Now there’s a lot of talk about thresholds and this can be very confusing. It basically refers to whether your body is burning fuel aerobically or anaerobically. That is, with or without oxygen. The latter is when when we chew through our glycogen.
One side-effect of using glycogen is that the body creates lactic acid and (thus lactate) as a waste by-product. Without enough oxygen this cannot be removed from the bloodstream fast enough so it builds up in our muscles.
Yet whilst we talk of a threshold as if we go from burning one source of fuel to another, it is in fact a transition.
That is, the percentage of each fuel changes. It’s suggested that this is quite dramatic at a certain HR percentage yet others contend that it’s a lot more gradual.
Nevertheless, whether it’s aerobic or anaerobic it’s not all or nothing. It’s always a mix or a combination of the two.
Kim | marathon runner