ArticleIn this article, expert witnesses specializing in pediatric biomechanics and child supervision discuss the standards and guidelines relevant to playground injuries associated with monkey bars and track rides. The discussion includes background information on injury statistics, biomechanics, and child behavior that the Consumer Product Safety Commission (CPSC) and other organizations consider during the development of standards/guidelines for safe playgrounds.
The experts at Robson Forensic are frequently retained to investigate injuries and assaults that occur on public and private playgrounds. The experts involved in these cases bring specific expertise in playgrounds, complemented by a background in biomechanics, child supervision, or architecture depending on the demands of each case.
Upper Body Playground Equipment – Standards & Guidelines for Monkey Bars & Track Rides
Each year, over 200,000 children are hospitalized in the United States for playground-related injuries, with the vast majority of these injuries affecting children under the age of 12 1,2,3. Fractures are the leading diagnosis of these injuries, of which falls are the leading injury mechanism.
ASTM International establishes nationally recognized safety standards for public playground equipment. Many of these standards are also reflected in the CPSC’s national guidelines and published in the Public Playground Safety Handbook. The standards and guidelines are developed to reduce the injury risk for children as they play and to address characteristics of specific types of equipment to promote safety.
This article focuses on upper body equipment, which is defined by standards and guidelines as “Equipment designed to support a child by the hands only”4,5. This type of equipment is designed to present a greater degree of physical challenge than other pieces of play equipment5. There are many types of upper body equipment found on playgrounds, but the scope of our discussion is limited to rigid and dynamic horizontal overhead ladders, sometimes referred to colloquially as “monkey bars,” and “track rides”. Focus on these specific pieces of upper body equipment provides the reader the opportunity to understand the interaction between children as they play on equipment common to many playgrounds.
Aside from the fun it offers its users, upper body equipment provides an opportunity for a child to challenge herself in a manner that can improve muscle strength and coordination, provide a sense of accomplishment, and interact with peers. However because of the nature of the equipment’s design and the potential danger associated with falls, a child’s abilities need to be in alignment with the challenges the equipment offers. This article will include discussion of the biomechanical abilities of a child to interact with this equipment, supervision on the playground, and the standards and guidelines to prevent injury and promote safe play on this equipment.
Horizontal Overhead Ladder (rigid)
This equipment is designed to strengthen the upper body by allowing children to move across the ladder from one end to the other using only their hands. This equipment is typically seen in the playground designed for school aged children (5 to 12 years of age inclusively) but can be found in preschool settings specifically designed for the size and ability of this age group. This equipment is not recommended for use by children under 4 years of age.
Safety standards and guidelines address the placement of the hand hold or gripping device on rigid overhead upper body equipment. Standards require that appropriate spacing between the rigid overhead horizontal rungs should be greater than 9 inches to prevent head entrapment. For school aged children the rungs should be no greater than 15 inches apart when measured center to center for traversing. For preschool aged children (aged four and older), rungs should be evenly spaced and no greater than 12 inches apart4.
Horizontal Overhead Rings (dynamic)
This type of equipment is similar to the rigid horizontal overhead ladder in terms of challenge to the child5. They differ, however, in that this piece of equipment is more dynamic in nature and swings with the child as she attempts to cross from one ring to the next. The movement of the rings creates an arc that varies the distance as the child progresses down the equipment.
This form of upper-body equipment requires the child to hold onto a handhold connected to a trolley that rides in a track, allowing for sliding from one end to another when the child is pushed or swings her body forward. Track rides require significant upper body and break-away strength as the child not only has to hold up her own body weight but also resist that weight being moved in another direction. Due to the amount of strength required for play on this equipment, it is recommended for use in school aged playgrounds only. Standards and guidelines specific to track rides require that there are no obstructions along the track path or in the take- off or landing areas.
Playground Injury Biomechanics
Standards and guidelines for upper body equipment address the child’s ability to grab and hold the equipment. It is recommended that rungs or gripping devices used to hold and/or traverse overhead equipment should be round, and of a diameter that is between .95 to 1.55 inches in size4.
Recent studies have shown that grip strength alone is not a reliable indicator of a person’s capacity to hang from handholds and support their own body weight. This is due to the fact that the magnitude of the force exerted onto an object before it slips free or is pulled from the grasp of a person’s hand, otherwise known as “break-away strength,” is dependent on multiple factors that can increase the strength demand beyond the physical abilities of the child. These include handhold design, orientation, and the frictional force between the handhold and the grasping fingers, as well as grip strength3,6.
When using upper body equipment, a child relies on the contraction of fingers grasping the handholds in a hooking fashion to support her hanging body. This position necessitates a child’s hand concentrating all its contractile properties to grip the object with the fingers with just a limited set of muscles in the forearm to support the hanging body. Albeit strong, the strength of these is disproportional to the hanging weight of the body6 .The texture of the handhold, its diameter, and the manner in which the child grasps the handhold play a contributory role in the ability of the child to hold on. Varying grip orientations affect flexibility and power of certain movements such as swinging from one ring to the next.
Manufacturers must design, and facility owners/operators must select, equipment that is appropriate for the targeted age of the child who will play on it and the environment in which it will be used. The alignment of equipment with child development and anthropometric abilities is critical to injury reduction. For example, while unique handle orientations may create an appropriate challenge for older school aged children, those same features may create an unreasonably dangerous condition when used in a playground for younger children.
