Maximixe Net Energy Cost for Greater Weight Loss

Thu, 8 Dec. 2011 - 5:44 p.m. MT
Credit: ARA Staff - American Running Association

The benefits to cardiovascular health, bone mineral density, blood pressure, and mood begin to appear with almost any quantity of regular, light-to-moderate exercise. However, when the primary goal of your workout regimen is weight loss, there are considerations that can render one person’s workout more effective than another person’s. These not only include voluntary behavioral factors, i.e., what else you did—as well as what you ate—that day, but also your individual metabolism and bodily response to physical fitness.

 

One key to understanding and therefore predicting your own personal weight loss is understanding the difference between net and gross energy cost. Essentially, you will need to approximate (if not determine) what the energy expenditure is that you are devoting directly to exercise. The net cost of the exercise is the exercise energy expenditure minus resting energy expenditure, that is, minus whatever else you would have been doing that day if you were not exercising. This goes not only for during the exercise, but also any dietary and physical activity changes due to the exercise. These factors can play a more significant role than many people think.

 

If you are regularly burning calories with moderate exercise of a half hour or more three or more times a week, but not seeing the weight loss results you had hoped, look for ways you might be compensating for the increase in activity. For example, you may be replacing with food the 400 or so calories you are burning off in your workout, due to increased hunger. Another possibility, particularly in marathon training, is that the extra exhaustion you feel after, say, a weekend long run could result in your taking a long nap that day—whereas you ordinarily would enjoy greater resting energy expenditure during those hours.

 

While it is not necessary (though certainly beneficial) to calculate resting metabolism and meticulously pore over every calorie consumed and burned, you may benefit from observation of a few important trends in types of exercise, and the effects they have on the body.

 

Specifically, we should look at walking versus running. This goes back to the ways you would have spent the time during your exercise if you had been doing something else. Your per-mile net energy cost for moderate-paced walking is going to be much lower than your per-mile net energy cost for moderate-paced running. The net caloric cost per mile of walking up to 3.5 mph is .77 calories per kg of body weight per mile. The gross cost per mile is between 90 and 100 calories. The net caloric cost of running 6 mph or 10:00 pace is 1.53 calories per kg of body weight per mile. (Treadmill calorie displays typically offer gross cost values, not net.) 

 

A 154-lb person burns a net of 54 calories per mile of walking at a rate of 3.5 mph. By contrast, this same person burns a net of 107 calories per mile running. The difference in caloric cost between an hour spent walking and an hour spent sitting is nearly half the difference between an hour spent running and an hour spent sitting. Therefore, there is a diminishing returns phenomenon with walking; the slower you go, the more time you are displacing from what you would have been doing anyway. The faster you go, the more closely net cost resembles gross cost. The time you need to spend in order to achieve a certain gross energy cost is a liability that keeps the net that much lower for any given bout of moderate walking.

 

Each person must come to know his/her habits and their body’s reaction to them. Many people find luck timing a workout just before a meal because they have observed a reduced appetite at the table in this situation. Others simply need to recognize their tendency to replace (and then try to avoid replacing) the same calories lost with a snack of equal caloric value immediately after a run. 

 

One of the best strategies is to try and keep the same level of everyday activity after a workout as you would perform on a day of recovery. Avoid relaxing in your recliner for an extra 90 minutes simply because you had a vigorous workout day. Data collected from the National Weight Control Registry suggests that people who successfully maintain long-term weight loss reported gross exercise cost at 2,800 calories per week. The American College of Sports Medicine recommends 2,000 calories per week for weight loss. Others recommend 2,500 calories per week gross expenditure. These numbers tell us little, given the real importance of net cost, but they do tell a similar story and can give us an idea of where we need to begin. To put these numbers in perspective, note that there are 3,500 calories per pound of fat. But take heart: actual weight loss will be greater than this simple calculation because of factors like lean tissue oxidation and water loss.

 

(ACE Certified News, 2006, Vol. 12, No. 5, pp. 3-6)

 

(RUNNING & FITNEWS®November/December/January  2006-2007 • Volume 25, Number 1)




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