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Mechanical properties of the lower extremity muscles in individuals with chronic stroke Lomaglio, Melanie Jane

Abstract

Lower extremity muscle weakness in individuals with stroke plays a significant role in limiting functional performance. In order to design more effective rehabilitation interventions to counteract this weakness, a better understanding of how stroke affects mechanical muscle properties is needed. The purpose of this thesis was to 1) quantify isometric torque and temporal parameters of torque production (times to develop and reduce torque), 2) assess isometric torqueangle relationships, and 3) determine whether concentric torque was more impaired than eccentric torque in the paretic and nonparetic legs of individuals with chronic stroke and the nondominant leg of control subjects. A dynamometer was used to assess the abovementioned muscle properties of the ankle, knee, and hip flexors and extensors. The results revealed reduced isometric torque throughout the paretic leg (ankle, knee, and hip) but only ankle plantarflexion was reduced in the nonparetic leg. Times to develop and reduce isometric torque were impaired bilaterally (ankle, knee, and hip). The paretic knee extensors revealed exaggerated weakness near terminal extension (short muscle lengths), whereas the nonparetic knee extensors and flexors were selectively stronger as the knee assumed a flexed position. Lastly, a relative preservation of eccentric torque in both the paretic and nonparetic legs was found, thus concentric torque was more affected by stroke than eccentric torque. The work of this thesis has identified muscle impairments in both the paretic and nonparetic legs of individuals with chronic stroke. Based on these findings, clinicians are encouraged to assess bilateral leg strength across joint range of motion. When designing strength training programs, exercises at high contraction speeds should be incorporated. Lastly, due to the relative preservation of eccentric torque, the 1- repetition maximum should be determined for both concentric and eccentric contractions to avoid underloading the muscle during the lengthening phase of movement.

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