Plantar Flexor Eccentric Training in Chronic Hemiparesis

The goal of this clinical trial is to assess the effects of a plantar flexor eccentric training on muscle health of these muscles and teir descending command in chronic spastic hemiparesis. The effects of the strength and lower limb function will also be explored.

The main question of this study is : do MG and SOL fascicle length and thickness can be modified after 2-months of eccentric training ? The experimental treatment will be compared to conventional therapy group (Gold standard).

At D1, participants will be randomized into 2 groups: eccentric training versus conventional therapy for 8-weeks. Every participant will be assessed by blinded investigators at D1 and W8.

In the eccentric training, patients will receive 3 sessions/week of a customized isokinetic eccentric program. in the control group, patients will follow their sessions of rehabilitation as before their inclusion.

Background: Functional deficits in stroke patients with hemiparesis result from muscular damage, known as spastic myopathy, and neurological damage, combining agonist paresis and antagonist hyperactivity. In the chronic phase, it has been shown that conventional rehabilitation does not improve function beyond an average 0.04 m/sec increase in walking speed in hemiparesis patients. On the other hand, eccentric exercise has been shown in healthy subjects to markedly improve muscle extensibility, neuronal efficiency and muscle strength. However, its effects on spastic muscles in the chronic post-stroke phase, and in particular on plantar flexors, remain poorly documented and contradictory. Such an intervention, targeting the plantar flexor muscles of the subjects, could act both on spastic myopathy by reducing passive stiffness and increasing length and thickness, but also on propulsion capacity in walking, thus improving their walking speed.

Primary objective: To evaluate the effect on plantar flexor architectural parameters of an isokinetic eccentric exercise protocol targeting these muscles compared with conventional rehabilitation.

Secondary objectives: To compare each of the changes in the secondary endpoints in subjects with chronic post-stroke hemiparesis after 8 weeks of a plantar flexor eccentric exercise program compared with conventional rehabilitation (W8-D1).

Participants: 20 subjects with hemiparesis will be recruited and randomly assigned to 2 groups: eccentric training (ECC) versus conventional rehabilitation (CONV) Inclusion criteria are (a) adults aged 18 to 80 years, (b) chronic hemiparesis (\> 6 months), (c) walking speed \> 0.2 m/sec, unassisted over 10m, (d) stable hemiparesis with plantar flexor involvement, (e) written consent.

Intervention: The plantar flexor eccentric training group will carry out its sessions on an isokinetic dynamometer (Contrex) at a rate of 3 sessions per week for 8 weeks. Each session will consist of a warm-up (10 concentric plantar flexions at 30°/s). The rehabilitation protocol will be carried out in 2 parts. The first 2 weeks will be a period of familiarization and adaptation to the contraction mode, to minimize risks and optimize tissue adaptations. Then, during the following 6 weeks, the intensity of the exercises will gradually increase, modifying the speed, the load and the volume (number of repetitions). Quantification of the subject's load and pain status will be assessed using the force curves of the isokinetic dynamometer and a visual analog scale, respectively.

Outcome measures: Assessments will be made at the first and last sessions. The primary outcome will be the structural changes (fascicular length and thickness) of medial gastrocnemius and soleus (through ultrasound). Secondary endpoints will be , biomechanical (change in peak isometric force of plantar flexors during maximal voluntary contraction, neurophysiological (changes in the agonist and the antagonist activation of the medial gastrocnemius and soleus, and functional (change in maximum barefoot walking speed over 10m (AT10)). Also, correlations between change in gait speed and change in fascicular length of the medial gastrocnemius and soleus on the paretic side, as well as between change in gait speed and change in peak force of the paretic plantar flexors will be investigated.

Eligibility Criteria:
Inclusion Criteria:

* adults with chronic hemiparesis (\> 6 months)
* XV1-GAS\<100°
* walking speed \> 0.2 m/sec
* unassisted over 10m
* stable hemiparesis with plantar flexor involvement
* written consent

Exclusion Criteria:

* cognitive impairment (MoCa\<26),
* orthopedic or traumatic ankle involvement,
* medical contraindication to maximal effort,
* follow-up of another research program,
* sural triceps toxin injection \< 3 months,
* adjacent neurological pathology,
* pregnant women,
* women of childbearing age who are not on effective contraception, either mechanical (IUD) or hormonal (pill),
* wearing a pacemaker or implanted defibrillator,
* persistent cardiovascular disorders following a cardiac accident,
* wearing an implanted medical device
* a history of epilepsy