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Dual-task improvement of older adults after treadmill walking combined with blood flow restriction of low occlusion pressure: the effect on the heart–brain axis
Journal of NeuroEngineering and Rehabilitation volume 21, Article number: 116 (2024)
Abstract
Objective
This study explored the impact of one session of low-pressure leg blood flow restriction (BFR) during treadmill walking on dual-task performance in older adults using the neurovisceral integration model framework.
Methods
Twenty-seven older adults participated in 20-min treadmill sessions, either with BFR (100 mmHg cuff pressure on both thighs) or without it (NBFR). Dual-task performance, measured through light-pod tapping while standing on foam, and heart rate variability during treadmill walking were compared.
Results
Following BFR treadmill walking, the reaction time (p = 0.002) and sway area (p = 0.012) of the posture dual-task were significantly reduced. Participants exhibited a lower mean heart rate (p < 0.001) and higher heart rate variability (p = 0.038) during BFR treadmill walking. Notably, BFR also led to band-specific reductions in regional brain activities (theta, alpha, and beta bands, p < 0.05). The topology of the EEG network in the theta and alpha bands became more star-like in the post-test after BFR treadmill walking (p < 0.005).
Conclusion
BFR treadmill walking improves dual-task performance in older adults via vagally-mediated network integration with superior neural economy. This approach has the potential to prevent age-related falls by promoting cognitive reserves.
Introduction
Adults aged 65 and above are subject to fall accidents. In addition to a reduction in muscle strength, fall accidents is related to cognitive decline due to loss of frontal integrity with aging [4]. The 'frontal aging hypothesis' predicts age-related impairments in attentional resource allocation and information processing speed [50], which impact executive functions for multitasking [29]. Due to frontal degeneration, it becomes challenging for older adults to flexibly shift attention between two concurrent tasks [34]. The loss of cognitive resilience partly contributes to age-related falls, particularly when they occur during dual-task scenarios [2, 49].
Blood flow restriction (BFR) is a training method originally used to stimulate muscular development under local hypoxia. It involves applying pneumatic tourniquets to impede venous outflow in the working musculature. The strength gain associated with combined BFR and low-load exercise results from the activation of protein synthesis signaling for enhanced mechanical tension and metabolic stress [38]. Despite its minimal exercise intensity, walking with BFR can augment muscle strength in the elderly [1]. BFR can also affect metabolic cost and cardiovascular responses [31]. It can induce vasoconstriction in the restricted muscles while causing vasodilation in non-restricted areas due to parasympathetic system activation and endothelial nitric oxide (NO) release [21]. The overall impact of BFR on cardiovascular responses is interactively influenced by factors such as occlusion pressure, exercise protocol (resistance vs. aerobic), and application mode (continuous vs. intermittent) [6].
To date, only a few studies have focused on the improvement of frontal executive function by the application of BFR. One study observed that patients with dementia who underwent 6 months of bilateral upper limb compression followed by reperfusion showed improvements in tests of attention and executive function [22]. In healthy older adults, an 8-week dual-task walking program with BFR (occlusion pressure up to 200 mmHg, 20 min/session, 3 sessions/week) resulted in greater improvements in Mini-Mental State Examination scores and increased levels of brain-derived neurotrophic factor (BNDF), compared to those of a control group that did not receive such training [25]. Interestingly, Sugimoto et al. [48] even demonstrated an immediate effect of 15-min BFR treadmill walking (occlusion pressure: 200 mmHg) on the color-word Stroop task, independent of the effect of BFR alone or walking alone. However, it remains uncertain whether a single bout of combined BFR with relatively low occlusion pressure and aerobic exercise can enhance the posture dual-task of older adults with superior neural efficiency. Answering this question is of clinical significance. Lower occlusion pressure (40% systolic artery pressure) has been shown to increase muscle strength without causing elevated blood pressure. Therefore, combining BFR of lower occlusion pressure with aerobic exercise may contribute to fall prevention in older adults by jointly addressing both age-related declines in cognitive function and muscle strength while minimizing the cardiac cost and sympathetic activity.
Supporting the neural connections between the prefrontal cortex, the central autonomic network, and the vagus nerve system [26], higher cardiac vagal activity is linked to superior executive functioning [45]. Within the context of the heart–brain axis, it is possible that dual-task performance can be improved through BFR-related regulation of the autonomic nervous system, which contributes to enhanced executive function and cognitive flexibility. The aim of this study was to compare the acute effects of treadmill walking with and without BFR of low occlusion pressure on posture dual-task performance in older adults, with a special focus on variations in heart rate and EEG characteristics. For older adults, we hypothesized the following: (1) treadmill walking with leg BFR of low occlusion pressure would lead to better performance on a posture dual-task compared to treadmill walking without leg BFR; and (2) the BFR-related organization of the HR kinetics, power spectra of local EEG, inter-regional EEG connectivity, and network topology in various sub-bands would differ from those observed during non-BFR treadmill walking. Scalp EEG of the theta (4–7 Hz), alpha (8–12 Hz), and beta (13–35 Hz) bands were targeted, as they link characteristically to cognitive workload during a posture dual-task in older adults [36].
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