2周低住高练对游泳运动员心肺功能和有氧运动能力的影响

目的:探讨2周低住高练(LoHi)对游泳运动员心肺功能及其有氧运动能力的影响。方法:15名游泳运动员进行为期2周的LoHi训练(模拟海拔2500m),分别在训练前后采用自行车递增负荷力竭运动测试各项气体代谢指标和有氧运动能力。结果:2周LoHi训练后,(1)同等负荷下男运动员VO2/kg低于训练前,第5min50s时相差最大(-21.8%),最大摄氧量平台(VO2/kgmaxPD)持续时间延长了1min;女运动员自第6min后,VO2/kg值与训练前差值逐渐加大,第12min30s时达到最大(-14.5%),VO2/kgmaxPD持续时间缩短了1min30s;(2)男女运动员R值总体上均处于略微下降的趋势,R=1标志点出现时间明显延后。男运动员从R>1到力竭的时间延长,女运动员则缩短;(3)男运动员fb值在中低负荷阶段略高于训练前,女运动员只在10min50s到13min10s阶段低于训练前。不同负荷阶段,男运动员HR值始终低于训练前。训练后女运动员在第5min后HR值略低于训练前。结论:2周LoHi训练提高了男子游泳运动员对负荷的适应能力,表现为一般有氧运动能力和高负荷状态下的无氧耐力水平提高,但女子运动员的运动能力未见明显改善,表现出一定的性别差异。     

自行车运动员骑车机械效率和氧耗经济性与摄氧能力关系的研究

目的:探讨骑车机械效率(GE)和骑车氧耗经济性(CE)与机体摄氧能力之间的关系。方法:16名男子自行车运动员进行自行车递增负荷练习,测试受试者每级负荷的骑车机械效率、骑车氧耗经济性和最大摄氧量。结果:从GE120开始,每级负荷的GE和CE与相对最大摄氧量(ml/min/kg)均呈现一定的负相关(P<0.05),GE360和CE360与最大摄氧量相对值(ml/min/kg)的相关系数分别高达-0.871(P<0.01)和-0.861(P<0.01),每级负荷的GE和CE与最大摄氧量绝对值(ml/min)均不存在相关。结论:个体之间,在中等强度以上最大有氧负荷强度范围内,机体的GE和CE与机体相对最大摄氧量呈现一定的负相关,有氧运动过程中机体运动的GE和CE与机体摄氧能力的强弱有一定关系。     

高住高练低训对优秀男子橄榄球运动员心功能的影响

目的:探讨高住高练低训对优秀男子橄榄球运动员心功能的影响。方法:将14名国家男子橄榄球队运动员随机分成HiHiLo组(n=8)和LoLo组(n=6),进行为期4周的实验。HiHiLo组每晚低氧居住10h(O2浓度:14.7%),每周除正常训练外,还有3次30min、O2浓度为15.4%、强度为72%个体VO2max的功率自行车运动,LoLo组训练方案与HiHiLo组基本相同,但无低氧居住和低氧运动,每周3次的30min功率自行车运动在常氧环境下进行,强度为80%个体VO2max;训练前后用多普勒超声诊断仪测定安静时、不同负荷及恢复时心脏结构和功能指标。结果:训练后两组心脏结构和安静状态下心功能无显著性变化;在负荷运动时,LoLo组心收缩指标SV、EF和心舒张指标E、E/A增大,HiHiLo组减小,且变化值在两组间有显著性差异(P<0.05);LoLo组运动后A、E/A恢复显著快于HiHiLo组(P<0.05)。结论:HiHiLo不利于运动员疲劳状态下心功能的恢复。     

应用专项训练器械结合不同训练方法提高自行车运动员专项体能的研究

目的:探讨自行车训练器材结合不同训练方法在场地自行车短距离项目运动员专项体能训练方面的应用及其效果。方法:山东省备战第十一届全运会的9名优秀自行车运动员,从2006年9月至2009年全运会前,在常规训练内容基础上,每周增加1～2次专项训练器训练,交替采用1min定量负荷间歇训练法、1min不定负荷间歇训练法和最大强度力竭训练法。定期测试上述训练过程中运动员最高心率、平均心率,最后一次运动后即刻心率、血乳酸和次日晨血清CK和BU等,比较分析测试结果以及年度最好比赛成绩。结果:(1)1min定量负荷间歇训练中,运动员最高心率、平均心率、血乳酸与第一次利用专项训练器械训练时相比明显降低,次日晨CK值也明显下降。(2)1min不定负荷间歇训练中,踏频在135次/分钟以上的运动持续时间明显增加(P<0.01),后2次测试运动员血乳酸显著升高。(3)最大强度力竭训练中,运动员最大强度运动至力竭运动时间,后3次与第1次比较均显著延长(P<0.01)。(4)从比赛成绩看,在全国自行车锦标赛中,运动员成绩每年都有大幅提高。这说明专项训练器械和上述训练方法相结合可提高自行车运动员专项体能。     

