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Why Doesn’t Exercise Lead to Weight Loss

Exercise and Slimming

Just because you exercise it doesn’t necessarily mean that you lose weight. A study published in The British Journal of Sports Medicine in September reported disappointing weight loss results. 58 obese people, in the study, completed 12 weeks of supervised aerobic training without changing their diets. The average weight loss for the group was a little more than 3 kilos, and many lost barely half that.

Calories from Fat or Carbohydrates

Apparently, few people lose weight with exercise alone, they must also change their eating habits. A study from the University of Colorado School of Medicine in Denver tries to explain why. The researchers studied several groups of people. Some were lean endurance athletes; some sedentary and lean; some sedentary and obese. The researchers could tell whether the calories expended were in the form of fat or carbohydrates. Burning more fat than carbohydrates is desirable if you want to lose weight, since the fat comes from body fat stores.



To their surprise, the researchers found that none of the groups, not even the athletes, experienced “afterburn.” They did not use additional body fat on the day when they exercised. Actually, many of the subjects burned slightly less fat over the period when they exercised than when they did not.

Heart Rates for Fat Burning

To reduce your body fat, and maximize fat burning, The Journal of Strength and Conditioning Research, recommends a range of heart rates. “Heart rates of between 105 and 134” beats per minute, Carey said, represent the fat-burning zone. “It’s probably best to work out near the top of that zone,” he says, “so that you burn more calories over all” than at the lower end.

How to Keep it Off

How to keep it offThankfully, exercise helps, physiologically, to keep off body fat once it has been lost, through resolute calorie reduction. Exercise seems to reset certain metabolic pathways that blunted the body’s drive to replace the lost fat. So don’t stop running marathons or participating in bike races, yet. The exercise keeps it off once you’ve lost it!


Does Exercise Improve Cognition ?

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?

human brain mri scans-cerebro humano

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.

Pattabji Jois teaching Ashtanga Vinyasa Yoga

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.