In 65 to 75 year old community-dwelling women, 12 months of progressive resistance training once- or twice-weekly improved selective attention and conflict resolution, relative to twice-weekly balance and toning exercises. We also found that resistance training twice-weekly improved peak quadriceps muscle power, and that resistance training once- or twice-weekly led to small but significant reductions in whole brain volume. To our knowledge, this is the first study to demonstrate that engaging in progressive resistance training as little as once a week can significantly benefit executive cognitive function in community-dwelling senior women.
Our study provides novel data relating the frequency and duration of resistance training with cognitive benefits in women. We observed a cognitive benefit after 12 months of training but not at the six-month time point. Cassilhas 8
reported cognitive benefits after six months of resistance training in men. There were differences in the frequency of resistance training between the two studies (i.e., once-weekly and twice-weekly training in our study versus thrice weekly in the Brazilian study); also different cognitive functions may have different change trajectories with resistance training. Sex may also be a moderating factor. Our study included women only and the participants trained less frequently than those in Cassilhas’ study 8
. Finally, differences in the control groups may have contributed to the lack of between-group differences in cognitive performance at six months. The Brazilian study’s 8
control group trained only once-weekly; our Canadian control group trained twice-weekly.
We also demonstrated that enhanced selective attention and conflict resolution was associated with increased gait speed. To our knowledge, this study is the first to demonstrate this relationship. Our current finding adds weight to previous observations of a strong relationship between gait speed and cognitive function 30
. The implication for clinicians is that improved gait speed is a predictor of substantial reduction in mortality 31
The design of our control group (i.e., BAT) may have also contributed to the lack of between-group differences at six and 12 months in quadriceps 1 RM. Our control group included balance training in their twice-weekly program. Previous studies have demonstrated that balance training exercises can improve muscle strength 32, 33
. In addition, in our own previous investigation of different types of exercise training (i.e., resistance training, agility training, and stretching (i.e., control) exercises) in senior women with low bone mass, we did not find any significant between-group differences in measures of quadriceps strength and mobility 34
We highlight that although both resistance training groups enhanced selective attention and conflict resolution by the end of the trial, there were more musculoskeletal adverse events in the once-weekly resistance training group than the twice-weekly resistance training group and the twice-weekly balance and tone group. Hence, the possible increased risk for musculoskeletal injury with once-weekly resistance training must be weighed against its benefit of reduced training time compared with twice-weekly resistance training.
An unexpected result was the reduced whole brain volume for the two resistance training groups. Although reduced brain volumes are commonly associated with impaired function 35
, those groups who improved cognitive executive function and muscular function had brain volume reductions. There are precedents that parallel our apparently paradoxical finding 36, 37
. In a beta-amyloid immunization trial among those with probable AD, immunization led to significant clinical benefit, reduced beta-amyloid load, and reduced brain volume 36
. The investigators hypothesized that removal of beta-amyloid and/or other protein constituents from brain tissue may have caused cerebral fluid shifts, resulting in brain volume reductions on MRI. However, we are very cautious in our interpretation of the whole brain volume results and emphasize that this facet of the study, although not the first report of such a phenomenon, needs further investigation.
Because our participant sample included women aged 65 to 75 years only, the findings may not generalize to men or to women of other ages. Also, although we observed reduced whole brain volumes, the study was not designed to image which specific brain regions demonstrated volumetric changes.