Different training responses to eccentric endurance exercise at low and moderate altitudes in pre-diabetic men: a pilot study

This pilot study aimed (a) to evaluate the effects of eccentric exercise training at low and moderate altitudes on physical fitness in pre-diabetic men and (b) to establish whether or not oxidative stress levels and antioxidant status were associated with performance improvements. In this crossover trial, five pre-diabetic men conducted nine downhill walking sessions (3 days/week, 3 consecutive weeks) at low altitude (from 1360 to 850 m) and one year later at moderate altitude (from 2447 to 2000 m). Exercise testing and the determination of parameters of oxidative stress and antioxidant capacity were performed pre- and post-training. The biological antioxidant activity of plasma (BAP) increased after eccentric training at moderate altitude (p < 0.001), whereas diacron reactive oxygen metabolites (dROMs) remained unchanged. Also, the BAP/dROMs ratio increased only after training at moderate-altitude training (p = 0.009). Maximum power output improved after training at low altitude and the changes were significantly related to baseline BAP/dROMs ratio (r = 0.90). No decrease was seen for fasting plasma glucose. Eccentric exercise training in pre-diabetic men improved performance only when performed at low altitude and this improvement was positively related to the baseline BAP/dROMs ratio. In contrast, 3 weeks of eccentric exercise training increased BAP levels and the BAP/dROMs ratio only at moderate altitude without improving the performance. Thus, one might speculate that the BAP/dROMs ratio has to increase before performance improvements occur at moderate altitude.

     

Hemodynamics and metabolism at low versus moderate altitudes

Despite the higher prevalence of diabetes and hypertension in populations residing at moderate altitudes, mortality in these populations is lower than in populations residing at low altitudes. To examine whether metabolic and hemodynamic differences can explain this apparent paradox, we performed a cross-sectional study of a general population sample recruited in the Canary Islands, Spain (n=6729). We recorded altitude of residence, age, heart rate, blood pressure, body mass index, social class, physical activity, energy intake, alcohol intake, smoking habit, prevalence of type 2 diabetes mellitus and hypertension. In a subsample (n=903), we recorded serum concentration of cholesterol, triglycerides, glucose, C peptide, leptin, soluble leptin receptor (sObR), C-reactive protein, resistin, soluble CD40 ligand (sCD40L), and paraoxonase activity (PON), and we estimated insulin resistance and free leptin index. We found an inverse association between altitude and heart rate (p<0.001), leptin (p<0.001), free leptin index (p<0.001), resistin (p<0.001), and sCD40L (p<0.05) and a direct association between altitude and hypertension (odds ratio=1.29 for altitude >600 m; 95% confidence interval=1.03-1.62), glycemia (p<0.05), C peptide (p<0.001), insulin resistance (p<0.001), sObR (p<0.05), and PON (p<0.05). When social class was included in the multivariate model, the association with PON was no longer significant. In conclusion, individuals residing at moderate altitudes have a lower heart rate and lower serum concentration of total leptin, free leptin, and sCD40L. These differences may partially explain the lower mortality in these populations.     

Physiological responses during submaximal interval swimming training: Effects of interval duration

The aim of the present study was to determine the time sustained near VO2max in two interval training (IT) swimming sessions comprising 4x400 m (IT(4x400)) or 16x100 (IT(16xl00)). Elite swimmers (Mean+/-SD age 18+/-2 yrs; body mass 66.9+/-6.5 kg: swim VO2max 55.7+/-5.8 ml.kg(-1).min(-1)) completed three experimental sessions at a 50-m indoor pool over a one week period. The first test comprised a 5 x 200-m incremental test to exhaustion for determination of the pulmonary ventilation threshold (VT, m.s(-1)), VO2max, the velocity associated with VO2max (VO2max, m(s(-1)) and maximum heart rate (HR(max), b.min(-1)). The remaining two tests involved the IT(4x400) and IT(16xl00) performed in a randomised order. The two IT sessions where completed at a velocity representing 25% of the difference between the VT and the VO2max (delta25%) and in the same work to rest ratio. During the IT sessions VO2 as well as HR were measured. The duration (s) >90% VO2max, also the duration (s) >90% HR(max), were not significantly different in the IT(16x100) and IT(4x400). However, limits of agreement (LIM(AG)) analysis demonstrated considerable individual variation in the time >90% VO2max (mean difference +/-2SD = 222+/-819 s) and the time >90% HRmax (mean difference +/-2SD = 61+/-758 s) between the two IT sessions. This factor deserves further research to establish the characteristics of those athletes which influence the physiological responses in IT of short or longer duration repetitions.     

