The 400-meter dash is one of the longer sprints, requiring aerobic as well as anaerobic fitness. This means that you need to include both types of exercises in your training regimen. The exact breakdown of anaerobic and aerobic training will vary based on the season and your training goals, so be sure to discuss your plan with your coach.
Pure endurance running is the simplest aerobic exercise. This can be as straightforward as going for a steady-state run for 15 to 45 minutes. Tempo runs are another aerobic exercise that benefit a 400-meter runner. Run a tempo run at a comfortably hard pace with short rests. For instance, you might run 200 meters and rest for two minutes, repeating this exercise eight times. If you can't recover in two minutes, you are running too fast, pushing yourself into the anaerobic zone.
To improve your anaerobic fitness, you need to run hard and fast. Do this with fast repeats and long breaks. Your sprints should be anywhere between 100 and 600 meters. If you run a shorter sprint, do more repetitions and if you run longer distances, perform fewer reps. For example, you could run 100 meters and rest for five to 10 minutes for 10 repetitions. Alternatively, you could run 400-meter repeats, doing so twice with a 10 minute break between repeats.