Everybody knows exercising is necessary and important to keep our health. How much exercise do we need? The exercise intensity is 100% when we are out of breath and can't move anymore. It is said that, in the case of 50% exercise intensity, we need to do aerobics for 30 minutes a day 5 times a week. Or in the case of 70% exercise intensity, we need to do cardio for 20 minutes a day three times per week. Unfortunately, many people find it hard to have time to exercise on weekdays. From the result of some experiments, it is recommended that we use a bicycle when we go to school, go to work and go shopping. Most exercise intensity from walking is less than 50% and it is not good enough to strengthen our health. On the flip side, the exercise intensity is more than 60% while cycling. That's because the intensity increases drastically when we pedal a bicycle up the hill and the start. Pedaling a bicycle in a high-speed rotation with a light gear is a key to keep over 60% exercise intensity. It is said that the number of rotations we pedal without thinking is between 55 and 60 per minute. According to experiment result, the proper number is between 70 and 75. I usually drive to work on weekdays, and it might be time for me to switching to cycling in the future.