The Effect of Synthetic Grass Sports Surfaces on the Thermal Environment and Human Thermoregulation
Creators: name: Singh, Gurpreet
Publisher: name: Southern Cross University
Year: 2024
Subjects: Thermoregulation
Heat stress
Synthetic Grass
Thermal Environment

description: Synthetic grass sports surfaces have been used as alternatives to natural grass in competitive sports since the 1960s. Although there were several variations of synthetic grass, sporting governing bodies (e.g., Fédération Internationale de Football Association) have embraced modern synthetic grass (i.e., third and fourth-generation synthetic grass) as suitable for competition use. However, there were concerns regarding high surface temperatures on synthetic grass sports surfaces in warm-hot conditions, and it has been suggested that this could increase heat strain and the risk of heat illness compared to sports played on natural grass. Therefore, this thesis featured three studies to determine (i) if synthetic grass sports surfaces used for association football (i.e., soccer) could increase the environmental heat stress compared to natural grass and (ii) investigate if such changes could have an influence on an athlete's physiology and perception during exercise. Chapter 1 provided background information, a problem statement, and a thesis overview. Chapter 2 was a series of narrative literature reviews summarising the published data relevant to this thesis. Chapter 2, Part A, included a narrative review of 49 studies that focused on core body temperature responses during competitive sports and discussed key factors that led to high core body temperatures and exertional heat illness/heat stroke during competition (Singh et al., 2023). Chapter 2, Part B, summarised and critiqued the research conducted on synthetic grass sports surfaces with a focus on athlete health and safety. Chapter 3 (Study 1; Singh et al., 2024) presented a systematic review of 23 studies to determine if there were differences in the thermal environment surrounding synthetic grass sports surfaces compared with natural grass surfaces, as well as comparing between different types of synthetic grass surfaces. While several environmental parameters were reported across the included studies, only air temperatures were consistently higher on synthetic compared to natural grass (range: 0.5-1.2°C) and surface temperature (range: 9.4-33.7°C). Other environmental parameters of the thermal environment (i.e., mean radiant temperature, humidity, and wind velocity) remained similar between surfaces. This chapter provided evidence that synthetic grass surfaces could influence specific environmental parameters of the thermal environment (i.e., air temperature). However, whether the differences were enough to increase the environmental heat stress risk was uncertain. Chapter 4 (Study 2) was an environmental study comparing the thermal environment over synthetic and natural grass surfaces at multiple locations in Australia to observe trends in the thermal environment across different locations. Air temperatures were 0.4 ± 0.1°C higher over synthetic grass, but mean radiant temperatures were similar. The mean surface temperature was 9.4 ± 4.6°C higher on synthetic grass, particularly with styrene butadiene rubber infill. Total body heat storage increased on synthetic grass at two of the three locations by 50.9-67.6 W, but one location showed higher heat storage on natural grass by 2.7 W. Despite these differences, the level of heat stress was similar between surfaces according to wet-bulb-globe temperature and Sports Medicine Australia heat policies. Chapter 5 (Study 3) was a randomised cross-over trial with thirteen trained/developmental athletes who completed intermittent running protocols on synthetic and natural grass surfaces to determine if synthetic grass could affect human physiological and perceptual markers of heat strain. The study found that final skin temperature, thermal sensation, and sweat rate were significantly higher on synthetic grass. However, final core body temperature was higher on natural grass, with no significant differences in delta core temperature, heart rate, thermal comfort, or rate of perceived exertion between surfaces. This thesis demonstrated that synthetic grass surfaces could influence specific environmental parameters of the thermal environment in warm and hot conditions. Nevertheless, the differences in the thermal environment were not significant enough to cause meaningful differences in core body temperature, which is a primary outcome measure of hyperthermia and exertional heat illness/heat stroke. Therefore, synthetic grass users should be aware that they may experience slightly hotter conditions than on natural grass and should consider scheduling matches/training in the early morning or evenings to avoid higher surface temperatures, air temperatures, skin temperatures, sweat rates and an increased thermal sensation.