HOUSTON – Exercise seems to improve some of the cognitive difficulties that can manifest in stroke survivors, even if patients don’t hit the gym for a couple of years after the incident.
A meta-analysis of 14 randomized, controlled studies has determined that the combination of aerobic and weight-bearing exercises is most effective at boosting brain function. The studies showed a moderate, but consistent, effect of exercise in both the acute and chronic phase, Lauren Oberlin said at the International Stroke Conference sponsored by the American Heart Association.
Lauren Oberlin
“This is an important message for stroke survivors who have experienced cognitive deficits for a long time: These may not be permanent, and they can be modified with physical activity,” she said.
Long-term cognitive impairment is a very common problem after stroke, she said, occurring to some degree in up to 85% of survivors. The most commonly affected domains are executive function, attention, processing speed, and memory.
“These deficits can also be highly persistent, and remain in the years after a stroke,” Ms. Oberlin said. “And they represent a major health and economic burden. Stroke survivors with cognitive deficits are at an increased risk for long-term disability, functional decline, dependent living, hospitalization, and even mortality. Despite all this, there is an absence of effective treatments. There are no effective pharmaceutical treatments and cognitive rehabilitation training has not been widely successful.”
Exercise has not been as well-studied in stroke as it has in other neurological disorders, including Parkinson’s disease, multiple sclerosis, and more recently, Alzheimer’s disease. Physical activity has also been shown to help maintain and boost cognitive function and memory in healthy aging populations.
Ms. Oberlin and her colleagues conducted a meta-analysis of 14 randomized, controlled studies conducted during 2001-2016. The studies enrolled a total of 736 subjects. All of them randomized subjects to 3-6 months of an active exercise arm or a control arm that did not involve physical training.
The researchers assessed effect sizes by Hedges’ g, calculated separately for intervention and control conditions within each trial. The results were interpreted as follows:
• Small effect = 0.2
• Moderate effect = 0.5
• Large effect = 0.8
Only four of the studies demonstrated a statistically significant benefit between the active and control arms. Seven trended strongly toward the positive, but had wide confidence intervals that crossed the null. Three studies showed no significant benefit. The overall effects size was 0.56 (moderate).
Ms. Oberlin and her colleagues then parsed the data to examine the effect of when the program was initiated after the stroke, the program’s duration, and the type of exercise it studied.
Length of the intervention (less than 3 months and more than 3 months) was not significantly related to cognitive outcome. However, the combination of aerobic and strength training exerted a significantly greater effect size (0.45) than did aerobic training or weight training alone (0.2 and 0.34, respectively). Programs that started more than 3 months after the stroke were also more effective than were those started earlier in recovery (0.45 vs. 0.16).
Finally, in a subset of five studies, she evaluated whether particular cognitive domains benefited most from physical activity. Attention and processing speed improved the most (0.4). Changes in memory and executive function were not significant.
“I will say this was only five studies, so we may have been underpowered to see any effects on these other domains,” Ms. Oberlin said.
The mechanistic link between physical activity and improved cognition has not been fully elucidated in humans, she said. However, animal studies have identified a number of associations. “In rodent studies, we see that exercise improves blood flow to the brain, and promotes both neurogenesis and synaptogenesis. This has been confirmed in imaging studies of healthy older adults. Exercise was associated with increased structural connectivity, changes in functional connectivity, and increases in brain volume in some regions, including the hippocampus and prefrontal cortex.”
She also acknowledged that preaching exercise in clinic is much easier than actually getting patients into the gym. “Stroke survivors often have mobility limitations, and these studies were primarily conducted in subjects who did not have those issues and who could work out on a treadmill or exercise bike. How we can adapt these programs to patients with limited mobility is certainly a challenge.”
Ms. Oberlin had no financial disclosures.
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