These, and other inappropriate upper limb muscle synergy patterns were attributed to abnormal torque generation about joints secondary to the intended, or primary, joint axis during maximal voluntary isometric contractions. In dynamic tasks, abnormal synergy patterns exist in the paretic upper limb between shoulder abduction with elbow flexion as well as shoulder adduction with elbow extension. In isometric conditions, it has been shown that stroke patients have a limited number of upper limb synergies available to them due to abnormal muscle coactivation patterns. Much of the literature attempting to quantify these abnormal muscle synergies is focused on the paretic upper limb of stroke patients. These coupled movements are known as synergies and, for the lower limb, have been grouped into the extension synergy (internal rotation, adduction, and extension of the hip, extension of the knee and extension and inversion of the ankle) and the flexion synergy (external rotation, abduction, and flexion of the hip, flexion of the knee, and flexion and eversion of the ankle) with varying levels of completeness and dominance. Following stroke, some patients lose independent control over select muscle groups, resulting in coupled joint movements that are often inappropriate for the desired task. Ī well documented factor limiting the motor rehabilitation of patients following stroke is the presence of abnormal muscle activation patterns. Spasticity has also been proposed as an alternative explanation for lower limb impairments in hemiparetic stroke, but more recent studies have found that spasticity may not play a significant role in gait abnormalities. It has also been reported that weakness following stroke may be the result of co-contraction of antagonistic muscles. In the lower limbs, this muscle weakness can be attributed to disuse atrophy and/or the disruption in descending neural pathways leading to inadequate recruitment of motorneuron pools. Muscle weakness, or the inability to generate normal levels of force, has clinically been recognized as one of the limiting factors in the motor rehabilitation of patients following stroke. The findings here suggest that the primary contributor to isometric lower limb motor deficits in chronic stroke subjects is weakness. The results of this study indicate that in a standing position stroke subjects are significantly weaker in their affected leg when compared to age-matched controls, yet showed little evidence of the classic lower-limb abnormal synergy patterns previously reported. The only time a different strategy was used was during maximal hip abduction exertions where stroke subjects tended to flex instead of extend their hip, which was consistent with the classically defined "flexion synergy." The EMG data of the stroke group was different than the control group in that there was a strong presence of co-contraction of antagonistic muscle groups, especially during ankle flexion and ankle and knee extension. Analysis of the secondary torques showed that the control and stroke subjects used similar strategies to generate maximum torques during seven of the eight joint movements tested. The stroke group was significantly weaker in six of the eight directions tested. Differences in mean primary torque, secondary torque, and EMG data were compared using a single factor ANOVA. In parallel, EMG data from eight muscle groups were recorded, and secondary torques generated about the adjacent joints were calculated. The subjects were asked to generate a maximum torque about a given joint (hip abduction/adduction hip, knee, and ankle flexion/extension) and provided feedback of the torque they generated for that primary joint axis. With the trunk stabilized, stroke subjects stood on their unaffected leg while their affected foot was attached to a 6-degree of freedom load cell (JR3, Woodland CA) which recorded forces and torques. Presented here are the lower limb joint torque patterns measured in a standing position of sixteen chronic hemiparetic stroke subjects and sixteen age matched controls used to examine differences in strength and coordination between the two groups. These abnormal muscle activation patterns, or synergies, have previously been quantified in the upper limbs. The presence of abnormal muscle activation patterns is a well documented factor limiting the motor rehabilitation of patients following stroke.
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