The strict training of the side of the body, especially the side waist, is never new. If you look at the heroes of ancient Greece or Rome, you will find that they all have impressive scalpel like oblique muscles and side waist. Those sculptures are based on athletes or soldiers who need strong side muscles to throw discus or javelin.
Don't forget, these are the first battlefield weapons. In ancient times, sports ability and combat ability can be basically equal. The thin and underdeveloped waist was what ancient Greece despised. In those days, if you didn't have strong oblique muscles, you wouldn't be a man. Writers often talk about the "perfect figure of ancient Greece" with broad shoulders and narrow waist. But in fact, the small waist as a symbol of masculinity, this has never been a Western point of view.
The importance of strong sideways is not limited to soldiers. The whole body around the trunk is surrounded by strong muscles, which is very important for the high-level force confrontation of real weapons. Some people who come out of the gym seem very strong because they can lift heavy barbells, but when you ask them to help you move, they can't lift a refrigerator or TV, which is far less heavy than their barbells.
Why? Because the weight in the gym, whether it's the equipment or the barbell, is symmetrical and balanced. But in real life objects such as tables, it's almost impossible for people to lift them in a "balanced" way. There will always be a heavier side. In the process of lifting, the distribution of weight may also change randomly or fluctuate. The muscle bullies out of the gym have strong front and back muscles, but their side muscles are the weakest.
The strong in the old days knew this very well. They have never cast iron adjustable dumbbells avoided training the muscles on the sides of the waist and buttocks like modern weightlifters. Their daily exercises include one arm push, one arm pull and so on, which can create a very strong side waist. A century ago, the legendary Arthur Saxon performed 370 pounds (167.8 kg) of curving one arm push on formal occasions, while he completed 385 pounds (174.6 kg) on informal occasions.
Can you imagine how powerful his hips and flanks are? In modern times, you'd be very lucky to find a top weight lifter who can do his average weight bent one arm push. One thing I'm quite sure is that Saxon doesn't need anyone to help him move.
Strong side muscles are also important for self weight skills. Look at the stunts performed by the acrobats, or look at the gymnasts who jump on the horse. As long as the legs extend to the side or support the weight, all the waist and hip muscles will participate. Due to the length and weight of the legs, this shows that strong side waist muscles are indispensable.