Changes In Jump Performance And Dynamic Balance At High Terrestrial Altitude

The purpose of this study was to examine the effects of altitude on dynamic balance and jump performance of a controlled landing during a 12-day high altitude trek. Following a two-legged jump, time to stabilization (5% of body mass for 0.5 s), maximum power, and jump height were measured in 11 participants using a portable force platform at sea level (BL), 3619 m (C1), and 5140 m (C3). Jump performance significantly decreased at C1 and C3 compared to BL (P=0.001). There were no significant differences found in time to stabilization and maximum power with increasing altitude. The present findings indicate that jump performance is significantly decreased with increasing altitude. However, dynamic balance and jump power remain unaffected

Working memory capacity and surgical performance whilst exposed to mild hypoxic hypoxaemia (3000m)

INTRODUCTION: Medical Emergency Response Team (MERT) helicopters fly at altitudes of 3,000m in Afghanistan (9,843ft). Civilian hospitals and disaster-relief surgical teams may have to operate at such altitudes or even higher. Mild hypoxia has been seen to affect the performance of novel tasks at flight levels as low as 5,000ft. Aeromedical teams frequently work in unpressurised environments; it is important to understand the implications of this mild hypoxia and investigate whether supplementary oxygen systems are required for some or all of the team members. METHODS: Ten UK orthopaedic surgeons were recruited and in a double blind randomised experimental protocol, were acutely exposed for 45 minutes to normobaric hypoxia (fraction of inspired oxygen (FiO2) ~14.1% - equivalent to 3000m/10,000ft) or normobaric normoxia (sea-level). Basic physiological parameters were recorded. Subjects completed validated tests of verbal working memory capacity (VWMC) and also applied an orthopaedic external fixator (Hoffmann® 3, Stryker UK) to a plastic tibia under test conditions. RESULTS: Significant hypoxia was induced with the reduction of FiO2 to ~14.1% (SpO2 87% vs. 98%). No effect of hypoxia on VWMC was observed. The pin-divergence score (a measure of frame asymmetry) was significantly greater in hypoxic conditions (4.6mm) compared to sea level (3.0mm), there was no significant difference in the penetrance depth (16.9 vs. 17.2mm). One frame would have failed early. DISCUSSION: We believe that surgery at an altitude of 3000m when unacclimated individuals are acutely exposed to atmospheric hypoxia for 45 minutes, can likely take place without supplemental oxygen use but further work is required

Military combat movements and exercises: is there a role for adopting sports nutrition carbohydrate recommendations during exercise?

The daily energy requirements for specialist military troops can reach 5000 kcal during training and wartime deployment. Maintaining energy balance is important for health and physical and mental performance in this population, who can effectively be considered as high-performance endurance athletes. In this regard, a balanced diet consisting of 50-60% carbohydrate (CHO), 20-25% protein and 25-30% fat is recommended for endurance athletes in the sporting world. Carbohydrate intake is regarded as a key dietary constituent of the high-performance athlete, as this substrate provides the sole fuel source during high intensity exercise. However, achieving such high CHO intake rates can be challenging, especially when military personnel are in the field. In sports nutrition, athletes commonly use dietary CHO supplements to reduce this deficit. There may be lessons and insight from nutrition and metabolism in sport that could provide Royal Marines, Medical Officers and other embedded medical professionals with strategies to increase CHO intake during intense training or combat situations. This review will highlight the exercise demands of infantry soldiering; it will suggest supplementary strategies to increase CHO intake, in addition to dietary intake, and will describe the metabolic effects of CHO ingestion during prolonged activity in the context of military exercise

Dietary nitrate supplementation enhances short but not longer duration running time-trial performance

