Solar radiation and the validity of infrared tympanic temperature during exercise in the heat

  • Hidenori OtaniEmail author
  • Mitsuharu Kaya
  • Akira Tamaki
  • Yuri Hosokawa
  • Jason K. W. Lee
Original Paper


We investigated the validity of infrared tympanic temperature (IR-Tty) during exercise in the heat with variations in solar radiation. Eight healthy males completed stationary cycling trials at 70% peak oxygen uptake until exhaustion in an environmental chamber maintained at 30°C with 50% relative humidity. Three solar radiation conditions, 0, 250 and 500 W/m2, were tested using a ceiling-mounted solar simulator (metal-halide lamps) over a 3 × 2 m irradiated area. IR-Tty and rectal temperature (Tre) were similar before and during exercise in each trial (P > 0.05). Spearman’s rank correlation coefficient (rs) demonstrated very strong (250 W/m2, rs = 0.87) and strong (0 W/m2, rs = 0.73; 500 W/m2, rs = 0.78) correlations between IR-Tty and Tre in all trials (P < 0.001). A Bland-Altman plot showed that mean differences (SD; 95% limits of agreement; root mean square error) between IR-Tty and Tre were − 0.11°C (0.46; − 1.00 to 0.78°C; 0.43 ± 0.16°C) in 0 W/m2, − 0.13°C (0.32; − 0.77 to 0.50°C; 0.32 ± 0.10°C) in 250 W/m2 and − 0.03°C (0.60; − 1.21 to 1.14°C; 0.46 ± 0.27°C) in 500 W/m2. A positive correlation was found in 500 W/m2 (rs = 0.51; P < 0.001) but not in 250 W/m2 (rs = 0.04; P = 0.762) and 0 W/m2 (rs = 0.04; P = 0.732), indicating a greater elevation in IR-Tty than Tre in 500 W/m2. Percentage of target attainment within ± 0.3°C between IR-Tty and Tre was higher in 250 W/m2 (100 ± 0%) than 0 (93 ± 7%) and 500 (90 ± 10%; P < 0.05) W/m2. IR-Tty is acceptable for core temperature monitoring during exercise in the heat when solar radiation is ≤ 500 W/m2, and its accuracy increases when solar radiation is 250 W/m2 under our study conditions.


Core temperature Heat stress Physical activity Sunlight 



The authors thank the participants who gave their time and effort to participate in the present study.

Funding information

This study was funded by the Japan Society for the Promotion of Science KAKENHI (grant number 26870759).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.


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Copyright information

© ISB 2019

Authors and Affiliations

  1. 1.Faculty of Health Care SciencesHimeji Dokkyo UniversityHimejiJapan
  2. 2.Hyogo University of Health SciencesKobeJapan
  3. 3.Faculty of Sport SciencesWaseda UniversityTokorozawaJapan
  4. 4.Department of PhysiologyYong Loo Lin School of Medicine, National University of SingaporeSingaporeSingapore
  5. 5.Global Asia InstituteNational University of SingaporeSingaporeSingapore
  6. 6.N.1 Institute for Health, National University of SingaporeSingaporeSingapore

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