LIght Physical Exercise Leads to Larger Brain Volume -- But not Moderate or Heavy Exercise?

This week's issue of ALZForum included information on recent research on exercise and brain health.  It's encouraging to couch potatoes and is getting wider attention.  The research claims to have found a correlation between light exercise and increased brain volume that does not appear with moderate or heavy exercise. 

The study used about 2,500 participants in the ongoing Framingham Heart Study with an average age of 53 who were cognitively normal.  Participants were wired up with accelerometers and recorders to measure how much light, moderate, and heavy exercise they got in an eight-day period.  Results were gathered from MRIs used to measure changes in brain volume.  The study did not report measuring cognition. 

Regarding moderate and vigorous activity, about half met a goal 150 minutes per week, and half did not.  Measurements of brain volumes found no meaningful difference between these two groups.  On the other hand, comparing participants who took more than 10,000 steps per day with those who took less than 5,000 steps per day found that 10,000 steps per day correlated with a brain volume that was 0.35% larger.  Based on conclusions of other studies, this in turn correlated with a brain that was effectively 1.75 years younger.  The earlier studies found that a normal brain loses 0.2% of its volume per year after age 60.

So just getting up and gardening or walking around the block can produce increased brain volume.  Does this translate into improved cognition?  The study made a number of references to the influence of exercise on Alzheimer's disease, but it did not associate their research with that.  It would have been good if, in addition to measuring brain volume, they also measured changes in cognition.

Are there other studies correlating light exercise with cognition?  In Beating the Dementia Monster, we cite research with women who just walk correlating their light exercise with signiticant delay in the onset of cognitive decline.