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Exercise Intensity(7 posts)

Exercise Intensitymwagner7700
Jan 12, 2004 11:56 AM
I got into a discussion with my sister and fiancee the other night regarding exercise intensity. They are both members of a Curves gym. The charts on the walls say not to exceed 65%-75% of your heart rate. When my fiancee inquired as to why, the gym owner told her that you don't burn fat, but muscle after 75%.

I remember reading a post about this very topic a few months back, but I can't find it. I know that above 75%, you are exercising anaerobically, but I always assumed the harder you work out, the more fat you burn.

HELP!!!
re: Exercise IntensityPEDDLEFOOT
Jan 12, 2004 12:53 PM
It is my understanding that the lower intensity and HR the exercise is percentage wise, you burn more fat calories then the glycogen in the muscles.As you increase the intensity and HR you start decreasing the percentage of fat calories and increasing the percentage of glycogen burned.You are still burning fat but at a lower percent.

At higher intensity you will burn more calories per hour. For most people it is harder to maintain this higher intensity.Therefore it may be wiser for less fit people to exercise at a lower intensity for a longer period of time.

If I understand the concept of Curves these are the type of people who most often go there.Thats probably why the person there told them that.By the way I don't beleive you burn muscle when you exercise.To get to such a state the body has to get to very high stress level .
Sort of truebimini
Jan 12, 2004 1:11 PM
I'm no expert but from what I have read, anaerobic / interval excercise does cause muscle "damage". To say you burn muscle sounds a bit like an over exageration or simplification unless you are dealing with endurance excercise. The way power and interval training works is you over stress the muscles and cause this "damage". Then, your body repairs the damage and while it is at it compensates by building additional muscle fiber. The reason it is important to have any easy day or two after a hard interval session is to give the muscles time to recover and rebuild.

Base training should be done at 75% or less. Interval training should be done at above that level but only 2-3 times a week with a day or two recovery in between.

The harder you work out the more calories you burn, unless it is a marathon work out session most of the calories you burn comes from the glycogen (sugars) in the blood. The body will convert fat to blood sugar but can only do this at a fixed rate. In performance cycling or exercise you use glocogen at a faster rate than the body can convert fat to sugar. This is why gatorade, powerbars, food is important for exercise of over an hour duration. Once the glycogen is depleated and you are using calories faster than the body can convert fat to sugar you bonk. The body will also start converting muscle to sugar at this point (unless you are eating or drinking sugars while you train). This is why post ride recovery drinks or just plain food is important after a hard workout.

If the primary goal is weight loss the recovery drinks etc. are counter productive. You are better off working out at a lower rate for a long period of time or working out at high intensity for a shorter period of time, stopping before you depleat your glycogen (bonk). Your body will continue to convert fat to glycogen after you stop exercising until your blood sugars return to normal.
re: Exercise Intensitymwagner7700
Jan 12, 2004 2:21 PM
Thanks all. I found this site, which 'sort of' describes the zones.

http://walking.about.com/library/walk/blex0720.htm
Fat burn is relatively constant w/changes in intensityKerry Irons
Jan 12, 2004 5:25 PM
While exercising, a conditioned person will get around 200 calories per hour from fat metabolism. On a bike, this is 12-13 mph/19-21 kph. This is all the faster you can ride when bonked (no carbs left in the system). As intensity goes up, the % of calories burned from fat goes down, simply because the number of fat calories remains constant and the total calories goes up. You do stress the muscles and do some damage as intensity increases, but muscles get stronger in response, which is why you need intensity workouts to increase speed and power. To say you are burning muscle is partly true, as there is some catabolism taking place, but it is not really much of an issue unless you flog yourself day after day. I'd guess the real reason they counsel people to keep the intensity down is so that they get more repeat customers - most people don't like it when they're asked to go hard.
Ahhh...divve
Jan 12, 2004 9:40 PM
...is that what they call bonking.....it ain't that bad aside from still having to go another 30 miles and feeling freezing cold even though it's midsummer:)
You're only exercising anaerobically if...Dwayne Barry
Jan 13, 2004 6:03 AM
you're holding your breath! However the relative percentages of the energy required to do the work being supplied by glycolytic vs. oxidative mechanisms does change with intensity. Burning muscle or at least proteins doesn't vary much with intensity and makes a relatively small contribution to the energy. It is the ratio of carbohydrates in the form of glucose/glycogen and fats that varies greatly with intensity.