不同海拔高原运动心率上限值的探讨

目的 分析不同海拔高原递增负荷运动心率的变化特征,探讨高原运动心率是否存在150次/min上限值.方法 以不同海拔高原(3000 m,30人;3700 m,30人;4300 m,28人)驻防男性青年军人为研究对象,进行功率自行车阶梯负荷踏车运动,从30 W开始,每5 min增加30 W,直至不能坚持;采用Polar V800心率表测量每一运动负荷的运动心率.结果 不同海拔运动心率均随运动负荷增加而增加;海拔3000m最大运动负荷为210W,对应的最大运动心率为(174.2±8.4)次/min;海拔3700 m最大运动负荷为180 W,最大运动心率为(167.4±12.0)次/min;海拔4300 m最大负荷为180W,最大运动心率为(172.2±12.0)次/min.结论 高原运动心率随运动负荷增加而增加,3000、3700和4300 m3个海拔最大负荷运动心率均超过150次/min,不存在150次/min的上限值.     

补充支链氨基酸对划船运动员不同负荷运动后血丙氨酸、葡萄糖及乳酸的影响

目的:探讨补充支链氨基酸(BCAA)对划船运动员不同负荷运动后及恢复期糖代谢和糖异生的影响.方法:20名划船运动员随机分为补充BCAA组和对照组,补充BCAA组每天补充BCAA胶囊(每粒含缬氨酸300mg, 亮氨酸250mg,异亮氨酸100mg),3次/日,4粒/次,对照组补充安慰剂.实验期间,两组运动员均进行相同负荷训练.4周后,在赛艇测功仪上分别进行递增有氧负荷实验(4mmol/L血乳酸)和模拟2km和5km极限负荷测试,分别在运动前、运动后即刻和运动后30min取血,测定血糖、血乳酸和丙氨酸水平.结果:在无氧阈测试中,两组运动员血乳酸和丙氨酸浓度在运动即刻和恢复期较安静时均明显增高(P<0.05),血糖则无明显变化(P>0.05),且两组间无显著性差异.在极限负荷运动中,补充BCAA组运动后即刻血糖显著低于安静水平(P<0.05),对照组运动后即刻和运动后30min均显著低于安静水平(P<0.05).补充BCAA组运动员血丙氨酸浓度运动后即刻和运动后30min均较对照组和安静水平明显增加 (P<0.05),而对照组运动后即刻显著低于安静水平(P<0.05).补充BCAA组运动后血乳酸显著低于对照组(P<0.05).提示:补充BCAA能促进极限运动后及恢复期糖异生,延缓疲劳发生和促进运动后疲劳的消除.     

男子青少年赛艇运动员递增负荷运动时肌氧含量变化特点--肌氧评定个体有氧代谢能力的可行性探讨

目的探讨肌氧含量与不同生理指标之间的关系及其评定有氧代谢能力的可行性.方法22名男子青少年赛艇运动员,按运动水平分为A、B两组,在功率自行车上以逐级递增负荷进行蹬车运动至力竭.A组完成6级负荷,B组完成5级负荷.将探测器固定于运动员右侧股外侧肌,测定运动过程中的肌氧含量,并同步测定摄氧量(VO2)、心率(HR)及血乳酸(BLa).结果A组运动员在进入第5级负荷时骨骼肌肌氧水平迅速下降,直到运动结束未达平衡;B组运动员运动开始阶段肌氧水平迅速下降,进入第5级负荷时肌氧水平出现新的平衡.所有受试在负荷较低时肌氧含量呈阶梯状下降,负荷较高时肌氧持续下降,运动停止后肌氧含量迅速超过安静水平.运动过程中,各级负荷末肌氧含量与摄氧量、HR及BLa呈高度负相关(r=-0.943～-0.993).结果提示运动时骨骼肌局部肌氧供需失衡可能与无氧阈有关.赛艇运动员递增负荷训练时肌氧含量下降拐点与乳酸拐点有一定的一致性,可考虑用肌氧含量评定赛艇运动员有氧能力.     

