Marching to the Beet: The effect of dietary nitrate supplementation on high altitude exercise performance and adaptation during a military trekking expedition.

PURPOSE: The aim was to investigate the effect of dietary nitrate supplementation (in the form of beetroot juice, BRJ) for 20 days on salivary nitrite (a potential precursor of bioactive nitric oxide), exercise performance and high altitude (HA) acclimatisation in field conditions (hypobaric hypoxia). METHODS: This was a single-blinded randomised control study of 22 healthy adult participants (12 men, 10 women, mean age 28 ± 12 years) across a HA military expedition. Participants were randomised pre-ascent to receive two 70 ml dose per day of either BRJ (~12.5 mmol nitrate per day; n = 11) or non-nitrate calorie matched control (n = 11). Participants ingested supplement doses daily, beginning 3 days prior to departure and continued until the highest sleeping altitude (4800 m) reached on day 17 of the expedition. Data were collected at baseline (44 m altitude), at 2350 m (day 9), 3400 m (day 12) and 4800 m (day 17). RESULTS: BRJ enhanced the salivary levels of nitrite (p = 0.007). There was a significant decrease in peripheral oxygen saturation and there were increases in heart rate, diastolic blood pressure, and rating of perceived exertion with increasing altitude (p=<0.001). Harvard Step Test fitness scores significantly declined at 4800 m in the control group (p = 0.003) compared with baseline. In contrast, there was no decline in fitness scores at 4800 m compared with baseline (p = 0.26) in the BRJ group. Heart rate recovery speed following exercise at 4800 m was significantly prolonged in the control group (p=<0.01) but was unchanged in the BRJ group (p = 0.61). BRJ did not affect the burden of HA illness (p = 1.00). CONCLUSIONS: BRJ increases salivary nitrite levels and ameliorates the decline in fitness at altitude but does not affect the occurrence of HA illness.

The Effects of Apnea Training, Using Voluntary Breath Holds, on High Altitude Acclimation: Breathe-High Altitude Study.

Introduction: There is evidence that intermittent hypoxic exposure (IHE) may improve high altitude (HA) performance. In this study, the effects of short-term IHE through voluntary apnea training on HA-related symptoms, including acute mountain sickness (AMS), were examined for the first time. Methods: Forty healthy adults were randomized to a self-administered apnea training (n = 19) or control (n = 21 no apnea training) group before ascent to an altitude of 5100 m in the Himalayas over 14 days. The apnea training was conducted at sea level (SL) and consisted of five breath holds per day in week 1, seven in week 2, followed by 10 per day from weeks 3 to 6 and until HA exposure. Saturation of arterial oxygen (SpO2), heart rate, sleep quality (Insomnia Severity Index [ISI]), rating of perceived exertion (RPE), blood pressure, and Lake Louise scores were measured at SL (in the United Kingdom) and at HA at 1400, 2700, 3400-3700, 4050-4200, 4800, and 5100-5200 m. Anxiety (Generalized Anxiety Disorder-7 [GAD-7]) scores were examined at SL, 1400, and 5100-5200 m. Results: Apnea training led to a significant increase in the mean longest breath-hold times from baseline (80.42 ± 32.49 [median 87.00] seconds) to the end of week 6 (107.02 ± 43.65 [113.00] seconds), respectively (p = 0.009). There was no significant difference in the prevalence of AMS (8/19 = 42.1% vs. 11/21 = 52.4%; RR 0.80; 95% confidence interval 0.41-1.57: p = 0.80) or in GAD-7, ISI and RPE, SpO2, heart rate, or blood pressure among the apnea versus control groups, respectively, at HA. Conclusions: Apnea training does not lessen HA-related symptoms in healthy adults traveling up to 5200 m. Larger studies using more challenging apnea protocols and at higher altitudes should be considered.

High Altitude Affects Nocturnal Non-linear Heart Rate Variability: PATCH-HA Study.

Background: High altitude (HA) exposure can lead to changes in resting heart rate variability (HRV), which may be linked to acute mountain sickness (AMS) development. Compared with traditional HRV measures, non-linear HRV appears to offer incremental and prognostic data, yet its utility and relationship to AMS have been barely examined at HA. This study sought to examine this relationship at terrestrial HA. Methods: Sixteen healthy British military servicemen were studied at baseline (800 m, first night) and over eight consecutive nights, at a sleeping altitude of up to 3600 m. A disposable cardiac patch monitor was used, to record the nocturnal cardiac inter-beat interval data, over 1 h (0200-0300 h), for offline HRV assessment. Non-linear HRV measures included Sample entropy (SampEn), the short (α1, 4-12 beats) and long-term (α2, 13-64 beats) detrend fluctuation analysis slope and the correlation dimension (D2). The maximal rating of perceived exertion (RPE), during daily exercise, was assessed using the Borg 6-20 RPE scale. Results: All subjects completed the HA exposure. The average age of included subjects was 31.4 ± 8.1 years. HA led to a significant fall in SpO2 and increase in heart rate, LLS and RPE. There were no significant changes in the ECG-derived respiratory rate or in any of the time domain measures of HRV during sleep. The only notable changes in frequency domain measures of HRV were an increase in LF and fall in HFnu power at the highest altitude. Conversely, SampEn, SD1/SD2 and D2 all fell, whereas α1 and α2 increased (p < 0.05). RPE inversely correlated with SD1/SD2 (r = -0.31; p = 0.002), SampEn (r = -0.22; p = 0.03), HFnu (r = -0.27; p = 0.007) and positively correlated with LF (r = 0.24; p = 0.02), LF/HF (r = 0.24; p = 0.02), α1 (r = 0.32; p = 0.002) and α2 (r = 0.21; p = 0.04). AMS occurred in 7/16 subjects (43.8%) and was very mild in 85.7% of cases. HRV failed to predict AMS. Conclusion: Non-linear HRV is more sensitive to the effects of HA than time and frequency domain indices. HA leads to a compensatory decrease in nocturnal HRV and complexity, which is influenced by the RPE measured at the end of the previous day. HRV failed to predict AMS development.