Effect of Hot Spring Therapy on Autonomic Nervous System and Exercise Performance During Altitude Training

Macao Polytechnic University27 enrolled

Overview

This randomized controlled trial aims to investigate the effects of balneotherapy (hot spring bathing) on cardiac autonomic nervous system function and exercise performance in healthy athletes undergoing high-altitude training. Participants will be randomly assigned to the intervention group (receiving hot spring baths three times per week (38°C, 20 minutes) combined with high-altitude training), the control group (receiving routine recovery protocols combined with high-altitude training), or the hot water immersion group (receiving hot water baths three times per week (38°C, 20 minutes) combined with high-altitude training). Primary outcome measures include heart rate variability (HRV) indices and exercise performance indicators. Secondary outcomes include blood lactate, peripheral oxygen saturation (SpO2), and subjective fatigue. These findings may provide evidence for non-pharmacological interventions to enhance high-altitude training adaptation and exercise recovery.

Study Type

INTERVENTIONAL

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

SINGLE

Enrollment

Conditions

Altitude Training Adaptation Autonomic Nervous System Hydrotherapy

Interventions

Control Group：Natural RecoveryBEHAVIORAL

Control group participants will undergo the same altitude training protocol (altitude 1600 meters) for 4 weeks. After each training session, participants will receive standard recovery procedures, including 20 minutes of passive rest in a thermoneutral environment (room temperature 24°C), supplemented with mild hydration and self-selected stretching. No hydrothermal intervention will be provided.

Hot water immersion groupBEHAVIORAL

The hot water immersion group will undergo a 4-week altitude training at 1600 meters above sea level. Subjects will receive a 20-minute hot water immersion (daily tap water, 38°C±1°C) in a standardized indoor hot spring facility. The immersion protocol includes whole-body immersion up to the neck for 20 minutes, followed by a 10-minute rest before leaving the facility. Three times per week.

hot spring immersion groupBEHAVIORAL

The hot spring immersion group will undergo a 4-week high-altitude training at an altitude of 1600 meters. Subjects will receive a 20-minute hot spring therapy (natural hot spring water, 38°C ± 1°C) in a standardized indoor hot spring facility. The immersion protocol includes whole-body immersion to the neck for 20 minutes, followed by a 10-minute rest before leaving the facility. Three times per week.

Eligibility

Sex: ALLMin age: 11 YearsMax age: 17 YearsHealthy volunteers:

Medical Language ↔ Plain English

Inclusion Criteria: * Male or female aged 11-17years * Regular endurance training (≥3 sessions/week) for ≥2 years * No history of altitude exposure \>2000m in the past 3 months * No contraindications to hot water immersion (e.g., uncontrolled hypertension, severe cardiovascular disease, open wounds, pregnancy) * Ability to provide written informed consent- Willingness to abstain from other recovery modalities (e.g., massage, cryotherapy, compression garments) during the study period Exclusion Criteria: * History of cardiovascular, respiratory, renal, or endocrine disorders * Current use of medications affecting autonomic function (e.g., beta-blockers, anticholinergics)- History of syncope or heat intolerance * Acute musculoskeletal injury within the past 6 months- Regular use of sauna, hot tub, or spa within the past month * Pregnancy or breastfeeding (for female participants)- Shift work or trans-meridian travel within 2 weeks prior to baseline assessment * Alcohol consumption \>14 units/week or smoking

Outcomes

Primary Outcomes

Heart Rate Variability (HRV) - RMSSD

Root mean square of successive differences (RMSSD) between normal heartbeats, measured from a 5-minute seated ECG recording in a quiet, temperature-controlled (22-24°C) room after 15 minutes of rest. A higher RMSSD value indicates stronger parasympathetic activity. Unit: milliseconds (ms). Baseline, Week 2, Week 3 (post-intervention).

Time frame: Baselines were measured at the formal start of the experiment, at night during the 2nd, 3rd, and 4th weeks (post-intervention) after ascending the plateau, and post-tests were conducted one week after descending the plateau.

1000-meter ergometer test.

Perform a 1000-meter all-out test on a rowing ergometer. Protocol: sprint at maximum effort to measure the shortest time. Record time. Units: seconds. Baseline, Week 3, Week 4.

Time frame: Baseline measurements were taken before the official start of the experiment and during the 3rd and 4th weeks after ascending to the plateau.

Secondary Outcomes

HRV - SDNN

Standard deviation of NN intervals (normal-to-normal R-R intervals), reflecting overall autonomic modulation. Unit: milliseconds (ms). Baseline, Week 2, Week 3, Week4, post-tests

Peripheral Oxygen Saturation (SpO2)

Resting peripheral oxygen saturation measured via fingertip pulse oximeter after 10 minutes of seated rest. Unit: percentage (%)

Time frame: one month.

Rating of Perceived Exertion (RPE)

Borg 6-20 scale rating of perceived exertion recorded immediately after each training session. Higher scores indicate greater subjective effort. Unit: score (6-20). Daily during intervention