If exercising by yourself whether walking, jogging, running, cycling, circuit training etc, use these guidelines as your own test of intensity. if you DON’T  have access to a heart rate monitor.

BORG INTENSITY CHART

1. Am i feeling any exertion. 2. Is it extremely light exertion.
3. Is it very light exertion. 4. Is it light exertion
5. Is it somewhat hard. 6. Is it hard.
7. Is it very hard. 8. Is it extremely hard
9. Is it maximal exertion (anaerobic)
The fuel for an ‘anaerobic’ exercise is creatine phosphate. No uptake of oxygen occurs. The intensity of effort is 95-100 percent of maximal explosive effort, e.g. 100 metre sprint, and the duration of this energy system in the body is 1-10 seconds of explosive work.

The recovery period is 30 seconds to 2 minutes. So our WHO (World Health Organisation) daily exercise requirements (300 minutes per week) would not require number 9 (anaerobic) on the Borg chart above, however the the WHO say that short bursts of vigorous intensity within your daily exercise routine, will increase your Cardiovascular health benefits.

If your aim, is low to medium intensity exercise (aerobic energy system) using carbohydrates and oxygen and working up to 70 percent approximate maximum heart rate intensity, then use above guidelines from 4-7 on the BORG CHART
4. Light exertion. 5. Somewhat hard. 6. Hard, 7. very hard, and increase the frequency from which you move from 3 to 7.
Exercising three times a week with varied intensity, will significantly improve your cardiovascular endurance (fitter heart and lung functioning).
The WHO recommendations are to aim to accumulate 300 minutes per week, 150 minutes moderate intensity and 150 minutes vigorous intensity,
and that some of these minutes and intensity can be achieved during our daily/weekly routines.

NOTE: Your maximum heart rate, based on someone who has a low weekly exercise intensity can be roughly calculated by subtracting your age from 220, so a 40 year old in the above category would have a maximum heart rate of approximately 180, which means that no matter how intense the 40 year exercises, or runs for a bus, his max heart rate will not exceed 180 beats per minute.

So for training/exercising purposes, and to improve his cardiovascular endurance, the 40 year old should exercise at between 70 and 80 percent of his maximum heart rate, i.e from 126 beats per minute to 144 beats per minute,