In my last post, I explained that metabolism refers to the sum of all the chemical reactions that occur in your body. Your metabolic rate refers to the speed at which these chemical reactions occur and is a measure of how many calories you expend. Your basal metabolic weight refers to your metabolic rate when you are sitting and relaxed, and your total metabolic rate adds the energy you expend when you are active to your basal metabolic rate. Total metabolic rate varies widely among individuals depending on their size, muscle mass, hormonal influences, and especially their activity level.
How active you are has a huge effect on your total metabolic rate. One of my sons, Nathan Trimble, is a serious athlete. In fact, he won the Houston Marathon twice in the 19 and younger category for men. He runs and rides his bike at least two hours a day–sometimes several hours a day. He’s not a very big person, yet he must eat about 6,000 calories every day just to maintain his very low body weight and meet his energy needs. (When he’s home, my grocery bill goes up big time!) Almost everyone else on the planet would quickly gain weight eating that many calories on a daily basis.
When I was in my late twenties, I joined a women’s running club. I remember our potlucks quite vividly. Everyone brought a lot of food, and we all dove into it like we were starving. No one thought about counting calories, and everyone was thin! That’s because we were all running at least 30 miles a week, plus doing interval training on a track once a week. We were burning off the calories we ate almost as quickly as we ate them.
Exercise increases your metabolic rate several ways. First, it increases your muscle mass. A pound of muscle uses three times the number of calories at rest than a pound of fat. Before you get too excited about that, muscle tissue at rest still doesn’t burn very many calories–just six calories per pound a day, but it certainly helps.
Muscle tissue burns a significant amount of calories when you are exercising, however, and your metabolic rate increases significantly, providing a huge help to weight control. (No surprise there!) I went on a two hour hike this weekend, for example, and probably burned over 600 calories during that activity.(1) If I had stayed home and watched TV during those two hours, I would have burned about 150 calories.(2) Not only that, my body’s metabolic rate stayed higher after my hike as as my body repaired itself from the effort–perhaps as long as 24 hours.(3)
Understanding the effect of exercise on metabolic rate is especially important for people as they get older. You’ve probably read that your metabolic rate slows down as the years pile on, leading to weight gain. Research suggests, however, that this is probably due more to a drop in activity levels rather than aging. As people get older, they tend to become less active, resulting in a loss of muscle mass and a drop in their total metabolic rate. Older people who keep their activity level high do not seem to experience the same drop in metabolic rate as those who exercise less.(4)
I think there is something else very significant about regular exercise. When I am faithful to exercise every day–even just a half an hour walk with my dog, I tend to be more active throughout the day. My mood is better, I have more energy, and the quality of my sleep is much higher. All this makes me want to move more. I tend to bound up the stairs instead of climbing them slowly. If I have some free time, I feel like working out in the garden instead of moping around the house. If I do watch TV, I’m more likely to pick up my hand weights and use them during that time, and I’m more willing to say “Yes!” if a friend wants to go on a bike ride.
So, that half hour walk has a huge payoff. I’m burning more calories while I exercise, I’m burning more calories after I exercise, and I tend to be more active throughout the rest of the day–again burning more calories. Not only that, but I want to eat more healthily as well. I firmly believe a half an hour daily walk can change a person’s life because of its ripple effects.
By Holly Trimble, MS, LPT
1. Calories Burned Calculator [Internet]. Changing Shape; Available from: http://www.changingshape.com/calculators/calories-burned/
2. Calories Burned Sitting Quietly and Watching TV [Internet]; Diet and Fitness Today; Available from http://www.dietandfitnesstoday.com/caloriesBurnedInfo.php?id=141
3. The Myth About Muscle and Metabolism [Internet]; Christian Finn. Available from: http://muscleevo.net/muscle-metabolis#.Ut7tt7TnZaQ
4. van Pelt, R.E., et al (2001). Age-related decline in RMR in physically active men: relation to exercise volume and energy intake. American Journal of Physiology, E281, 633-630
Disclaimer: Nothing in this blog should take the place of advice from your own health care provider. Anyone starting an exercise program should consult with his or her physician and follow their recommendations.
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