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Back to Basics Part Two: How Exercise Fits In

Posted Oct 23 2011 3:59pm

Last week, we talked about how your nutrition affects your weight. There are websites where you can automatically calculate these numbers, but sometimes it’s important to understand the basics. In summary, this is where we were:


Exercise
So remember how last week, I gave a breakdown of how calories are processed? How does exercise fit in? Your body simply uses more of that energy you consumed from food to do more intense activities that just digesting food or talking. And of course, continuous exercise raises the metabolic rate you get from activity. So while the 5 basic steps I listed last week are still valid, the amount of energy your body would use to function regularly would go up too. So it’s a win-win all around.

Basic BMR
Now back to our example from last week, we are using a male with the following stats Age – 30
Weight – 192 pounds
Height – 6ft (72 inches)

Our basic BMR with no exercise came down to 2000 calories.

2000
General Activity
With only basic low intensity once-in-a-while exercise, metabolic rate increases by BMR x 20% (see the diagram at the top of this post). So his metabolic rate would come down to 2000 + (2000 x 20%) = 2400 calories, meaning his body is burning about 2400 calories a day.

Now consider this: If he amped up his exercise, and starts exercising most days a week, he could increase his metabolic rate by BMR x 40%. This brings his metabolic rate to 2000 + (2000 x 40%) = 2800. That’s a considerable difference! He just burned an additional 800 calories a day by exercising most days! I guess that crazy Michael Phelps diet doesn’t seem so crazy to you now…

Heart Rate
Granted, this is just an approximation, and it varies based on what “most days” and “intensity” mean to you. So the most accurate way to see how much you are actually losing is to calculate it for the types of exercises you do. Yes, there’s a formula for that too.

What the machines at the gym seem not to mention is that the number of calories you burn during exercise heavily depends on your heart rate. The good part is that most machines do have heart rate monitors. What I would advise is to calculate your heart rate during a few different workouts at the gym, and just note the average so you can use it to calculate the amount of calories you burn doing non-machine exercises.

The average resting heart rate is somewhere between 60 and 80bpm. However, if you are very fit or an athlete, your resting heart rate would usually be somewhere between 40 and 60bpm (usually 50 to 60bpm for women). This is just because the more you exercise, the more efficient your body’s circulation becomes.

During exercise, the average heart rate should increase. It would go higher based on the intensity of the exercise. The higher your heart rate, the more calories you should be burning. However, take care not to get above your maximum heart rate.

How do you calculate your maximum heart rate? Here is where I’ll introduce a little caveat. So far, experts have said there is no perfect way to calculate your maximum heart rate. However, the generally accepted estimate is
Women: Maximum Heart Rate = 226 – Age Men: Maximum Heart Rate = 220 – Age
This is not particularly scientific, but just what is generally accepted. It assumes that the older you get, the less intense you should be with your heart. Generally, when you exercise, your heart rate can go anywhere from 50% to 100% of this rate above. Fairly intense exercise is usually about 80% of this number. So back to our example, his maximum heart rate would be 220 – 30 = 190.

Maximum Heart Rate = 190
One last point I will make with the heart rate is that when machines spell out a “Fat Burning Zone”, it does not necessarily mean anything. Strive to go as high as you can below your maximum, rather than aiming to be within some phantom fat burning zone.

Actual Calories Burned
So we have the maximum heart rate. Now, we can calculate the number of calories burned during exercise. Here is the formula
Women: Calories Burned = [(Age x 0.074) + (Weight x 0.05741) + (Heart Rate x 0.4472) – 20.4022] x Time / 4.184Men: Calories Burned = [(Age x 0.2017) + (Weight x 0.09036) + (Heart Rate x 0.6309) – 55.0969] x Time / 4.184
My question is: Why does it always have to be different for men and women. Well, I guess only God can answer that one…

Back to our example, if our chosen man was doing average intensity cardio for 30 minutes, and had his heart rate at 70% of the maximum, he would have burned the following
Heart Rate = 70% x 190 = 133bpm
Calories Burned = [(30 x 0.2017) + (192 x 0.09036) + (133 x 0.6309) – 55.0969] x 30 / 4.184 = 374 calories

That sounds like what you see on the treadmill, right? Now you know how they calculated it. We now have a more accurate calculation of how many calories he is burning based on the intensity of his physical activity.

In summary, our 192 pound, 6 foot, 30 year old man with a BMR of about 2000 calories working out moderately for an hour a day would actually be surviving on approximately 2000 + (374 x 2) = 2748 calories per day. You see that this is pretty close to the 2800 number we had calculated before.

We like our diagrams on Eights & Weights, so here’s one for today

Questions, comments, feedback, concerns? Leave a comment, hit me up at editor@eightsandweights.com , find me on Twitter @eightsnweights , or join us on Facebook by searching for ‘ Eights and Weights ’.

Cheers Eights & Weights!
Photo credit: Weightloss-Systems.us


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