In shot put, the athlete and the ball form a system, and the sum of MVs before and after hitting the ball remains unchanged. If you want to hit the ball faster, you need to maximize the total momentum The quality of the shot put itself is constant. Only the quality and speed of athletes can change. The larger the product, the greater the momentum transferred to the ball. Muscle athletes may have a slight advantage over obese athletes in improving speed, but there is an upper limit to the quality, that is, weight. Even a 2-meter athlete can weigh 100 kg. But the acceleration distance of shot put is too short. Even muscular athletes can improve their speed in such a short distance. Even if you die, it will increase 10%. However, obese athletes have a lot of room to gain weight, and it is easy to increase to 150kg, so the total exercise amount is 150%*90%= 135% of that of muscle athletes. Therefore, athletes with good grades are obese athletes.

Ground friction is used in the run-up stage of the acceleration ball. The athlete's speed increases to the highest at the moment before the ball is released, and decreases to zero after the ball is released. Is it because of ground friction? Obviously not, otherwise the athlete's upper body will definitely rush out, because the ground friction acts on the athlete's feet. It is precisely because the athlete's arm transfers the momentum to the shot put that the shot put gets a higher speed and the athlete can stop. At this time, even if the ground friction is zero, the athlete can still stand, so there is basically no friction or even little friction when the shot is put back to the foot.

In contrast, we can see that javelin athletes are not so fat, but after throwing javelin, athletes still have to run two steps forward to slow down, because javelin is too light to fully absorb the momentum of athletes, and the speed of athletes can not be reduced to zero after shooting, so they can only run two steps forward and slow down by ground friction.

If the arm strength remains the same, a sandbag around the waist will be effective. The heavier you are, the less you bounce when you hit the ball. However, improving self-weight also has a disadvantage, that is, automatic acceleration from zero will be slower. FL = 1/2mV 2, the force F generated by the leg and the run-up distance L are constant, and the square of the speed is inversely proportional to the mass. The greater the mass, the slower the speed, so the self-weight cannot be improved indefinitely. Every athlete should have an optimal weight under a given strength.