Effect of hypoxic "dose" on physiological responses and sea-level performance

Live high-train low (LH+TL) altitude training was developed in the early 1990s in response to potential training limitations imposed on endurance athletes by traditional live high-train high (LH+TH) altitude training. The essence of LH+TL is that it allows athletes to "live high" for the purpose of facilitating altitude acclimatization, as manifest by a profound and sustained increase in endogenous erythropoietin (EPO) and ultimately an augmented erythrocyte volume, while simultaneously allowing athletes to "train low" for the purpose of replicating sea-level training intensity and oxygen flux, thereby inducing beneficial metabolic and neuromuscular adaptations. In addition to "natural/terrestrial" LH+TL, several simulated LH+TL devices have been developed to conveniently bring the mountain to the athlete, including nitrogen apartments, hypoxic tents, and hypoxicator devices. One of the key questions regarding the practical application of LH+TL is, what is the optimal hypoxic dose needed to facilitate altitude acclimatization and produce the expected beneficial physiological responses and sea-level performance effects? The purpose of this paper is to objectively answer that question, on the basis of an extensive body of research by our group in LH+TL altitude training. We will address three key questions: 1) What is the optimal altitude at which to live? 2) How many days are required at altitude? and 3) How many hours per day are required? On the basis of consistent findings from our research group, we recommend that for athletes to derive the physiological benefits of LH+TL, they need to live at a natural elevation of 2000-2500 m for >or=4 wk for >or=22 h.d(-1).     

糖皮质激素变化对高原急性缺氧后脑损伤的影响

目的:探讨高原急性缺氧(7000 m,24 h)下糖皮质激素变化对脑损伤和血清S100B蛋白表达的影响。方法:成年Wistar大鼠随机分为地塞米松给药组、美替拉酮给药组、高原对照组和平原对照组,第3天给药后1 h,前三组置于低压低氧模拟舱中,模拟海拔7000 m,24 h后出舱,酶联免疫法检测血清皮质酮(CORT)、S100B,干湿重法测定脑含水量及肺含水量。结果:与平原对照组比较,高原各组的CORT、S100B、脑含水量和肺含水量均明显增高(P<0.01)。与高原对照组比较,地塞米松给药组CORT显著增高(P<0.01),S100B显著降低(P<0.05),脑含水量有一定降低、肺含水量降低(P<0.05)。美替拉酮给药组CORT显著降低(P<0.01),S100B显著增高(P<0.01),脑含水量增高,肺含水量降低(P<0.05)。结论:在急性重度缺氧期,大鼠皮质酮水平增加对脑缺氧损伤有一定保护作用,其机制可能与下调S100B蛋白和稳定血脑屏障有关。     

Hematological and lipid profile changes in sea-level natives after exposure to 3550-m altitude for 8 months

The aim of this epidemiological study was to determinate the effects on hematological and lipid profile in a young group of newcomers to altitude after being exposed chronically for 8 months to 3550 m (n = 50), age 17.8 +/- 0.7; and not overweight, BMI 22.9 +/- 0.5). Readings taken at altitude on day 1 and on month 8 were hematocrit (Hct, %), hemoglobin (Hb, g/dL), Sa(O(2)), total leukocyte and subset count (mm(3), %), and lipid profile (mg/dL). The same measurements were taken in a comparative group (CG) at sea level (SL). At altitude, elevations of Hct (44.6 +/- 0.4; 51.2 +/- 0.4) and Hb (15.5 +/- 0.1; 17.3 +/- 0.1) were seen (p < 0.001) and none with Hb >/= 21 g/dL. No correlation was observed between Hb and Sa(O(2)), r = 0.11, p > 0.05. Total leukocyte count showed no changes (6037 +/- 74; 6002 +/- 43), but a relative neutropenia (55.2 + -1.5; 50.6 + -1.3) and lymphocytosis (34.2 + 1; 42.4 + 1, p < 0.001) between periods were found and also when compared to SL. Also, an inverse relationship between Sa(O(2)) and total leukocytes on month 8 (r = 0.46; r(2) = 0.204), suggesting a probable representation of a hypoxia effect. Total cholesterol (153.8 +/- 4.5; 157.3 +/- 5.1; p, ns) showed no changes, but a mild decrease of LDL-cholesterol (88.4 +/- 3.3; 81.0 +/- 3.9; p < 0.05), and a rise in triglycerides (121.6 +/- 10.9; 178.8 +/- 11.7; p < 0.001) was found. Changes observed in leukocytes subset count and triglycerides could suggest a contributory role of hypoxic conditions, raising some future epidemiological concerns regarding immune system and fatty acid behaviour at altitude.     

