It is recommended not to use sandbags. If you don't stick to it for half a year or longer, it won't have any effect, and it will not only be inconvenient at ordinary times, but also affect growth and joints. Maybe it will cause total strain arthritis, which will be quite troublesome in the future. If you want to improve significantly, you'd better go to the gym to consult the coach. Jump more at ordinary times, and it will be fine naturally. This kind of thing will not happen soon.