So the leg weights as a set of weights that are worn on the legs, particularly above the ankle area. Once worn, the weight would reduce the speed of whoever wears it, sometimes too heavy even to walk. You get used to the weight by training and doing everything while putting it on and once you are back to your normal movement speed as before, you have mastered it.
By then removing the weights, your speed would drastically increase due to you already conditioned yourself to the weights. You gain 2x speed and your kick are faster than normal thus gains more power, giving you a plus twenty to taijutsu done through the legs.
Any question?