To maximize force in a  back handspring the gymnast starts with their arms beside their legs and then swings them backwards while bending their knees. By going into a squating position the gymnast is placing the quadracep muscle group in a take off position. Then the gymnast will follow a sequential summation of forces now; throwing their arms up very fast backwards, create an arch position in the back and then pushing off of the legs. This all happens in a split second while in the air in which the power comes from the legs as the squat position has built up kinetic energy. The arms swinging backward will create the rotation. As the hands hit the floor the back is still arched allowing for the legs to be behind the shoulders. This is ideal because from that position the legs will snap down (the rectus adominis and gluteus maximus must contract to pull the legs down). At the same time the gymnast will rebound off of the floor from their arms and push off of their hands. If the gymnast has tight and ridged arms the transfer of force will be quick and in full, but if the gymnast bends their arms then the transfer of force will be less. From there the gymnast will come to a stand or rebound for the next skill.