Faculty Mentor: Amy McDonnell (Psychology, University of Utah)

 

Abstract

Prior research demonstrates that a walk in nature can aid in efficient recovery from stress. This study explored whether cell phone usage influences the stress-related benefits of a 40-minute walk in nature. 88 participants from the Salt Lake Valley were randomized to either walk in nature while talking on their cell phone or walk in nature not on their cell phone. It was hypothesized that the group that was not on their cell phone would show a decrease in stress after their walk whereas the cell phone users would not, suggesting cell phone use may interfere with the stress-related benefits of immersion in nature. Stress was measured in 5-minute intervals before and after the walk using electrocardiography (EKG). Heart rate (HR) and heart rate variability (HRV) measures were extracted from the EKG trace as indicators of stress and stress recovery, respectively. There were no significant changes in HR for either group. HRV decreased significantly from before to after the walk for the group that was not on their cell phone but did not change for the group that was, indicating less efficient stress recovery for the participants not on their cell phone. It is possible that the cell phone group had better stress recovery due to the social benefits of talking to a loved one on the phone during their walk in nature.

Keywords: electrocardiography, heart rate, heart rate variability, stress, nature, stress recovery

Introduction

In a time when accessibility to mobile phones and other connected devices are at an all-time high, technological overconsumption is easier than ever. The World Health Organization has highlighted excessive technology use as a public health concern (Organization, 2015), and researchers have demonstrated that excessive cell phone use can lead to stress and anxiety (Cheever et al., 2014). How can we unwind? Many seek relaxation by spending time in nature, but if we aren’t fully disconnecting from technology, how effective can it really be?

Ulrich and colleagues (1991) have shown that natural environments can help individuals recover from stress more efficiently than urban environments can. Their theory, Stress Reduction Theory (SRT), states that being in nature activates the parasympathetic nervous system—the body’s ‘rest and digest’ system—and increases affect. This helps the body recover from stress more efficiently (Ulrich et al., 1991). Scott et al. (2021) expanded this theory by emphasizing the interconnectedness of the peripheral nervous system (PNS) and the central nervous system (CNS). Activity in the vagus nerve—which connects the PNS to the CNS—is associated with positive improvements in cognitive function, affect, and is linked to parasympathetic activation. Vagus nerve activity can be measured using heart rate variability (HRV; Uchino et al., 2007), which is defined as the variability between heart beats. High HRV is associated with efficient stress recovery and low variability is linked to poor stress recovery.

While nature has been shown to be restorative (McDonnell & Strayer, 2024), it is possible that technology can inhibit this effect (Jiang et al., 2018). Jiang and colleagues (2018) demonstrated that using a laptop while immersed in nature interfered with nature’s restorative effectsAdditionally, excessive cell phone use is associated with lower nature contact and subsequently lower levels of subjective well-being, psychological well-being, and mindfulness (Wang et al., 2021). It is possible that the more time one allocates to being on their cell phone, the less time available to go outdoors and do other activities. Likewise, cell phone usage often leads to more cell phone usage to achieve the same level of satisfaction, suggesting some level of habituation to the rewarding aspects of technology (Wang et al., 2021).

There is a gap in the literature regarding how technology use in natural environments influences stress levels. Moreover, there are very few studies investigating technology use in green spaces overall, and virtually none involving mobile phones. The current study explores the influence of cell phone use on the stress-related benefits of a 40-minute walk in nature by randomizing participants to walk in nature on their cell phone or not on their cell phone and measuring HR and HRV before and after their walk. It was hypothesized that participants walking in nature without talking on their cell phone would be less stressed (lower HR) and have better stress recovery (higher HRV) than participants talking on their phone.

Methods

All methods were approved by the University of Utah Institutional Review Board and informed consent was obtained from each participant prior to the beginning of the study.

Participants. Participants (N = 88; 18-40 years old) were recruited from the University of Utah SONA Participant Pool, social media, and flyers.

Procedure. Upon arrival to the laboratory at Red Butte Garden, participants completed a consent form and demographics survey. They were then set up in the BIOPAC ECG equipment, which comprised of three electrodes affixed to the torso—one on the right collarbone and two on their abdomen (one on each side). Once ECG electrodes were set up, the researcher collected a 5-minute, “pre-walk” recording before participants went for a 40-minute, 2-mile walk in nature. Participants were randomized to either walk while talking on the cell phone or without their cell phone. The cell phone group was instructed to call someone of their choosing. The walk was the same for each participant and averaged about 40 minutes. Physical movements were tracked using a Garmin GPS- an exercise-tracking watch to ensure comparable conditions for both groups. Once the walk was completed participants came back to the lab for a 5-minute, “post-walk” ECG recording.