两种速度型间歇训练对自行车运动员有氧能力的影响

目的:比较单节训练课采用功率自行车骑行次数不变和骑行次数递减两种方案的阶段速度型间歇训练(Sprint Interval Training,SIT)对自行车运动员有氧能力的影响。方法:配对设计法将14名男性短距离自行车运动员分入骑行次数不变组(CG组)和骑行次数递减组(DG组),每组7名。两实验组完成6周相同内容的常规训练(NT)后开始6周SIT(共12节课),将NT中的场地速度耐力训练替换为SIT,其它训练不变。单节SIT课方案为20次20 s高强度骑行分4组完成,次间10 s低强度放松骑行,组间完全休息30 min,CG组4组骑行次数为5-5-5-5次,DG组为8-6-4-2次,强度设定为SIT前个人VO2peak强度的150%。两阶段训练前后进行功率自行车递增负荷运动实验,breath by breath法测试气体代谢参数。每级负荷结束前10 s、测试终止后即刻和3 min测试血乳酸(BLa)。阶段训练前后数据采用双因素重复测量的方差分析,两实验组各参数的两阶段训练前后差值采用秩和检验分析组间差异,显著性水平设为α=0.05。结果:与NT前相比,6周SIT后DG组O2pulsepeak增加了15.5%(P<0.05),且SIT后DG组增幅较CG组高41.4%(P<0.05);6周SIT后CG和DG组R-VO2peak较NT前分别提高了8.1%和7.9%(P<0.05),组间并无显著差异;6周SIT后两实验组VT1和VT2均出现了显著性的提高,其中DG组VT2值较CG组高3.7%(P<0.05),增加趋势更加显著;6周SIT后DG组的BLaEND和BLa-R3min与训练前相比分别降低和提高了10.3%和20.5%(P<0.05),且与CG组相比差异显著。两实验组6周SIT后GXT中第2~7级的乳酸-负荷曲线明显右移,DG组较CG组右移程度更大;两实验组在GXT测试中的Pmax-GXT和Tmax仅在SIT训练后出现了显著性提高(P<0.05),但两实验组间并无显著性差异。结论:12节大负荷功率车速度型间歇训练可有效提高短距离自行车运动员的有氧代谢和功率车递增负荷骑行能力,骑行次数递减速度型间歇训练方案的训练强度和量更高,可能导致有氧代谢能力更加显著的适应性变化。     

优秀男子短距离场地自行车运动员脑电变化分析

目的:观察不同水平男子短距离场地自行车运动员脑电变化,为探讨自行车运动员技术动作发挥的中枢机制提供依据.方法:研究对象为8名二级和7名健将级男子自行车运动员,应用脑电图(EEG)仪测试受试者在安静闭目和表象1公里场地计时赛时的脑电变化.结果:(1)安静时,二级运动员和健将级运动员EEG的功率谱成对称性分布,且两组运动员的EEG对应各区总功率无显著性差异(P＞0.05).(2)表象时,二级运动员EEG发生去同步化,但健将级运动员EEG的功率谱成对称性分布.(3)二级运动员左、右侧顶区与枕区α指数比值表象与安静状态下相比均无显著性差异(P＞0.05),健将级运动员左、右侧有显著性差异(P＜0.05).(4)安静时,健将级运动员顶区和枕区脑电活力比值(β/α,%)与二级运动员比较无显著性差异(P＞0.05);表象时,两组运动员脑电活力比值有显著性差异(P＜0.05).结论:健将级男子短距离场地自行车运动员中枢神经系统对外界信息的整合及技术动作协调能力优于二级运动员.     

全军第五届高原医学专业学术会议论文综述

一、高原适应锻炼 人体在模拟3000m低压舱内每天进行负荷300～600和600～900kg·m锻炼4小时,2周后再到模拟5000m停留24小时,发现动脉血氧分压(PaO_2)、肺泡动脉氧压差(A-aDO_2)和心功能等均优于单纯适应组和对照组(直接升到5000m)。在青藏高原现场验证中,见到在2800m适应锻炼16天后再到4800m时,与单纯适应组相比,肺氧合效率增高(PaO_2增加,A-aDO_2减小),高原反应发生率也明显减少。对运动员进行阶梯缺氧适应,发现急速进入4000m,心率170次的作功量(PWC_(170))明显下降,返回平原后即恢复正常。而阶梯式到达4000m者,PWC_(170)不下降,返回平原后反而增加,表明阶梯缺氧可防止4000m时有氧工作能力下降,在此高度运动     

Effect of work duration on physiological and rating scale of perceived exertion responses during self-paced interval training

