Cortical priming strategies for gait training after stroke: a controlled, stratified trial

And your doctor will 100% guarantee that HIT will not cause a stroke?

Do you really want to do high intensity training?

Because Andrew Marr blames high-intensity training for his stroke. 

Can too much exercise cause a stroke?

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Cortical priming strategies for gait training after stroke: a controlled, stratified trial

• Sangeetha Madhavan,
• Brice T. Cleland,
• Anjali Sivaramakrishnan,
• Sally Freels,
• Hyosok Lim,
• Fernando D. Testai &
• Daniel M. Corcos 

Journal of NeuroEngineering and Rehabilitation volume 17, Article number: 111 (2020) Cite this article

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Abstract

Background

Stroke survivors experience chronic gait impairments, so rehabilitation has focused on restoring ambulatory capacity. High-intensity speed-based treadmill training (HISTT) is one form of walking rehabilitation that can improve walking, but its effectiveness has not been thoroughly investigated. Additionally, cortical priming with transcranial direct current stimulation (tDCS) and movement may enhance HISTT-induced improvements in walking, but there have been no systematic investigations. The objective of this study was to determine if motor priming can augment the effects of HISTT on walking in chronic stroke survivors.

Methods

Eighty-one chronic stroke survivors participated in a controlled trial with stratification into four groups: 1) control–15 min of rest (n = 20), 2) tDCS–15 min of stimulation-based priming with transcranial direct current stimulation (n = 21), 3) ankle motor tracking (AMT)–15 min of movement-based priming with targeted movements of the ankle and sham tDCS (n = 20), and 4) tDCS+AMT–15 min of concurrent tDCS and AMT (n = 20). Participants performed 12 sessions of HISTT (40 min/day, 3 days/week, 4 weeks). Primary outcome measure was walking speed. Secondary outcome measures included corticomotor excitability (CME). Outcomes were measured at pre, post, and 3-month follow-up assessments.

Results

HISTT improved walking speed for all groups, which was partially maintained 3 months after training. No significant difference in walking speed was seen between groups. The tDCS+AMT group demonstrated greater changes in CME than other groups. Individuals who demonstrated up-regulation of CME after tDCS increased walking speed more than down-regulators.

Conclusions

Our results support the effectiveness of HISTT to improve walking; however, motor priming did not lead to additional improvements. Upregulation of CME in the tDCS+AMT group supports a potential role for priming in enhancing neural plasticity. Greater changes in walking were seen in tDCS up-regulators, suggesting that responsiveness to tDCS might play an important role in determining the capacity to respond to priming and HISTT.

Trial registration

ClinicalTrials.gov, NCT03492229. Registered 10 April 2018 – retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03492229.

Background

Many stroke survivors experience chronic gait impairments. After rehabilitation, 36% of stroke survivors cannot walk independently [1] and walk ~ 50% slower than age-matched peers [2], which is well below the speed required for safe community ambulation (1.06 m/s) [3]. Walking endurance is also markedly reduced after stroke [4]. Reduced walking speed and endurance are major barriers for community participation [4, 5] and are associated with decreased physical activity [6] and quality of life [7, 8]. Gait rehabilitation has focused on development of interventions to restore ambulatory capacity, and there is a critical need to maximize benefits of current walking training interventions.

Because of its clinical and home accessibility, treadmill training has long been utilized as an effective and feasible method of walking training for post-stroke individuals [9]. Recent studies have explored high-intensity interval training (HIIT) as a way to reduce training time and volume while maximizing intensity [10]. HIIT involves alternating periods of walking at a high intensity and recovery intensity. Speed-based HIIT (HISTT) is one type of HIIT designed to improve an individual’s walking speed by training at the maximum tolerated treadmill belt speed. HISTT leads to greater improvements in overground walking speed than progressive treadmill training in chronic [11, 12] and sub-acute [13] stroke. The effectiveness of HISTT at improving clinical gait and neurophysiological outcomes post-stroke has not been thoroughly investigated.

Cortical priming with neurostimulation or movement is a promising adjuvant therapy to enhance effects of motor rehabilitation [14]. The premise behind neural priming is that the brain retains its capacity to reorganize after stroke, and priming may improve the effect of associated motor training by correcting the imbalance in interhemispheric inhibition observed post-stroke and facilitating long-term potentiation and depression like mechanisms [14]. One clinically translatable type of cortical priming is non-invasive transcranial direct current stimulation (tDCS). After stroke, tDCS has been used to correct interhemispheric imbalance in two primary ways: 1) anodal tDCS, in which the anode is placed over the ipsilesional hemisphere to increase ipsilesional cortical excitability and 2) cathodal tDCS, in which the cathode is placed over the contralesional hemisphere to decrease contralesional cortical excitability. Anodal tDCS has been shown to upregulate corticomotor pathways and improve motor learning and function [14,15,16]. Although cathodal tDCS has also shown beneficial effects, suppressing the contralesional hemisphere may be maladaptive in individuals with limited neural resources in the ipsilesional hemisphere [16, 17]. These findings support the role of tDCS to potentially enhance the effects of other types of motor training [15]. Movement-based priming, another priming technique, often involves the performance of a repetitive movement, such as wrist flexion and extension, prior to performance of motor training [18]. Like tDCS, movement-based priming may also increase corticomotor excitability (CME) and enhance the effects of motor training [18, 19]. Thus, movement-based priming is also a potential adjuvant to enhance the effects of HISTT, and combining tDCS and movement-based priming may yield greater benefits than either type of priming in isolation.

Despite the potential benefits of tDCS and movement-based priming, there have been no systematic investigations on the effects of motor priming on HISTT-induced improvements in walking. Our lab recently found that a single session of HISTT paired with tDCS and movement priming increases excitability of the ipsilesional hemisphere and decreases excitability of the contralesional hemisphere, supporting the potential efficacy of priming for enhancing HISTT [20]. In this controlled trial with stratification, our objective was to determine if motor priming can augment the effects of HISTT. As it is critical that the optimal priming technique be paired with gait rehabilitation, we compared the effects of three types of priming techniques on 4-weeks of HISTT: tDCS, movement-based priming, and both combined. Based on pilot data, we hypothesized that tDCS and movement-based priming would enhance the effects of HISTT on walking speed with corresponding changes in CME and combining both types of priming would lead to even greater improvement.