Effects of mind-body exercise on dual-tasking performance and cardiovascular functions in chronic stroke survivors

Abstract

Regaining functional ability and preventing cardiovascular complications are two of the primary objectives in stroke rehabilitation. Turning and stepping down are common daily activities, but they often cause falls in stroke survivors. These activities demand a high level of physical skill and additional cognitive tasks may be challenging. Few studies emphasize these dual-tasking activities, and consensus on rehabilitation exercises has yet to be reached. Further, strokes have detrimental effects on arterial compliance and cardiac autonomic regulation, leading to various cardiovascular pathologies. Tai Chi is a mind-body exercise and is dual-tasking in nature. It has been shown to improve dual-tasking ability and cardiovascular function in older community-dwelling adults. However, the effects on stroke survivors are still unknown. This study is therefore designed to: 1) Investigate how stroke survivors respond to dual-tasking, and 2) Examine the effects of Tai Chi training on dual-tasking ability and cardiovascular function among stroke survivors. There were two phases in this study: a cross-sectional study and a randomized controlled trial (RCT) to achieve the first and second objectives, respectively. In the first phase, stroke survivors were tested under two dual-tasking situations: turning-while-walking and stepping down combined with an auditory Stroop test respectively. The performance when dual-tasking was compared with both the single-tasking performance and the performance of controls. In the second phase, stroke survivors were randomized into either Tai Chi, conventional exercise or control groups. The two dual-tasking conditions employed in the first phase, together with arterial compliance, blood pressure, and heart rate variability were assessed before, immediately after, and one month after the intervention. In the cross-sectional study, stroke survivors showed a decreased composite score in the auditory Stroop test when performing turning-while-walking (n=59; dual-tasking: 71.5±24.2, single-tasking: 83.5±22.8) or stepping down (n=26; dual-tasking: 76.4±31.2, single-tasking: 90.0±25.6). However, physical task performances when both single-tasking and dual-tasking were similar. Moreover, stroke survivors performed less well than the controls in all measures. These findings may be explained by the hypothesis that stroke survivors had insufficient resources during dual-tasking and they employed a posture-first strategy to preserve control of balance. In the RCT phase, the composite score improved in both dual-tasking conditions after Tai Chi training [turning-while-walking (n=47): pre-assessment: 73.1±27.6, post-assessment: 89.9±23.4, follow-up: 91.7±26.9; stepping down (n=23): pre-assessment: 64.6±22.7, post-assessment: 91.9±19.2, follow-up: 94.4±20.6]. The score of the Tai Chi group was higher than that of the conventional exercise group (55.7±11.1) in the follow-up period when dual-tasking with a stepping down test. Subjects in the Tai Chi group completed the dual-tasking turning-while-walking faster in the follow-up (14.9±4.9 sec) than in the pre-assessment (17.7±6.9 sec). For the cardiovascular function (n=56), significant improvement in small arterial compliance (pre-assessment: 3.7±2.0 ml/mmHg*100, post-assessment: 4.2±2.2 ml/mmHg*100) and systolic blood pressure (pre-assessment: 129.2±17.3 mmHg, post-assessment: 125.0±18.6 mmHg), but not heart rate variability, was observed in subjects who practiced Tai Chi. The results showed that Tai Chi enhanced dual-tasking ability, and is possibly more effective than conventional exercise for the stepping down task. The observed improvements might imply that the effect of Tai Chi training transfers to other dual-tasking activities. Further, Tai Chi improved arterial compliance and blood pressure but not cardiac autonomic regulation. Further studies with a larger sample and exploring the underlying mechanisms of mind-body exercise are needed.