Data Collection


Microclimate measurement Microclimate conditions of the soccer fields were measured on hot, sunny summer days (September 7, 8, 21, and 22 of 2021). Two sets of weather sensors (Maximet 501 and ATOMS 41) were installed at the center of each natural turfgrass and artificial turf field. Te microclimate—air temperature (degrees F), relative humidity (percentage), wind speed (miles per hour [mph]), wind direction, and solar radiation (watts per square meter [W/m2])—was collected from 11:00 AM to 6:00 PM CST with a one-minute recording interval. In addition, the surface temperature was measured every 15 minutes on both field types by two trained surveyors using a thermal infrared camera (FLIR IR E5). Te measurement height of those sensors was five feet above the ground to represent the thermal conditions at an athlete’s chest level. Te summary of measured microclimate over four days is presented in Table 1. Although the same weather sensors were not used for data collection, they were thoroughly calibrated prior by multiple field tests.


Table 1) Summary of Microclimate Condition on Penberthy Soccer Field Date Sep 7 Sep 8


Air temperature (°F)


Sd Sd


Mean 91.92 2.52


Mean 91.49 1.65


Sep 21 Mean 91.27 Sd


3.09


Sep 22 Mean 83.18 0.40


Sd Total


Mean 89.46 Sd


1.91 * Standard deviation (Sd)


Questionnaire survey An on-site questionnaire survey was adopted to measure the perceived thermal stress that the soccer players felt during matches. Over the four days of data collection, six soccer matches (6 versus 6) were played with TAMU Men’s Club Soccer players who volunteered as study participants. Two matches were held approximately 11:00 AM to 1:00 PM CST, and the other four matches approximately 2:00 to 4:00 PM CST to have a wide range of daytime field thermal conditions. Matches consisted of four quarters, where each quarter of a match lasted 22.5 minutes with a 10-minute break in between. At each break, three out of 12 players were randomly asked to respond to eight questions about how thermally comfortable they were during the matches with a 10-point rating scale, where 0 represented “much too cold” and 10 represented “much too hot”. Tese questions can be grouped in three parts: 1) perceived exertion (i.e., a laborious or perceptible effort), 2) perceived surface heat conditions, 3) perceived thermal stress. Te response


TPI Turf News September/October 2022


rate was 87.5 percent, meaning 63 out of 72 participants responded to the survey without missing values.


Estimation of objective thermal stress To evaluate the athlete’s physiological thermal stress, the COMFA energy budget model was employed. It is an outdoor thermal comfort index that estimates the objective thermal comfort of a person based on energy budget equation. In other words, it calculates the physiological thermal load that the human body receives to maintain thermal balance with the surrounding outdoor environment. Te energy budget is described as follows:


where ∆S is the change in heat storage (W/m2 ). When the


change in heat storage is near 0, the inputs and outputs of energy would nearly balance, and a person would be thermally comfortable. A large positive value would suggest that a person is receiving much more heat than they are giving off, and they would feel too hot. A large negative


15


Solar radiation (W/m2


)


810.26 156.61 622.89 314.81 570.96 136.72 736.66 105.07 685.19 178.30


Relative humidity (%)


33.75 7.25


32.23 3.43


55.71 8.53


26.15 0.36


36.96 4.89


Wind speed (mph)


3.81 0.46 7.41 1.70 6.54 1.84 8.27 0.59 6.50 1.15


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