, 2002;Lam et al, 2003).…”

“…While several investigations have studied the effects of perturbations applied to the whole limb during the swing phase of walking (Dietz et al, 1986;Lam et al, 2003;Ghori and Luckwill, 1989;Ghori and Luckwill, 1990), the present displacements have been applied at a single joint of a limb that is not freely moving. For this reason comparison with other studies is limited.…”

“…Prior investigations have examined the effect of perturbations applied at various times in the gait cycle in neurologically intact animals, intact adult humans, intact human infants (in whom descending tracts are not yet mature), humans with movement disorders and spinal animals (Zehr and Stein, 1999)). Perturbations applied during swing and/or stance phases of human locomotion have been of various forms, including tactile stimulation (Lam et al, 2003), electrical stimulation (Duysens, 1992;Zehr et al, 1997), unexpected treadmill or support surface accelerations/decelerations (Dietz et al, 1987;Pang and Yang, 2002) or mechanical resistance (Ghori and Luckwill, 1989;Ghori and Luckwill, 1990). The adaptive response pattern observed in the locomotor output was shown to be highly dependent upon the form of the perturbation (Zehr and Stein, 1999).…”

Loading the Limb During Rhythmic Leg Movements Lengthens the Duration of Both Flexion and Extension in Human Infants

“…Leg muscles compensate quickly so that the animal does not fall (Gorassini et al 1994). Many of these rapid responses are carefully controlled by the nervous system so that they are expressed only when it is appropriate for the successful completion of the task (Buford and Smith 1993;Lam et al 2003). Slower changes are also needed, for example, to accommodate growth as animals and humans mature.…”