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But while supervised weight-lifting seemed to boost mental functioning among those struggling with incipient memory loss, aerobics-based activity programs did not confer a similar mental health benefit, the study team found.
"Most studies have looked at aerobic training, but this study compares both aerobic and strength training," explained study co-author Teresa Liu-Ambrose, an assistant professor in the department of physical therapy at the University of British Columbia. "And among people who don't yet have dementia but are already at a high risk in terms of mild memory and executive function impairment, our study shows that strength training, but not aerobics training, does have benefits for cognition."
Liu-Ambrose, also an investigator at the university's Center for Hip Health and Mobility and the Brain Research Center, and her colleagues outlined their findings in the April 23 issue of the Archives of Internal Medicine.
The authors noted that dementia is a huge public health concern, with a new case diagnosed somewhere in the world every 7 seconds.
Among the elderly, mild "cognitive," or mental, impairment is viewed as an indicator of future full-blown dementia risk, as well as a chance to perhaps intervene with some form of treatment that might lower that risk.
Previously, the study team found that a year of twice-weekly resistance (strength) classes seemed to boost overall cognitive capacity among mentally healthy elderly women.
This time, the team focused on women between 70 and 80 years old who had complained of memory difficulties and were deemed to have "probable" mild cognitive impairment.
For six months, the women engaged in 60-minute classes twice a week. One-third were randomly assigned to a strength-training program that included lifting weights; one-third walked outdoors in an aerobics program; and one-third took basic balance and toning classes.
Seventy-seven women completed the program, which included standard verbal and visual memory tests, and decision-making and problem-solving tasks. Almost one-third underwent functional MRI at the start and end of the study to look for brain activity changes.
After 6 months, compared to those in the balance/tone classes, the strength-training group was found to have experienced "significant" cognitive improvement.
The strength-training group also experienced activity changes in three specific parts of the brain's cortex associated with cognitive behavior, the researchers found. These changes were not seen among the balance/tone group.
As for the aerobics group, while significant physical improvements were cited relative to the balance/tone group, this group did not appear to accrue the same mental benefits as the strength-training group.
The findings might even be conservative, the authors said, because many women skipped classes.
The team cautioned that their findings may not necessarily apply to women of a different age group, or to men in general.
Catherine Roe, an assistant professor of neurology at the Washington University School of Medicine in St. Louis, hailed the effort as a "worthwhile avenue of exploration" while also expressing some surprise.
"There is certainly other work that has also suggested that exercise can be beneficial cognitively," she noted. "Participation in physical activity definitely seems to help preserve memory and thinking skills."
On the other hand, Roe said, this study "surprises me, because I can't think of a mechanism off-hand why one (exercise method) would work and not the other."
To that point, Liu-Ambrose said that for now, her team could only hypothesize.
"It could be that resistance-training requires more learning and monitoring by its very nature," she said. "If you're lifting weights you have to monitor your sets, your reps, you use weight machines and you have to adjust the seat, etc. But with walking it's much more natural for most, so there's less cognitive involvement. But at this point we don't have a clear idea of what's going on at the mechanistic level."
Liu-Ambrose also acknowledged that longer-term benefits remain unknown. "But I would say that overall physical activity of this sort is a pretty promising strategy, because it's one of the few interventions that can be delivered globally, and it's pretty inexpensive compared with other approaches."
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