This test is used to evaluate the durability of the sample to withstand horizontal forces applied to the backrest over time. The test applies to backrests with a height greater than 8 inches from the seat. The sample will be secured without inhibiting movement of the back and arms. For backrests greater than 17.8 inches from the seat, the force will be applied 16 inches from the seat. For backrests less than 17.8 inches from the seat, the top of the loading device will be flush with the top of the backrest. The loading device will be attached and initially apply a force 90 degrees in relation to the backrest to all seating positions simultaneously. A force of 75 lb. will be applied to each seating position for 120,000 cycles. The cycle rate will be between 10 and 30 cycles per minute and each seating position will be loaded will 225 lb. of dead weight.