Investigating the reproducibility of maximal oxygen uptake responses to high-intensity interval training

ObjectivesTo test the hypothesis that observed maximal oxygen uptake (VO₂max) and time to fatigue (TTF) responses to two identical periods of standardized high-intensity interval training are reproducible.DesignFourteen recreationally active and healthy young males completed two identical four-week periods of high-intensity interval training (4 × 4-min intervals at 90–95% maximum heart rate [HR_max] separated by 3-min periods of active recovery at 70–75% HR_max). Training periods were separated by a three-month washout period.MethodsVO₂max and TTF were assessed via incremental tests with supramaximal verification before and after each training period. Pearson correlation coefficients (r), intraclass correlation coefficients (ICC), and within-subjects coefficients of variation (CV) were used to assess reproducibility of observed VO₂max and TTF responses.ResultsVO₂max and TTF values before the second training period were not significantly higher than baseline values and there were no significant (p > 0.05) interaction effects (period 1: VO₂max: +4.04 ± 2.29 mL/kg/min, TTF: +70.75 ± 35.87 s; period 2: VO₂max: +2.83 ± 2.74 mL/kg/min, TTF: +83.46 ± 34.55 s). We found very weak-to-moderate correlations and poor reproducibility for observed VO₂max (mL/kg/min: r = 0.40, ICC = 0.369, CV = 74.4) and TTF (r = 0.11. ICC = 0.048, CV = 45.6) responses to training periods 1 and 2.ConclusionsOur ANOVA results confirmed that the three-month washout period returned VO₂max and TTF levels to baseline and prevented carryover effects. Contrary to our hypothesis, our results suggest that individual observed VO₂max and TTF responses to identical training stimuli are not reproducible.     

预先吸入不同浓度富氧气体对急性低压缺氧暴露的生理影响

通过人体急性暴露到低氧性缺氧环境和动物高空迅速减压实验，观察了预先吸入模拟分子筛产氧系统不同富氧浓度的气体对应急减压瞬间的生理影响。模拟暴发性缺氧实验结果表明，当预先供氧浓度低于60％，在暴露到暴发性缺氧环境10s内出现缺氧反应，而高于70％供氧浓度时未出现缺或变化；动物高空迅速减压缩果进一步表明，减压前预先吸入氧浓度为70％～100％，在迅速减压瞬间的生理反应是等效的，吸入各种富氧浓度气体与纯氧之间的血氧饱和度及静脉氧分压光明显差别（P＞0.05），但与迅速减压前呼吸空气（21％氧）的结果之间有显著的差别（P＜0．05）。高空迅速减压时氧自体内向外界的反向弥散有两个过程，它与减压瞬间生理效应和有效意识时间有密切关系。此结果为机教分子筛氧气系统的研制与应用提供了生理依据。     

The effect of high Intensity interval training versus moderate intensity continuous training on arterial stiffness and 24 h blood pressure responses: A systematic review and meta-analysis

Objectives

Greater arterial stiffness and poor 24 h blood pressure (BP) are recognized as indicators of poor cardiovascular health. Evidence has shown that high intensity interval training (HIIT) may be a superior alternative to moderate intensity continuous training (MICT) for improving cardiovascular disease risk factors such as cardiorespiratory fitness and vascular function. However, there are limited data comparing the effect of HIIT to MICT on central arterial stiffness and/or 24 h BP response. The purpose of this study was to compare HIIT versus MICT on central arterial stiffness and 24 h BP outcomes by systematic review and meta-analysis.

不同地区新兵在高海拔地区体能训练致膝关节损伤的MRI研究

 目的 对比研究不同海拔地区新兵在高海拔地区体能训练各阶段致膝关节损伤的MRI表现特点,为减少其发生提供理论依据。方法 120名新兵,分为低海拔组和高海拔组,在新训的第1、2、3个月行右膝关节MRI扫描,观察各阶段的膝关节骨质(骨髓、骨皮质、关节软骨)、半月板、韧带、软组织及关节腔损伤情况。结果 (1)低海拔组新兵第1阶段骨髓水肿及关节腔积液检出率(85.0%、65.0%)高于高海拔组新兵检出率(46.7%、33.3%;P<0.01);低海拔组新兵第2阶段骨髓水肿及关节腔积液检出率(91.7%、86.7%)高于高海拔组新兵检出率(71.7%、65.0%;P<0.01);(2)低海拔组新兵第2、3阶段半月板损伤检出率(16.7%、20.0%)高于同阶段高海拔组新兵检出率(1.7%、3.3%;P<0.01);(3)两组新兵各阶段骨皮质、关节软骨、韧带及软组织损伤检出率差异均无统计学意义。结论 低海拔地区新兵新训期膝关节损伤率高于高海拔地区,应该根据新兵来源地区的海拔高度制定正确施训策略和防护措施,以减少其发生。     

Beta-blockers may provoke oxygen desaturation during submaximal exercise at moderate altitudes in elderly persons

