None listed
Conditions
Brief summary
Exercise in the heat stimulates cardiovascular strain and subsequent adaptations to all major components of the cardiovascular system (heart, blood, vasculature). Physical activity outdoors - for work, recreation or exercise - is more frequently occurring in the heat in our warming world. Such activity often occurs under the sun, yet it is unknown if solar radiation elicits further strain and thus also enhanced adaptation responses. These questions will be addressed in a study with six experimental conditions to isolate the effect of solar radiation, establishing the effect of ultraviolet light alone and when combined with the heat energy of the sun, and of exercise. We hypothesise that (i) exercise under solar radiation will generate greater rebound/compensatory cardiovascular adaptive responses due to greater strain during exercise, and (ii) ultraviolet radiation alone will do likewise but to less extent than the combined thermal and ultraviolet effect. We will also investigate cerebrovascular and perceptual responses during the exposure which we predict will be greater during solar arms of the study.
Interventions
This study utilises a semi-randomised crossover design. Participants will complete six trials in total (two interventional and four control; detailed below and in the following section) separated by a minimum of three days, under direct observation from researchers. The two summer trials will be conducted first, in random order, and will determine the environmental conditions for the four subsequent winter trials, which will also be performed in random order. In all trials (experimental arm or c
This study utilises a semi-randomised crossover design. Participants will complete six trials in total (two interventional and four control; detailed below and in the following section) separated by a minimum of three days, under direct observation from researchers. The two summer trials will be conducted first, in random order, and will determine the environmental conditions for the four subsequent winter trials, which will also be performed in random order. In all trials (experimental arm or control arm) the same measures will be conducted, detailed below. If participants are unable to complete all six trials (due to time commitments) then their data may still be used where appropriate comparisons can still be made. After a screening visit and description of experimental procedures, the participant will return to the lab for control or experimental arm visits. Upon arriving to the lab, the participant will be asked to empty their bladder, and a urine sample of 1-2 drops will be taken to measure urine specific gravity (a 500-mL bolus of water will be provided if urine specific gravity is higher than 1.021). Height and weight (semi-nude; ±20 g) will be measured using a calibrated stadiometer and scales, respectively. A heart rate monitor will be attached around the torso. The participant will then be given the instructions for self-inserting the rectal or oesophageal thermistor to measure core temperature and proceed to do this in a private space (rectal) or with the guidance of researchers (oesophageal). Thermistors will be attached on several skin sights to measure skin temperature. Non-invasive measures of blood vessel function, arterial blood pressure using a stethoscope and sphygmomanometer, end tidal carbon dioxide and cerebral blood flow will then be obtained while resting supine. Participants will also wear a finger cuff for continuous blood pressure monitoring by finger photoplethysmography, which will remain on the participant’s finger for the duration of the session. The participants will then rest, seated for 10 minutes, before collection of capillary blood samples and perceptual ratings of thermal sensation, thermal discomfort, and affect, using standardised scales. Arterial blood pressure will also be measured manually at this time. After completing all the baseline measurements, participants will enter the environment associated with the condition (i.e., environmental chamber or outdoors). During the exposure (experimental arm or control) participants will undergo a 60-minute exercise trial (Arm 1 and 2, Control 1 and 2; 2 x 20 min exercise bouts with supine resting measures in between) of upright cycling at 50% VO2max, or will be at rest under solar radiation (Control 3 and 4; sun and simulated sun). During the exposure, core temperature, skin temperature, and heart rate will be monitored constantly and recorded throughout. Water will be provided to limit dehydration to <1%, and will be weighed and recorded, to account for body water changes. Drinking will occur following rather than before key measurements to avoid effects of swallowing-related reflexes. Perception ratings (as per above, including rating of perceived exertion if exercising) and manual blood pressure measurements will be taken at 20 minutes and 50 minutes from the start of exposure. At these time points, and once the aforementioned measures have been taken, participants will stop cycling (in the case of exercise trials) for 5-10 minutes and lie supine where manual blood pressure, cerebral blood flow, and respiration will also be measured in the same environment. At 50 minutes, before lying supine, a capillary blood sample will be taken. After completion of all measures (at 60 minutes of exposure), participants will exit the environment and a semi-nude, de-instrumented body weight will be recorded to provide an accurate measure of body water losses. A ~30-minute resting period outside of the exposure will occur whereby participants will be free to spend as they wish yet remain seated in the laboratory with continuous Finometer recordings of blood pressure. The first set of follow-up measures (heart rate, manual blood pressure, cerebral blood flow, and blood vessel function) will then be completed. Participants will be then be free to leave the laboratory. Participants will return to the laboratory at 24 hours from the start of the exposure for the second set of follow-up measures, i.e., heart rate, blood pressure (manual), change in plasma volume (from capillary samples), and blood vessel function (from ultrasound assessment of arterial reactivity). Two experimental arms are detailed below and the other 4 control arms are detailed in the following sections. Arm 1 - Ex Solar: Will occur outdoors under the sun in summer. Erythemal weighted ultraviolet radiation will be dosed to one standard erythemal dose (100 J/m2). Arm 2 - Ex Lamp: Arm 1 may be confounded by chronic/prior solar exposure on participants outside of experimental trials in summer. Thus, this trial aims to account for that by taking place in winter months (i.e., low solar radiation) and will occur indoors in an environment replicating Arm 1 (environmental chamber), however using a solar simulator lamp in place of the sun. Erythemal weighted ultraviolet radiation will be dosed to one standard erythemal dose (100 J/m2).
Sponsors
Prof. Jim Cotter University of Otago
Study design
Allocation
Non-randomised trial
Intervention model
Crossover
Primary purpose
Prevention
Masking
Open (masking not used)
Eligibility
Sex/Gender
All
Age
18 Years to 65 Years
Healthy volunteers
Yes
Inclusion criteria
Males and females between 18 and 65 years old; Able to complete 60 minutes of moderate intensity cycling exercise; Do not have any pre-existing condition (e.g. musculoskeletal injuries, or cardiovascular, respiratory, musculoskeletal, or neurological diseases) that could put an individual at elevated risk during the tests, and can therefore pass the current Physical Activity Readiness Questionnaire (PARQ); Have not suffered from heat illness (heat syncope, heat exhaustion, or heatstroke); Provide written consent at the start of the study; Have a regular menstrual cycle (21-35 days) for female participants or are post-menopausal and have not used hormone replacement therapy in at least the previous 12 months.
Exclusion criteria
Have any injuries or consume medications that may impair the ability to exercise in a hot environment (e.g., have high anticholinergic properties, non-selective beta-blockers, and adrenaline) or do not pass the physical activity readiness questionnaire (PARQ); Have a respiratory illness or recent fever (<3 weeks); Are a habitual smoker/e-cigarette user; Have pre-existing or history of menstrual-related disorders (e.g., dysmenorrhoea, amenorrhoea (if not postmenopausal), oligomenorrhoea, premenstrual dysphoric disorders, polycystic ovary syndrome, endometriosis) or any other conditions (e.g., currently pregnant, or disordered eating) known to affect the hypothalamic-pituitary-ovarian axis; Are currently undergoing perimenopause or are post-menopausal but using hormone-replacement therapy.
Outcome results
None listed