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High-intensity walking exercise helped chronic stroke patients regain walking capacity compared with more moderate training, a pilot randomized trial showed.

While there was no significant difference between high-intensity interval training (HIIT) and moderate-intensity aerobic training in 6-minute walk test distance changes after 4 weeks (27 vs 12 m, P=0.28), the more vigorous training had greater effects after 8 weeks (58 vs 29 m, P=0.02) and 12 weeks (71 vs 27 m, P=0.005), reported Pierce Boyne, PT, DPT, PhD, NCS, of the University of Cincinnati, and colleagues.

Some secondary measures of gait speed and fatigue also favored HIIT, according to the findings in .

"These findings show proof of concept that vigorous training intensity is a critical dosing parameter for walking rehabilitation," Boyne and team concluded. "In patients with chronic stroke, vigorous walking exercise produced significant and meaningful gains in walking capacity with only 4 weeks of training, but at least 12 weeks were needed to maximize immediate gains."

Thus, one take-away is that "longer durations of HIIT (>4 weeks) should be considered to realize optimal gains," wrote David J. Lin, MD, of Massachusetts General Hospital and Harvard Medical School in Boston, and Joel Stein, MD, of Columbia University and Weill Cornell Medical College in New York City, in an .

More than two-thirds of patients with stroke have difficulty walking, they noted. "Patients with stroke identify walking independently as a top priority in their rehabilitation goals, and improvements in gait are linked to better quality of life."

A key question now is implementation into practice, Lin and Stein said.

"The reality today is that most patients with stroke spend only about 20% of their time in physical therapy doing activities related to gait recovery," they wrote, adding that "lower limb movements and task-specific practice remain severely underdosed in poststroke rehabilitation today."

"Will this new study simply join continued evidence pointing to the need for high-intensity training but challenged by lack of clinical translation?" they asked. "Early implementation science and education for clinicians focused on delivery of HIIT in the clinical setting will be key."

Boyne and co-authors agreed that reimbursement constraints and adherence issues could be an obstacle. "Thus, a 12-week duration for a clinician-led HIIT program may be an optimal standard to target," they wrote. "Future studies might also consider transitioning to home- or community-based training after clinician-led HIIT to test longer training durations."

The trial included 55 patients ages 40 to 80 (mean age 63, 34.5% women) who had a single prior stroke and persistent walking limitations 6 months or more after the stroke. They were a mean of 2.5 years and up to 5 years post-stroke at baseline.

All patients participated in aerobic exercise training sessions comprising 45 minutes of walking practice three times per week for 12 weeks. They were randomized to either high intensity -- targeting a mean aerobic intensity above 60% of the heart rate reserve, using 30-second bursts of walking at maximum safe speed, alternating with 30-60 seconds of rest -- or moderate intensity through continuous walking with speed adjusted to initially target 40% of the heart rate reserve and then progressing up to 60% as tolerated.

The interventions had the expected impact, with a higher peak training speed in the HIIT group (161% vs 96% of the baseline fastest 10-m speed) and higher mean bout steady state heart rate (75% vs 59% of the heart rate reserve).

Among the secondary outcomes, both groups significantly improved self-selected gait speed, fastest gait speed, and aerobic capacity, but the HIIT group improved significantly more on self-selected and fastest gait speeds.

Fatigue improved only in the HIIT group, with significantly decreased PROMIS Fatigue Scale T scores versus the moderate-intensity exercise group at the 8-week point (-3.0 vs 1.0, P=0.02). Although not significant at the 12-week time point, the researchers noted that this was possibly due to insufficient statistical power, since all the effect estimates were in the same direction.

One potential mechanism by which HIIT may improve outcomes could be related to neuromotor, rather than cardiopulmonary, adaptations, Boyne and colleagues suggested, given the lack of significant between-group differences in aerobic capacity gains. "However, it is also possible that this lack of significant between-group differences was due to greater measurement error for VO₂ measurement vs other outcomes or confounding effects of gait efficiency changes on VO₂ during exercise testing (improved gait efficiency decreases measured VO₂)."

Lin and Stein said that "further defining what constitutes neuromotor adaptations for gait after stroke will be important for generalizing findings from this study."

No serious adverse events related to exercise training or between-group differences in any adverse event categories were observed, which the researchers said supports the safety of poststroke HIIT for further study.

According to the editorialists, "future studies should evaluate timing of intervention poststroke (i.e., HIIT training in the acute vs subacute vs chronic stages of stroke recovery). Indeed, there is evidence from the upper extremity rehabilitation that similar interventions delivered early after stroke may have a magnified effect."

One limitation of the study was the relatively modest sample size for the proof-of-concept design. However, participants' average self-selected gait speed matched what's typically seen in outpatient stroke rehabilitation, supporting generalizability.

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