High-intensity progressive resistance training (PRT) improves cognition in older adults with mild cognitive impairment (MCI), and these improvements are mediated through gains in strength, not aerobic capacity, a randomized trial indicates.
"Older adults commonly have symptoms such as musculoskeletal pain, claudication, or shortness of breath that may limit their exercise capacity," Yorgi Mavros, PhD, University of Sydney, in Australia, told Medscape Medical News.
"And high-intensity PRT may improve these symptoms which may result in participants being able to achieve a higher workload before becoming fatigued, resulting in a higher peak VO2," he added.
Furthermore, approximately 50% of the loss in peak VO2 with aging is explained by age-related muscle loss. By directly targeting the working capacity of skeletal muscle, PRT improves aerobic fitness.
"Thus, the increase in peak VO2 is not necessarily due to improvements in cardiorespiratory function that would be observed with aerobic exercise but rather due to changes in skeletal muscle," said Dr Mavros.
The study was published online October 24 in the Journal of the American Geriatrics Society.
The Study of Mental and Resistance Training (SMART) randomly allocated older adults to receive one of four interventions:
Resistance exercise and computerized cognitive training (multimodal and multidomain exercises targeting memory, executive function, attention and speed of information processing)
Resistance exercise and placebo computerized training (ie, watching nature videos)
Brain training and a placebo exercise program (seated stretching/calisthenics designed not to increase heart rate or enhance either aerobic capacity or strength)
Placebo physical exercise and placebo cognitive training
Each participant engaged in one of the four interventions for 6 months; they were followed for 78 months.
Initially, the PRT program was scheduled for 3 days a week, but the schedule was reduced to 2 days a week to minimize the travel burden.
"At baseline, neither peak VO2 nor strength was associated with cognition," the researchers write.
At the end of 6 months, investigators found that patients who engaged in PRT had significant improvement in scores on the Alzheimer's Disease Assessment Scale–Cognitive Scale (ADAS-Cog).
Indeed, "normal cognitive scores [were] achieved in 47% of all participants who received PRT and [there was] a trend for improvement in executive function," the investigators report.
In contrast, positive changes in peak VO2, which were seen after 6 months of PRT, were not associated with positive changes in scores on the ADAS-Cog or in any other domain, including global, executive, or memory domains, across the whole cohort, they add.
A mediation model showed that improvements in strength mediated almost two thirds of the effect of high-intensity PRT on cognitive function.
"In other words, once the effect of strength on cognitive function was accounted for, there was no residual effect of PRT, suggesting that the primary factor underpinning the observed improvements in cognitive function [were due to] improvements in strength," said Dr Mavros.
Notably, this was only true for improvements in lower body strength, not for improvements in upper body strength or whole body strength.
This observation likely reflects the fact that the lower limbs represent the largest muscle group in the body and thus have a greater influence on the cognitive effect from PRT than upper body or whole body strength.
"We also stratified linear regression analyses to see if changes in strength were directly associated with improvements in cognitive function within the PRT group alone, as this is the group that had an improvement in strength," Dr Mavros said.
"And overall, our data suggest that improvements in strength mediate improvements in cognitive function in adults with MCI, and the greater the gains in strength, the greater the improvement in cognitive function observed."
Dr Mavros acknowledged that both high-intensity aerobic and PRT regimens are important for improving health outcomes in older adults, as both reduce the risk for future morbidity and mortality resulting from cardiometabolic diseases and other disorders.
"However, older adults typically present with comorbidities that make even simple walking difficult, including knee and hip osteoarthritis, peripheral vascular disease, frailty, fall risk, osteoporosis, and obesity, and as such, prescriptions [for aerobic exercise] may be difficult or unsafe," he said.
Because PRT can be performed while seated, it is a much more practicable modality for older individuals, and exercises can be modified to accommodate a patient's limitations without compromising the intensity of the exercise performed.
"In addition, PRT is the only exercise modality known to significantly increase muscle mass and strength, so it's not interchangeable with aerobic prescriptions," said Dr Mavros.
Gains in muscle strength achieved from PRT are not only important for brain health, as the SMART results suggest, but also help prevent sarcopenia and related conditions, including osteoporosis.
Commenting on the findings for Medscape Medical News, Teresa Liu-Ambrose, PhD, PT, associate professor, University of British Columbia, Vancouver, Canada, noted that the reason the benefits of aerobic exercise are so widely extolled is that many more studies have explored the value of aerobic exercise than have examined the value of strength training.
"But...to think that only one type of exercise training is beneficial for the brain is akin to saying only one type of vegetable is good for you," she said.
Dr Liu-Ambrose also believes that the more evidence-based options practitioners can offer patients to promote brain health, "the better the chances are that they will adopt the recommendation to exercise, because they can choose what they want to do and sustain it over the long term."
The SMART trial was funded by Australia's National Health and Medical Research Council. Neither Dr Mavros nor Dr Liu-Ambrose have disclosed any relevant financial relationships.
J Am Geriatr Soc. Published online October 24, 2016. Abstract
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Cite this: Resistance Training Improves Memory in MCI - Medscape - Oct 31, 2016.