The distance, 400 meters long, is the longest sprint. To learn how to run 400 meters, you need to train your legs and be able to correctly distribute forces over a distance.
400m leg workout
It is important for any sprinter to have strong legs. Therefore, at least half of the training time must be devoted to general physical preparation for training leg muscles.
For this, such exercises as: squats, squats with a barbell, “pistol”, lunges with a barbell or dumbbells, foot training, stepping on a support with dumbbells, leg press, etc. are suitable. You can alternate them in different ways, but after doing 5-6 repetitions, you need to run 100-200 meters for a hitch. Then continue to exercise.

It is important to stop strength training no later than 2 weeks before the race itself, otherwise the legs may not have time to “scatter”.

Explosive strength training for the 400m
Explosive power is essential for a quick start. Since 400 meters is a sprint, though long, a quick start is no less important than passing the entire distance. He trains with jump work. Such exercises include high jumps, “frog”, jumping on a support, jumping from a place, jumping from foot to foot, jumping rope.
As well as in the case of leg muscle training, jumping exercises must be “diluted” with periodic runs. It is best to stop jumping work no later than one and a half weeks before the start.

Speed ​​endurance training for the 400m
Speed ​​endurance is the most important component of running this distance. It is very important after gaining speed at the start to keep it until the very finish. It is best to train speed endurance by running segments of 200-400 meters 10-15 times with little rest.
Here are examples of work options to increase speed endurance:

10 x 400m, rest 3 minutes or 400m easy run
200m 15 reps, 200m rest with easy run or walk

20-30 times 100 meters with a rest of 1-2 minutes.

There are many options, the main thing is to understand the principle itself. It is also important to understand that for such a distance there is no need to run longer stretches, say 600 or 800 meters, since this is already a workout not of speed, but of general endurance, which is more needed for intermediates, and not sprinters.

Tactical understanding of how to deploy forces at a distance of 400 meters
Very often, inexperienced athletes, and often professionals, make mistakes by starting very quickly. But there is no strength left to the finish line, and such runners are overtaken by those who spread their strength more competently.

In running 400 meters, it is important to know your strengths and understand how fast you need to run the distance so as not to “fall off” at the end of the path. There is only one way to understand this – by running this distance. That is why competitive experience is important for an athlete.
You can build one of the strength endurance workouts so that at the beginning of the workout after the warm-up, immediately try to run 400 meters to the maximum strength. Then you will understand how fast you need to run. This can be done no later than 1.5 weeks before the start.
It is best to decompose the forces at a distance as follows:

– Starting acceleration of 50-60 meters in order to take an advantageous position at the curb and accelerate your body from a resting position as quickly as possible.

– After that, look for your maximum speed at which you understand that you can cover the entire distance. So run 200-250 meters

– 100 m before the finish line, start the finishing acceleration. Here the task is to move your legs as quickly as possible. Increasing the frequency of manual work will also help with this. Even if the work of the hands goes faster than the work of the legs, the legs will still try to “catch up” with the hands, and the speed will be faster.
Even without physical training in just a month, you can show a good result at a distance of 400 meters. It is advisable to train 4-5 times a week, alternating the load. That is, today you train leg strength, tomorrow you do jumping work, and the day after tomorrow you train strength endurance, after which you return to leg training. Two weeks before the start, exclude strength work from the legs and leave only running and jumping. And 1.5 weeks before the start, remove jumps and leave only running. Three days before passing the standard or before the competition, leave in your training only a couple of runs of 100-200 meters and a good warm-up and hitch.