A special section of Medicine & Science in Sports & Exercise, the journal of the American College of Sports Medicine detailed a continuing controversy in the field of sports science about exactly how exercise works on bone and why sometimes, it doesn’t. “There was a time, not so long ago,” when most researchers assumed “that any and all activity would be beneficial for bone health,” says Dr. Daniel W. Barry, an assistant professor of medicine at the University of Colorado, at Denver, who has studied the bones of athletes and the elderly.
Recent findings are showing that competitive swimmers had lower-than-anticipated bone density, and that competitive cyclists sometimes had fragile bones and, finally, some studies suggest, that weight lifting did not necessarily strengthen bones much. Too much endurance exercise may actually reduce bone density. In a study by Dr. D.W. Barry, competitive cyclists lost bone density during a long training season. Dr. Barry says that it’s possible that exercise that is too prolonged or intense may lead to too much calcium loss through sweat. The endocrine system may interpret this loss of calcium as serious enough to start leaching the mineral from bone.
The Best Exercise
The current message about exercise and bone building may be that the best exercise is to simply jump up and down. "Jumping is great, if your bones are strong enough to begin with,” Dr. Barry says. “You probably don’t need to do a lot either.” (If you have a family history of osteoporosis, check with a doctor.)
Hopping also aids in balance, which may be as important as bone strength in keeping fractures at bay. Dr. Barry says, “fragile bones don’t matter, from a clinical standpoint, if you don’t fall down.
Exercise changes the Brain
It has been known for a long time that exercise changes the structure of the brain and affects thinking. A groundbreaking finding was published ten years ago by scientists at the Salk Institute in California showing that exercise stimulates the creation of new brain cells. But there are still some important questions to resolve, like whether exercise should be strenuous to create new brain cells. What about weight lifting? Should it be aerobic? Are the cognitive improvements temporary or permanent?
What Exercise makes you Smarter?
The American College of Sports Medicine, studied 21 students at the University of Illinois to see how well they could memorize a string of letters and then pick them out from a list flashed at them. Immediately afterwards they were asked to perform one of three things for 30 minutes —run on a treadmill, lift weights or sit quietly, — before doing the letter test again. After a 30-minute cool down, they were tested once again. A few days afterwards, the students came back to try the other two options. The students were much quicker and more accurate after they ran than with the other two options, and they performed better when tested after the cool down. “There seems to be something different about aerobic exercise,” says Charles Hillman, an associate professor in the department of kinesiology at the University of Illinois and an author of the study..
Brisk walking or Stretching?
Similarly, in studies with elderly people, performed by scientists at the University of Illinois, assigned a six-month program of either stretching exercises or brisk walking. Those who did the stretching improved their flexibility but did not improve on tests of cognition. Those who practiced brisk walking did.
Why Does the Exercise need to be Strenuous?
Why does exercise need to be aerobic to improve brain function? “It appears that various growth factors must be carried from the periphery of the body into the brain to start a molecular cascade there,” so that new neurons and brain connections are created, says Henriette van Praag, an investigator in the Laboratory of Neurosciences at the National Institute on Aging. To create new brain cells, “you need a fairly dramatic change in blood flow,” like what happens when you run, cycle or swim. Weight lifting, produces “growth factors in the muscles that stay in the muscles and aren’t transported to the brain,” van Praag says.
The current research findings suggest that, “It would be fair to say that any form of regular exercise should be able to maintain or even increase our brain functions [if ii is aerobic].” says Chauying J. Jen, a professor of physiology at National Cheng Kung University, in Taiwan.. What we need to keep in mind is that there are many kinds of exercise and their effects may be quite different. As we become better informed we can choose our own combination of exercise practices - aerobics, Ashtanga Vinyasa Yoga of Pattabhi Jois, Power Yoga, Vinyasa Yoga, swimming. tennis etc., each type for its specific contribution to health and wellbeing.
See Gretchen Reynolds in the New York Times, 16/09/2009.