The nature and severity of injuries, which include but are not limited to fractures, brain injury, and even death, are influenced by factors such as equipment height, the impact attenuation and maintenance of the surfacing material under and around the equipment, and supervision.
Upper body equipment poses a greater risk for a fall from height as compared to other types of playground equipment. The greater the distance over which a child falls, the more energy and force they have when they hit the ground surface. For this reason, it is imperative that the surfacing material be adequate to absorb and thus dissipate the impact energy of the child, lessening the forces felt by the child when they hit.
The utilization of adequate protective surfacing with proper maintenance over the life of the equipment and playground proves to lessen the severity of and even prevent injuries2. Therefore it is critical to the owner and operator or user of the play equipment to be cognizant of the surfacing material under and around the upper body equipment and maintain the surfacing material in a manner that complies with standards and guidelines.
While not a substitute for safe equipment in a safe playground environment, supervised play may reduce the likelihood of injuries to children on a playground.
Supervision in a play environment takes many forms and is affected by varying circumstances including the structure and design of the playground, the type of equipment available to the children, the age of the children on the playground at any given time, and the activities being conducted in the play environment.
Every teacher or parent can note, by experience, that children of the same age may look and behave completely dissimilar due to developmental abilities and differences. These differences may be observed through gender, size, ability to problem solve, body coordination and strength, interest in risk taking, and interaction with peers. This variation in development can clearly affect the manner in which a child interacts with their play environment. As a result, adult supervision on the playground is recommended to promote safety and reduce injury.
Playgrounds are designed to meet the developmental abilities of the targeted user of the equipment. Equipment should incorporate a low risk of injury with a high degree of challenge7. It is essential for a supervisor to know the targeted age user of the equipment and be able to identify its appropriateness for the children being supervised. This is particularly important when focusing on upper body equipment as the height of the equipment and the manner in which a child accesses, exits, and uses the equipment varies with age, ability, and the anthropometrics of the child.
Supervision will vary based upon the activity on the playground. Whether an activity is facilitated by the supervisor or teacher, or an activity that involves free play, will affect the method of supervision. An example of facilitative play is when a teacher leads an activity for a specific group of children only. Supervision during an unstructured activity allows children the choice of activity and equipment usage. This free play type of activity widens the parameters and surface area of play and requires active supervisory skills that include, among other methods, circulation, attention, communication, and visual scanning7.
Supervision of children using overhead upper body equipment during free play activity, like school recess, can be particularly challenging. Educating children and supervisors on the safe usage of this equipment can not only prevent child injury but can train supervisors to identify the physical skills necessary to use upper body equipment.
Playground Injury Investigations
While playground safety standards and guidelines are developed to prevent head and other debilitating injuries, they cannot prevent all injuries to children on playgrounds. Robson Forensic Experts can help to analyze available information to determine the linkage between the mechanism of injury and how it relates to playground equipment, design, safety guidelines and supervision.
For more information submit an inquiry or contact the authors of this article.
Carrie A. O’Donel
Applied Physics & Pediatric Biomechanics Expert
Carrie earned her Master’s degree in Mechanical Engineering with dual concentrations in Pediatric Biomechanics as well as Mechanics & Materials from Villanova University. She was instrumental in a 2015 pilot study as well as a 2016 follow-up study conducted by Robson Forensic to determine the effect of rear-facing child restraint system design and installation method on the severity of infant head and neck injuries. Carrie applies this research experience to forensic investigations involving occupant kinematics, injury mechanics, and human injury tolerance at various stages of maturation.
Lisa A. Thorsen Ed.D., C.R.C., C.P.S.I.
Supervised Care Expert
Lisa Thorsen is a care expert who evaluates the adequacy of administrative, procedural and safety issues related to injuries at organizationally based facilities. She has nearly 30 years of experience working in or administering care facilities and programs and is an expert in operations and compliance for the care and safety of children and adults, including individuals with disabilities, in public and private facilities and programs.
- Tinsworth, D., & McDonald, J. (2001). Special study: Injuries and deaths associated with children’s playground equipment. Washington, DC: Consumer Product Safety Commission.
- Vollman, D., et al. (2009). Epidemiology of playground equipment-related injuries to children in the United States, 1996-2005. Clinical Pediatrics. Vol 48:1:pp 66-71.
- Ehrlich, P., & Young, J. (2013). Maximum hang-run coupling forces in children: The effects of handhold diameter. Human Factors and Ergonomics Society. Human Factors. Vol. 55:3: pp 545-556.
- American Society for Testing and Materials. (2017). Standard consumer safety performance specification for playground equipment for public use. ASTM F1487–17. West Conshohocken, PA: Author.
- U.S. Consumer Product Safety Commission. (2010). Public playground safety handbook (Publication #325). Washington, DC: Author.
- Szychlinska, M. et al. (2017). Ergonomics of prehensility in pushing and pulling motions: An anatomical and biomechanical overview. Journal of Functional Morphology and Kinesiology.
- Thompson, D., Hudson, S., & Olsen, H., (2007). S.A.F.E. Play Areas. Creation, maintenance and renovation, Champaign, Il: Human Kinetics.