Lower back pain accounts for more than half of all reported on-the-job ailments, escalating from a personal challenge to a broader societal challenge. Researchers have developed a power assist suit intended prototype to reduce the incidence of lower back pain in the workplace when process automation is not possible. Equipped with two pneumatic actuators, the prototype suit is lightweight, flexible, and efficient. The prototype suit can assist human motion using passive and active forces. In this study, researchers confirmed the effectiveness of passive assistive force. Two types of motion were considered: lifting and unloading in a crouching position and carrying. Researchers first analyzed the subject motions using video analysis software. Waist joint loads were estimated using motion analysis results and a human link model. Second, researchers determined the power assist suit's operational parameters and developed a power assist suit model. Lastly, researchers confirmed the passive force prototype suit's effectiveness based on measured changes in generated force and electromyography.