ECG Recording and Processing. ECG data was processed using AcqKnowledge software following a standard protocol created using guidelines from BIOPAC. Bandpass filters were put on ECG recordings from 0.5-35 Hz. QRS peaks were marked using an algorithm built into AcqKnowledge and kept for analysis. Data was visually inspected for missing peaks and artifacts, which were manually replaced or edited using the detection algorithm of Bernston and colleagues (1990). Data were epoched into 60 second intervals, for a total of 5 intervals per recording. Frequency domain (RSA) and time domain (HR; beats per minute) parameters were retrieved from each epoch and then averaged to create overall RSA and HR metrics per file.

Data Analysis. All analyses were conducted in Python using Google Collab and linear mixed effects models were run to understand the interaction of interest (Time [pre-walk versus post-walk] by Condition [Cell Phone vs. No Cell Phone]. This was intended to identify whether any pre- to post- walk changes differed between the cell phone and the non-cell phone group. For each outcome measure (HR and HRV), we ran a model testing the main effect of condition, the main effect of time, and the interaction between time and condition.

Results

no main effect of condition (β = 2.190, z = 0.657, p = 0.511; 95% CI [-4.343, 8.724]) nor time (β = 1.850, z = -1.686, p = 0.092; 95% CI [-6.747, 0.506]) on HR, nor a significant interaction between condition and time (β = 2.617, z = -0.513, p = 0.608; 95% CI [-6.470, 3.787]). This suggests that resting HR did not change from pre-walk to post-walk for either group.

There was no main effect of condition (β = 0.344, z = -1.p = 0.283; 95% CI [-1.044, 0.305]), nor time (β = 0.260, z = 0.325, p = 0.745; 95% CI [-0.425, 0.594]) on HRV. There was a significant interaction between condition and time (β = 0.368, z = 2.072, p = 0.038; 95% CI [0.041, 1.482]), such that the group that was not on their cell phone showed a significant decrease in HRV after their walk while the cell phone group did not.

Discussion

The intent of this study was to provide insight into a neglected area in research concerning the interaction between technology usage and time in nature. Participants were randomized to either walk in nature undistracted (N=44) or walk in nature while talking on their cell phone (N=44). We hypothesized that participants not on their cell phone would exhibit more efficient recovery from stress after their walk (higher HRV) than those on their cell phones; however, the results indicate otherwise. The cell phone group did not display any significant changes in HRV whereas the no cell phone group displayed a significant decrease in HRV from before to after their walk, indicating a stress response. It is possible that the cell phone group displayed a buffering effect against the stress effect that the no cell phone group exhibited, potentially due to the social connection felt from talking on the cell phone, as all the participants chose to chat with a loved one on their walk.

Deits-Lebehn and colleagues (2023) found that the quality and valence of social interactions can influence stress recovery. If we apply this to the current study, the supposed positive social interaction of talking to someone they love could have increased their stress recovery. Negative social interactions can have an impact on HRV as well, leading to decreases in stress recovery (Deits-Lebehn et al., 2023). Additional investigations can explore negative social interactions in nature, which can be done with or without cell phones. Furthermore, subsequent research can be done examining different types of cell phone use while in nature. This could be scrolling on their phones (social media, email, etc.) listening to music, or playing a game. There are many implications to be explored in this field of technology use and nature.

There may be other confounds as well, like exercise. It is known that causes oxidative stress within the body (Powers et al., 2011). To see the effect nature has on the participant’s stress after the walk, future work may consider waiting 20-30 minutes before collecting the post-walk recording (Javorka et al., 2002). This would allow the body to fully recover from the stress caused by walking.

Another study could be done in this same design, but have the participant sit in a natural environment instead of walking. This would remove the confound of exercise, all together.

To conclude, this study sought to determine the impact cell phone usage has on stress levels within a natural environment, incorporating electrocardiographic measures of HR and HRV to understand how the body responds to and recovers from a 40-minute nature walk. Interesting results revealed stress recovery was significantly greater in individuals who talked on their cell phone during their walk as opposed to those with no cell phone. This effect could be due to the social restoration from talking to a loved one (Deits-Lebehn et al., 2023). This has opened the door for future research to continue investigating the effects of technology use in nature.

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