Effects of Solar Radiation on Human Function and Cognition
Condition: Heat Stress; Heat Strain
MeSH terms: Heat Stress Disorders
Study type: Interventional

Summary: 
      Solar radiation is a physical phenomenon which interacts with any human being throughout its
      life on earth. This interaction is associated with numerous physiological functions, as well
      as a broad spectrum of deleterious effects on human health and wellbeing. The aim of this
      study is to elucidate the effects of solar radiation on human function and cognition in
      environmental conditions characterized by the same thermal stress.
    

Detailed description: 
      Volunteers were exposed to four different environmental conditions [two hot environments:
      30°C WBGT (1st: air temperature = 32.6°C; relative humidity = 30%; wind speed = 0.5 m/s;
      solar radiation = 800 W/m2 and 2nd. air temperature = 40.6°C; relative humidity = 30%; wind
      speed = 0.5 m/s; solar radiation = 0 W/m2) and two neutral environments: 20°C WBGT (1st: air
      temperature = 19.1°C; relative humidity = 30%; wind speed = 0.5 m/s; solar radiation = 800
      W/m2 and 2nd. air temperature = 28.5°C; relative humidity = 30%; wind speed = 0.5 m/s; solar
      radiation = 0 W/m2], over an equal number of days. The aforementioned environmental scenarios
      were randomly allocated for each volunteer. To minimize participant bias, the true purpose of
      the study was hidden from the volunteers. Of course, once the data collection was completed,
      all volunteers were informed about the true purpose of the study and gave their permission to
      analyze and publish these data. During this blinded randomized controlled trial, all
      volunteers participated four times in an experimental protocol with a total duration of
      03:20:00, following an hour of preparation and baseline tests. The protocol had three main
      time periods [rest (two hours), work (cycling) at 100 W (one hour), and recovery (twenty
      minutes)]. Anthropometrical data [age; body stature (Seca 213; seca GmbH & Co. KG; Hamburg,
      Germany); body mass (BC1000, Tanita corporation, Tokyo, Japan); body fat (DXA scan: Lunar DPX
      Madison, GE Healthcare, Wisconsin, USA); and lean mass (DXA scan: Lunar DPX Madison, GE
      Healthcare, Wisconsin, USA)] were collected two days prior to the experiments.

      Volunteers were euhydrated prior to the experiments. Hydration status was assessed using a
      handheld refractometer (ATAGO Ltd, Tokyo, Japan) and determined as either euhydrated (USG <
      1.020) or dehydrated (USG ≥ 1.020) according to the current guidelines. Water consumption was
      restricted during the experimental protocol. The same clothing consisting of a light-blue
      t-shirt (100% cotton), a black exercise short pant (100% polyester), and a pair of
      medium-high socks (100% cotton) were used by volunteers throughout the experiments. A pair of
      sunglasses was mandatory to be worn throughout the experiments. Furthermore, experiments took
      place during the same hour of the day for each participant and an 8-hour fasting was ensured
      prior to the experiments. Furthermore, participants were requested to avoid caffeine and
      alcohol consumption for at least twelve hours before the experiments, as well as to avoid
      salt and sugar consumption eight hours before the experiments.

      During the study, continuous heart rate, core temperature, mean skin temperature, skin blood
      flow, and sweat rate were measured. Specifically, heart rate was collected using wireless
      heart rate monitors (Polar Team2. Polar Electro Oy, Kempele, Finland). Core temperature was
      collected using telemetric capsules (BodyCap, Caen, France). Skin temperature from four sites
      was measured using wireless thermistors (iButtons type DS1921H, Maxim/Dallas Semiconductor
      Corp., USA) and was expressed as mean skin temperature according to Ramanathan [mean skin
      temperature = 0.3(chest + arm) + 0.2(thigh + leg). Skin blood flow was measured with a laser
      Doppler flowmeter (PeriFlux 4000, Perimed, Stockholm, Sweden) at right forearm
      (brachioradialis) and leg (gastrocnemius). The probe (PROBE 413 Integrating Probe, Perimed,
      Stockhold, Sweden) was held in place with a plastic holder (PH 13, Perimed, Stockhold,
      Sweden). Sweat rate was measured at three regions [forehead, thigh (quadricep), and arm
      (bicep)] using ventilated capsule method. Thermal comfort (1 = comfortable; 5 = extremely
      uncomfortable), thermal sensation (-3 = cold; +3 = hot), and perceived exertion (6 = no
      exertion at all; 20 = maximal exertion), alongside cognitive performance (vigilance, divided
      attention, memory test, and reaction time) were assessed at baseline, pre work condition
      (01:40:00), and post work (03:00:00) conditions. Volunteers entered the chamber five minutes
      prior to the experiments to install data loggers and accompanied sensors on their body.
    

Intervention name(s): Radiation and warm environment; Warm environment; Neutral environment with radiation; Neutral environment without radiation
Intervention type(s): Other; Other; Radiation; Other
Intervention description(s): Exposure to hot environment (30°C WBGT) with radiation (800 W/m2)
Exposure for 03:20:00:
rest (two hours)
work (cycling) at 100 W (one hour)
recovery (twenty minutes); Exposure to hot environment (30°C WBGT) with radiation (0 W/m2)
Exposure for 03:20:00:
rest (two hours)
work (cycling) at 100 W (one hour)
recovery (twenty minutes); Exposure to neutral environment (20°C WBGT) with radiation (800 W/m2)
Exposure for 03:20:00:
rest (two hours)
work (cycling) at 100 W (one hour)
recovery (twenty minutes); Exposure to neutral environment (20°C WBGT) with radiation (0 W/m2)
Exposure for 03:20:00:
rest (two hours)
work (cycling) at 100 W (one hour)
recovery (twenty minutes)
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Single (Participant)
Primary purpose: Prevention
Keywords: heat stress; heat strain; solar radiation; responses; cognition; thermal