Most people have heard of Zone 2 and the importance of staying in this zone for certain training sessions. But how do you know if you are running in this zone? There are various tests that can be done for this, some in the lab (lactate threshold testing for example) and some you can do yourself. These will usually give you a target heart rate.
However, not everyone can get these tests done and the estimates from watches are often inaccurate.
Even if you have got an accurate heart rate to use, this is not reliable all the time. It can vary a little day to day but the biggest variations will be if you are dehydrated, or even more so, if you are hot (see my other blog regarding heat-related issues when running).
But there is another way. Have you ever noticed how you breathe when you run? You will nearly always inhale and exhale in sync with your foot strikes. Counting both feet (i.e. left and right), you might be breathing in on step 1, out on step 5 and then in again on step 9. This would be a 4:4 rhythm, 4 strikes breathing in and 4 breathing out. Or you might be breathing 3:3. This rhythm is the key to knowing what zone you are in.
A 4:4 rhythm puts you in the Zone 1/Zone 2 boundary. A 3:3 rhythm will put you at the top of Zone 2.
The beauty of this method is that this is independent of how hydrated or hot you are. Why? Because your breathing is determined by how much CO2 you have in your blood – this is a direct result of how hard your muscles are working. Even if your heart rate increases during a hot run due to cardiac drift, if you keep your breathing at 4:4 or 3:3 then you are likely to be in Zone 2.
Next time you go out for a run, be conscious of your breathing and see what rhythm you have. If you already know what your Zone 2 heart rate should be, does the 3:3 rhythm correlate to that?
On a side note, a cheetah is locked into a strict 1:1 rhythm when running. This is because their breathing mechanics rely heavily on the movement of their internal organs, which act like a piston to compress and decompress their lungs with every stride. At a full sprint, this forced breathing becomes incredibly shallow. A cheetah can only sustain this top speed for 20 to 30 seconds before they are forced to stop, simply because their rigid breathing rhythm prevents them from clearing the accumulating CO2 from their blood.