MEDICAL PRACTICE - Energy Expenditure and Exercise

How to manipulate energy expenditure through exercise

Many people assume that they have slow metabolisms and must starve themselves to lose any weight at all. In fact, the opposite is true in many cases: An individual can have fairly hefty caloric needs, and undercutting themselves by more than 500 calories per day will cause undue hunger and drastically decrease diet adherence. Resting metabolic rate (RMR) represents about 60% to 65% of daily caloric needs and is largely determined by organ, muscle and bone tissue: your metabolically active tissues. Total daily energy expenditure consists of RMR, the thermic effect of foods, spontaneous physical activity, and exercise. The table below gives you a great indication of how much energy your tissues demand.

Body Compartment	Organ/Tissue Metabolic Rate kJ/kg (kcal/kg)	% Body Weight
Fat Mass
Adipose tissue	19 (4.5)	21 - 33
Fat Free Mass
Skeletal muscle	55 (13)	30 - 40
Organs
Liver	840 (200)	5 - 6
Brain	1004 (240)
Heart	1840 (440)
Kidneys	1840 (440)
Residual	50 (12)	33

Residual includes bone, skin, intestine, glands.
Adapted from Elia (1992)

Many investigators agree that the process of weight reduction on a low calorie diet is associated with a decline in RMR. Some studies report that RMR remains depressed in subjects undergoing dietary weight loss with the addition of exercise, while others report that exercise in addition to weight loss preserves RMR at pre-weight-loss levels. This is why many of your personal trainers have you undertaking resistance training, as it can increase resting energy expenditure simply by virtue of increasing or preserving fat free mass during weight loss. As you can see from the table above it's not the extra kilo of muscle that's going to make the difference (burning an extra 13 calories).

But there is also another very important reason why many of you are pushed so hard in the gym either through high intensity weight training or high intensity, short duration cardio workouts. The exercise after-burn, or the calories expended (above resting values) after an exercise bout, is referred to as 'excess post-exercise oxygen consumption' or EPOC. This represents the oxygen consumption above resting level that the body is utilising to return itself to its pre-exercise state. Although there appears to be variation in individual responses, the positive news is that any additional caloric expenditure following exercise can add up over time and may contribute to long-term weight management. To maximise energy expenditure through EPOC, focus on performing higher intensity exercise for periods of 20 minutes or more. Additionally, engage in resistance training at least 2 times a week. Not only will resistance training maintain or increase muscle mass in weight-loss interventions, studies report a meaningful EPOC effect following high intensity and circuit resistance training.

See Also:

Body Composition Measurements (DEXA)

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