Inverse relationship between sensation of effort and muscular force during recovery from pure motor hemiplegia: a single-case study.

A 39-year-old patient with a right pure motor hemiplegia, who complained of a striking sensation of effort when he performed a movement, was regularly examined during 4 months. The effort sensation and the force recovery have been measured during the execution of upper limb movements: shoulder antepulsion up to horizontal, supined elbow flexion up to horizontal and full hand digital grip. The subject was asked to realize a movement with the paretic arm and to concentrate on the felt effort; then he had to perform the same movement against a resistance with the healthy arm, until the perceived heaviness matched the effort sensation felt on the other side. Recovery of force and evolution of effort sensation did not follow linear trends over time. The curves displayed significant steps and plateaus, which were mainly observed for the proximal movements. The steps tended to be clustered within a few days, consistent with crucial periods in the restoration process. Within these, significant reduction of the effort sensation and increase of the force were together observed. These critical moments of the motor recovery could be analyzed as the result of an improvement of the neural traffic in the internal capsule and an activation of specific structures involved in the representation of the force and effort.