Ischemic Conditioning Reduces Neuromuscular Fatigability During Dynamic Exercise Post Stroke

Abstract

INTRODUCTION: In addition to baseline muscle weakness, stroke survivors often demonstrate increased neuromuscular fatigability (an acute exercise-induced reduction in power, hereafter referred to as fatigability), which limits endurance during functional tasks. Ischemic conditioning (IC) is a non-invasive and easy-to-administer intervention that can reduce fatigability in stroke survivors during a sustained isometric contraction of their paretic knee extensors. However, IC’s effects on fatigability during dynamic contractions are unknown, despite the greater relevance to everyday activities. Additionally, fatigability is known to be task specific. Thus, the purpose of this study was to quantify the effects of IC on fatigability (percent reduction in power) during dynamic contractions of the paretic knee extensors in stroke survivors. We hypothesized that fatigability would be less after a single session of IC versus IC-sham treatment in stroke survivors. Methods: Eight stroke survivors (66 ± 6 years of age, 6 male) performed 60 maximal voluntary concentric contractions (1 every 4 seconds) with their paretic knee extensors against a resistance of 30% of their maximal voluntary isometric contraction torque through a 60-degree range of motion after receiving a single session of IC and IC-sham treatment on two separate days. IC consisted of 5 sets of 5-minute upper thigh blood flow occlusion at 225 mmHg (25 mmHg for IC-sham) with 5 minutes of no occlusion between each set. The order of the 2 sessions was randomized. All participants visited the laboratory on a different day for functional measurements (Fugl-Meyer Assessment, 10-meter walk test, and 6-minute walk test). Reduction in power was calculated as the difference between the highest average power output from 5 consecutive contractions within the first 15 contractions and the average power output from the last 5 contractions. A paired t-test was used to compare if fatigability during dynamic exercise would differ between the 2 sessions after IC and IC-sham treatment. Pearson correlation was performed to determine the relationship between the difference in fatigability (after IC versus IC-sham treatment) and functional measurements. Results: After a single session of IC treatment, stroke survivors were less fatigable compared to IC-sham treatment (21.9 ± 19.2% power reduction vs. 29.4 ± 19.0%, p = 0.016). Improvement in fatigability after IC versus IC-sham treatment was positively correlated with Fugl-Meyer Assessment lower extremity motor score ( r = 0.82, p = 0.013). CONCLUSION: These preliminary results indicate that IC could serve as a potential intervention to reduce fatigability during dynamic exercise in stroke survivors, especially those who are mildly affected by stroke. Funding Source: American Heart Association Predoctoral Fellowship (903373, ZZ) and Eunice Kennedy Shriver National Institute of Child Health and Human Development R01 Grant (HD099340, AH & MD). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.