Work Rate Adjustments During a High-intensity Interval Training on a Stationary Bike in a Hot and Temperate Environment

Study Overview
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Brief Summary
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The goal of this repeated measures study is to evaluate acute work rate adjustments during high-intensity interval training (HIIT) in a hot and temperate environment in healthy and active adults when using target heart rate to prescribe the exercise intensity. The main questions it aims to answer are: Will HIIT based on target heart rate in a hot environment result in increased cardiovascular (i.e., elevated recovery HR) and thermal strain compared to HIIT in a temperate environment? Will work rate be lowered to a greater extent during HIIT in a hot environment compared to a temperate environment in order to maintain target heart rate? Will maximal aerobic capacity (V̇O2max) decrease to a greater extent after HIIT in the heat compared to a temperate environment? Procedures: Participants will complete 5 trials on a cycle ergometer. Trial 1 (Control Visit): Participants (n = 7) will have their maximal heart rate and V̇O2max measured in a temperate environment ( 22 °C, 40% RH). Experimental Trials 2-5: The order of the trials will be counterbalanced and randomly assigned to participants. 15TEMP: Participants will cycle at 70% of their maximum heart rate for 8 minutes as a warm-up, followed by one round of HIIT. The HIIT protocol consists of 4 minutes at 90% of maximum heart rate followed by 3 minutes at 70% of maximum heart rate, totaling 15 minutes, in a temperate environment ( 22 °C, 40% RH). After the HIIT session, a graded exercise test will measure V̇O2max. 15HEAT: Similar to 15TEMP, but participants will perform the HIIT protocol in a hot environment ( 35 °C, 40% RH). 43TEMP: Participants will cycle at 70% of their maximum heart rate for 8 minutes as a warm-up, followed by the HIIT protocol repeated four times (4 minutes at 90% of maximum heart rate and 3 minutes at 70% of maximum heart rate), totaling 43 minutes, in a temperate environment ( 22 °C, 40% RH). 43HEAT: Similar to 43TEMP, but participants will perform the HIIT protocol in a hot environment ( 35 °C, 40% RH).

Official Title
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Acute Work Rate Adjustments During High-intensity Interval Training in a Hot and Temperate Environment

Conditions
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High-Intensity Interval Training, Heat

Intervention / Treatment
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* Behavioral: 15 minutes of high-intensity interval training
* Behavioral: 43 minutes of high-intensity interval training
* Other: Hot environment
* Other: Temperate environment


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Participants were healthy males and females who are 18 to 39 years of age, recreationally active as defined by the American College of Sports Medicine, performing moderate-intensity aerobic exercise 30 min or more per session for at least 3 sessions per week for at least the past 3 months, and free of metabolic, cardiovascular, and renal disease Exclusion Criteria: Individuals classified as needing medical clearance according to American College of Sports Medicine (ACSM) Guidelines were not allowed to participate. Needing medical clearance is defined by ACSM as 1) not being physically active and having known cardiovascular, metabolic, or renal disease and asymptomatic; 2) not being physically active and having any signs or symptoms suggestive of cardiovascular, metabolic, or renal disease; 3) participating in regular exercise and having known cardiovascular, metabolic, or renal disease and asymptomatic; or 4) participating in regular exercise and having any signs or symptoms suggestive of cardiovascular, metabolic, or renal disease .

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 39 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Other
Allocation: Randomized
Intervention Model: Crossover Assignment
Interventional Model Description: Participants completed all trials and were compared to themselves.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: 15TEMP<br>Participants cycled at 70% heart rate max for 8 min as a warm-up and then completed one round of HIIT, i.e., 4 min at 90% heart rate max followed by 3 min at 70% heart rate max for a total of 15 minutes in a temperate environment, followed by a graded exercise test to measure maximal aerobic capacity. | Behavioral: 15 minutes of high-intensity interval training<br>* Participants completed an 8 min warm-up and 1 round of high-intensity interval training<br>Other: Temperate environment<br>* Participants exercised in a temperate environment,   22 °C,  40% relative humidity.<br>|
| Experimental: 15HEAT<br>Participants cycled at 70% heart rate max for 8 min as a warm-up and then completed one round of HIIT, i.e., 4 min at 90% heart rate max followed by 3 min at 70% heart rate max for a total of 15 minutes in a hot environment, followed by a graded exercise test to measure maximal aerobic capacity. | Behavioral: 15 minutes of high-intensity interval training<br>* Participants completed an 8 min warm-up and 1 round of high-intensity interval training<br>Other: Hot environment<br>* Participants exercised in a hot environment,   35 °C,  40% relative humidity.<br>|
| Experimental: 43TEMP<br>Participants cycled at 70% heart rate max for 8 min as a warm-up and then performed the HIIT protocol (4 min at 90% heart rate max and 3 min at 70% heart rate max, repeated 4 times for a total of 43 minutes) in a temperate environment followed by a graded exercise test to measure maximal aerobic capacity. | Behavioral: 43 minutes of high-intensity interval training<br>* Participants completed an 8 min warm-up and 5 rounds of high-intensity interval training<br>Other: Temperate environment<br>* Participants exercised in a temperate environment,   22 °C,  40% relative humidity.<br>|
| Experimental: 43HEAT<br>Participants cycled at 70% heart rate max for 8 min as a warm-up and then performed the HIIT protocol (4 min at 90% heart rate max and 3 min at 70% heart rate max, repeated 4 times for a total of 43 minutes) in a hot environment followed by a graded exercise test to measure maximal aerobic capacity. | Behavioral: 43 minutes of high-intensity interval training<br>* Participants completed an 8 min warm-up and 5 rounds of high-intensity interval training<br>Other: Hot environment<br>* Participants exercised in a hot environment,   35 °C,  40% relative humidity.<br>|
| No Intervention: Control<br>Participants completed a graded exercise test on a stationary bicycle in a temperate environment (  22 °C (72 °F),  40% RH) to measure maximal aerobic capacity and maximal heart rate. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Work rate adjustments | In a hot and temperate environment by how much does work rate need to be adjusted to maintain target heart rate? | From the first work interval (min 9-12) to the last work interval (min 37-40). | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cardiovascular strain | In a hot and temperate environment by how much does heart rate in the recovery intervals increase? | From the first recovery interval (min 13-15) to the last recovery interval (min 41-43). | 
| Thermal Strain | In a hot and temperate environment by how much do rectal temperature and skin temperature increase? | From the first work interval (min 9-12) to the last work interval (min 37-40). | 
| Maximal aerobic capacity | In a hot and temperate environment by how much does maximal aerobic capacity decrease? | The end of the 15 min trials compared to the end of the 43 min trials. |