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July 28, 1999 2:00 p.m. EDT http://www.nandotimes.com) For many of his 88 years, Harry S. Truman left reporters breathless as he offered sharp-tongued commentary during his morning walk. John Glenn credits his celebrated return to orbit at age 77 to daily exercise, including a two-mile power walk. Now, brain researchers finally are catching up with senior pedestrians. A new study suggests that taking an invigorating walk gives older people's brains a good workout, boosting memory and sharpening judgment. Anaerobic exercise - stretching and weightlifting - did not produce similar cognitive improvements. The experiment was conducted at the University of Illinois and reported in Thursday's issue of the journal Nature. The mental benefits of walking were especially significant, researchers said, because the senior citizens had not exercised regularly before joining the study. "People who have chosen a lifetime of relative inactivity can benefit mentally from improved aerobic fitness," said the study's lead author, cognitive neuroscientist Arthur Kramer. "It's never too late." Researchers recruited 124 sedentary men and women ages 60 to 75. They were randomly assigned to either a walking program or an anaerobic regimen of stretching and muscle-toning. The experiment lasted six months. Walkers eventually were completing an hour-long loop around the university's Urbana-Champaign campus three times a week. Kramer and others administered a variety of simple tests to gauge the participants' ability to plan, establish schedules, make and remember choices and rapidly reconsider them if circumstances changed. Neurologists call these brain functions "executive control processes" because they help a person live independently. They are controlled in the brain's frontal and prefrontal lobes. "These areas of the brain decline the earliest with aging," Kramer said. "So executive control is more severely affected by the normal aging process than other brain functions." Among other things, participants were shown alternating letters and numbers, and asked to quickly determine between vowels and consonants, and odd and even numbers. The exercise is known as task switching. The walkers' ability to switch tasks improved by 25 percent, while the non-walkers' showed little improvement. Previous studies have shown that regular exercise may reduce the risk of developing Alzheimer's disease later in life, possibly because exercise enhances the production of certain hormones and other protective compounds in the brain. But those studies involved only people with long-term exercise habits. And Alzheimer's involves the death of brain cells, which is different from more generalized memory lapses that frequently accompany aging. Experts who reviewed the Illinois study said it is not clear how walking might stimulate memory and planning ability. "It might just be more a function of people in the study interacting with other people," said William Thies of the Alzheimer's Association. "Being isolated is bad for your health and bad for your day-to-day functioning." Answering that question is the goal of the Illinois experiment's second phase, which began this week. Researchers are taking magnetic resonance images of participants' brains to see if there is enhanced blood flow in their executive control centers and if it corresponds to the walkers' improved test performance.