EXERCISE INTENSITY

To derive health benefits the national guidelines recommend using exercise to burn about 1,000 Calories per week.  For weight loss and even greater health benefits an expenditure of 2,000 Calories per week is suggested. This is equivalent to about 1600 MET minutes per week. (for more about the meaning of METs see my previous blog “Exercise and Oxygen”  and also the glossary page of this site)

Measuring exercise intensity

Unfortunately it is not easy to measure exercise intensity or dose however we choose to do it or to express it. Very few exercises are sufficiently independent of the effort we put into them or our skill in their performance to predict an amount of energy which is more or less the same for everyone. Those which are predictable include walking, cycling and running – on the flat without a wind. For most other exercise we can only give approximations of energy expenditure. For instance it is possible to give rough estimates of the energy costs of playing tennis or of various gym activities but they will be very dependent on the amount of effort put into the activity by the performer.

Using modern accelerometer devices (Fitbits and the like) should allow more accurate estimates of the amount of exercise taken. They would have to rely on heart rate responses and would need to be calibrated for the individual to produce anything like accurate measures of energy expenditure.

Light, moderate and vigorous

The DoH guidelines refer to light, moderate and vigorous exercise. For general purposes, light is less that 3 METs, moderate is between 3 and 6 METs and vigorous if more that 6 METs.

Here is a table of energy expenditure for a number of different activities:

Physical activity	MET value	VO2 ml/min/kg	Cals/hour
Light intensity activities	< 3
Sleeping	0.9	3.1	63
watching television	1.0	3.5	70
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 at 50 watts	3.0	10.5	212
walking 3.0 mph (4.8 km/h)	3.3	11.5	233
playing golf	3.5	12.2	247
calisthenics, home exercise	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
doubles tennis	5.0	17.5	353
heavy gardening	5.5	19.2	388
bicycling, stationary, 100 watts	5.5	19.2	388
sexual activity	5.8	20.3	409
Vigorous intensity activities	> 6
jogging	7.0 +	24.5	494
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
rope skipping	10.0	35.0	706

 

This table can only give a very rough estimate of the energy cost of these activities – a guide to the cost to the average sized individual making an average effort. More detailed estimates can be found elsewhere. You can 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 exercise¹.

Walking

The exercise of which most people do most is walking – and very good exercise it is too. Brisk walking is all you need to satisfy the recommendations of the health gurus so here is a table giving you the exercise intensities of walking at different speeds. The figures given are for walking on the flat with neither a following nor a head wind. The MET values are the same for everyone irrespective of weight. The Calories consumed column is for a 70kg (11 stone) individual. Lighter people will expend fewer calories and heavier people will expend more, so one advantage of being overweight is that the heavier you are the easier it should be to lose weight:

 

Speed mph	Mins per mile	METs	VO2 ml/min/kg	Cals/hour
2.0	30	2.5	8.9	176
2.5	24	2.9	10.2	205
3.0	20	3.3	11.5	233
3.5	17	3.7	12.9	261
3.75	16	4.4	15.3	310
4.0	15	4.9	17.1	346

The relationship between walking speed and oxygen need is a straight line at lower speeds but above 3mph it becomes harder to increase speed – and each increment in speed becomes more costly in terms of oxygen demand. For most people brisk walking means travelling at between 3 and 4 mph.

Running and jogging

Jogging/running is the most straightforward form of exercise – it is a highly efficient way of increasing fitness, it is quick to do, needs minimal equipment and cost and does not require an opponent – and even so it can be a most satisfying social occasion. Here are the exercise intensities of running at different speeds. Again the figures presume the unlikely scenario of no hills and no wind. The calorie expenditure is that of an individual weighing 70kg (11 stone):

Speed mph	Mins per mile	METs	VO2 ml/min/kg	Cals/hour
3.5	17min	6.4	22.3	451
4.0	15min	7.1	24.9	501
4.5	13min 20sec	7.9	27.6	558
5.0	12min	8.7	30.3	614
5.5	10m 54sec	9.4	33	663
6.0	10min	10.2	35.7	720
6.5	9m 13sec	11	38.3	776
7.0	8m 34sec	11.7	41.0	826
7.5	8min	12.5	43.7	882
8.0	7min 30sec	13.3	46.4	939
8.5	7min 04sec	14	49.1	988
9.0	6min 40sec	14.8	51.7	1045
9.5	6min 19sec	15.5	54.4	1094
10.0	6min	16.3	57.1	1150

 

You will see that running at low speeds is less efficient than walking. If you wish to go at 4mph, walk don’t run!

Cycling

Cycling is another exercise for which it is possible to calculate energy expenditure. Here are the very approximate figures for the MET value, oxygen cost and calorie expenditure for cycling on the flat without wind for a 70kg (11 stone) individual. Real life conditions means that the energy costs out there are usually much higher:

Speed in MPH	METs	VO2	Cals/hour
10	5	17.5	470
12	7	24.5	514
14	9	31.5	661
16	11.5	40.2	845
18	14	49.0	1200

Next week I will write about how much exercise we need to take for good health – which is more complicated than the DoH guidelines.

1. https://www.brianmac.co.uk/energyexp.htm

PS
Dementia and exercise: The debate continues with most, but by no means all, evidence pointing to benefits of exercise in reducing the risk of dementia and in treating dementia once it has developed. A new study supports this view. It found that Individuals at risk for Alzheimer’s disease because of family history or genetic predisposition who engaged in six months of aerobic exercise training improved their brain glucose metabolism and higher-order thinking abilities (e.g., planning and mental flexibility) called executive function; these improvements occurred in conjunction with increased cardio-respiratory fitness². I will discuss the evidence for and against in a future blog.

2. DOI: 10.3233/BPL-190093