Monday, August 8th, 2011 - 1:49 pm

Fit Tip


John Bobalik is an exercise physiologist and coordinator of the Purdue University Calumet Fitness Center, a comprehensive exercise and workout facility for students, faculty, staff and community members. It also serves as a laboratory setting for fitness management students.

Fit Tip Dude Exercising

Q. Is there an optimal heart rate range for burning fat during aerobic exercise?

A. Yes, but it requires you to exert yourself at a very moderate heart rate-intensity, which won’t do much for your level of cardiovascular fitness.

Jeffrey A. Potteiger, in his textbook, ACSM’s Introduction to Exercise Science, writes, “Recent evidence would indicate that the exercise intensity at which there is maximal fat utilization is approximately 65 percent of an individual’s max heart rate.”(1)

The intensity at which a person chooses to perform aerobic exercise (running, walking, bicycling, etc.) dictates whether a high percentage of carbohydrates or fat will be used as muscle fuel during aerobic exercise. Since one never uses 100 percent of one fuel source exclusively, expenditure becomes a percentage mix of carbohydrates and fat fuel.

The general rule is the higher the heart rate intensity, the higher the percentage of carbohydrates being expended. Conversely, the slower and more moderate the pace, the higher percentage of fat calories being utilized.

At the moderate heart rate intensity suggested by Potteiger, which represents 65 percent of one’s maximum heart rate, 90 percent of total calories expended during 30 minutes of aerobic exercise would come from fat.

Running three miles in 30-minutes at an energy cost of 100 calories per mile would burn 300 calories. Assuming 90 percent of the energy came from fat, 270 calories expended would be fat energy.

Research suggests that one burns approximately 100 calories for every mile run, independent of how fast or slow one moves. While pace or intensity has little effect on the number of total calories expended, the difference lies in the percentage of carbohydrates or fat used as fuel.

Albeit running at a pace that is 65 percent of one’s maximum heart rate can keep that individual in an optimal fat burning zone, thereby burning a high percentage of fat calories, that pace does little to improve that individual’s level of cardiovascular fitness.

However, there’s another option that provides the best of both worlds.

Exercising at a faster speed or higher heart rate intensity for a longer period of time will burn more total calories, including fat calories, as well as improve one’s level of cardiovascular fitness.

Using the previous example, running six miles at a faster pace or greater intensity would enable one to burn more carbohydrate fuel and less fat fuel. Let’s say the faster pace of the six-mile run physiologically equates to only 70 percent of one’s total calories coming from fat.

Moving at a faster pace on a six-mile run would burn more total calories, including more fat calories, compared to what one would expend during the three-mile/30-minute run. (70 percent of 600 total calories = 420 fat calories vs. 90 percent of 300 total calories = 270 fat calories)

Hence, one gains aerobic, fat burning and overall fitness benefits.

1. Achten J, Gleeson M, Jeukendrup AE. Determination of the exercise intensity that elicits maximal fat oxidation. Med Sci Sports Exerc. 2002; 34;92-7.

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