High-Intensity Interval Training Across Exercise Environments: Acute Effects on Physiological Stress, Cardiovascular Responses, Executive Function, and Psychological Experience

High-Intensity Interval Training Across Exercise Environments: Acute Effects on Physiological Stress, Cardiovascular Responses, Executive Function, and Psychological Experience

The goal of this clinical trial utilizing a randomized crossover design)is to explore the modulating effects of different exercise environments （green parks, outdoor athletic tracks, and indoor settings) on acute responses to High-Intensity Interval Training (HIIT). It aims to determine if environmental factors can optimize an individual's stress regulation, cognitive improvement, and psychological exercise experience. The study involves 25 healthy full-time college students aged 18 to 25.

The main questions it aims to answer are：

1. Are there significant differences in physiological stress (e.g., salivary cortisol, HRV) and cardiovascular responses when performing HIIT in different exercise environments (indoor, track, park)?
2. How does the exercise environment influence executive function (inhibitory control and cognitive flexibility) and subjective psychological experiences (e.g., emotional state, enjoyment, and exercise motivation) following HIIT? Researchers will compare the performance of participants across three conditions-Green Park (natural environment), Outdoor Athletic Track (conventional outdoor environment), and Indoor Venue (artificial environment)-to identify the modulating effects of different environments on exercise outcomes.

Participants will ：

Sign the informed consent form and complete baseline health screenings and psychological scales.

Undergo resting physiological measurements (Heart Rate, Heart Rate Variability, Blood Pressure, Salivary Cortisol) and complete computerized executive function tasks (Stroop task and More-odd-shifting task).

Perform approximately 15 minutes of standardized preparation activities (warm-up).

Complete a 15-minute high-intensity interval jump-rope training session (using a protocol of 30 seconds of high-intensity exercise followed by 30 seconds of recovery) in a randomly assigned environment.

Immediately following the exercise, undergo repeated physiological measurements, psychological assessments, and cognitive function tests.

The current study utilizes a randomized, counterbalanced crossover design to investigate how different exercise environments modulate the acute physiological and psychological responses to High-Intensity Interval Training (HIIT). Each participant will complete three experimental sessions corresponding to three distinct environments: a green park (natural environment), an outdoor athletic track (conventional outdoor environment), and an indoor venue (artificial environment).

To eliminate carry-over effects and fatigue accumulation, a minimum washout period of 48 hours is mandated between each experimental session for every participant. The experimental procedures for each session are highly standardized, lasting approximately 60 minutes in total, and are structured into four main phases:

1. Pre-Exercise Baseline Assessment (approx. 20 minutes) Upon arrival at the designated exercise environment, participants will undergo a brief health and safety screening. Researchers will then collect baseline physiological data, including Heart Rate (HR), Heart Rate Variability (HRV), Blood Pressure (BP), and salivary cortisol samples. Following physiological sampling, participants will complete subjective psychological scales and perform two computerized cognitive tasks: the Stroop task (assessing inhibitory control) and the More-odd-shifting task (assessing cognitive flexibility).
2. Standardized Warm-Up (approx. 15 minutes) Participants will perform a standardized warm-up consisting of light jogging, dynamic lower-limb stretching, and low-intensity jump rope exercises. The intensity of this phase is strictly controlled at approximately 60% of the participant's maximum heart rate (HRmax) to ensure safety and physiological readiness for the subsequent high-intensity training.
3. HIIT Intervention Phase (15 minutes) Participants will engage in a standardized jump-rope HIIT protocol. The protocol involves 15 continuous rounds, with each round comprising 30 seconds of high-intensity jumping followed by 30 seconds of active recovery (e.g., slow walking or light ropeless jumping at 60-80 steps/minute). The high-intensity phases target an intensity of 85-90% HRmax (Rating of Perceived Exertion [RPE] 15-17), while the recovery phases target 55-60% HRmax (RPE 9-10). The jump rope variations are systematically divided into basic fast jumps (rounds 1-5), run-jumps (rounds 6-10), and mixed jump patterns including jumping jacks (rounds 11-15). Heart rate, movement quality, and physical status are continuously monitored by the research team throughout the session.
4. Post-Exercise Assessment (approx. 20 minutes) Immediately upon completing the 15-minute HIIT protocol, participants will undergo a second round of assessments identical to the baseline measurements. This includes the immediate collection of post-exercise physiological data (HRV, BP, Salivary Cortisol), completion of post-exercise psychological scales (assessing exercise enjoyment, affect, and perceived restorativeness), and a re-test of the computerized cognitive tasks.

This rigorous and highly controlled methodology ensures that any observed differences in stress regulation, executive function, and psychological exercise experience can be reliably attributed to the modulatory effects of the specific exercise environment.

Inclusion Criteria:

• Full-time college students aged 18 to 25 years old.
• Healthy, with no history of major cardiovascular, respiratory, neurological, or endocrine diseases.
• No exercise contraindications or lower limb injuries, able to safely complete high-intensity interval training (including jump rope).
• No recent events affecting physiological or psychological status, such as severe insomnia, anxiety, depression, or extreme fatigue.
• Have not taken medications or supplements affecting heart rate, blood pressure, mood, or attention in the past week.
• Normal vision or corrected-to-normal vision, capable of smoothly completing computerized cognitive tasks.
• Able to comprehend and truthfully complete psychological questionnaires.
• Voluntarily participate, fully understand the research procedures, and sign the informed consent form.

Exclusion Criteria:

• Severe cardiovascular diseases (e.g., myocardial infarction, severe arrhythmias, uncontrolled hypertension).
• Severe respiratory diseases (e.g., severe asthma, chronic obstructive pulmonary disease, or recent acute respiratory infections).
• History of neurological diseases or brain injuries (e.g., epilepsy, recent concussion) that may affect safety or cognitive tasks.
• Uncontrolled endocrine or metabolic diseases that may interfere with cortisol or metabolic measurements.
• Severe psychological disorders or receiving psychiatric treatment in the past month.
• Use of drugs or supplements significantly affecting heart rate, blood pressure, cortisol, or attention in the past 7 days.
• Currently pregnant or lactating.
• Acute illness in the past 48 hours (e.g., fever, acute gastroenteritis).
• Severe bleeding tendencies or blood disorders, unable to provide biological samples.
• Substance use interference, such as heavy drinking or substance dependence in the past 2 weeks.
• Unable to meet pre-experiment control requirements (e.g., avoiding caffeine, heavy exercise, tobacco).
• Unable to complete cognitive tasks (e.g., poor vision, inability to use a keyboard/mouse).
• Injuries or conditions limiting the safety of HIIT (e.g., recent severe lower limb injury).
• Participation in similar HIIT environmental intervention studies within the past 3 months.
• Insufficient ability to give informed consent or unwilling to sign the consent form.