Muscle torque preservation and physical activity in individuals with stroke.

BACKGROUND: A greater percent loss of concentric versus eccentric muscle torque (i.e., relative eccentric muscle torque preservation) has been reported in the paretic limb of individuals with stroke and has been attributed to hypertonia and/or cocontractions. Stroke provides a unique condition for examining mechanisms underlying eccentric muscle preservation because both limbs experience similar amounts of general physical activity, but the paretic side is impaired directly by the brain lesion. PURPOSE: The purpose of this study was to determine 1) whether eccentric preservation also exists in the nonparetic limb and 2) the relationship of eccentric or concentric torque preservation with physical activity in stroke. We hypothesized that the nonparetic muscles would demonstrate eccentric muscle preservation, which would suggest that nonneural mechanisms may also contribute to its relative preservation. METHODS: Eighteen patients who had stroke and 18 healthy control subjects (age- and sex-matched) completed a physical activity questionnaire. Maximum voluntary concentric and eccentric joint torques of the ankle, knee, and hip flexors and extensors were measured using an isokinetic dynamometer at 30 degrees x s(-1) for the paretic and nonparetic muscles. Relative concentric and eccentric peak torque preservations were expressed as a percentage of control subject torque. RESULTS: Relative eccentric torque was higher (more preserved) than relative concentric torque for paretic and nonparetic muscles. Physical activity correlated with paretic (r = 0.640, P = 0.001) and nonparetic concentric torque preservation (r = 0.508, P = 0.009) but not with eccentric torque preservation for either leg. CONCLUSIONS: The relative preservation of eccentric torque in the nonparetic muscles suggest a role of nonneural mechanisms and could also explain the preservation observed in other chronic health conditions. Loss of concentric, but not eccentric, muscle torque was related to physical inactivity in stroke.

Nonuniform weakness in the paretic knee and compensatory strength gains in the nonparetic knee occurs after stroke.

BACKGROUND: This study was designed to quantify torque production at different joint angles in the paretic and nonparetic knee joints of individuals with stroke. METHODS: Extension and flexion torques were measured at 6 angles of the knee joint and normalized to peak torque in 19 subjects with stroke and 19 controls. RESULTS: Paretic knee extension torque was lower than controls when the knee was positioned near extension. In contrast, nonparetic knee extension and flexion torques were higher than controls when the knee was positioned near full flexion. CONCLUSIONS: The paretic knee extensors demonstrated exaggerated weakness at short muscle lengths and the nonparetic knee extensors and flexors demonstrated selective strength gains. Clinicians should therefore consider paretic knee extensor strengthening near full extension and promote symmetrical use of the legs to prevent compensatory overuse of the nonparetic leg.

Muscle strength and weight-bearing symmetry relate to sit-to-stand performance in individuals with stroke.

This study investigated the relationship of lower extremity joint torques and weight-bearing symmetry to sit-to-stand (STS) performance in individuals with chronic stroke. A motion analysis system and two force plates measured STS duration and weight-bearing symmetry (determined by ground reaction forces) during three self-paced and three fast-paced conditions. An isokinetic dynamometer measured maximum concentric joint torques of the paretic and non-paretic ankle, knee, and hip, which were normalized by body mass. Pearson correlations indicated that (a) paretic ankle dorsiflexion and knee extension torques related to the duration of the self-paced STS condition (r = -0.450, -0.716, respectively), (b) paretic ankle dorsiflexion, plantar flexion, and knee extension torques related to the duration of the fast-paced STS condition (r = -0.466, -0.616, -0.736, respectively), and (c) greater weight-bearing symmetry related to faster STS performance for both self-paced and fast-paced STS conditions (r = -0.565, -0.564, respectively) (P < 0.05). This evidence suggests that paretic muscle strength and the ability to load the paretic limb are important factors underlying the ability to rise from a chair in individuals with chronic stroke.