Weight loss vs Cardiovascular training
The human body has 3 sources of fuel:
1. Carbohydrates – fast burning, high energy yield
2. Fat – slow burning, low energy yield
3. Protein – the body will only use protein as an energy source as an absolute last resort.
Carbohydrates are converted into glucose and stored in the body as glycogen or muscle glycogen. Carbohydrates are the prime source of energy for the first 20 minutes.
After 20 minutes is when fat becomes the prime source of energy. If your goal is fat loss, you have a better chance of burning fat if you train for greater than 20 minutes. Ideally reducing intensity (via heart rate) & increasing duration is the way to do this.
People mistake calories for weight loss. Calories are a representation of energy, so if you train at a higher intensity you will burn more calories which does not equate to fat loss.
Another school of thought suggests that if you train at a higher intensity or even do weight based training you will increase your muscle to fat ratio. This increases your metabolism which turn means you burn fat quicker and easier.