The Effects of High Intensity Circuit Training in Nature Vs. Indoor on Exercise Performance, and Wellbeing

Introduction: Nature environments are "any outdoor spaces that retain noticeable elements of nature, ranging from pristine or seminatural areas to urban green or blue spaces, including green infrastructure". Exercising in nature settings has been shown to improve well-being outcomes such as lower anxiety and greater positive mood, more so than exercising in artificial environments like urban spaces or indoors.

Over the past decades, the well-being benefits of nature-based exercise have been extensively reported in the literature, but exercise and sport performance have not been studied as much, in spite of some studies showing that performance may be better in natural settings than indoor conventional settings (e.g., dancing more vigorously, more power in cycling, ability to run more distance until exhaustion). This raises the question of how nature may impact performance efficacy (the product of performance, i.e., running faster) and efficiency (the psychological and physiological processes that may enhance performance efficacy) in exercise and sport activities, especially since many studies show, for example, that achieving the same goal in nature is less effortful than doing the same activity indoors.

The relationship between the exercise factor and the environment factor for potential health and performance benefits can be seen as sub-additive (less than total independent benefits of both exposures), additive (equal to the sum of the parts), and synergistic (greater than the sum of the parts).

Mechanisms: The mechanism by which physical activity in nature environments induces greater health and may enhance performance is not yet fully understood. Historically, the exercise and sport communities have created "proper" spaces to undertake their physical activities, such as gyms, stadiums, tracks. However, these standardized and artificial spaces are believed to offer limited variability in action. The ecological dynamics perspective views nature settings as a more varied and challenging landscape of affordances (possibilities for action) than that of built environments. Variability in the environment turns into variability in body systems, allowing for degenerate behavior (changing movement structure without compromising functionality). Assuming that the nature environment presents a richer and more variable landscape of affordances to exercisers has given birth to a theory within the ecological dynamics framework, labelled EVA, or the Empowering Variability of Affordances of Nature. To this end, EVA assumes that the uneven surfaces, objects and obstacles of nature settings such as grassland and trees allow for more variable athletic behavior, which has been deemed beneficial for exercise and sport performance. It must not be a coincidence that activities mostly practiced in natural environments such as extreme sports, are notorious for their demand for adaptability and creativity, and for promoting health.

Furthermore, for exercisers, the nature environment is known to elicit dissociative/exteroceptive attentive focus (i.e., focus on the environment), while the built/indoor environment elicits associative attentive focus (i.e., focus on the task itself). An associative cognitive process (focus on the task) is known to cause lower affective responses and greater exertion during exercise, particularly in high intensity physical activities. In short, exercising in nature may improve wellbeing and athletic performance due to inherent variability in action, and by eliciting exteroceptive attentive focus.

Need for a trial: Variability in behavior depends also on the task. Running or walking is essentially a journey throughout the environment in which interaction with obstacles, puddles, and other runners is part of the variability of the activity. However, HICT is done in a small area, and is a scripted, prescribed activity, lowering the amount of variability in behavior (e.g., push-ups, sit-ups). Thus, the aim of this study is to test if a closed circuit, scripted, anaerobic exercise (HICT) shows differences in movement variability, performance, and wellbeing, depending on the exercise environment (nature vs. indoor), in healthy, fit adults.

Familiarization session: Each participant goes individually to the Sport Expertise Laboratory (Spertlab) in Faculdade de Motricidade Humana and delivers the Informed Consent. The investigator then places the chest band (Polar H10) on the participant according to the correct usage guidelines, for familiarization purposes.

The participant is then shown and instructed on the Greenness Rating Scale and International Physical Activity Questionnaire (baseline questionnaires), followed by the Feeling Scale, Felt Arousal Scale, and Rating of Perceived Exertion (pre- and post-exercise measurement scales). Then the investigator demonstrates all the exercises planned for the exercise sessions, explaining to the participant the correct way to perform each one. The investigators remind that the participant should not exercise for 24 hours before the exercise sessions, and schedule two exercise sessions 48 hours apart (to prevent carry-over effects) in the following two weeks. Finally, the investigators collect the chest band and inform the participants that they must avoid ingesting caffeine, alcohol, and practicing high intensity physical activity in the 24 hours prior to the intervention sessions, and avoid ingesting food and liquids (except water) in the 3 hours prior to the sessions.

Placement of the Inertial Measurement Units (IMUs): Two IMUs are placed at the midpoint between the lateral epicondyle and the greater tubercle of the humerus, and between the lateral epicondyle and the greater trochanter of the femur, both on the right side. The upper (UL) and lower limbs (LL) are the body segments with greater activity during these calisthenic exercises; additionally, the proximal segment of the limbs is biarticular and does not run the risk of being fixed to the ground, as is the case of the hands/forearms during push-ups, and the feet/legs during squats, which would reduce the range of motion, and consequently have lesser detectable acceleration.

Intervention: As the exercise session approaches, the investigators get in touch to remind the participants about the session, to bring comfortable clothes (sports equipment). On the appointed day and time, the investigators and the participants meet at Faculdade de Motricidade Humana (FMH), and are escorted to the exercise site (Spertlab if indoor, Jamor park if outdoor). The investigators place the IMUs and the chest band on the participants as defined, deliver the Greenness Rating Scale, Feeling Scale, Felt Arousal Scale, and Rating of Perceived Exertion (available on a tablet or paper support) and inform participants that they can exercise at whatever pace they wish. The exercise session is made of 12 calisthenic exercises and is 20 minutes long (60 seconds active and 30 seconds resting per exercise), including warm-up and cool-down. The exercise session intervention will be conducted by a certified fitness instructor who will not know the objectives of the study (blinding). Exercise times will be controlled by the instructor, who will remind and if needed demonstrate to the participants what the next exercise is during the rest periods. Immediately after performing the exercises, before cool-down, participants complete the Rating of Perceived Exertion, and after returning to calm, they complete the remaining post-exercise questionnaires, and the investigators collect the chest bands and IMUs. After the session, the investigators accompany the participants again to FMH, confirm the next session in a minimum of 48 hours, and answer any queries. Participants who performed the indoor session will do the next session outdoors, and vice versa.