This is an important part of the Japanese Human/Samurai determination process.
You see, by the time World War 2 had begun, the Japanese had already invented the atomic bomb decades ago. But when they sent their samurai scouts in to the U.S. to investigate the country before unveiling their new weapon, they discovered their was a large population of Americans who considered Japanese culture to be the greatest thing on this Earth. These people were called "Weeaboos," and when the Japanese heard of them it brought tears to their eyes. Unable to bring themselves to kill their allies in spirit, the Japanese realized the only solution would be to intentionally lose World War 2. Thus allowing them to bide their time until they could find a way to ensure the safety of their great brothers in Desu.
But their plan did not unfold as they had expected. Instead of being granted a steady military defeat, a group of cold and unfeeling scientists in America stole the Japanese plans for the atomic bomb, and used it to make their own weapons of mass destruction. But unlike the Japanese who planned on only using the atomic bombs as a means of displaying military dominance, the heartless Americans chose a more sadistic route. The Japanese were informed of the American's plans to bomb two of their cities, but they were unable to act on it. For they knew that if they did, it would blow the lid off their secret Samurai Rekindling operation. Seeing no other option that would convince the Americans that their loss was genuine, the Japanese realized the only thing they could do was allow the Americans to go through with their plan, as if they never knew a thing. The American's loaded two atomic bombs in to their bomber aircraft's and deployed them on two high-population cities, which resulted in the deaths of hundreds of thousands of Japanese civilians. This horrible and pointless act of bloodshed was enough, the Japanese knew that they could now surrender without the U.S. being suspicious. And with that, World War 2 came to an end.
As a result, many of the Japanese' samurai operatives and Desuian spirits were lost. Because of this, Japan must now wait for the day to come where their mighty samurai army is ready to rise again. And only when the day comes where that army is great enough, will they reveal their true power. And in doing so, we proud weeaboos will be taken in to Japan's bosom. And we will be granted safety as the world is reborn, in to the glorious land that will be known as... THE UNITED STATES OF JAPAN!
And that's the story of how Weeaboos saved America, and how Japan purposely let the U.S. win World War 2.
At any rate. This intense form of physical training is a way to weed out the mortals from the samurais. Which is important for Japan in rebuilding the great Desuian army.