Frequency of therapeutic beta-blocker use in elderly mountaineers is unknown. Therefore, the aim of this field study was to measure the regular beta-blocker intake in elderly persons visiting moderate altitudes. In a subset of mountaineers on beta-blockers, exercise response at two different altitude levels was compared to matched controls. The observed frequency of beta-blocked persons among the interviewed elderly mountaineers (age >35) was 7%, mainly (65%) due to hypertension. In subjects taking beta-blockers, arterial oxygen saturation (84 +/- 6% vs. 90 +/- 3%, p < 0.05) was decreased and heart rate (120 +/- 17 bpm vs. 112 +/- 14 bpm, p = 0.01), rate pressure product (22,192 +/- 6459 vs. 17,576 +/- 4010, p < 0.05), and ratings of perceived exertion (14 +/- 3 vs. 12 +/- 3, p < 0.05) were increased during a submaximal step test at 2311 m compared to 1480 m. Mountaineers without beta-blocker intake showed no changes. Although the epidemiological data have to be interpreted with caution because of the small sample size and the limitation to a single geographical site, a large number of beta-blocked persons visiting high altitudes was observed. If confirmed in further studies, the increased heart work and exertion could indicate a reduced exercise tolerance of people taking beta-blockers during acute high altitude exposure.     

高强度间歇运动加重溃疡性结肠炎小鼠炎性反应的影响

 目的 探讨8周高强度间歇运动(high-intensity interval training,HIIT)预适应对溃疡性结肠炎(ulcerative colitis, UC)小鼠临床症状和炎性反应的影响。方法 45只雄性C57BL/6小鼠随机分为安静对照组(RC)、安静造模组(RM)和运动造模组(EM),RC组安静饲养8周后自由饮用蒸馏水7 d,RM和EM组分别安静饲养或进行8周HIIT后自由饮用葡聚糖硫酸钠(DSS)溶液7 d行UC造模。每天记录小鼠疾病活动指数(disease activity index,DAI);取结肠组织测量长度,HE染色行组织病理学观察;结肠组织匀浆后测定炎性反应因子白细胞介素-1β(IL-1β)、IL-6和肿瘤坏死因子-α(TNF-α)mRNA表达量。结果 与RC组比较,RM组小鼠结肠长度缩短(P＜0.05),DAI、组织病理学评分及炎性反应因子(IL-1β、IL-6和TNF-α)表达量升高(P＜0.05);与RM组比较,EM组结肠长度缩短(P＜0.05),DAI、组织病理学评分及IL-1β和TNF-α mRNA含量进一步上调(P＜0.05)。结论 长期HIIT预适应加重UC小鼠临床症状和炎性反应,因此HIIT的健康效应尚需进一步证实。     

Dynamics of biochemical indices of dog blood serum at high altitudes and on return to low altitude]

The transfer of male dogs from lowlands to an altitude of 3370 m was accompanied by hypoproteinemia and reduction of albumins and beta-globulins, stable increase of activity of alanine aminotransferase, decrease of activity of alkaline phosphatase and content of phosphate. This can be interpreted as a manifestation of adaptive changes of metabolic processes to altitude hypoxia. The return of dogs to lowlands was accompanied by the normalization of the changes during the first 20 days.     

Thermoregulatory responses to ice slurry ingestion during low and moderate intensity exercises with restrictive heat loss

ObjectivesWe investigated the thermoregulatory responses to ice slurry ingestion during low- and moderate-intensity exercises with restrictive heat loss.DesignRandomised, counterbalanced, cross-over design.MethodsFollowing a familiarisation trial, ten physically active males exercised on a motorised treadmill at low-intensity (L; 40% VO_2max) or moderate-intensity (M; 70% VO_2max) for 75-min, in four randomised, counterbalanced trials. Throughout the exercise bout, participants donned a raincoat to restrict heat loss. Participants ingested 2 g kg^?1 body mass of ambient water (L + AMB and M + AMB trials) or ice slurry (L + ICE and M + ICE trials) at 15-min intervals during exercise in environmental conditions of T_db, 25.1 ± 0.6 °C and RH, 63 ± 5%. Heart rate (HR), gastrointestinal temperature (T_gi), mean weighted skin temperature (T_sk), estimated sweat loss, ratings of perceived exertion (RPE) and thermal sensation (RTS) were recorded.ResultsCompared to L + AMB, participants completed L + ICE trials with lower ΔT_gi (0.8 ± 0.3°C vs 0.6 ± 0.2 °C; p = 0.03), mean RPE (10 ± 1 vs 9 ± 1; p = 0.03) and estimated sweat loss (0.91 ± 0.2 L vs 0.78 ± 0.27 L; p = 0.04). Contrastingly, T_gi (p = 0.22), T_sk (p = 0.37), HR (p = 0.31), RPE (p = 0.38) and sweat loss (p = 0.17) were similar between M + AMB and M + ICE trials. RTS was similar during both low-intensity (4.9 ± 0.5 vs 4.7 ± 0.3; p = 0.10) and moderate-intensity exercise (5.3 ± 0.47 vs 5.0 ± 0.4; p = 0.09).ConclusionsPer-cooling using ice slurry ingestion marginally reduced thermal strain during low-intensity but not during moderate-intensity exercise. Ice slurry may be an effective and practical heat mitigation strategy during low-intensity exercise such as in occupational and military settings, but a greater volume should be considered to ensure its efficacy.