A standard hospital bed frame (Transport stretcher®, 760 x2110 mm, 228 kg, Stryker Co., Kalamazoo, Michigan, USA), a foam mattress (660 x 920 x 80 mm, soft foam with polyurethane coverage, Stryker Co., USA), a backboard (450 ×600 ×10 mm, 3 kg Lifeline Plastic, Sung Shim Medical Co., Bucheon, Korea), and a step stool (395 x 450 x 410 mm, Gunica Co., Gyeongsangnam-do, Korea) were used in the experiment. A Resusci Annie Modular System Skill Reporter® manikin (Laerdal Medical, Orpington, UK) was used to perform CPR in the evaluations. We added weight to the manikin to equal 34 kg for simulating the upper body weight of an adult human as in a previous study.