None listed
Conditions
Brief summary
Background: People over breathe and reduce their brain blood flow when severely heat stressed. High body core (especially brain) temperature is considered the main determinant of a person's heat tolerance. The purpose of this study is to assess how normal daily changes in core temperature affect heat tolerance, brain blood flow and respiratory control, and whether these responses differ between males and females, or with opportunity to improve their comfort. We hypothesise that heat tolerance will be impaired more in (a) the afternoon, (b) in females, and (c) in the absence of any ability to improve one's comfort. Methods: Twelve healthy, aerobically fit individuals (six females) will exercise on a semi-recumbent cycle ergometer (30% VO2 max) in a water-perfused suit (~48 °C) until volitional exhaustion on three separate occasions (one in the morning, two in the afternoon).
Interventions
Using a repeated measures cross over design, each participant will cycle (at 25-35% of maximal oxygen consumption) on a semi-recumbent exercise bike while wearing a warm water-perfused suit (48-50 °C) until volitional exhaustion. Sessions will be performed with one participant at a time, and a minimum of two researchers, as elaborated on below. Work rate will be monitored continuously and automatically adjusted by the cycler ergometer's computer software to maintain appropriate work rate (at 25-
Using a repeated measures cross over design, each participant will cycle (at 25-35% of maximal oxygen consumption) on a semi-recumbent exercise bike while wearing a warm water-perfused suit (48-50 °C) until volitional exhaustion. Sessions will be performed with one participant at a time, and a minimum of two researchers, as elaborated on below. Work rate will be monitored continuously and automatically adjusted by the cycler ergometer's computer software to maintain appropriate work rate (at 25-35% of maximal oxygen consumption). This fixing and standardisation of workload will be used to ensure adherence to the trial demands, i.e., this dictates the rate of application/imposition of heat stress. Adherence then ceases when the fixed workrate cannot be sustained. Participants will be asked to participate on three separate occasions, i.e. once in the morning and twice in the afternoon. Time of sessions will be standardised to onset of instrumentation and data recording within 7-9 am and 2.30-5.00 pm. The washout period between sessions will be a minimum of 5 days. The protocol and measures taken will be identical across all three trials, however, one afternoon condition will involve the addition of a fan, which the participant can use to make themselves more comfortable (i.e., allowing behavioural thermoregulation). The sessions will be run by at least two researchers (i.e. the lead student researcher and an experienced ultrasound technician for blood flow measures. The technician is also an academic supervisor).
Sponsors
Jim Cotter
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Prevention
Masking
Open (masking not used)
Eligibility
Sex/Gender
All
Age
18 Years to 55 Years
Healthy volunteers
Yes
Inclusion criteria
Volunteers may participate if they: Meet ACSM physical activity guidelines (i.e. exercise >3 times per week for 30 minutes or more) and have experience exercising at maximal intensity; have no current or recurring injuries that may affect ability to exercise maximally; are not consuming medications (except contraceptives) where heat exposure or exercise are contraindicated; have a history of heat intolerance or fainting; have any medical conditions that will impair the ability to exercise maximally and/or endure moderate- to severe- heat stress (e.g. core temperature above 40ºC).
Exclusion criteria
Contraindication to exercise (as indicated by PARQ(+)), or exposure to extreme heat stress.
Outcome results
None listed