Acute effects of outdoor versus indoor exercise: a systematic review and meta-analysis.

Exercise and nature exposure are independently recognised for their positive relationship with health, but their combined effects are not fully understood. The present review summarises the evidence that compares physiological and perceptual differences of a single bout of exercise performed outdoors versus indoors. Nine databases were searched for articles published before March 2021 which utilised controlled designs to assess at least one physiological outcome during or after a single acute bout of outdoor exercise. When appropriate, quantitative analyses were completed. Quality of articles was assessed using the Cochrane Risk of Bias Assessment Tool. The findings of 38 articles (Total N = 1168) were examined. Participants were primarily healthy. Summarised outcomes included objective exercise intensity, perceived exertion, performance, neuroendocrine and metabolic responses, cardiovascular responses, thermoregulation, enjoyment, intention for future exercise, and perceptions of the environment. Outdoor environments increased enjoyment (N = 234, K = 10, g = 1.24, 95% CI = [0.59, 1.89], p < 0.001). Findings for remaining outcomes were non-significant or inconclusive and challenging to interpret due to high risk of bias. Overall, outdoor exercise appears to feel more enjoyable than indoor exercise when matched for intensity, with equivocal physiological benefit.