Purpose This study evaluated the effects of dietary nitrate (NO3-) supplementation on physiological functioning and exercise performance in trained runners/ triathletes conducting short and longer distance treadmill running time-trials (TT). Method Eight trained male runners or triathletes completed four exercise performance tests comprising a 10 minute warm up followed by either a 1500 m or 10,000 m treadmill TT. Exercise performance tests were preceded 3 hours before the exercise by supplementation with either 140 ml concentrated nitrate-rich (~ 12.5 mmol nitrate) (BRJ) or nitrate-deplete (~ 0.01 mmol nitrate) (PLA) beetroot juice. Results BRJ supplementation significantly elevated plasma [NO2-] (P 0.05). However, post-exercise blood [lactate] was significantly greater in BRJ following the 1500 m TT (6.6 ± 1.2 vs. 6.1 ± 1.5 mM; P 0.05). Performance in the 1500 m TT was significantly faster in BRJ versus PLA (319.6 ± 36.2 vs. 325.7 ± 38.8 s; P 0.05). Conclusion Acute BRJ supplementation significantly enhanced 1500 m but not 10,000 m TT performance. These findings suggest that BRJ might be ergogenic during shorter-distance TTs which allow for a high work rate, but not during longer-distance TTs, completed at a lower work rate

Erythropoietic responses to a series of repeated maximal dynamic and static apnoeas in elite and non-breath-hold divers

Serum erythropoietin (EPO) concentration is increased following static apnoea-induced hypoxia. However, the acute erythropoietic responses to a series of dynamic apnoeas in non-divers (ND) or elite breath-hold divers (EBHD) are unknown. Participants were stratified into EBHD (n=8), ND (n=10) and control (n=8) groups. On two separate occasions EBHD and ND performed a series of five maximal dynamic apnoeas (DYN) or two sets of five maximal static apnoeas (STA). Control performed a static eupnoeic (STE) protocol to control against any effects of water immersion and diurnal variation on EPO. Peripheral oxygen saturation (SpO2) levels were monitored up to 20s post each maximal effort. Blood samples were collected at 30, 90, and 180-min after each protocol for EPO, haemoglobin and haematocrit concentrations. No between group differences were observed at baseline (p>0.05). For EBHD and ND, mean end-apnoea SpO2 was lower in DYN (EBHD,62±10%,p=0.024;ND,85±6%;p=0.020) than STA (EBHD,76±7%;ND,96±1%) and control (98±1%) protocols. EBHD attained lower end-apnoeic SpO2 during DYN and STA than ND (p<0.001). Serum EPO increased from baseline following the DYN protocol in EBHD only (EBHD,p<0.001;ND,p=0.622). EBHD EPO increased from baseline (6.85±0.9mlU/mL) by 60% at 30-min (10.82±2.5mlU/mL,p=0.017) and 63% at 180-min (10.87±2.1mlU/mL,p=0.024). Serum EPO did not change after the STA (EBHD,p=0.534;ND,p=0.850) and STE (p=0.056) protocols. There was a significant negative correlation (r=-0.49,p=0.003) between end-apnoeic SpO2 and peak post-apnoeic serum EPO concentrations. The novel findings demonstrate that circulating EPO is only increased after DYN in EBHD. This may relate to the greater hypoxemia achieved by EBHD during the DYN

The relationship between anxiety and acute mountain sickness.

