Validity of common body temperature sites and gait parameters during a heat tolerance test

A heat tolerance test (HTT) can aid in return-to-play decision making following exertional heat stroke (EHS). The HTT uses rectal temperature (T_REC, >38.5°C) and heart rate thresholds (HR; >150 bpm) to identify "heat intolerance." Unfortunately, T_REC is prohibited in some clinical settings (e.g. secondary schools), making a standard HTT unusable. Recently, gait sensors were used to identify heat illness, but have never been correlated with T_REC during a HTT. No research has compared gait or noninvasive body temperature sites to T_REC to determine their surrogacy for T_REC during a HTT. Eighteen subjects underwent a standard HTT (12 men, 6 women; age: 22 ± 2y; height: 168.3 ± 8.5 cm; mass: 76.6 ± 14.8 kg). Rectal, oral, aural, forehead, and axillary temperatures, gait metrics, and HR were measured every 5 minutes during a HTT. Temperature sites were invalid if bias (i.e. difference from T_REC) was >±0.27°C. Spearman correlations examined the relationship between T_REC and gait variables. Mean aural, oral, axillary, and forehead bias were -0.19 ± 0.56°C, 0.70 ± 0.53°C, 0.85 ± 0.45°C, and 1.38 ± 0.69°C, respectively (F_2,35 = 42.3, <i>p</i> < 0.001). Aural, oral, forehead, and axillary measurements exceeded our validity threshold 48 ± 30% (169 of 353), 87 ± 16% (307 of 353), 91 ± 15% (321 of 353), and 93 ± 10% (328 of 353) of the time, respectively. T_REC was significantly negatively correlated to shock (<i>r</i> =-0.28, <i>p</i> < 0.001), impact g (<i>r</i> =-0.28, <i>p</i> < 0.001), and braking g (<i>r</i>=-0.24, <i>p</i> < 0.001), and positively correlated with pronation excursion (<i>r</i> = 0.30, <i>p</i> < 0.001). Clinicians should use T_REC during an HTT as no alternative, valid temperature site was found. Some gait variables showed promise for tracking T_REC during a HTT, but more research is necessary.