It is clear that exercise is good for you, but what are you trying to achieve?
Weight loss? General Fitness? Running a marathon? Dragon Boat Racing? Boxing? Triathlon?
If you want to lose weight as your primary goal, fat burning requires oxygen. This means much less intense exercise than it takes to train for a Triathlon. If you train at the wrong pace you won’t achieve your fitness goals efficiently, no matter how hard you work.
Fat burning needs oxygen. If you are exercising too hard,or too fast you can’t get enough oxygen into your lungs and then blood to allow fat burning to happen.
When this happens your body switches to burning carbohydrate stores, known as Glycogen. Glycogen can be used without oxygen and when we run very fast or play intense sport we burn up glycogen. This is known as anaerobic (or without oxygen) exercise. However we can only go flat out for a short period of time before we have to stop. This exercise is mainly used for extreme exercise such as life threatening, flight or fight responses. Glycogen is a very heavy form of energy storage for us compared to fat. 1 gram of glycogen releases about half of the energy that 1 gram of fat does but also needs needs an extra 1 gram of water to store it in our bodies.
So if your main objective is to lose weight, then your exercise should be mostly long slow sessions of things like, walking, swimming and cycling. A good rule of thumb is you should be slightly out of breath but still able to talk easily.
If you want to get fit for a more active sport, then you have to train with high intensity intervals.
If you want to do both then you should vary your training accordingly.
Remember you need carbohydrate in your diet to replace the Glycogen that you burn up during high intensity training.
Also remember to be safe and check with your doctor before doing any training.