Adaptational and learning processes during human split-belt locomotion: interaction between central mechanisms and afferent input

Abstract

Split-belt locomotion (i.e., walking with unequal leg speeds) requires a rapid adaptation of biomechanical parameters and therefore of leg muscle electromyographic (EMG) activity. This adaptational process during the first strides of asymmetric gait as well as learning effects induced by repetition were studied in 11 healthy volunteers. Subjects were switched from slow (0.5 m/s) symmetric gait to split-belt locomotion with speeds of 0.5 m/s and 1.5 m/s, respectively. All subjects were observed to adapt in a similar way: (1) during the first trial, adaptation required about 12-15 strides. This was achieved by an increase in stride cycle duration, i.e., an increase in swing duration on the fast side and an increase in support duration on the slow side. (2) Adaptation of leg extensor and flexor EMG activity paralleled the changes of biomechanical parameters. During the first strides, muscle activity was enhanced with no increase in coactivity of antagonistic leg muscles. (3) A motor learning effect was seen when the same paradigm was repeated a few minutes later--interrupted by symmetric locomotion--as adaptation to the split-belt speeds was achieved within 1-3 strides. (4) This short-time learning effect did not occur in the "mirror" condition when the slow and fast sides were inverted. In this case adaptation again required 12-15 strides. A close link between central and proprioceptive mechanisms of interlimb coordination is suggested to underlie the adaptational processes during split-belt conditions. It can be assumed that, as in quadrupedal locomotion of the cat, human bipedal locomotion involves separate locomotor generators to provide the flexibility demanded. The present results suggest that side-specific proprioceptive information regarding the dynamics of the movement is necessary to adjust the centrally generated locomotor activity for both legs to the actual needs for controlled locomotion. Although the required pattern is quickly learned, this learning effect cannot be transferred to the contralateral side.

Single joint perturbation during gait: neuronal control of movement trajectory

“…This pattern is based on the organisation of the central pattern generator. The responses to the single joint displacements applied here were similar in their organisation to those seen during unilateral whole limb perturbations during gait in adults (Dietz et al 1987;Ghori and Luckwill 1989;Prokop et al 1995; for review see Dietz 1992) and infants (Pang andYang 2000, 2001). However, in the present study, the strength of bilateral leg muscle activation depended on the direction of the displacement.…”

Split-Belt Treadmill Stepping in Infants Suggests Autonomous Pattern Generators for the Left and Right Leg in Humans

“…This type of flexible coordination has been reported for many animal preparations, including stick insects (Foth and Bassler, 1985), spinal (Forssberg et al, 1980), decerebrate (Kulagin and Shik, 1970) and intact cats (Halbertsma, 1983), and spinal turtles (Stein and McCullough, 1998). Split-belt studies in human adults showed some independence of the pattern generators for each leg in relation to learning (Prokop et al, 1995), but asymmetrical stepping has not been reported. We confirm here that the putative human infant pattern generator for each limb shows some autonomy much like that in other animals.…”

“…All previous reports of human adults stepping on split-belt treadmills have reported alternate stepping, with left and right steps alternating in a 1:1 manner (Dietz et al, 1994;Prokop et al, 1995;Jensen et al, 1998). No asymmetrical stepping rhythms were reported.…”

Effects of Gait Variations on Grip Force Coordination During Object Transport

“…This alternative hypothesis is supported by studies showing subjects are remarkably adept at predicting the overall timing of locomotion associated with regularly paced steps using motor imagery (Bakker et al 2007;Decety et al 1989;Papaxanthis et al 2002a). Thus the strength of the grip-inertial force coupling may be determined by the regularity of the walking cycle in a manner similar to the coordination of breathing with walking, running, or other cyclical limb movements (i.e., via entrainment) (Bernasconi et al 1995;Ebert et al 2000;Kohl et al 1981;Rassler and Kohl 2000;Seebauer et al 2003), and a shift from a regular pattern to an irregular one could disrupt this relationship (e.g., Nishino and Hiraga 1991;Prokop et al 1995;Reisman et al 2005).…”