While both your basal metabolic rate and mass-specific metabolic rate are ways of measuring your metabolic output, they are fundamentally different. Your basal metabolic rate is expressed as the energy you release while at rest. Your mass-specific metabolic rate is how much oxygen you have consumed in a defined amount of time with respect to 1 gram of mass.
Units of Measurement
Since the basal metabolic rate is defined by the caloric requirement that your body needs while inert, it is measured directly in calories. Mass-specific metabolic rate is measured in milliliters, providing the amount of carbon dioxide produced per 1 gram of an individual. If your basal metabolic rate is high, this means that your body has a higher than average amount of muscle mass. For an average male, 42 percent of his body is composed of muscle. For an average female, 36 percent of her body is composed of muscle. In terms of your BMR rate, an average rate can range anywhere from 1,200 to 2,000 calories depending on body and muscle mass.
Explaining Mass-Specific Metabolic Rate
The mass-specific metabolic rate, a seemingly abstract number, is a direct result of a person's surface area-to-mass ratio. You expend a large amount of energy keeping your internal body temperature constant. If you are tall and thin, your mass-specific metabolic rate will be high, simply because your body must work harder to keep a constant temperature than someone who has the same surface area but either more muscle or overall body mass. The increase in muscle or body mass helps keep your internal body temperature constant. In terms of actual numerical amounts, a high mass-specific metabolic rate, for someone with a high surface area and low body mass, would be 2.4 ml per gram per hour. A low metabolic rate would be .4.
Weight Considerations
The basal metabolic rate is specifically affected by the weight of an individual. If you are heavy with a large fat percentage, this will lower your basal metabolic rate. With mass-specific metabolic rates, the goal is to get an accurate measure of carbon dioxide output from a single gram of an individual. Despite this, an increase in either muscle mass or body fat without an increase in surface area will raise an individual's mass-specific metabolic rate.
Increase vs. Decrease
With respect to traditional data, the larger your overall body mass, the higher your basal metabolic rate will be. In contrast, the larger your overall body mass, the lower your mass specific metabolic rate. This inverse correlation is a direct result of an overall decrease in oxygen consumption and carbon dioxide emission per gram as your weight increases. This decrease in respiratory function is the reason why overweight individuals suffer from a variety of breathing and respiratory ailments.
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