Examination of the acute heart rate and salivary cortisol response to a single bout of walking in urban and green environments: A pilot study

Background: Regular physical activity can help prevent noncommunicable diseases, and improve mental health, quality of life, and well-being. ‘Green exercise’ is physical activity performed in natural settings such as parks and open green spaces. It is important to understand whether green exercise can provide additional physiological benefits over and above those of physical activity in urban environments. This pilot study compared the acute effects of a 30-min walk in a green environment to a 30-min walk in urban streets on adults’ heart rate and salivary cortisol. Methods: Using a 2 × 2 randomised cross-over design, groups of 2–5 adults completed two experimental sessions involving a randomly assigned walk in an urban or a green environment. Heart rate and salivary cortisol were collected at regular intervals before, during, and in the 1.5 h following the walks and were compared within and between participants. Peak height, reactivity, area under the curve with respect to ground (AUCg) and area under the curve with respect to increase (AUCi), were also calculated for heart rate and cortisol and compared between walking conditions. Results: The sample included 20 participants (50 % female, mean =24.4 ± 4.0 years). Changes in heart rate (Condition × Time: F[5.8, 103.8]=1.67, p = 0.140) or cortisol (Condition × Time: F[2.6, 49.5]=0.81, p = 0.482) in response to walking were not statistically significantly different between the urban and green walking conditions. There were also no statistically significant differences in heart rate or salivary cortisol for the peak height of the response, reactivity, or AUCi or AUCg between the urban and green walking conditions. Conclusion: Our findings suggest that physical exertion is the main driver of the acute physiological response to walking. Notwithstanding psychological benefits reported elsewhere, the acute physiological response to walking was not influenced by the green compared with the urban environment in the current study. Further research is warranted to understand the longer-term effects of regular green exercise.