Contents lists available at ScienceDirect Infrared Physics & Technology journal homepage: www.elsevier.com/locate/infrared A methodology to assess the effect of sweat on infrared thermography data after running: Preliminary study Jose Ignacio Priego-Quesada a,b, ⁎ , Alvaro S. Machado c , Marina Gil-Calvo a , Irene Jimenez-Perez a,b , Rosa Mª Cibrian Ortiz de Anda b , Rosario Salvador Palmer b , Pedro Perez-Soriano a a Research Group in Sports Biomechanics (GIBD), Department of Physical Education and Sports, University of Valencia, Valencia, Spain b Research Group in Medical Physics (GIFIME), Department of Physiology, University of Valencia, Valencia, Spain c Applied Neuromechanics Group, Laboratory of Neuromechanics, Federal University of Pampa, Uruguaiana, Brazil ARTICLE INFO Keywords: Thermal imaging Skin temperature Exercise Sport Thermal contact sensors Ibuttons ABSTRACT The aim of this technical report is to present a preliminary study carried out to define the methodology to be employed for further research on assessing the effect of sweating on infrared thermography and thermal contact sensors after moderate intensity running. Nine recreational runners participated in this preliminary study. Participants ran for 35 min (5 min warm-up and 30 min at a rate of perceived exertion rate of 12 points on the 6–20 points Borg scale). Skin temperature (infrared thermography, Flir E60bx; four thermal contact sensors, IButton DS1923 Hygrochron) and relative humidity (thermal contact sensors) were measured on the anterior thigh on both lower limbs before and after running. Two thermal contact sensors were located on each lower limb, one being attached throughout the complete protocol (fixed) and the other just 5 min before each data acquisition (non-fixed). The fixed sensor presented a higher skin temperature after running than infrared thermography (33.9 ± 1.3 vs. 33.2 ± 1.4 °C). The skin temperature of the non-fixed sensor was lower than the other methods, before (28.3 ± 3.3 vs. 31.8 ± 1.4 [thermography] vs. 31.3 ± 1.3 °C[fixed]) and after running (31.8 ± 1.8 vs 33.2 ± 1.4 [thermography] vs. 33.9 ± 1.3 °C[fixed]). The fixed sensor presented higher relative humidity after exercise than the non-fixed sensor (101 ± 2 vs. 83 ± 16.2%). The mean relative humidity of the fixed sensor suggests sweat saturation caused by the method of attaching the sensor. After this preliminary study, some modifications were proposed for future research, the most important being attaching the non-fixed sensors 10 min before acquiring the data. 1. Introduction Infrared thermography is a non-invasive technique to measure skin temperature [1,2]. Its use has gained popularity over the last decade for sport applications such as detecting injuries and pathologies, thermo- regulatory assessment or the study of the effect of clothing and equip- ment [3–5]. Various studies have compared infrared thermography with thermal contact sensors such as thermocouples, before and after exercise [1,6–8]. It has been observed that thermal contact sensors present higher skin temperature due to reduced convective and evaporative heat loss [1,6,7,9]. Also, sweat can accumulate as a result of the method employed to attach the sensor, so producing a drop in the evaporative cooling efficiency of this region [7,10]. With regard to infrared ther- mography, profuse sweating may act as a filter for infrared radiation and this could lead to an error in the estimation of skin temperature [7,11]. However, the results of a previous investigation suggested that after 45 min of moderate cycling, the sweat produced was not enough to perform a water layer and affect skin temperature [7]. Studies of other sports (e.g. running) with specific methodological designs are, therefore, necessary to corroborate the effect of sweat on thermal contact sensors and infrared thermography data. It is difficult to investigate the effect of sweat on thermal images or thermal contact sensors because neither methods can be considered gold standards [12,13]. For this reason, preliminary studies are neces- sary to define an experimental protocol that guarantees validity. Al- tering the time the contact sensor has been attached to the skin (throughout the complete protocol or only before and after running) could change the amount of sweat that accumulates at the point where it is attached and so its influence on the measured temperature values. The aim of this technical report is, therefore, to present a preliminary study carried out to define the methodology to be employed for further https://doi.org/10.1016/j.infrared.2020.103382 Received 8 April 2020; Received in revised form 26 May 2020; Accepted 26 May 2020 ⁎ Corresponding author at: Department of Physical Education and Sports, Faculty of Physical Activity and Sport Sciences, St: Gascó Oliag, 3. 46010 Valencia, Spain. E-mail address: j.ignacio.priego@uv.es (J.I. Priego-Quesada). Infrared Physics and Technology 109 (2020) 103382 Available online 30 May 2020 1350-4495/ © 2020 Elsevier B.V. All rights reserved. T