Fitness articles

Energy Expenditure

28/01/2011by in ,

When dealing with the area of managing body fat levels we must have a basic understanding of how energy is balanced in the body. We consume on average anywhere from 1500kcals – 2500kcals per day.

So what about expenditure? The 3 main components of energy expenditure are:

1. resting metabolic rate (RMR)
2. thermogenic effect of food
3. exercise, or daily physical activity and spontaneous physical activity.

The vast majority of daily energy expenditure (EE) in the average person is accounted for by RMR. Thermogensis contributes about 15% and daily physical activity is the most variable being around 10-25%.

Resting Meabolic Rate (RMR)

RMR is the sum total of energy needed to keep the body going at rest. It can be likened to an idling engine. Body size is also related – a bigger person has a generally higher metabolic rate.

There are 2 basic factors which determine metabolic rate at any given moment: the number & size of respiring cells, and the metabolic intensity of those cells as determined by the work being done and how efficiently energy transformation occurs to meet the body’s demands.

The main determinants of metabolic rate are fat free mass (FFM), fat mass (FM), age and sex. A determinant is a factor which explains differences in metabolic rate between individuals.

Thermogenic Responses

Thermogensis describes increases in MR above RMR in response to things such as food intake, exposure to cold or heat and the body’s physiological responses to fear and stress.

Increasing RMR resulting from the energy costs of digestion, absorption, transport, metabolism an storage of food consumed. When the processes are complete, MR returns to the pre-meal state.

Energy Cost of Physical Activity

The energy cost of physical activity can account for significant energy expenditure in very active people. There are different ways of categorising movement, but one helpful way when looking at whole populations is to divide it into occupational, recreational and incidental physical activity. Occupational activity has been declining for decades as automation and energy saving machines continue to increase. Recreational activity is that chosen by a person to do in his or her leisure time. Incidental PA is essentially all the rest of the movement and is activity such as fidgeting, arm movements, getting in and out of cars and so on. There is no information about changes in incidental exercise, but it seems highly likely that energy saving devices that are used today add up to a sizeable decrease in incidental physical activity.