Effect of Aging and Aerobic Fitness Level on Heat Dissipation

In the context of global aging, the health risk factors associated with exercising or working in the heat for aging population are exacerbated by the rising in global surface temperatures. The purpose of this investigation is to determine at what age the heat loss decrements occur and to examine if aerobic fitness level can affect the heat loss capacity in neutral environmental conditions.

All trials were conducted to indoor gyms with the same environmental temperature and relative humidity, 26 - 30oC and 40-50% respectively, to ensure no difference in body temperature were due to the external thermal stress. The participants were instructed to refrain from intense exercise as well as alcohol and caffeine consumption for 24 hours prior to experimental trial and to had a light meal 2h before their arrival. Upon arrival, participants would have to wear running shoes, light and short running shorts and light cotton socks. Participants received comprehensive instructions about the shuttle run test and the whole process of measurements. Firstly participants answered the International Physical Activity Questionnaire (IPAQ). Thereafter, anthropometrics data (weight and height) were evaluated as well as the body temperature in external ear canal and axillary. All participants followed five minutes warming up and then performed to 20 m shuttle run test until their volitional limit. Once the participants could no longer run, the test was over and the number of laps was recorded. After the end of the shuttle run, were evaluated the body temperature and the weight of each participants. No fluids consumptions were permitted until the second weighing. They were weighed twice, at baseline and at the end of the running test with a precision weight scale (Kern DE 150K2D, KERN & SOHN GmbH, Balingen, Germany). Environmental data including air temperature and relative humidity were measured continuously using a portable weather station (LCD Digital Temperature & Humidity Meter HTC-1). The weather station was placed 1 meter above the ground according to the manufacturer's guidelines.

At the shuttle run test, participants were required to run between two lines 20 meters apart, while keeping pace with audio signals emitted from a pre-recorded CD. The frequency of the sound signals increases in such way that running speed was increased by 0.5 km h-1 each minute from the starting speed 8.5 km h-1.

At the shuttle run test, participants were required to run between two lines 20 meters apart, while keeping pace with audio signals emitted from a pre-recorded CD. The frequency of the sound signals increases in such way that running speed was increased by 0.5 km h-1 each minute from the starting speed 8.5 km h-1.

Aerobic fitness level was defined by peak oxygen uptake (VO2peak). VO2peak was determined by a 20m shuttle run test. The number of the last announced stage and the equivalent maximal speed from participants' performance were used for its VO2peak estimation

Ear canal temperature was recorded twice, at baseline and at the end of the shuttle run test (three times each at the left ear and recorded the mean value), using ear thermometer (IR100, MicrolifeSwitzerland)

Axillary temperature was recorded twice, at baseline and at the end of the shuttle run test, using the electronic digital thermometer (EcoTemp, OMRON, Japan)

Physical activity of the subject in a usual week was recorded via International Physical Activity Questionnaire. Scores include steps/day and METs/week, with no lower and upper limit

Weight was recorded twice, at baseline and at the end of the shuttle run test, using a precision weight scale (Kern DE 150K2D, KERN & SOHN GmbH, Balingen, Germany

Whole Body Sweat Rate was determined by the difference of the pre-test and post-test weight of the participants

Air temperature was measured continuously using a portable weather station (LCD Digital Temperature & Humidity Meter HTC-1placed) 1 meter above the ground according to the manufacturer's guidelines

Relative humidity was measured continuously using a portable weather station (LCD Digital Temperature & Humidity Meter HTC-1) placed 1 meter above the ground according to the manufacturer's guidelines

Inclusion Criteria: Healthy children and adults Exclusion Criteria: Diagnosed chronic medical condition; Symptoms of acute illness; Recent (past 4 weeks) usage of medications known to affect the circulatory system, the thyroid, the pituitary function, or the metabolic status