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!?
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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.
Some of this will be slightly wrong, but this is ELI5 so:
The body has two different types of fuel available, *fat* and *carbs*.
Fat has very efficient storage, it can store a lot of energy in a relatively small volume. It’s slow though, since it’s so efficiently stored, it takes a while to “unpack” it before the energy can be used.
Carbs on the other hand take up a lot of space, and stores a relatively small amount of energy. But this energy can be utilized very quickly, and is ready to go whenever.
At rest we get almost 100% of the energy we need from fat, like I said it’s not fast, but it’s fast enough. A “cardio zone” is basically just a ratio between fat and carb usage, since as we increase the workload, we need to access our stored energy faster, and fat alone isn’t fast enough to keep up.
Why do we care about this? Most of us shouldn’t really, because it doesn’t matter. Our bodies will spend the hours/days after a workout returning to status quo, so it doesn’t matter if you spent 90/10 or 30/70 fat/carbs *during* the workout, all your body will remember afterwards is how much energy was used in total.
I said most of us, some people do have to care. If you’re competing in some sport, you might want to spend as much carbs as possible (because more carbs = faster energy = better performance), but you don’t want to “run out”, because being left with nothing but fat at the end of a race is not a winning strategy.
Zones 1-2 are primarily fueled with fat and some glucose stores. As you go higher in intensity/heart rate (Zone 3-5), you start “maxing out” your aerobic system and the glycolytic system kicks. This is how you compensate for the mismatch between energy supplied and energy needed. However, a side effect of glycolysis is lactate + Hydrogen ion production. So the higher the intensity, the more glycolysis, the faster you reach muscle failure.
Training in zone 1-2 is essential for building up your aerobic system, which in turns determine how hard you can work without requiring the glycolytic system to kick in. A strong aerobic system also helps with removing the lactate/H+ from your muscle. Even the strongest endurance athletes (Tour De France riders, for example) will spend the vast majority (up to 80%) of their training in Z1-2 depending on their training cycle.
Hope that helps!
As far as weight loss: There are no real zones. Calories out is calories out. Period. The only reason it’s considered “fat loss” zone is because it is easier to maintain for longer periods and lower impact on your body.
There is literally no difference in burning 400 calories in 30 mins at a fast pace, and burning 400 calories in 2 hours at a walk.
If you are talking heart and cardio vascular health, 30 mins or more at ~150 bpm can improve your health health and lower blood pressure
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