Measuring exercise dose
Last week I explained the various ways of measuring dose of exercise and I gave some reasons for wanting to do so. For instance one use is to assess the balance between calories consumed as food and calories expended in physical activity.
The most popular measures of energy expenditure are Calories, volume of Oxygen consumed (VO2) and Metabolic Equivalents (METs) multiplied by time.
Calories expended are very difficult to measure and for most activities are estimated. Exercise intensity may be assessed as Calories per minute or Calories per hour.
Oxygen consumption can be expressed as litres or millitres but is seldom used in this way. Oxygen use, however, is an excellent measure of exercise intensity – mostly as litres per minute (L/min) or millitres per minute (ml/min). To give a measure of how hard this may feel for the individual, this is usually converted into oxygen consumed per kilogram of body weight – millitres of oxygen per minute per kilogram – ml/min/kg.
Metabolic Equivalents are measures of exercise intensity – energy use per unit of time – and are related to body weight . One MET is the rate of energy used by a person at rest. It is the energy needed to fuel all those metabolic processes which keep us alive – the work of the brain, heart and lungs, liver, kidneys, digestion etc. METs are another way of expressing oxygen use and are remarkably constant across a wide range of body weights at about 3.5 ml/min/kg. METs can be converted to total energy expended by multiplying by the time spent in that activity such as Met minutes or MET hours.
Some examples of different activities
Here is a table giving a very rough estimate of the energy cost of a variety of activities – a rough guide to the cost to the average sized individual making an average effort. You can also go on line for a calculator which will give you the energy cost of walking, running, cycling, skipping and rowing taking into account your weight, speed and duration of exercise. The true cost is always subject to the amount of effort you put into it.
|Physical activity||MET value||VO2 ml/min/kg||Cals/hour|
|Light intensity activities||< 3|
|writing, desk work, typing||1.5||5.2||106|
|strolling, 1.7 mph (2.7 km/h), level ground||2.3||8.1||162|
|walking, 2.5 mph (4 km/h)||2.9||10.1||205|
|Moderate intensity activities||3 to 6|
|Stationary bicycling, 50 watts, very light||3.0||10.5||212|
|walking 3.0 mph (4.8 km/h)||3.3||11.5||233|
|calisthenics, home exercise, light or moderate effort||3.5||12.2||247|
|walking 3.4 mph (5.5 km/h)||3.6||12.6||254|
|bicycling, <10 mph (16 km/h)||4.0||14.0||282|
|bicycling, stationary, 100 watts, light||5.5||19.2||388|
|Vigorous intensity activities||> 6|
|singles tennis, squash, racketball||7.0-12.0||24.5-42.0||494-847|
|Calisthenics (e.g. pushups, situps, pullups, star jumps, vigorous effort||8.0||28.0||565|
|running on the spot||8.0||28.0||565|
The effect of energy on body weight
Just how much food does it takes to fuel a certain amount of effort? I regret to tell you that it takes a disappointingly small quantity of food to fuel enormous efforts! One Mars Bar will provide enough energy for 40 minutes of brisk walking at 4mph for a person of normal build. An often quoted index of high calorie food is its equivalence in teaspoonfuls of sugar. A teaspoonful is just slightly over 5ml which converts to about 4grams of sugar which is worth about 15 Calories.
Next week I will talk some more about energy expenditure and health benefits.