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Knee bends make you smarter?

October 5th, 2011

The best way to improve your cognitive function is to… strengthen your quadriceps muscles?! That (sort of) is the message of a new study in the European Journal of Applied Physiology by researchers in Japan.

In brief: they measured cognitive function in a group of 39 older men (average age 69) using the “Mini-Mental State Exam” (MMSE), and compared to results to measures of elbow, knee and ankle strength. They found that knee extensor strength (i.e. quadriceps) was significantly correlated with MMSE scores, but elbow and ankle strength weren’t. To some extent, this isn’t surprising: cognitive decline is often linked to declining ability to carry out everyday tasks, though it’s not entirely clear which is the cause and which is the effect. (Does physical weakness condemn you to sit helplessly in your chair, causing your mental faculties to atrophy? Or is it mental decline that stops you from doing your usual activities, causing your muscles to weaken?)

But this doesn’t explain why knee strength predicted cognitive function while elbow and ankle strength didn’t. One possibility is that the knee is more significant because it’s a larger muscle mass, so it’s more capable of affecting the levels of hormones like insulin-like growth factor 1 circulating in your body, which in turn affect brain health. This is pretty speculative. A simpler possibility is that knee strength is more important to mobility (e.g. getting in and out of chairs) than ankles or elbows. (And a third possibility is that the result is simply a fluke due to small sample size.)

Anyway, this raises the question: can you get smarter by doing deep knee bends? The study tried this, putting 27 of the subjects through a three-month, six-day-a-week home training program involving simple things like sitting in a chair then standing up. The results were a little unclear because the changes were very small after such a light training program — but the increases in MMSE score were indeed correlated (with p<0.05) with increases in knee extensor strength. In other words, those who achieved the biggest gains in knee strength also saw the biggest gains in MMSE score.

So what does this mean? I don’t think it’s anything earth-shatteringly new. To keep your wits about you, you have to stay active; to stay active, you need to have the physical ability to get around. Most previous studies on exercise and cognition have focused on aerobic exercise, which produces very strong effects on the brain. The message here is that you can’t neglect your muscles — particularly the big ones that get you out of your chair and walk you down the street.

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