Role of Electrically Evoked Muscle Hypertrophy on Spasticity in Persons with Spinal Cord Injury

TL;DR

This study found that electrically induced muscle growth in people with spinal cord injury did not worsen spasticity, suggesting it could be a safe way to build muscle without increasing stiffness.

Contribution

The study is the first to investigate whether electrically evoked muscle hypertrophy affects spasticity indices in individuals with chronic spinal cord injury.

Findings

Electrically induced muscle hypertrophy did not increase spasticity indices at different angular velocities.

Muscle hypertrophy was significantly greater in the NMES-RT+TT group compared to TT-only in leg lean mass and thigh CSA.

Extensor passive torque increased at higher angular velocities but did not significantly change spasticity indices.

Abstract

Study Design: Pilot randomized clinical trial. Objective: To examine the effect of electrically evoked muscle hypertrophy on indices of spasticity, as measured by Biodex after spinal cord injury (SCI). Setting: Medical research center. Methods: Thirteen males with chronic SCI were randomized into sixteen weeks of either surface neuromuscular resistance training (NMES-RT) + testosterone treatment (TT) (n = 7) or a TT-only group (n = 6). A Biodex isokinetic dynamometer was used to measure knee extensor and flexor muscle spasticity at the beginning (baseline; BL) and at the end (post-intervention; PI) of 16 weeks. The passive tension of the right knee extensor and flexor muscle groups were evaluated at angles of 5°, 30°, 60°, 90°, 180°, and 270° per second (sec). Dual energy X-ray absorptiometry and magnetic resonance imaging were used to measure leg lean mass and thigh muscle cross-sectional areas (CSAs). Results: Robust muscle hypertrophy was noted in leg lean mass [11%, p = 0.023] as well as whole thigh [17%, p = 0.001] and knee extensor muscle [28%, p = 0.001] CSAs in the NMES-RT+TT compared to the TT-only group. There was no difference in extensor or flexor spasticity between the NMES-RT+TT or TT-only groups at different angular velocities following 16 weeks of intervention. Collapsing the extensor passive torques indicated an (24–28%) increase (p < 0.004) in response to angular velocities at BL and following PI measurements [180 deg/sec (23%; p = 0.03) and 270 deg/sec (32%; p = 0.009)] compared to 5 deg/sec. The extensor slope showed a non-significant (p > 0.05) decrease of 15–28% across all angular velocities. The catch-AB slopes were non-significantly lower in the TT-only group compared to the NMES-RT+TT at higher speeds [90 deg/sec and 270 deg/sec] and attained a trend towards lower passive torque at 180 deg/sec [180 deg/sec: 15.5%, p = 0.05]. Conclusions: Evoking skeletal muscle hypertrophy did not increase spasticity indices at different angular velocities following sixteen weeks of NMES-RT+TT or TT in persons with chronic SCI. Augmenting muscle hypertrophy is likely to attenuate the hyper reflexive slope of the extensor spasticity. The findings may suggest that evoking muscle hypertrophy following NMES-RT does not increase indices of spasticity after SCI. The clinical implications are highly important in managing spasticity after SCI.

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