Psychophysiological Effects of Green Exercise in Outdoor Green vs. Indoor Control

Lincoln University College80 enrolled

Overview

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.

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.

Interventions

Outdoor Green GroupBEHAVIORAL

Participants perform a supervised 30-minute walk at a moderate pace (4.0-5.5 km/h) along a pre-defined 2.5 km loop trail within a suburban forest park. The environment is characterized by high canopy cover (\>60%) and diverse natural vegetation. To ensure consistency, all sessions are conducted under stable weather conditions (Temperature: 20-26°C; Humidity: 40-60%). Participants walk individually to prevent social interaction, ensuring the restorative experience is derived solely from the individual-nature interaction.

Indoor Control GroupBEHAVIORAL

Participants perform a 30-minute walk on a treadmill in a windowless indoor laboratory. To ensure consistency with the outdoor environment, the laboratory is climate-controlled with a temperature range of 20-26°C and humidity of 40-60%. The treadmill is set to a fixed moderate speed (4.0-5.5 km/h) with a 1% incline. The 1% incline is specifically applied to compensate for the lack of air resistance indoors and to accurately match the physiological energy expenditure and biomechanical demands of outdoor ground walking. The laboratory walls are neutral-colored to eliminate visual nature stimuli.

Outcomes

Primary Outcomes

Change in Profile of Mood States - Total Mood Disturbance (ΔTMD)

The POMS TMD is a self-report scale consisting of 6 subscales: Tension, Depression, Anger, Fatigue, Confusion, and Vigor. Each item is rated on a 5-point scale (0 = Not at all to 4 = Extremely). The TMD score is calculated as: (Tension + Depression + Anger + Fatigue + Confusion) - Vigor. The final outcome (ΔTMD) is the difference between the post-intervention TMD score and the pre-intervention (baseline) TMD score \[ΔTMD = TMD (Post) - TMD (Pre)\]. TMD scores range from -120 to 120. A larger negative ΔTMD value indicates a greater reduction in negative emotions and more significant psychological restoration.

Time frame: From Baseline (Pre-test) to 30 minutes post-intervention (Post-test)

Secondary Outcomes

Nature Relatedness (NR)

This scale assesses the individual's levels of self-identification and connection with the natural world across three specific dimensions: NR-Self (e.g., "I feel that I am a part of nature"), NR-Experience (e.g., "I enjoy being outdoors, even in unpleasant weather"), and NR-Perspective (e.g., "Animals and plants should have rights similar to humans"). Items are rated on a 5-point Likert scale (1 = Strongly Disagree to 5 = Strongly Agree). The Nature Relatedness (Final Score) is calculated as the average of all item scores. Total scores range from 6 to 30, where higher scores represent a stronger subjective connection and identification with nature.

Time frame: Baseline (T0, before intervention)

Nature Sensory Sensitivity Index (NSSI)

The NSSI is a composite index designed to quantify objective and subjective sensory information harvesting across three sections:1. Section A: Free Recall: Participants have 2 minutes to list specific natural details perceived through sight, sound, smell, or touch. The score is the total number of valid natural items recalled.2. Section B: Sensory Recognition: A checklist of sensory items (e.g., fragrance of pine, rustling leaves) where participants tick items actually perceived. The score is the number of correct hits, excluding distractors (e.g., traffic noise).3. Section C: Aesthetic Immersion: A 3-item scale assessing immersion and "oneness" with the environment. Items are rated on a 5-point Likert scale (1 = Strongly Disagree to 5 = Strongly Agree).The final NSSI score is a weighted composite of these three sections. The total score ranges from 0 to 100, higher scores indicate a greater volume, accuracy, and depth of sensory stimuli captured during the intervention.

Time frame: Immediately after the 10-minute intervention (T1)

Change in Perceived Restorativeness Scale (ΔPRS)

This scale assesses the participant's subjective perception of the environment's restorative qualities across four dimensions: Being Away, Fascination, Extent, and Compatibility. Each item is rated on a 5-point scale (1 = Not at all to 5 = Extremely). The final outcome (ΔPRS) is calculated as the difference between the post-intervention score and the pre-intervention baseline score \[ΔPRS = PRS (Post) - PRS (Pre)\]. The score for this change measure ranges from -4 to 4 (based on the average score difference). A positive ΔPRS indicates an increase in the perceived restorative quality of the environment.

Time frame: From Baseline (T0) to Immediately after the 10-minute intervention (T1)

Change in Total Digit Span Score (ΔDigit Span)

This measure assesses the restoration of attention and working memory through two tasks: Digit Span Forward (Part A) and Digit Span Backward (Part B). For each task, participants are tested on span lengths from 3 to 9 digits, with two trials provided for each length. The Total Digit Span Score is the sum of the maximum spans or total successful trials from both tasks (A+B). The total score for this measure ranges from 0 to 18. The final outcome is the change score calculated as \[ΔDigit Span = Digit Span (Post) - Digit Span (Pre)\]. An increase in the score represents improved cognitive focus and restoration of directed attention.

Time frame: From Baseline (T0) to immediately after the 30-minute intervention (T2)

Change in Self-Esteem (ΔSelf-Esteem)

This scale measures the participant's state self-esteem and sense of self-worth based on their feelings "RIGHT NOW". It consists of 4 items assessing self-worth, positive qualities, attitude toward oneself, and self-satisfaction. Each item is rated on a 4-point scale (1=Strongly Disagree to 4=Agree). The total self-esteem score ranges from 4 to 16. The final outcome (ΔSelf-Esteem) is calculated as the difference between the post-intervention score and the pre-intervention baseline score \[ΔSelf-Esteem = Self-Esteem (Post) - Self-Esteem (Pre)\]. The score for this change measure ranges from -12 to 12. A positive ΔSelf-Esteem indicates an improvement in the individual's sense of self-worth following the intervention.