Muscle architecture and torque production in stroke survivors: an observational study

Objective: Spasticity poststroke leads to muscle weakness and soft tissue contracture, however, it is not clear how muscle properties change due this motor neural disorder. The purpose was to compare medial gastrocnemius muscle architecture and mechanical properties of the plantarflexor muscles between stroke survivors with spasticity and healthy subjects. Methods: The study included 15 stroke survivors with ankle spasticity and 15 healthy subjects. An isokinetic dynamometer was used for the evaluation of maximal isometric plantarflexor torque and images of the medial gastrocnemius muscle were obtained using ultrasonography. Images were collected at rest and during a maximum voluntary contraction. Results: The affected limb showed reduced fascicle excursion (0.9 +/- 0.7 cm), shorter fascicle length, and reduced muscle thickness (0.095 +/- 0.010% of leg length and 1.18 +/- 0.20 cm, at rest) compared to contralateral (1.6 +/- 0.4 cm, 0.106 +/- 0.015% of leg length and 1.29 +/- 0.24 cm, respectively) and to healthy participants (1.8 +/- 0.7 cm, 0.121 +/- 0.019% of leg length and 1.43 +/- 0.22 cm, respectively). The contralateral limb showed lower force (between 32 and 40%) and similar architecture parameters compared to healthy participants. Conclusion: The affected limb had a different muscle architecture that appears to result in lower force production. The contralateral limb showed a decrease in force compared to healthy participants due to the other neural impairments than muscle morphology. Spasticity likely leds to adaptations of muscle architecture in the affected limb and in force reductions in both limbs of stroke survivors.