大鼠低压缺氧心肌及线粒体腺苷酸含量及分布的变化

目的:探讨模拟高原低压缺氧暴露过程中大鼠心肌腺苷酸含量及分布变化特点.方法:雄性Wistar大鼠随机分为正常对照组、缺氧1、5、15和30d组.缺氧组于模拟海拔5000m高原低压舱内连续缺氧23h/d.提取心室肌线粒体,HPLC法测量腺苷酸含量.结果:缺氧5、15、30d组,心室肌组织及线粒体外ATP含量明显下降,缺氧1d和5d,心肌线粒体ATP含量降低,缺氧15d时恢复,缺氧30d时则再次降低.结论:高原低压缺氧可影响心肌腺苷酸含量和分布,可能是高原心功能异常的主要原因.     

Game performance and intermittent hypoxic training

Live high-train low altitude exposure simulated by hypoxic devices may improve athletic performance. In this study, intermittent normobaric hypoxia was achieved with the GO2altitude hypoxicator to determine its effects on sea level performance in rugby players. Ten players were randomly assigned to two groups. Players in each group received 14 sessions of either hypoxic (10-15% O(2)) or normoxic (21% O(2)) exposure at rest over 14 consecutive days in a single blind fashion. Various performance measures were obtained consecutively in a single testing session pre- and post-exposure. Effects of hypoxic exposure on maximum speed and sprint times were trivial (<1.0%) but unclear (90% likely range, +/-5% to +/-9%). In rugby simulation, hypoxic exposure produced impairments of peak power in two scrums (15%, +/-8%; 9%, +/-7%) and impairments of time in offensive sprints (7%, +/-8%) and tackle sprints (11%, +/-9%). Pending further research, rugby players would be unwise to use normobaric intermittent hypoxic exposure to prepare for games at sea level.     

Effects of hypoxic interval training on cycling performance

PURPOSE: The aim of this study was to test the hypothesis that intermittent hypoxic interval training improves sea level cycling performance more than equivalent training in hypoxia or normoxia. METHODS: Thirty-three well-trained cyclists and triathletes (25.9 +/- 2.7 yr, VO(2max) 66.1 +/- 6.1 mL.min(-1).kg(-1)) were divided into three groups: intermittent hypoxic (IHT, N = 11, P(I)O(2) of 100 mm Hg), intermittent hypoxic interval training (IHIT, N = 11) and normoxia (Nor, N = 11, P(I)O(2) of 160 mm Hg) and completed a 7-wk training program, consisting of two high-intensity (100 or 90% relative peak power output) interval training sessions each week. Each interval training session was performed in a laboratory on the subject's own bicycle, in normoxic or hypoxic conditions for the Nor and the IHT group, respectively. The IHIT group performed warm-up and cool-down plus recovery from each interval in hypoxic conditions. In contrast to IHT, interval exercise bouts were performed in normoxic conditions. RESULTS: Mean power output during a 10-min cycle time trial improved after the first 4 wk of training by 5.2 +/- 3.9, 3.7 +/- 5.9, and 5.0 +/- 3.4% for IHIT, IHT, and Nor, respectively, without significant differences between groups. Moreover, mean power output did not show any significant improvement in the following 3 wk in any group. VO(2max) (L.min(-1)) increased only in IHIT during the training period (8.7 +/- 9.1%; P < 0.05). No changes in cycling efficiency or in hematological variables (P > 0.05) were observed. CONCLUSION: Four weeks of interval training induced an improvement in endurance performance. However, short-term exposure to hypoxia (approximately 114 min.wk(-1)) did not elicit a greater increase in performance or any hematological modifications.     

