Doing weighted chin ups is usually done in one of three ways. The first involves using the lower body to apply weight while pulling the body up to the bar. The second utilizes a dip belt and the third suspends a dumbbell in between the ankles while hoisting the body.
Normally, one would keep the body straight and rigid during chin ups. This is a requirement for people who are just starting to do the exercise and people who do not have enough muscular strength. The reason behind the restriction is that when the lower body is bent upwards, the tension in the region of the buttocks and knees can increase the weight of the body beyond safe limits for the strength of the person training himself.
The usual way to use the body to perform weighted chin ups is to bend the knees prior to hoisting the body up the bar. This builds tension in the arm and shoulders and provides protection against spraining and dislocation. Then as the body moves upwards, the buttocks are also bent by swinging the upper legs forward until they are parallel to the ground. When the body is lowered, the buttocks slowly unbend by bringing the upper legs straight down. The knees, however are kept bent throughout the session.
A dip belt is a wide band of leather or some other durable material. At both of its ends, a chain is usually attached. On that chain it is possible to add or remove weights and adjust the downward force during chin ups. The band of the belt is wrapped over the buttock region of the body and fastened loosely in front to keep the belt from falling off. The chain and suspended weights are allowed to hang down in front.
At the start of the routine, the lower legs are bent backward while the upper leg remains vertically oriented. The lower legs are kept in that position as the body is pulled up and brought down until the exercise is done.
When doing weighted chin ups in this way, it is better for the person training to have an assistant. The role of his helper will be to place the barbell shaft in between his ankles prior to lift off. There should also be some allowance below to keep the barbell from going horizontal when the body goes down. The routing is done in the usual way chin ups are performed, with the body held straight and still as it goes up towards and down from the bar.
Exercise buffs have come up with many variations on the basic weighted chin up techniques. Some people wrap heavy chains on their body. Others suspend the dip belt on their shoulders rather than on their hips. People who feel the need to develop the muscles of the abdomen suspend weights on their thighs and bend the upper legs forward for support. An amusing and fun way to do weighted chin ups is to seat a smaller person on the upper legs which are bent slightly forward while doing the exercise. The feet have to be crossed to prevent the passenger from falling through the legs of the person training.