1. Research Purpose Intensive training often causes autonomic nerve imbalance, poor microcirculation and slow fatigue recovery in elite sailing athletes. This study adopted 1.3 ATA mild hyperbaric oxygen with 28% oxygen concentration for a 6-week intervention. It aimed to explore whether mild hyperbaric oxygen can improve athletes' autonomic nerve function, microcirculation and fatigue-related biochemical indicators. Meanwhile, it intended to estimate the effect size, provide basis for future large-scale formal trials, and optimize fatigue recovery strategies for sailing athletes and other endurance athletes.

2. Study Population A total of 16 elite male sailing athletes were enrolled and randomly divided into two groups with 8 participants in each group.

   Inclusion criteria: aged over 18 years; holding national first-class athlete certificate or above; participating in systematic sailing training at least 5 times a week with more than 5 years of professional training experience.

   Those with cardiovascular diseases, absolute contraindications to hyperbaric oxygen, training suspension due to injury and other ineligible conditions were excluded.

3. Primary Outcome Measures Autonomic nerve function: Heart rate variability (HRV) indicators were tested to observe whether hyperbaric oxygen balances sympathetic and parasympathetic nerves and relieves training-induced autonomic disorder.

Microcirculation function: Measured muscle microcirculation blood flow velocity, capillary perfusion and thermal stimulation microvascular reserve capacity to evaluate the improvement of peripheral blood circulation.

Fatigue and biochemical biomarkers:

Routine blood indexes: red blood cell, hemoglobin, white blood cell; Exercise injury and metabolic indexes: creatine kinase (CK), blood urea nitrogen (BUN), testosterone and cortisol; Oxidative stress indexes: malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), to assess the body's oxidation-antioxidant status, inflammation level and fatigue recovery degree.

Inclusion Criteria:

• Male elite sailing athletes aged 18-35 years
• Holding a national first-class athlete certificate or above
• With at least 5 years of professional sailing training experience
• Engaging in regular sailing training ≥ 5 times per week
• Voluntarily sign the informed consent form

Exclusion Criteria:

• - Presence of cardiovascular, respiratory, or neurological diseases
• Absolute contraindications to hyperbaric oxygen therapy
• Current injury or illness requiring medical treatment or training suspension
• Use of any medications or supplements that may affect fatigue recovery or autonomic function
• Participation in other concurrent recovery interventions during the study