This randomized controlled trial investigates the effects of hot spring balneotherapy on central fatigue elimination in adolescent rowers undergoing altitude training at approximately 1600 meters (Tengchong, Yunnan). Thirty adolescent athletes (aged 12-16 years) will be stratified by sex and randomly allocated to three groups: Group A (natural recovery, no immersion), Group B (38°C pure water immersion), and Group C (38°C sodium bicarbonate hot spring immersion). Interventions will be administered 3 times per week for 4 weeks. The primary outcomes are central fatigue indices including voluntary activation (VA) and central activation ratio (CAR). Secondary outcomes encompass cognitive function (Stroop test, Psychomotor Vigilance Test), cerebral hemodynamics (functional near-infrared spectroscopy, transcranial Doppler ultrasound), exercise performance (maximal oxygen uptake, 1000m test, 500m test), blood lactate, and hematological parameters (white blood cells, neutrophils, platelets).

Altitude training induces central fatigue characterized by decreased descending neural drive from the brain to skeletal muscle, reduced voluntary activation, and impaired cognitive function. This study employs a stratified randomized block design to evaluate whether post-exercise hot spring immersion can accelerate central fatigue recovery compared to pure warm water immersion and natural recovery. All participants will undergo standardized rowing training at approximately 1600 meters altitude. Group C will receive immersion in natural hot spring water at 38°C for 20 minutes. Group B will receive immersion in pure water at the same temperature and duration as a thermal control. Group A will undergo standard training recovery without immersion. The study incorporates partial blinding: Groups B and C are single-blinded to participants (identical appearance and protocol); Group A serves as an open-label control. Assessments will be conducted at baseline (pre-altitude), mid-intervention (Week 2), end-intervention (Week 4), and follow-up (1-2 weeks post-altitude).

Inclusion Criteria:

• Male or female aged 12-16 years- Healthy with no serious chronic diseases or skin conditions
• At least 1 year of systematic rowing training experience
• Currently undergoing centralized altitude training at approximately 1600 meters- No history of systematic hot spring or spa immersion within the past month
• No allergy history to sodium bicarbonate or hot spring minerals- Ability to provide written informed assent (participant) and written informed consent (parent/guardian)- No acute infection, fracture, or surgery within the past month
• Not currently taking non-steroidal anti-inflammatory drugs (NSAIDs), immunosuppressants, or medications affecting autonomic or cognitive function

Exclusion Criteria:

• History of cardiovascular, respiratory, renal, endocrine, or neurological disorders- Uncontrolled hypertension or hypotension
• History of syncope, heat intolerance, or severe dizziness during hot water immersion- Open wounds, severe eczema, or other skin conditions contraindicating water immersion
• Current use of beta-blockers, anticholinergics, stimulants, sedatives, or other medications affecting central nervous system function
• Color blindness or uncorrected visual impairment affecting Stroop test performance- Pregnancy (for female participants)- Alcohol consumption or smoking
• Shift work or trans-meridian travel within 2 weeks prior to baseline assessment
• Any condition deemed by the investigator as unsafe for participation

The project is still ongoing, and there are no current plans to contribute the data. Whether to share it will be considered after the data is officially published.