This study compared running velocity, physiological responses, and perceived exertion during self-paced interval training bouts differing only in work bout duration. Twelve well-trained runners (nine males, three females, 28+/-5 years, VO2 max 65+/-6 mL min(-1) kg(-1)) performed preliminary testing followed by four "high-intensity" interval sessions (Latin squares, 1 session week(-1) over 4 weeks) consisting of 24 x 1, 12 x 2, 6 x 4, or 4 x 6-min running bouts with a 1:1 work-to-rest interval (total session duration 48 min). The average running velocity decreased (93%, 88%, 86%, 84% vVO2 max, P < 0.01) with increasing work duration. Peak VO2 averaged about 92+/-4% of VO2 max for 2-, 4-, and 6-min intervals compared with only 82+/-5% for 1-min bouts (P < 0.001). Six of 12 athletes achieved their highest average VO2 and heart rate during 4-min intervals. The average RPEpeak (rating scale of perceived exertion) was approximately 17+/-1 for all four interval sessions. RPE increased by 2-4 U during an interval training session. The mean lactate concentration was similar across sessions (4.3+/-1.1-4.6+/-1.5 mmol L(-1)). Under self-paced conditions, well-trained runners perform "high-intensity" intervals at an RPE of approximately 17, independent of interval duration. The optimal interval duration for eliciting a high physiological load is 3-5 min under these training conditions. Increases in RPE during an interval bout are not associated with increasing blood lactate concentration.     

Reliability of the long-range power-law correlations obtained from the bilateral stride intervals in asymptomatic volunteers whilst treadmill walking

Stride intervals measured during steady-state walking are irregular. These stride interval fluctuations are not random but exhibit long-range power-law correlation (alpha) such that a given stride interval is 'influenced' by earlier variations in the stride intervals. To estimate alpha, one requires a minute long sequence of right or left side stride interval data. However, to obtain a reliable alpha point estimate, the minimal stride sequence length is unknown. Additionally, it is unknown if the right and left side alpha are equivalent. In this study, the within-day and the right and left side reliabilities of alpha point estimates were examined in 23 volunteers performing three 8-min treadmill walks. In addition, eight volunteers were retested on three additional days to estimate between-day reliability. The standard error of measurement (S.E.M.) and the within- and between-day intraclass correlation (ICC) values, and their 95% confidence intervals, each calculated using the combined right and left leg 8-min alpha estimates were acceptable [0.047 (0.044-0.051); 0.914 (0.882-0.932) and 0.769 (0.689-0.815), respectively]. The left alpha (0.688 +/- 0.93) was greater than the right alpha (0.664 +/- 0.094), albeit this finding was underpowered (0.55). The alpha point estimates obtained from the full 8-min walks provided minimal S.E.M. and maximal within- and between-day ICCs. However, the minimal S.E.M. was statistically indistinguishable from the 6- and 7-min walk durations and all of the within-day and between-day ICCs were similar except for the 3- and 8-min between-day ICCs. This study suggests that data from four 3 min, three 6 min or two 8 min walk duration trials provide reliable alpha point estimates from a short series of short treadmill walks.     

Influence of continuous and interval training on oxygen uptake on-kinetics

PURPOSE: To examine the relative effectiveness of moderate-intensity continuous training and high-intensity interval training on pulmonary O2 uptake (VO2) kinetics at the onset of moderate- and severe-intensity cycle exercise in previously sedentary subjects. METHODS: Twenty-three healthy subjects (11 males; mean +/- SD age 24 +/- 5 yr; VO2peak 34.3 +/- 5.5 mL x kg(-1) x min(-1)) were assigned to one of three groups: a continuous training group that completed three to four sessions per week of 30-min duration at 60% VO2peak (LO); an interval training group that completed three to four sessions per week involving 20 x 1-min exercise bouts at 90% VO2peak separated by 1-min rest periods (HI); or a control group (CON). Before and after the 6-wk intervention period, all subjects completed a series of step exercise tests to moderate and severe work rates during which pulmonary VO2 was measured breath-by-breath. RESULTS: ANOVA revealed that continuous and interval training were similarly effective in reducing the phase II VO2 time constant during moderate (LO: from 31 +/- 8 to 23 +/- 5 s; HI: from 32 +/- 9 to 21 +/- 4 s; both P < 0.05; CON: from 30 +/- 6 to 29 +/- 7 s; NSD) and severe exercise (LO: from 35 +/- 6 to 24 +/- 7 s; HI: from 32 +/- 11 to 24 +/- 7 s; both P < 0.05; CON: from 27 +/- 7 to 25 +/- 5 s; NSD) and in reducing the amplitude of the VO2 slow component (LO: from 0.38 +/- 0.10 to 0.29 +/- 0.09 L x min(-1); HI: from 0.41 +/- 0.28 to 0.30 +/- 0.28 L x min(-1); both P < 0.05; CON: from 0.54 +/- 0.22 to 0.66 +/- 0.38 L.min; NSD). CONCLUSIONS: Six weeks of low-intensity continuous training and high-intensity interval training were similarly effective in enhancing VO2 on-kinetics following step transitions to moderate and severe exercise in previously untrained subjects.     

