For those who do just one sport tracking your level of exercise is much
simpler and is often done with something like miles per week, or yards
swimming. Of course this simple measurement doesn't take into account
things like speed but it is sufficient for most people. When you
have multiple sports, such as the triathlete, tracking your progress is much
more difficult because a mile swim is a lot more than a mile running and
much more than a mile cycling.

One method is to equate different forms for exercise with the number of calories burned. Here are calorie calculators for cycing, running and swimming. Try to put your weight in each and pick one hour for the time, and your the best pace you can do for an hour. How many calories do you burn for each type of exercise? Are the results the same for both running and cylcing?

Estimate the calories you burned cycling:

Pace:

Weight:

Time:

Estimate the calories you burned running:

Pace:

Weight:

Time:

Estimate the calories you burned swimming:

Pace:

Weight:

Time:

The above calorie calculators are basic and will meet the needs of most people. For a more sophisticated cycling calculator, see Bike Calculator

Things are somewhat complicated because of the impact of wind resistence in cyclinging, which is a factor of square of the speed. But if you keep things on an hourly basis and you are putting out the same amount of energy for each sport, you would think you would get equivalent exercise. If I do this exercise of estimating calories for myself I get about the same number of calories burned in one hour, either cycling, running or swmming. That is one reason why cycling has helped me lose weight. I can cycle for many hours in a day but I can not run that much day after day

Here are all the methods I have used to attempt to equate different forms of exercise with each other, starting with the least accurate to the most accurate.

Total Exercise Hours. It is the most simplistic approach since it does not
factor in the intensity of individual exercises or the variation between
sports on energy expenditure per hour. However for most people it fully meets their needs.

Equivalent Miles. Some research shows that I can convert to equivalent running as follows: road cycling divide by 4, mountain bike divide by 2, swimming multiple by 5. This is not the factors you would obtain using the above calorie calcualtors, but my experience show this to be a relatively good, if simplistic, approach. Even within one sport, such as cycling, it is not just miles that impact how much you put into the route, but also speed, terrain and the wind. Unlike running, in cycling air resistance is a factor and since it increase by the square of the speed, as you increase your speed, the energy required increases much faster than the miles covered in a given period. Some work was done by Dr. Edward Coyle of the University of Texas. He determined the amount of oxygen consumption by cyclists, as a function of speed. The Divider is the factor that would convert cycling miles to running mile and equates the to the factor of "4" I suggested above for road cycling. Your speed, size, and terrian will have a bearing. I am working on some calculators that take into consideration climbing to get an estimate.

Cycling Speed Calorie Conversion

MPH

Cal. per mile

Divider

10

26

4.2

15

31

3.5

20

38

2.9

25

47

2.3

30

59

1.9

Total Calories Expended. Using the above calculators for the
amount of calories burned for each exercise session you could just add them
up since a calorie is the same regardless of sport. Or if you have a Polar Heart
Rate Monitor or other sophisticated heart rate monitors, they will give you a better estimate because it measures your
heart rate and the time of the exercise.

Total Exertion Units. The most sophisticated method I have found
is offered by some of the Polar heart rate monitors, called Total Exertion
units. You establish a factor for each of the heart rate zones and the
units are calculated by multiplying the time in that zone by the factor and
summing them up for the entire exercise. This not only gives you a
better way of seeing your total exercise, but it is useful for knowing what
recovery time you need. Of course to use this method you have to be
using the HRM for all exercises. Since I do not always wearing a HRM,
sometimes I estimate the exertion units based on the average heart rate and
time exercise.

A comparision of the four methods

Although the above chart does not mean that each of the four methods give you a real measure of equivalent exercise, what it does show is that for most people the variation between method is not that significant looking at an annual basis.