I need to do CV for at least an hour a day to stay in the fat burning zone. False.
Traditional theories show that our bodies use the most fat as a fuel source during exercise up to 60% of our maximum heart rate. In the gym or park this roughly equates to a steady pace that can be maintained for some time, leaving the participant breathy but not breathless. Although for the average person this is true recent studies show that for different individuals the point at which fat burning decreases as intensity of exercise increases varies greatly. Some subjects tested were still burning a relatively high proportion of fat right up to maximal effort (90% of maximum heart rate) while others went anaerobic (making energy without using fat or oxygen) at 40% of maximum heart rate. So although the theory can be true for many, the rule of thumb is that intensity wins over duration. Doing interval training or exercising at a higher intensity for less time (20 minutes for example) will not only make you fitter faster, leave you burning calories after exercise for longer (afterburn) but will also burn more fat. Although you are burning a smaller percentage of fat at this higher level, it’s a smaller percentage of a much higher total of overall calories burned. It’s like selling 50 t-shirts at a profit of £5 each (low intensity) as opposed to selling 100 t-shirts at £3 each. Exercising at a higher intensity for a shorter time also has the advantage of fitting into the day a bit better.