For example, if you have been training for a marathon and you are injured or want to reduce your impact on your body, switching up some of your workouts with cycling can help. If you are a runner who has never cycled before, you can try to improve your cycling fitness by taking a few spin classes or visit a bike shop and rent a bike for the day and see if you like it. You can also invest in a turbo trainer for your bike to train indoors during the winter months.
When comparing biking to running, the standard ratio is often used that one mile of running equals three miles of biking. This is based on the fact that cycling has a lower minimum energy expenditure than running. However, this conversion is not completely accurate, as it does not take into account other variables such as terrain and wind.
Cycling is a very different exercise than running in that it targets different muscles and requires more of a mix of movement. It builds muscle in the lower half of your body (gluteus maximus, hamstrings, plantar flexors) and in the upper body (shoulders and back). Running involves the entire body and is much more of a cardio exercise.
In addition, the kinetic energy needed to run a mile is far greater than that required to ride a bike for a mile at a similar speed. The minimum energy expenditure to run a mile is around 100-120 calories depending on your running pace and terrain.