According to your situation, your legs are shaking because your leg muscles are weak or have no endurance. It means that your training method is wrong. As the saying goes, if you don't practice martial arts, you will get nothing!

You should practice like this:

Practice time, three times a day, half an hour each time, can improve muscle endurance. Learn to adjust your breath when you squat, so that you can exercise your muscles and bones, and practice lifting your legs and stretching your muscle ligaments after each squat. This exercise can improve the endurance of muscles and ligaments. After stretching muscles and ligaments, you can jump 200 meters. This is the explosive force of practicing muscles over time. You can put something on your hands and shoulders for weight training. As shown in the picture: according to my method, after three months of training, you can succeed!