Bilateral limb phase relationship and its potential to alter muscle activity phasing during locomotion post-stroke

Hemiparesis is a major consequence post-stroke and can result in loss of locomotor function. Specifically, muscle coordination deficits are well recognized in both the paretic and non-paretic limbs. In this series of studies, we examined the extent to which inappropriate muscle phasing in the paretic limb can be influenced by the relative angular relationship of the non-paretic limb, both for an exposure period and after short bouts of adaptation training using a split-crank bicycle ergometer.;Our results showed that manipulating the relative angular positions of limbs in a pedaling task caused muscle activity phasing changes that were either delayed or advanced, dependent on the relative spatial position of the two cranks and this relationship is well-explained by a sine curve. More importantly, these findings provided new evidence that muscle phasing can be "systematically" influenced by interlimb pathways. Then, we sought to examine the extent to which the impaired nervous system can adapt new patterns of muscle activity phasing following short bouts of training. We demonstrated that both intact and impaired nervous systems are capable of generating muscle phasing aftereffects that persisted for at least ten minutes. However, for neurologically intact individuals, these aftereffects were observed only in the leg that was in the following position whereas for people with cerebral stroke, the aftereffects were found only in the leg that was in the leading position during the adaptation period. Since the results were dependent on whether the leg was following vs leading, we describe these states as "temporal" rather than "spatial". Our findings provided novel evidence to suggest that adapting a new muscle phasing pattern during a bilateral locomotor task depends critically on the relative "temporal" position of the contralateral limb.;Our results provide a better understanding of the neural mechanisms underlying muscle phasing abnormalities and the capability of the impaired, post-stroke nervous system to produce a more normalized phasing pattern. The neurophysiological and functional knowledge from these studies are expected to lead to the development of a novel rehabilitation intervention that can impact functional outcomes associated with walking ability.