It depends. Surprised by that answer?
When scheduling my athletes, a lot of it comes down to the individual. What are their goals, current fitness level, and time commitments outside of training?
There is no right or wrong answer to this. Both can give you results if you’re using them right.
I have seen great improvement and confidence growth in using training by time for athletes who are just getting back after a baby, injury, time off running, or burnout. For example, instead of getting overwhelmed by a 4 mile run when you’re just not feeling it, set a goal for 40 minutes. Just move your body for 40 minutes. You can walk/run if you need to. It’s a good way to get those shoes on and get out the door. Oftentimes, you’ll end up surprising yourself in a good way!
If you’re chasing a PR in a longer distance (think 10K +) running by mileage tends to work better. You know what your splits should be to hit your goal. In a race setting (side note, I can’t wait for those again), adrenaline runs high and it’s easy to go out too fast. Knowing your pace per mile helps you reign it in so you can finish strong. It also helps most runner’s confidence to know they can run a certain number of miles of a race going into it.
Which do you prefer? Why?