Myth: Training outdoors offers no real added benefit compared to the gym – as long as the heart rate is right. Evidence challenges this image. Nature-based interventions such as forest visits, green exercise, or trails not only produce similar physical stimuli, but they also lower stress markers, improve mood, and can enhance the sense of performance. In a review article on nature interventions, several randomized studies showed stronger improvements in depression, anxiety, and stress compared to control conditions – with no indication of inferiority compared to established therapies (e.g., cognitive behavioral therapy) ^[1]. The outdoors is not just a backdrop. It is a biological amplifier for body and mind.

Why does nature have such a strong effect? It combines three levers: multisensory stimuli, variable topography, and reduced cognitive load. The forest reduces mental overstimulation and promotes parasympathetic activitythe "recovery mode" of the autonomic nervous system, which dampens heart rate and stress hormones. Hills and elevation provide natural intermittent loadalternating intensity peaks and recovery phases that improve cardiometabolic adaptation. Waterways activate the proximal muscle chainsmuscle groups of the shoulder girdle, back, and trunk, important for posture and force transmission. At the same time, outdoor training challenges thermoregulationthe body's own temperature control, which can sharpen heat tolerance – with direct benefits for performance in summer. The crucial factors are dosage: short, regular, diverse. And: Nature is not a free pass – sun protection, hydration, and allergy/tick protection are part of the performance strategy.

The psychological gain is measurable. In a systematic review of nature interventions, anxiety and stress scores improved significantly more often than in control groups; nature-based offerings showed no inferiority compared to standard therapies ^[1]. Forest bathing reduced acute stress markers such as salivary cortisol and heart rate in studies, and improved subjective well-being significantly more than urban exposure or virtual simulations ^{[2] [3]}. External stimuli also enhance performance: Even mild dehydration of about 1% body mass worsened times in an outdoor mountain time trial by nearly 6%, increased core body temperature, and heightened the perception of exertion – a clear indication that fluid management outdoors is critical for performance ^[4]. At the same time, safety must not be overlooked: Excessive UV exposure accelerates skin aging and increases the risk of skin cancer – prevention through clothing, shade, and appropriate sun protection is essential ^[5]. In addition, activity windows and the frequency of ticks are increasing due to climate change; therefore, the risk for tick-borne infections is rising – education and protective measures are central ^[6]. Pollen can also trigger asthma exacerbations, especially in children and sensitized individuals; prevention is part of asthma management ^[7].

Two lines of research are particularly relevant for high performers. First: Nature as a stress modulator. In a randomized crossover study with highly sensitive individuals, the real forest clearly outperformed a high-quality 360° simulation – resulting in greater reductions of anxiety, stronger drops in heart rate, and better vitality scores. The added value lay in the full multisensory input: smells, microclimate, depth of spatial experience ^[2]. Additionally, a quasi-experimental study with eight sessions of forest bathing showed significant cortisol reduction and clinically meaningful shifts towards "normal" anxiety and stress values compared to guided urban walks – an argument for integration into prevention programs ^[3]. Second: Hydration as a performance factor in outdoor settings. In an outdoor climbing time trial, well-trained cyclists performed faster and with lower core body temperature and less subjective effort when euhydrated than with mild dehydration. Already a -1% loss of body mass was enough to provoke speed losses – presumably due to higher heat stress and reduced sweating response ^[4]. Complementary, a field study with female athletes showed that drinking amounts outdoors are often lower than indoors, even though sweat rates are similar; more than half exhibited signs of chronic underhydration. The authors recommend 24-hour fluid management and individual protocols (e.g., based on urine specific gravity) – pure practice for every outdoor session ^[8].

- Forest bathing, specifically: 1–2 times per week for 40–60 minutes in the forest without performance pressure. Breathe consciously, slow down the pace, and use all senses. Goal: noticeably calmer pulse and greater clarity after the session. Studies show stronger anxiety and stress reduction in the real forest than in simulations, as well as decreased cortisol after repeated sessions ^{[2] [3]}.
- Green Runs & Nature Walks: Plan 2–3 outdoor sessions per week in parks, along riverbanks, or in the forest. Utilize the natural interval dynamics (inclines/declines). Nature-based interventions improve anxiety and stress levels and do not fall short of established therapies – ideal as a building block for mental fitness ^[1].
- Hydration strategy for performance: Start euhydrated (light urine color, regular drinking in the 24 hours prior). Outdoors, many lose more fluid unnoticed but drink less. Adjust the amount of fluid to the weather, duration, and sweat rate, and check your individual protocol through morning urine color or USG, especially in heat ^[8]. Even -1% dehydration cost around 6% time in outdoor mountain time trials – drink accordingly (e.g., 0.4–0.8 L/h depending on conditions) ^[4].
- Kayaking/Canoeing for upper body & heart: 1–2 sessions per week lasting 30–45 minutes on calm water or on the ergometer. Studies show trends towards better trunk control, functional independence, and VO2 – valuable for posture, shoulder health, and cardiovascular diversity ^[9].
- Hilly terrains & mountains: Include one tour with elevation gain each week. Moderate hiking provides solid cardiometabolic stimuli and is well-tolerated by most, even those with non-severe cardio-pulmonary conditions. Increasing height/intensity enhances the exertion response, so progressive adaptation and building base fitness are essential ^[10].
- Sun protection as a performance standard: Prefer shade from 11 AM to 4 PM, wear UV-dense clothing, hat/glasses, use broad-spectrum SPF 30–50, and reapply every 2 hours. This minimizes DNA damage and long-term risks without compromising training ^[5].
- Tick and pollen management: In endemic areas, wear permethrin-treated clothing, use repellents with DEET/icaridin, perform daily body checks after outings; during high pollen exposure, time training (after rain, in the evening), use a filter mask during peaks, and consider medication prophylaxis following a doctor's plan. This significantly reduces infection and asthma risks ^{[6] [7]}.

The future of fitness is "Nature-Integrated": real-world stimuli plus precise self-management. We expect studies to develop personalized outdoor protocols based on stress profiles, heat tolerance, and sensitivity – including sensors for hydration and UV exposure. Those who smartly transition to the outdoors today will benefit tomorrow from increased resilience, performance, and longevity.