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

This registered clinical trial, currently recruiting, tests whether soaking in natural hot springs can help athletes adapt better to training at high altitude — an environment that stresses the body by reducing available oxygen. Athletes will be split into three groups: one bathing in natural hot spring water, one bathing in plain hot water at the same temperature, and one following standard recovery routines, all while undergoing the same high-altitude training programme. The clever three-arm design lets researchers separate the thermal effect of warm water from any additional biological effect unique to mineral-rich hot spring water. The main measures are heart rate variability (HRV) — a sensitive index of how well the autonomic nervous system is balancing stress and recovery — along with objective exercise performance tests. Secondary measures capture blood lactate (a marker of metabolic stress), blood oxygen saturation, and how tired athletes feel. If hot spring bathing improves HRV and performance beyond plain hot water, it would point to a mineral or specific balneological mechanism rather than just heat. The findings could offer athletes and coaches a low-cost, non-pharmacological recovery tool validated under controlled conditions. As a trial that is still recruiting, no results are yet available.

• No results reported yet — the trial is actively recruiting as of May 2026; all findings listed here are prospective outcomes the study is designed to detect.
• Primary outcomes to be measured: time-domain and frequency-domain HRV indices (reflecting cardiac autonomic modulation) and standardised exercise performance indicators collected across the altitude-training block.
• Secondary outcomes to be measured: blood lactate concentration, peripheral oxygen saturation (SpO2), and subjective fatigue scores — collectively indexing metabolic, respiratory, and perceptual adaptation to hypoxia.

Three-arm randomised controlled trial conducted in healthy athletes undergoing high-altitude training. Participants are randomly assigned to (1) hot spring immersion (38 °C, 20 minutes, three sessions per week), (2) hot water immersion at identical temperature and duration, or (3) a routine recovery control condition. The inclusion of a hot-water arm is a methodological strength: it allows thermal load to be held constant, isolating any effect attributable specifically to hot spring mineral content or balneological properties. Sample size, blinding procedures, altitude site, and total intervention duration are not yet specified in the public registration; study design details are rated best-effort from available metadata.

Because the trial is still recruiting, no empirical effect sizes, confidence intervals, or safety data are available, making all mechanistic interpretation premature. The absence of HPA-axis biomarkers (e.g., cortisol, ACTH) means the study cannot distinguish autonomic recovery from neuroendocrine stress adaptation, leaving a significant mechanistic gap. Athlete-only sampling limits generalisability to clinical or sedentary populations, and the three-session-per-week dose was selected pragmatically rather than derived from a dose-finding study. The next logical experiment would add salivary or urinary cortisol, extend the washout period, and test whether benefits persist after athletes return to sea level.

This trial extends [§69], which tested manual therapy techniques aimed at autonomic nervous system modulation in healthy adults, by substituting a thermal-hydrological intervention and embedding it within an altitude-stress model — both studies use HRV as the primary readout of autonomic tone. It runs parallel to [§110], which also examines physiological responses to hypoxic/altitude stress but focuses on respiratory control rather than recovery interventions, together framing altitude adaptation as a multi-system challenge addressable from different angles. The cryostimulation RCT [§83] offers a direct methodological comparator: like the present trial it applies a whole-body thermal stressor repeatedly to healthy men and measures cardiovascular autonomic outcomes, but in the cold rather than heat direction, making the two studies natural bookends for understanding thermal dose–direction effects on autonomic balance. The psychophysiological biomarker work in [§82] is relevant because IBS-constipation patients show measurable HRV-based autonomic dysregulation, illustrating how HRV stratification frameworks developed in clinical stress biology could be imported into athletic recovery research. Confidence in corpus placement is moderate-to-low given that no results are yet published and protocol details remain sparse.

• Repeated whole-body cryostimulation promotes a blood pressure reduction at rest in healthy adult men
  Most direct methodological comparator: also a repeated whole-body thermal-stressor RCT in healthy adults measuring cardiovascular autonomic outcomes, but uses cold (cryostimulation) rather than heat, allowing comparison of thermal direction on autonomic recovery.
• Effect of a Sequence of Specific Manual Therapy Techniques Targeting the Autonomic Nervous System in Healthy Adults
  Both trials use HRV as the primary endpoint to quantify autonomic modulation in healthy adults via a non-pharmacological physical intervention, making them directly comparable on outcome methodology despite different treatment modalities.
• Distinct psychophysiological biomarkers and risk stratification models for irritable bowel syndrome with constipation (IBS-C) and diarrhea (IBS-D)
  Demonstrates how HRV-based autonomic profiling can stratify biological stress responses in a clinical population; reading alongside this trial clarifies how the same metric functions across healthy athletic versus pathological stress contexts.
• The Impacts of Trauma Exposure on Emotion Regulation and 2 Vagally Mediated Heart Rate Variability
  Examines vagally mediated HRV as a biomarker of stress exposure and emotion regulation, providing mechanistic grounding for interpreting HRV shifts observed under altitude stress and hot spring recovery in the present trial.
• The Effect of Physiotherapy Integrated With Yoga and Mindfulness on Individuals With Fibromyalgia
  Tests a multimodal non-pharmacological intervention (physiotherapy plus yoga/mindfulness) on a stress-related condition, offering a comparative example of how combined recovery protocols are designed and their autonomic outcomes measured.