so, how much exercise do you have to do?

In case you're wondering how much exercise you need to build your brain, the answer is: not much. A plethora of research papers over the last decade or so has shown that short bouts of exercise-even just a few minutes of swimming-boosts BDNF (Brain-Derived Neurotrophic Factor ) in rats.

The experts are somewhat divided on the optimal workout regimen to optimize your brain-building. Recommendations range from 8 to 12 minutes a day at 60 percent of your maximum heart rate, to a brisk 45-minute walk three days a week for six months, to 30 to 60 minutes of walking, hiking or swimming four to five times a week. (Don't know what your target heart rate zones are? go to: www.healthchecksystems.com)

Sottovia says that many of the cardio-enhanced brain functions derive from the intensity of the workout, and she recommends that "people work out at a level where they're huffing and puffing."

Erickson says there's evidence that a combination of aerobic and strength training may be optimal. "We're starting to address the question of what types of exercise are best-whether it's better to walk or play tennis-but since most of our studies are with older adults (ages 55
to 80 ), we want to make sure they don't overexert themselves."

While all evidence suggests that younger adult brains also benefit from working out, the extent of those benefits is not known. Erickson says, "We're trying to measure sedentary, obese college students against highly fit athletes to see whether there are differences in brain structure and function. However, that measurement will be tricky, because young people perform pretty well in cognitive tests regardless of their fitness level."

The societal repercussions of this research are enormous. Data from the Census Bureau and World Health Organization show that the number of people age 65 and older is growing rapidly. If scientists can find low-cost ways to prevent brain loss, they can markedly reduce medical costs related to Alzheimer's, Parkinson's and related illnesses. Erickson says, "A lot of people are looking for a perfect pill for those illnesses, but a simpler solution to avoid dementia might be to go outside and walk."

Research on the coginitve benefits of exercise is in its infancy-most of the studies have been conducted within the last five years-and there are a lot of unanswered question. Some of the most provocative issues are:

• How long do the benefits of exercise last? Can you work out for six months, stop and then resume without sacrificing your initial gains?
• What are the effects of exercise combined with nutritional supplementation? Will they be linear or exponential? Erickson says that researchers are particularly interested in studying the effects of B vitamins on the nonessential amino acid homocystine, elevated levels of which are related to a higher risk of dementia.
• What is the interrelationship of exercise and genetic predispositions? Do some people with specific genetic markers receive more or less benefit from working out?

We already know that exercise imporves stamina, lowers cholesterol and triglycerides, helps regulate blood sugar levels, controls body fat and increases longevity.

If we extrapolate from that, based on the studies of its effects on cognitve funtion, we might conclude that working out might also boost I.Q. or even SAT scores.

So the next time one of those 100-pound weaklings taunts you about your devotion to physical fitness, tell him you're getting smarter while you're sweating. Then kick a little sand in his face.