Common body temperature sites provide invalid measures of body core temperature in hyperthermic humans wearing American football uniforms.

Valid body core temperature measurements are essential for diagnosing and monitoring athletes with exertional heat stroke (EHS). Experts question the validity of body temperature sites that vary by >±0.27°C from the gold standard, rectal temperature (T). No research has established the validity of body temperature sites when American football uniforms (PADS) are worn during simulated EHS scenarios. Thirteen men (age, 22 ± 2 y; mass, 77.5 ± 8.8 kg; height, 181.3 ± 5.7 cm) donned PADS and entered an environmental chamber (38.7 ± 0.8°C, 38.9 ± 2.4% relative humidity). We compared T to a forehead liquid crystal temperature monitor (T), axillary (T), oral (T), and aural temperatures (T) 34 times over four consecutive periods: 10-minutes of rest; exercise until participants T was between 39.7°C and 39.8°C; cold-water immersion (CWI, 10.0 ± 0.1°C) until all temperature sites indicated ≤38°C; and a 15-minute post-immersion recovery period. Body temperatures varied between sites during all periods (F ≥ 2.5, ≤ 0.001). T and T statistically differed from T and exceeded the 0.27°C bias threshold at all 34 measurement times (100%). T differed from T eight times during rest; eight times during exercise; 0 times during CWI; and twice during recovery (18/34, 53%). T exceeded the bias threshold 28 times (82%). T differed from T five times during rest; 0 times during exercise; five times during CWI; and once during recovery (11/34, 32%). T exceeded the 0.27°C bias threshold 15 times during testing (44%). T, T, T, and T should not be used to diagnose or monitor American football players with EHS. analysis of variance; CWI: cold water immersion; EHS: exertional heatstroke; PADS: full American football uniform consisting of a helmet; shoulder, knee, thigh, hip and tailbone pads; a jersey top; undergarments; and half-length pants; T: axillary temperature; T: aural temperature; T: liquid crystal temperature monitor; T: oral temperature; T: rectal temperature.