Psychophysiological Effects of Green Exercise in Outdoor Green vs. Indoor Control (GREEN-OI)

Lincoln University College

Status: Completed

Conditions: Healthy Volunteers; Emotional Well-being; Psychological Stress; Mental Fatigue; Cognitive Dysfunction

Treatments: Behavioral: Indoor Control Group; Behavioral: Outdoor Green Group

Study type: Interventional

Funder types: Other

Identifiers

NCT07379164

WTU-IRB-2025-0113

Details and patient eligibility

About

Core Purpose: Researchers want to learn if walking in an outdoor green environment helps people recover from mental tiredness and stress better than walking indoors. This study investigates how a 30-minute walk in an outdoor green setting affects the mind and body compared to a 30-minute walk on a treadmill in a room without windows.

The Study Process: The study included 80 healthy young adults between the ages of 18 and 35. Researchers randomly split the participants into two groups.

1. The Outdoor Green group: Participants walked for 30 minutes on a path in an outdoor green environment.
2. The Indoor Control group: This group walked for 30 minutes on a treadmill in a windowless room.

What is Being Measured: To understand how the environment helps the brain recover, researchers used a "Sensory-to-Appraisal" model to measure several factors.

1. Information Harvesting: Researchers used a new tool called the Nature Sensory Sensitivity Index (NSSI). This measures how well participants notice and "capture" sensory details from their surroundings, like the sounds of birds or the textures of plants.
2. Restorative Feelings: Using the Perceived Restorativeness Scale (PRS), participants reported if they felt the environment helped them "get away" from daily stress and if the setting was interesting or beautiful.
3. Overall Mood Changes (POMS TMD): Researchers used the Profile of Mood States (POMS) to calculate a Total Mood Disturbance (TMD) score. This helps show if participants feel less tense, angry, or tired, and more energetic after the walk.
4. Connection to Nature (NR): Researchers measured each participant's Nature Relatedness (NR). This describes how much a person naturally feels connected to the natural world, which may influence how much they benefit from the green walk.
5. Attention and Thinking: Participants performed a "Digit Span Task" (repeating sequences of numbers) to test if their focus improved.
6. Physical Stress: The study used objective markers, including salivary cortisol (a stress hormone) and heart rate variability (a measure of how the nervous system relaxes).

Why This Matters: The goal of this research is to see if actively noticing an outdoor green environment (sensory harvesting) is the "key" that unlocks mental recovery. By comparing the Outdoor Green group with the Indoor Control group, this study helps us understand why nature is good for public health and how to design better spaces for stress relief.

Full description

Study Overview and Theoretical Framework This randomized controlled trial (RCT) aims to investigate the psychophysiological restorative effects of green exercise. The study is grounded in Attention Restoration Theory (ART) and Stress Recovery Theory (SRT). It specifically tests a "Sensory-to-Appraisal" model, which proposes that the restorative benefits of nature are driven by an initial stage of objective sensory information harvesting, followed by subjective restorative appraisal.

Experimental Design A total of 80 healthy young adults (aged 18-35) were recruited and randomly assigned to one of two groups with a 1:1 allocation ratio.

1. The Outdoor Green group: Participants performed a standardized 30-minute walk along a pre-defined route in a forest park environment.
2. The Indoor Control group: Participants performed a 30-minute walk on a treadmill in a controlled laboratory setting (windowless room, neutral environment) at a self-selected moderate pace to match the physical intensity of the outdoor group.

Experimental Procedure The experiment followed a five-stage longitudinal design.

1. Baseline (T0): Collection of demographic data, Nature Relatedness (NR) scales, and initial physiological/psychological measurements.
2. Stress Induction: Participants underwent a cognitive stressor to induce mental fatigue and psychological stress.
3. Intervention (T1): The 30-minute walking intervention in the assigned environment.
4. Post-Intervention (T2): Immediate post-test measurements including sensory harvesting (NSSI), perceived restorativeness (PRS), and emotional states.
5. Recovery Monitoring: Follow-up assessment of cognitive function and physiological recovery markers.

Key Measures

1. Sensory Harvesting: Measured by the Nature Sensory Sensitivity Index (NSSI), a tool designed to quantify the objective capture of environmental stimuli.
2. Psychological Appraisal: Evaluated via the Perceived Restorativeness Scale (PRS).
3. Cognitive Function: Assessed through the Digit Span Task (Forward and Backward) to measure working memory and directed attention.
4. Affective States: Measured using the Profile of Mood States (POMS) to calculate Total Mood Disturbance (TMD) and self-esteem scales.
5. Physiological Response: Objective stress recovery was monitored via salivary cortisol levels and Heart Rate Variability (HRV), specifically the RMSSD (Root Mean Square of Successive Differences) to assess parasympathetic activation.

Statistical Analysis The study uses a serial mediation model to analyze how the environment intervention influences restorative outcomes through the sequential mediation of NSSI and PRS. Mixed-model ANOVAs are used to compare between-group differences across time points.

Enrollment: 80 patients

Sex: All

Ages: 18 to 30 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

1. Healthy adults aged 18 to 30 years.
2. University students or individuals with equivalent educational background.
3. Normal or corrected-to-normal vision and hearing.
4. Willingness to comply with all study procedures and sign the informed consent form.

Exclusion criteria

1. Physical Health: History of cardiovascular disease, respiratory illness, or chronic pain that may affect Heart Rate Variability (HRV).
2. Mental Health: Diagnosis of clinical depression, anxiety disorders, or other psychiatric conditions.
3. Substance Use: Current smokers or individuals with a history of alcohol or drug abuse.
4. Medication: Recent use of any medications that affect the autonomic nervous system or endocrine function (e.g., steroids, beta-blockers, or hormonal medications) within the past month.
5. Cognitive/Physical Impairment: Any disability that prevents walking for 30 minutes or completing the Digit Span cognitive task.

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Parallel Assignment

Masking: None (Open label)

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80 participants in 2 patient groups

Outdoor Green Group

Experimental group

Description:

Participants in this arm perform a standardized 30-minute walk at a moderate pace along a pre-defined route in an outdoor green enviroment. This arm focuses on the effects of exposure to natural environmental stimuli.

Treatment:

Behavioral: Outdoor Green Group

Indoor Control Group

Active Comparator group

Description:

Participants walk on a treadmill at a fixed moderate speed (4.0-5.5 km/h) with a 1% incline. This specific incline is used to compensate for the lack of air resistance indoors and to more accurately match the physiological energy expenditure of outdoor ground walking.

Treatment:

Behavioral: Indoor Control Group