Mécanique et énergétique de la locomotion des patients hémiparétiques et spastiques

(eng) This thesis aimed to investigate the heightened energy consumption of walking in hemiparetic stroke patients, and to establish its origin, i.e. either an increased mechanical work, or a decreased muscular efficiency. The effect of a focal spasticity treatment was also studied on these variables. The speed-dependent reference values were obtained in twelve healthy subjects walking at different steady speeds. These data established normal values for kinematics, kinetics, electromyography, mechanics, and energetics for healthy subjects walking on the same treadmill that was used for stroke patients. The energy consumption of stroke patients pedaling with one sole leg (healthy or pathological one) was compared with that of healthy subjects also pedaling with one leg. For an equal amount of mechanical work, the energy consumption was similar in patients (pathological or healthy leg) and in healthy subjects. In other words, the efficiency of work production by muscles was similar for the pathological and healthy legs of stroke patients as compared to the legs of healthy subjects. Thus, alterations in efficiency cannot explain the increase in energy consumption observed in stroke patients during walking. The effects of walking speed on energy cost were then evaluated, as the relationships between energy cost, mechanical work, and muscle work efficiency. Energy cost was increased in stroke patients compared to healthy subjects, and the effect of speed was similar in both groups, giving a typical U-shaped curve. The increase in energy cost observed in stroke patients was mainly determined by the mechanical work done by muscles and, particularly, the mechanical work done by the healthy limb to lift up the center of body mass. The efficiency was globally normal, confirming the results obtained on the cycle ergometer. Finally, this thesis analyzed the effects of Botulinum toxin injection in the rectus femoris muscle on the stiff-knee gait of stroke patients. Our results showed a real improvement of knee kinematics, dynamics, and electromyography. A lowering of the energy cost was observed, but only in patients presenting a knee flexion greater than 10°. These results suggest that a focal treatment as botulinum toxin injection is likely to have a favorable effect on energy expenditure.