How do Cardio “Zones” work?


I’ve been cycling a lot and I always end up in Zone 3 or 4. People say Zone 2 is the best and the “fat burning” Zone.

Does this mean I’ll lose more fat/weight in the same amount of time exercising if my hear rate is lower than it has been!?

In: 8


They don’t. They are a gross simplification of a very complex topic. There is no universal rule that “X beats per minute means fat burning, Y beats per minute means cardio health”. They are general guidelines for you to consider, but don’t spend too much time focused on them.

The idea is that your body burns different things for energy based on how hard you are working. They are actually two very different chemical reactions, taking place in two different parts of the cell.

In the aerobic zone, your body is using fats and proteins as the primary fuel source, while in anaerobic zones you are using glucose.

Your heart rate is a decent approximation of which of these two fuel sources you are using at any given time. If you are in Zone 1 thru lower Zone 3 you are going to be mostly aerobic; if you are in higher Zone 3 thru Zone 5 you are going to be mostly anaerobic.

Now, don’t assume that means that aerobic is better for weight loss. While it uses a different fuel source, it also uses _a lot more_ of that fuel, forcing your body to convert stored fats to sugar to provide that energy. There are some studies that show things like HIIT are great for weight loss, and that is anaerobic exercise.

So, the short story is that both have a place in your workout routine. Go hard some days, go easier others.

Generally, the harder you work the higher your heart rate and the more calories you burn. So zone 2 will not burn calories faster.

The zone advice is more about pacing yourself. For a given calorie burn, you may find zone 2 significantly more *pleasant* than burning the same number of calories at a higher heart rate. It will take more time, but you’re also in a better position to use that time thinking, chatting, or being entertained rather than just focusing on how exhausted and winded you are.

What are you using to determine your zones?
Your zones change as your fitness changes so you really need to be doing a FTP test if you are making progress.
This is where a power meter becomes important.