Heat
Conditions
Brief summary
This study had three aims: 1. To determine the impact of consecutive days of exercise on thermoregulation and cardiovascular strain. 2. To determine the efficacy of a hand cooling device to cool individuals throughout a heat acclimation period. 3. To assess the maintenance of thermoregulatory and cardiovascular adaptations derived from heat acclimation during a 25-day intermittent exercise-heat exposure protocol.
Detailed description
Participants completed 14 days of exercise heat acclimation in either a hot or cool environment, followed by a heat or cool exercise exposure every 5th day for 25 days. Cardiovascular, thermoregulatory, and perceptual strain were measured throughout exercise each day. Hydration assessment and stress response via blood biomarkers were measured before and after exercise. Aerobic capacity was measured before and after heat acclimation as well as after the intermittent exercise-heat exposure. Hand cooling was implemented periodically during exercise-heat stress visits to determine cooling efficacy before and after heat acclimation.
Interventions
OTHERHeat acclimation
14 days of aerobic exercise in a hot environment
OTHERExercise in a cool environment
14 days of aerobic exercise in a cool environment
Sponsors
University of Connecticut
Study design
Allocation
RANDOMIZED
Intervention model
PARALLEL
Primary purpose
OTHER
Masking
NONE
Eligibility
Sex/Gender
MALE
Age
18 Years to 35 Years
Healthy volunteers
Yes
Inclusion criteria
* no chronic health problems * no previous history of exertional heat stroke within the past 3 years * no history of cardiovascular, metabolic or respiratory disease * no current musculoskeletal injury that limits physical activity
Exclusion criteria
* women * exercise less than once per week * VO2max \< 45 ml/kg/min
Design outcomes
Primary
| Measure | Time frame | Description |
|---|---|---|
| Internal Body Temperature | 5 days | Rectal temperature was assessed five days following measurement at baseline. |
Secondary
| Measure | Time frame | Description |
|---|---|---|
| Heart Rate | 5 days | Heart rate was assessed five days following baseline. |
Participant flow
Pre-assignment details
Participants were excluded if they did not reach the aerobic fitness criteria or if there were foreseen scheduling conflicts.
Participants by arm
| Arm | Count |
|---|---|
| Exercise in Heat Group Exercise in a hot environment
Heat acclimation: 14 days of aerobic exercise in a hot environment | 22 |
| Exercise in Cool Group Exercise in a cool environment
Exercise in a cool environment: 14 days of aerobic exercise in a cool environment | 12 |
| Total | 34 |
Withdrawals & dropouts
| Period | Reason | FG000 | FG001 |
|---|---|---|---|
| Overall Study | Withdrawal by Subject | 4 | 4 |
Baseline characteristics
| Characteristic | Exercise in Heat Group | Exercise in Cool Group | Total |
|---|---|---|---|
| Age, Categorical <=18 years | 0 Participants | 0 Participants | 0 Participants |
| Age, Categorical >=65 years | 0 Participants | 0 Participants | 0 Participants |
| Age, Categorical Between 18 and 65 years | 22 Participants | 12 Participants | 34 Participants |
| Race (NIH/OMB) American Indian or Alaska Native | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Asian | 2 Participants | 0 Participants | 2 Participants |
| Race (NIH/OMB) Black or African American | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) More than one race | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Native Hawaiian or Other Pacific Islander | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) Unknown or Not Reported | 0 Participants | 0 Participants | 0 Participants |
| Race (NIH/OMB) White | 20 Participants | 12 Participants | 32 Participants |
| Region of Enrollment United States | 22 participants | 12 participants | 34 participants |
| Sex: Female, Male Female | 0 Participants | 0 Participants | 0 Participants |
| Sex: Female, Male Male | 22 Participants | 12 Participants | 34 Participants |
| VO2max | 53.5 mL/kg/min STANDARD_DEVIATION 1.7 | 56.9 mL/kg/min STANDARD_DEVIATION 2.2 | 54.6 mL/kg/min STANDARD_DEVIATION 5.3 |
Adverse events
| Event type | EG000 affected / at risk | EG001 affected / at risk |
|---|---|---|
| deaths Total, all-cause mortality | 0 / 22 | 0 / 12 |
| other Total, other adverse events | 0 / 22 | 0 / 12 |
| serious Total, serious adverse events | 0 / 22 | 0 / 12 |
Outcome results
Primary
Internal Body Temperature
Rectal temperature was assessed five days following measurement at baseline.
Time frame: 5 days
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Exercise in Heat Group | Internal Body Temperature | 39.6 degrees Celcius | Standard Deviation 0.47 |
| Exercise in Cool Group | Internal Body Temperature | 38.2 degrees Celcius | Standard Deviation 0.3 |
Secondary
Heart Rate
Heart rate was assessed five days following baseline.
Time frame: 5 days
| Arm | Measure | Value (MEAN) | Dispersion |
|---|---|---|---|
| Exercise in Heat Group | Heart Rate | 178 beats per minute | Standard Deviation 17 |
| Exercise in Cool Group | Heart Rate | 173 beats per minute | Standard Deviation 4 |