I’ve commented here before that what I like to see for intensity in base 1 (block 2) for those athletes I coach is a lot of zone 2 time. The accompanying power distribution chart for an athlete shows this quite vividly. Here you can see that almost exactly half of his training is in block 2 (he’s an “advanced” athlete). That’s excellent. It means we are developing robust aerobic endurance.
While this is a power chart, for running a pace distribution chart would look like this also. If you only have a heart rate monitor then it would be the same sort of distribution. The problem with heart rate is you don’t know what you are accomplishing since you aren’t measure output. Unfortunately, all heart rate tells you is input, which is similar to effort. You don’t win races on based on effort (input). Everyone is trying hard. You win them on pace or power (output). Knowing both input and output makes training multi-dimensional.
Keeping a watchful eye on your intensity distribution, as with this chart, is very effective at this time in the season. It keeps you focused on what’s important. If you are in the early stages of your training season then now is not the time to be doing race-intensity workouts. There’s plenty of time for that later on in the build period. The most basic ability for an endurance athlete is aerobic endurance and now is when you should be developing it.