European Journal of Cardiovascular Medicine

Altitude training is widely recognized as a performance-enhancing strategy for athletes, with benefits including improved oxygen utilization, cardiovascular efficiency, and metabolic adaptation¹. Training at high altitudes or in simulated altitude environments induces physiological responses that may enhance athletic performance². However, the impact of simulated altitude training on hydration status, body composition, and heart rate variability (HRV) remains insufficiently explored, particularly in Indian athletes³.

Hydration plays a critical role in endurance and recovery, as altitude exposure can lead to increased respiratory water loss, dehydration, and changes in total body water⁴ (TBW). Monitoring urine osmolality and TBW can provide valuable insights into an athlete's hydration status during prolonged exposure to hypoxic conditions⁵. Similarly, body composition changes are essential to assess the impact of altitude training on lean muscle mass and fat metabolism, as previous studies have suggested a potential increase in lean body mass and a reduction in fat mass due to altered metabolic demands⁶.

Additionally, HRV is a key indicator of autonomic nervous system adaptation, reflecting the balance between sympathetic and parasympathetic activity. An increase in root mean square of successive differences (RMSSD) and a reduction in the low-frequency to high-frequency ratio (LF/HF) indicate improved recovery and cardiovascular adaptation. Understanding these responses is essential for optimizing training regimens and recovery strategies.

This study aims to evaluate hydration status, body composition, and HRV changes in 100 Indian athletes undergoing 6 weeks of simulated altitude training at 3000m, providing insights into physiological adaptations that may enhance athletic performance.

Place of Study

This study was conducted at the Department of Exercise Physiology, Sports Authority of India (SAI), Netaji Subhas National Institute of Sports (NSNIS), Patiala, India.

Study Period

The study was carried out over a period of 6 weeks, from August 2024 to 2^nd week of September 2024.

Study Design and Participants

A total of 100 Indian athletes were recruited for this prospective interventional study. Required permissions were obtained before starting the study,  Informed consent was obtained from all participants before enrollment, ensuring voluntary participation and data confidentiality.

The inclusion criteria were:

Age 18–35 years

Competitive athletes engaged in endurance and strength-based training

No history of cardiovascular, metabolic, or respiratory disorders

Athletes were exposed to simulated altitude training at 3000m using a normobaric hypoxic chamber while maintaining their regular training schedules.

Measurements and Assessments

Hydration Status

Urine osmolality (mOsm/kg): Measured using a digital osmometer

Total body water (TBW %): Assessed using bioelectrical impedance analysis (BIA)

Body Composition

Lean body mass (%) and fat mass (%): Evaluated using dual-energy X-ray absorptiometry (DXA) and BIA

Heart Rate Variability (HRV)

RMSSD (ms): Indicator of parasympathetic activity

LF/HF Ratio: Represents autonomic balance

Measurements were taken using ECG-based HRV monitors before and after training sessions.

Statistical Analysis

Data were analyzed using paired t-tests to compare pre- and post-training values, with statistical significance set at p < 0.05. Results were presented as mean ± standard deviation (SD).

The study assessed hydration status, body composition, and heart rate variability (HRV) over a 6-week simulated altitude training period in 100 Indian athletes. The key findings are summarized below.

Hydration Status

Hydration status was evaluated using urine osmolality and total body water percentage (TBW). The results indicate a significant reduction in urine osmolality from 584.42 ± 135.54 mOsm/kg at baseline to 533.75 ± 142.25 mOsm/kg at week 6, showing improved hydration levels. Additionally, TBW increased from 55.19 ± 3.24% to 56.80 ± 3.35%, reflecting better fluid retention during training (Table 1& Figure No:1).

Table 1: Hydration Status Over 6 Weeks

Figure No:1 Hydration Status Over 6 Weeks

Body Composition Changes

The study observed notable improvements in body composition over 6 weeks of altitude training. Lean body mass increased from 78.52 ± 4.11% to 80.15 ± 4.32%, while fat mass decreased from 16.21 ± 3.87% to 14.98 ± 3.75%. These changes indicate a positive shift towards improved muscular composition and fat reduction (Table 2 & Figure No:2).

