Forces and Postures During Child Climbing Activities

Abstract

Many children are injured every year due to furniture and appliances tipping over and displacement of objects on furniture. Injuries are due to the furniture unit falling onto the child as well as falling objects supported by the furniture, particularly televisions. Clothing storage units, such as dressers, are a common type of furniture to tip over onto children. The current U.S. voluntary standard addressing the stability of clothing storage units, ASTM F2057-19, mandates a test procedure that involves applying a 50-lb weight at the edge of an opened drawer. No studies have previously assessed the forces that children exert when climbing under conditions similar to those associated with furniture tip overs. To address this need, a laboratory study was conducted with a convenience sample of 40 children ages 20 to 65 months from Southeast Michigan. Children were directed through a set of climbing behaviors on two instrumented bars (handles) to simulate a dresser, and with a simulated drawer and tabletop. Forces and moments gathered from load cells in the test apparatus were analyzed for 1173 behavior instances. The primary dependent measure was the tip-over moment calculated around a virtual fulcrum simulating the contact point between the floor and the front of the dresser. Five climbing behaviors — ascend, bounce, lean, yank, and leaning back while supported with one hand and one foot –– were extracted from trials with a range of handle positions, and the maximum tip-over moment was computed from the handle force data. For the simulated drawer and table conditions, the moments at the time of ascent and descent were computed, as well as the peak moment during ascent. Tip-over moments in all of the handle-trial behaviors exceeded the moment associated with body weight located one foot from the fulcrum. On average, the moments generated in the ascend, bounce, lean, and yank behaviors were equivalent to exerting 1.8, 2.7, 2.7, and 3.9 times body weight, respectively, at a distance of one foot from the fulcrum. The location of the child’s center of mass (CM) was estimated in side-view images from the times of maximum moment. The results demonstrate that climbing, with vertically separated contacts for the hands and feet, enables children to exert tip-over moments that exceed those associated with the action of their body weight under their feet. Dynamic behaviors, such as stepping up, bouncing, or yanking can greatly increase the tip-over moment. In contrast, children climbing into or out of a simulated drawer tend to place their CM more inboard and thereby generate less tip-over moment than when climbing with vertically separated hand and foot placements. These data provide the first available information on forces and moments associated with child climbing behavior and may be used to inform the design of furniture and the development of associated performance standards.