A cart had been loaded with 2"x4"s. The cart has two wheels in the middle, front, and back on both sides. The day shift had used half of the lumber, pulling the lumber from one side. Approximately 40 2"x4"s remained stacked on the other side of the cart. The second shift employee started to move the cart to his saw, where he cuts the lumber to specified lengths. As the employee was moving the cart, the cart fell over onto the employee's legs breaking both legs below the knee.