Hemo- and neurodynamics of the human brain during exposure to moderate hypoxic hypoxia

Synchronous electro- and rheoencephalography were used to study tolerance to moderate hypoxic hypoxia for 30 min at an altitude of 5000 m without additional oxygen supply. As test subject, men with autonomic-vascular dystonia (29-39 years old), 15 men over 40 (41-56 years old), and 16 essentially healthy controls (23-36 years old) were used. The aged volunteers (41-56 years old) did not differ from the controls with respect to their tolerance to hypoxic hypoxia. The men with early symptoms of hypertonic-type dystonia also showed high tolerance to hypoxic hypoxia. The subjects with hypotonic-type dystonia displayed lower tolerance.     

Deficits in functional performance and gait one year after total knee arthroplasty despite improved self-reported function

Purpose

The current literature lacks sufficient information about improvements in gait patterns and function after total knee arthroplasty (TKA) and whether patients return to full function. This study evaluated change in gait, performance-based function, and self-reported function 1 year after TKA in patients with symptomatic knee osteoarthritis and how these aspects interrelate.

Methods

A total of 28 patients (64 % female) with knee osteoarthritis, with a mean age of 66 (±7) years, and 25 age- and gender-matched controls participated in this prospective cohort study. Three-dimensional gait analysis generated comprehensive measures of kinematic and kinetic gait deviations, respectively. Participants completed the Five Times Sit-to-Stand (5STS) test, and the self-reported questionnaire Knee Injury and Osteoarthritis Outcome Score (KOOS), at baseline prior to surgery and 1 year after TKA.

Results

Kinetic gait deviations of both the operated and non-operated limb persisted in patients with knee osteoarthritis at 1 year after surgery, while kinematic gait patterns were comparable to controls. Performance on the 5STS and KOOS scores in patients with knee osteoarthritis improved significantly 1 year after surgery (effect size 0.5–1.5), but did not reach the level of controls. Ten patients with knee osteoarthritis (36 %) exceeded the minimally detectable change on the 5STS.

Conclusion

Measures of overall gait patterns and the 5STS revealed improvements in function 1 year after TKA, but were not restored to the level of healthy controls. Based on change in 5STS performance, we identified patients with substantial improvements in gait patterns. Self-reported measures of function could not detect differences between patients improving in 5STS performance and those who did not. These findings highlight the use of the 5STS in clinical practice since improvement on this test seems to follow the reduction in gait pattern deviations.

Level of evidence

II.

     

ECG-synchronized DSA exposure control: improved cervicothoracic image quality

An electrocardiogram (ECG)-synchronized x-ray exposure sequence was used to acquire digital subtraction angiographic (DSA) images during 13 arterial injection studies of the aortic arch or carotid bifurcations. These "gated" images were compared with matched "ungated" DSA images acquired using the same technical factors, contrast material volume, and patient positioning. Subjective assessments by five experienced observers of edge definition, vessel conspicuousness, and overall diagnostic quality showed overall preference for one of the two acquisition methods in 69% of cases studied. Of these, the ECG-synchronized exposure series were rated superior in 76%. Linear intensity gradients across vessel margins generally showed improved or unchanged edge definition in the gated subtraction images as compared with their ungated pairs. These results, as well as the relatively simple and inexpensive modifications required, suggest that routine use of ECG exposure control can facilitate improved arterial DSA evaluations of suspected cervicothoracic vascular disease.     

Biochemical assessment of individual sports for improved performance

Biomechanists are able to offer a scientific service which aids the process of achieving improved sports performance. They are able to provide measurement tools to quantify key mechanical variables related to performance. Biomechanists use different methods to define these key variables, although there is no generally accepted approach on how this should be done. The process of intervention should be undertaken using information gained from a biomechanical assessment. This is often not conducted by the biomechanist and is usually left to other specialists. The success of this intervention is rarely evaluated so as to provide evidence to validate the earlier stages of the assessment. Biomechanists who have considerable experience and have conducted applied research programmes with specific sports seem to be able to demonstrate success. It is concluded that biomechanists need to support their claim to be able to influence performance outcome with more evidence based practice.     