INTRODUCTION: Whilst the link between physical factors and risk of high altitude (HA)-related illness and acute mountain sickness (AMS) have been extensively explored, the influence of psychological factors has been less well examined. In this study we aimed to investigate the relationship between 'anxiety and AMS risk during a progressive ascent to very HA. METHODS: Eighty health adults were assessed at baseline (848m) and over 9 consecutive altitudes during a progressive trek to 5140m. HA-related symptoms (Lake Louise [LLS] and AMS-C Scores) and state anxiety (State-Trait-Anxiety-Score [STAI Y-1]) were examined at each altitude with trait anxiety (STAI Y-2) at baseline. RESULTS: The average age was 32.1 ± 8.3 years (67.5% men). STAI Y-1 scores fell from 848m to 3619m, before increasing to above baseline scores (848m) at ≥4072m (p = 0.01). STAI Y-1 scores correlated with LLS (r = 0.31; 0.24-0.3; P<0.0001) and AMS-C Scores (r = 0.29; 0.22-0.35; P<0.0001). There was significant main effect for sex (higher STAI Y-1 scores in women) and altitude with no sex-x-altitude interaction on STAI Y-1 Scores. Independent predictors of significant state anxiety included female sex, lower age, higher heart rate and increasing LLS and AMS-C scores (p<0.0001). A total of 38/80 subjects (47.5%) developed AMS which was mild in 20 (25%) and severe in 18 (22.5%). Baseline STAI Y-2 scores were an independent predictor of future severe AMS (B = 1.13; 1.009-1.28; p = 0.04; r2 = 0.23) and STAI Y-1 scores at HA independently predicted AMS and its severity. CONCLUSION: Trait anxiety at low altitude was an independent predictor of future severe AMS development at HA. State anxiety at HA was independently associated with AMS and its severity

Substrate oxidation and the influence of breakfast in normobaric hypoxia and normoxia

Purpose: Reported substrate oxidation responses in hypoxia are divergent, and may be due to differences in methodological design, such as pre-exercise nutritional status and exercise intensity. This study investigated the effect of breakfast consumption versus omission on substrate oxidation at varying exercise intensities in normobaric hypoxia compared with normoxia. Methods: Twelve participants rested and exercised once after breakfast consumption and once after omission in normobaric hypoxia (4300 m: FiO2 ~11.7%) and normoxia. Exercise consisted of walking for 20-minutes at 40%, 50% and 60% of altitude-specific V̇O2max at 10-15% gradient with a 10 kg backpack. Indirect calorimetry was used to calculate carbohydrate and fat oxidation. Results: The relative contribution of carbohydrate oxidation to energy expenditure was significantly reduced in hypoxia compared with normoxia during exercise after breakfast omission at 40% (22.4 ± 17.5% vs. 38.5±15.5%, p = 0.03) and 60% V̇O2max (35.4±12.4 vs. 50.1±17.6%, p = 0.03), with a trend observed at 50% V̇O2max (23.6±17.9% vs. 38.1± 17.0%, p = 0.07). The relative contribution of carbohydrate oxidation to energy expenditure was not significantly different in hypoxia compared with normoxia during exercise after breakfast consumption at 40% (42.4±15.7% vs. 48.5±13.3%, p = 0.99), 50% (43.1±11.7% vs. 47.1±14.0%, p = 0.99) and 60% V̇O2max (54.6±17.8% vs. 55.1±15.0%, p = 0.99). Conclusions: Relative carbohydrate oxidation was significantly reduced in hypoxia compared with normoxia during exercise after breakfast omission but not during exercise after breakfast consumption. This response remained consistent with increasing exercise intensities. These findings may explain some of the disparity in the literatur

The Effects of Pre-Race Apnoeas on 400-m Freestyle Swimming Performance

This study aimed to establish whether a series of three apnoeas prior to a 400-m freestyle time-trial affected swimming performance when compared to, and combined with a warm-up. Nine (6 males, 3 females) regional to national standard swimmers completed four 400-m freestyle time-trials in 4 randomized conditions: without warm-up or apnoeas (CON), warm-up only (WU), apnoeas only (AP) and warm-up and apnoeas (WUAP). Time-trial performance was significantly improved after WUAP (275.79 ±12.88 s) compared to CON (278.66 ±13.31 s, P = 0.035) and AP (278.64 ±4.10 s, P =0.015). However, there were no significant differences between the WU (276.01 ±13.52 s, P >0.05), and other interventions. Spleen volume compared to baseline was significantly reduced following the apnoeas by a maximum of ~45% in the WUAP and by ~20% in WU. This study showed that the combination of a warm-up with apnoeas could significantly improve 400-m freestyle swim performance compared to a control and apnoea intervention. Further investigation into whether long-term apnoea training can enhance this response is justified