Ergonomics examines how humans interact and perform within a system such as a place of employment. Examples of ergonomic analyses include computer workstation assessments and factory production lines. An essential part of an ergonomic analysis is identifying the risk factors contributing to injury in the specific setting.
In sports, these risk factors can be intrinsic or extrinsic. Intrinsic factors include biomechanical abnormalities, previous injuries, and muscle imbalance. Extrinsic factors include clothing/footwear, the natural environment, and the playing surface used. An ergonomic analysis will contribute significantly to the design of surfaces to reduce injury risk while improving performance.
Different playing surfaces include sand, gravel, natural grass, synthetic turfs and hybrid turfs for outdoor use, and indoor hard courts made of various materials (wood, concrete, synthetic rubber). Some indoor gymnasiums are composites that flex and “breathe” in response to player activity and humidity. The surface chosen will depend on affordability, suitability for training or competition, durability, fall risk, absorbency and glare, impact on athletes’ performance, and ball behaviour. The choice will also depend on the country. For example, soccer is played predominantly on natural grass in Europe, while it varies by state in the US. Northern states mostly use synthetic turfs, while Florida uses grass.
The advantages of natural grass include reduced ground reaction forces, stable temperatures, a genuine playing experience, and ball bounce. In addition, reduced ground reaction forces will result in less soft tissue and joint stress and injuries. However, natural grass is costly to maintain, and any unevenness increases the risk of falls and acute injuries such as ankle sprains. Synthetic turfs are mostly made of polyethylene and resist wear and tear better, provide good shock absorption, and mimic grass thanks to advanced technology. Earlier designs had denser, shorter fibres, while current fibre designs are less dense and longer with rubber and sand infill. One disadvantage of synthetic turf is that it doesn’t tear away and release a cleat (divot) like grass when an overload injury is imminent. As a result, this is a possible explanation for some lower limb injuries which occur on synthetic turf.
The types of musculoskeletal injuries sustained on grass or synthetic turf vary by sport. Synthetic turfs are associated with ankle, shoulder, and back injuries in soccer and a higher incidence of injuries in males. Rugby injuries related to synthetic turf occur more in the lower limb, while grass-related rugby injuries include chest injuries and concussions. Knee, ankle, and “turf toe” (tendonitis usually in the big toe) are common injuries on synthetic turf in American football. There are other contributory factors to injury risk: sex, footwear, weather, level of skill, surface the player is used to, length of time spent using the surface, and whether the player is training or competing. Psychological factors also exist - for example, some elite soccer and NFL players perceive that synthetic turf is more dangerous than grass - which sometimes leads to changing out the surface. Synthetic turfs also have potential risks of exposure to heat and toxins (potential but unproven carcinogenic and lead hazards). In Texas, where synthetic turfs are a common choice in universities, surface temperatures in the summer months can exceed 120 degrees Fahrenheit. In American football games, they will address the risk of heat stroke by providing cooling fans, IV fluids, and rehydration fluids. Other risks of synthetic turfs include abrasions and infections, eye contamination from rubber infill particles, and concussions. Concussions are common in American football, with up to resulting from head contact with the playing surface.
Sporting performance parameters can also be influenced by the surface used. Softer and loose surfaces, such as sand, result in physiological responses of increased energy use, lactate levels, and heart rate compared to playing on hard surfaces. Unsurprisingly, speed and jump height is lower on sand than on hard surfaces. Regarding ball behaviour, hard surfaces will result in higher bounce and faster travel.
Apart from the injury risks and performance profiles of grass or synthetic turf, each has environmental pros and cons. Grass allows the return of rainwater to the soil but requires more water consumption for maintenance. Synthetic turf requires less water but creates heat islands that radiate heat back into the atmosphere. There are many considerations to be factored when choosing a playing surface. However, the perceived and actual risk of injuries should always be a priority.
Cecile Hosang is a physical therapist and assistant lecturer in the Faculty of Sport. She is also a pain specialist.