The effect of intermittent hypoxic training via a hypoxic inhaler on physiological and performance measures in rowers: A pilot study

Intermittent hypoxic training and discontinuous exposure to altitude were used to improve performance at sea level in elite rowers. Altitude was simulated with a newly patented device which allowed athletes to experience altitude by re-breathing oxygen-depleted expired air. Seven elite rowers (five females, two males) used inhalers for a 90-min supervised daily session (alternating 6 min on and 4 min off) for 3 weeks, while four female elite rowers used placebo devices in the same sessions. The inhalers were adjusted to produce a progressive decrease in oxygen saturation over the 3 weeks (initially 90%; finally 80%). Immediately before and 7-10 days after altitude exposure, the rowers performed an incremental lactate test to determine power output equivalent to 4 mM [BLa], a 500-m time trial and a 5000-m time trial, all on a rowing ergometer. Relative to the control group, the altitude group showed a slight improvement in mean power for the 5000-m time trial (0.6%, 90% likely limits +/-3.7%), and a substantial impairment in mean power for the 500-m trial (2.2%, +/-4.1%). Power at 4-mM lactate declined in both groups, but overall the altitude group improved by 0.4% (+/-3.5%) relative to control. The device represents a practical way to simulate altitude exposure, but it is unlikely to have major effects on performance of elite rowers.     

Pulse modulated radiofrequency exposure influences cognitive performance

Purpose: To investigate whether exposure to pulse modulated radiofrequency (PM RF) influences human cognitive performance, and whether it does so in a dose-dependent manner.

Materials and methods: Thirty-six healthy adults participated in a randomized, double-blind, counterbalanced provocation study. Cognitive performance was assessed using a visual discrimination task and a modified Sternberg working memory task, which were calibrated to individual performance levels in a preliminary testing session. An sXh920 planar exposure system was used to generate a 920?MHz GSM-like signal, providing three conditions (peak-spatial SAR averaged over 10?g) of 0?W/kg (sham), 1 W/kg (low RF) and 2 W/kg (high RF).

Results: A significant decrease in reaction time (RT) in the Sternberg working memory task was found during exposure compared to sham. This effect was not dose-dependent.

Conclusions: Cognitive performance was shown to be faster under PM RF conditions, relative to sham, in a working memory task. While the majority of the literature has not found effects of PM RF exposure on cognitive performance, it is possible that the methodological improvements employed in the present study increased sensitivity, and thus the ability to detect potential effects.     

The mechanisms of central regulation disorder under combat exposure conditions

Results of research in central regulation system's disorders in the local wars' participants suffering from environmental psychoemotional and traumatic stress. It has been established, that there was an upsetting of interaction between neurodynamic processes in the sub-dominant hemisphere and a reduction of the functional reserve of the brain. Neurophysiology disorders discovered come from the pathological system that had been formed up in the central nervous system preserve their persistence for several years after the war.     

缺氧习服大鼠骨骼肌葡萄糖代谢特点研究

目的 :探讨缺氧习服后组织物质代谢特点。方法 :将大鼠置模拟海拔 5 0 0 0m低压舱内 ,30d后取动脉血 ,测定血气、血糖等 ;取双后肢骨骼肌用3 H 脱氧葡萄糖测定葡萄糖摄取率 ,用葡萄糖氧化酶法测定葡萄糖、糖原含量 ;用酶法测定ATP、磷酸肌酸、乳酸水平 ,并以平原动物作为对照组进行对比分析。结果 :与对照组相比 ,缺氧组血糖、骨骼肌葡萄糖摄取率、葡萄糖含量显著增加 ,而糖原显著降低 ,骨骼肌ATP、磷酸肌酸、乳酸在缺氧组与对照组之间没有显著性差异。结论 :经过缺氧习服之后 ,组织能量代谢能达到平衡状态 ,葡萄糖利用能力加强