Air walkers are widely used fitness equipment among the elderly, offering benefits for improving physical fitness. However, improper handrail usage behaviors are frequently observed during actual use, which may increase potential risks and even lead to injuries. This study aims to investigate the primary factors influencing improper handrail usage behaviors among elderly users and their mechanisms of impact. Field observations and data analysis identified Forearm Resting (FR) as the most common improper handrail usage behavior among elderly users. Further analysis of usage data from two fitness routes and comparisons of facility parameters revealed that handrail height is the critical factor contributing to behavioral differences. Interview results indicated that comfort perception in different postures is a major determinant of behavioral choices. Subsequently, JACK simulation was used to explore the specific effects of handrail height (106 cm and 95.8 cm) on comfort. The results showed that handrail height influences comfort by altering low back (L4/L5 spine) compression forces under different postures, which may in turn impact handrail usage behavior. At lower handrail heights, elderly users were more likely to adopt proper handrail gripping behaviors due to the significantly increased lower back discomfort in the forearm resting posture. This study provides valuable insights to guide the design of air walkers for the elderly.