Changes

In an ideal world, we’d be able to easily measure our running economy [[Running Economy]] and see if things are improving. If we could measure our breath, find out how much O₂ we consumed and how much CO₂ we produce, we’d know how much energy we burned (and from fat or carbohydrate). Sadly, this is not practical, so the best measure we have of energy consumption is our heart rate. This is far from perfect, as heart rate can vary for other reasons besides supplying O₂ for energy production. However, I believe it is a useful approximation.