The weight varies from person to person. I'll tell you a basic principle: the weight tied to your feet should ensure that your legs can take the biggest step when running like no load! This will not affect the length of your steps. You can't walk with a heavy sandbag, which will affect the length of your steps and the flexibility of your lower limbs more or less, and affect your speed as a whole. If each step can be 10cm long, the total time will be much less and the score of 800 meters will be much better. There is also the problem of muscle contraction speed. The faster the muscle contracts, the faster the movement will be, and the slower the muscle contracts, the slower the movement will naturally be. Therefore, when you increase your weight, you must be able to ensure that you have the ability to increase your speed when running, so as to improve the contraction speed of your muscles, thus achieving the effect of improving your running speed. Finally, I will tell you a training principle of explosive force: when training explosive force, we must use explosive force to complete the action, and explosive force is the key to improve the speed.