If you're a beginner, you must have heard of interval training - a method of training in which you step out of your comfort zone for a certain period of time and then rest. The reason why interval training is so popular is that working out at higher levels of intensity helps you develop endurance faster and helps you burn more calories, which is great for losing weight.

Interval training is popular among athletes ever since the birth of fitness. They combine a short phase of intensive exercise on speed and long recovery phase, repeated during exercise. An early form of interval training - fartlek ("speed play") – was incorrect; the runner just increases and decreases the tempo at will.