Table 2: Body Composition Changes Over 6 Weeks

Figure No:2. Body Composition Changes Over 6 Weeks

Heart Rate Variability (HRV) Adaptations

HRV analysis revealed enhanced autonomic regulation after 6 weeks of training. The RMSSD values increased from 39.44 ± 10.58 ms at baseline to 44.09 ± 10.70 ms, indicating improved recovery and parasympathetic activity. Furthermore, the LF/HF ratio decreased from 1.82 ± 0.56 to 1.42 ± 0.51, suggesting a shift towards better autonomic balance and cardiovascular adaptation to altitude training (Table No:3 & Figure No:3).

Table 3: Heart Rate Variability (HRV) Over 6 Weeks

NSNIS

Figure No:3 Heart Rate Variability (HRV) Over 6 Weeks

This study examined the effects of six weeks of simulated altitude training at 3000m on hydration status, body composition, and heart rate variability (HRV) in Indian athletes. The findings suggest significant improvements in hydration maintenance, lean body mass, and autonomic recovery, reinforcing the physiological benefits of altitude training for endurance and performance enhancement.

Hydration Status Adaptations

The reduction in urine osmolality from 584.42 ± 135.54 to 533.75 ± 142.25 mOsm/kg (Table 1) suggests that athletes improved fluid retention and hydration efficiency during the training period. These findings are consistent with Castro-Sepulveda et al⁷. (2014), who demonstrated that hydration status influences resting metabolic rate and HRV, further supporting the importance of maintaining adequate fluid balance during altitude training. Additionally, the increase in total body water (TBW) percentage from 55.19 ± 3.24% to 56.80 ± 3.35% highlights better intracellular and extracellular water balance, crucial for thermoregulation and optimal performance. This aligns with Zito et al⁸. (2019), who emphasized that even mild dehydration can negatively impact gastrointestinal function and overall well-being in athletes.

Body Composition Changes

A significant increase in lean body mass (78.52 ± 4.11% to 80.15 ± 4.32%) and a decrease in fat mass (16.21 ± 3.87% to 14.98 ± 3.75%) (Table 2) suggest that altitude training promotes positive metabolic adaptations. This supports the hypothesis that hypoxia enhances muscle adaptation and fat oxidation, leading to a favorable shift in body composition, as noted by Schmitt L et al⁶. (2010). Additionally, elevated erythropoietin (EPO) production at altitude likely contributed to enhanced oxygen delivery and muscle function, facilitating lean muscle retention and fat metabolism (Adams et al⁹., 2014).

Heart Rate Variability (HRV) Adaptations

The increase in RMSSD (39.44 ± 10.58 ms to 44.09 ± 10.70 ms) and the reduction in LF/HF ratio (1.82 ± 0.56 to 1.42 ± 0.51) (Table 3) indicate improved parasympathetic nervous system activity and recovery capacity. These findings align with Mourot¹⁰ (2018), who reported that altitude exposure can influence autonomic control and HRV, contributing to cardiovascular efficiency. Moreover, Dhar et al¹². (2014) found that acclimatized individuals exhibit enhanced autonomic regulation over prolonged high-altitude exposure, further validating the HRV improvements observed in this study.

The findings of this study align with previous research demonstrating that altitude training improves hydration status, body composition, and autonomic regulation (Karpęcka-Gałka et al¹¹., 2024). However, studies conducted at higher altitudes (>4000m) have reported greater dehydration and muscle catabolism. In contrast, the moderate altitude (3000m) used in this study appears to optimize physiological benefits while minimizing risks, making it a suitable strategy for training adaptation.

Limitations and Future Directions

Despite its strengths, this study has some limitations. First, the use of a simulated hypoxic environment differs from real high-altitude exposure, which may affect adaptation. Second, individual hydration strategies and dietary intake were not strictly controlled, which could influence results. Future studies should explore longitudinal effects of altitude training on hydration and performance and compare simulated vs. real altitude exposure in different climatic conditions.

This study demonstrates that six weeks of simulated altitude training at 3000m significantly improved hydration status, body composition, and heart rate variability (HRV) in Indian athletes. The reduction in urine osmolality and increased total body water indicate enhanced hydration maintenance. Additionally, the increase in lean body mass and decrease in fat mass suggest positive metabolic adaptations. Improved HRV parameters reflect better autonomic balance and recovery capacity. These findings support the use of simulated altitude training as an effective strategy for optimizing athletic performance and physiological efficiency. Future studies should explore individual adaptation responses and performance outcomes in competitive settings.

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