Following a stroke, patients see their motor function impaired, in particular by the establishment of muscular retractions. These affect motor performance of the patients, as for example by impairing their walking capabilities and are responsible for long-term orthopedic deformities. Muscular structure influencing ankle and foot mobility are particularly evaluated in daily practice due to the major impact of muscle retraction on patients' mobility.~During clinical examination, the evaluator searches the presence of the clinical markers of muscle retraction. However their clinical evaluation remains subjective and does not always allow to identify the precise location (which muscles) and origin (muscle contraction or retraction) of the observed response.~In that case, the sensitive nerve block (BNS)can complete the clinical examination. Its efficacy and selectivity are difficult to evaluate in a precise manner by a clinical examination on its own. Moreover, the possibility to predict the effect of a long-lasting spasticity treatment, like a botulinum toxin injection (ITB), from the effect of a BNS, has not been proven on the sural triceps muscle.~The study will use several evaluation techniques by biomechanical, neurophysiological and ultrasound (elastography) study which allow to quantify the response level within a muscle (measure of the muscle stiffness and retraction).~This study will take place within the rehabilitation and physical medicine department, patients are hospitalized or seen during stroke follow-up examination for uncomfortable sural triceps spasticity. They are evaluated by a quantified walking test, followed by a BNS, if the BNS result is positive, they are treated by a botulinum toxin injection in the sural triceps. The stiffness measurements before BNS (J0), after BNS (J0 post BNS) and after ITB (at day 28) will be standardized and additional instrumental examinations will be realized to understand the effects of the BNS and ITB procedure. The stretching will be performed by an isokinetic dynamometer and the muscle response to the stretching will be achieved by simultaneous evaluation of the response of the leg muscles by elastography and electromyography. In addition, clinical and neurophysiological data (exploration of nerve conduction on the tibial nerve) will be measured
The research Biomechanical and neurophysiological evaluation of the effects of a motor block and an injection of botulinum toxin on the stiffness of the paretic sural triceps muscle will study the response to passive stretching in the neurological patient presenting spastic paresis after a stroke.