Introduction: Individuals living with chronic stroke have weakness and increased neuromuscular fatigue in the paretic leg, which can limit walking ability and endurance. In cardiac and healthy populations, ischemic preconditioning (IPC) is a widely studied, effective, non-invasive stimulus which not only improves vascular function, but also motor performance. IPC occurs when the tissue of interest is exposed to repeated, short bouts of ischemia, which can improve motor function by enhancing vascular, neural and muscle function. IPC has not been tested as a method to improve motor function in individuals post-stroke.
Hypothesis: Two weeks of IPC training on the paretic leg will improve leg strength and time-to-task failure (TTF) during a fatiguing muscle contraction.
Methods: A feasibility study of 4 individuals (3 female, 1 male) with chronic stroke (20 ± 4 years) was conducted. A Biodex dynamometer was used to assess paretic leg knee extensor maximal voluntary contraction (MVC). To assess muscle fatigability, subjects maintained a sustained contraction equal to 30% of their MVC until failure using visual feedback. After baseline testing, subjects made six visits to the laboratory over a two week period to have IPC performed on their paretic leg. A blood pressure cuff was inflated on the thigh to 225 mmHg for five, five-minute bouts per session. Five minutes of rest was given between inflation cycles. After the last session, subjects returned within 48 hours to have MVC and TTF reassessed.
Results: Three subjects completed all study procedures. One subject withdrew for medical reasons unrelated to the study. The IPC procedure was well tolerated by all subjects. After two-week IPC training, knee extensor MVC increased in the paretic leg (45.0 ± 2.7 Nm vs. 52.6 ± 5.7 Nm). Fatigability of the muscles was dramatically reduced after IPC training as TTF tripled (359 ± 180 seconds vs. 1097 ± 343 seconds).
Conclusions: We are the first group to show that IPC is a well-tolerated and effective stimulus to improve paretic leg strength and reduce muscle fatigability in subjects with chronic stroke. The results of this pilot study warrant a larger study to determine whether IPC improves muscle performance post-stroke through neural, vascular, or muscle-related mechanisms.