A review of the pharmacology, pharmacokinetics and behavioral effects of procaine in thoroughbred horses.

Since procaine has both local anaesthetic and central stimulant actions its presence in the blood or urine of racing horses is forbidden. After rapid intravenous injection of procaine HC1 (2.5 mg/Kg) in thoroughbred mares plasma levels of this drug fell rapidly (t 1/2 alpha = 5 min) and then more slowly (t 1/2 beta = 50.2 min). These kinetics were well fitted by a two compartment open model (Model I). This model gave an apparent Vdbeta for procaine in the horse of about 3,500 litres. Since procaine was about 45% bound to equine plasma protein this gives a true Vdbeta for procaine of about 6,500 litres. After subcutaneous injection of procaine HC1 (3.3 mg/Kg) plasma levels peaked at about 400 ng/ml and then declined with a half-life of about 75 minutes. These data were well fitted by Model I when this was modified to include simple first order absorption (K = 0.048 min-1) from the subcutaneous injection site (Model II). After intramuscular injection of procaine penicillin (33,000 I.U./Kg) plasma levels reached a peak at about 270 ng/ml and then declined with a half-life of about 9 hours. These data were approximately fitted by Model II assuming a first order rate constant for absorption of procaine of 0.0024 min-1. After intramuscular injection of procaine HC1 (10 mg/Kg) plasma levels of procaine peaked rapidly at about 600 ng/ml but thereafter declined slowly (+ 1/2 = 2 hours). A satisfactory pharmaco-kinetic model for this intramuscular data could not be developed. An approximation of these data was obtained by assuming the existence of two intramuscular drug compartments, one containing readily absorbable drug and the other poorly absorbable drug (Model III). After intra-articular administration of procaine (0.33 mg/Kg) plasma levels of this drug reached a peak at about 17 ng/ml and then declined with a half-life of about 2 hours. These data were not modelled.     

Endurance training and obesity: effect on substrate metabolism and insulin sensitivity

PURPOSE: Obesity and type 2 diabetes mellitus are disease states associated with hallmark features such as insulin resistance and an impaired ability to oxidize lipids. It has recently been reported that an optimal exercise intensity for fat oxidation (FATmax) exists; we hypothesize that continuous exercise training at this specific intensity can lead to greater improvements in fat oxidation and insulin sensitivity than a eucaloric interval training program. METHODS: In a counterbalanced, crossover design, eight sedentary, obese, but otherwise healthy male participants performed two 4-wk blocks of endurance training, either at a predetermined intensity eliciting maximal fat oxidation (TPCON) or at 5-min intervals of +/- 20% FATmax (TPINT). During the week preceding the exercise training and 48 h after the final exercise bout, an OGTT, V O2max test, steady-state exercise, and measurements of body composition were undertaken. Diet was controlled the day before all trials (50% carbohydrate, 35% fat, and 15% protein; approximately 2900 kcal.d). Variables were compared using two-way repeated-measures analyses of variance. RESULTS: It was shown that fat oxidation rates were increased by 44% after TPCON (0.24 +/- 0.01 vs 0.35 +/- 0.03 g.min, P < 0.05) but not after TPINT, and the whole-body insulin sensitivity index was increased by 27% after TPCON (P < 0.05). These changes occurred despite no change in body weight, body mass index (BMI), waist to hip ratio (WHR), percent body fat (%BF), or V O2max. CONCLUSIONS: A continuous exercise training protocol that can elicit high rates of fat oxidation increases the contribution of fat to substrate oxidation during exercise and can significantly increase insulin sensitivity compared with a eucaloric interval protocol.     

Application of Normative Occipital Condyle-C1 Interval Measurements to Detect Atlanto-Occipital Injury in Children

BACKGROUND AND PURPOSE:Prior studies have found that widening or asymmetry of the occipital condyle-C1 interval on CT is a sensitive and specific marker for atlanto-occipital dislocation. Previously reported abnormal occipital condyle-C1 interval values are not age-specific, possibly leading to false-positive findings in younger children, in whom this joint space is normally larger than that in adults. This study assesses the utility of applying age-specific normative occipital condyle-C1 interval ranges to documented cases of atlanto-occipital injury compared with previously reported abnormal cutoff values.MATERIALS AND METHODS:Retrospective review of CT and MR imaging of 14 subjects with atlanto-occipital injury was performed, and occipital condyle-C1 interval measurements were made for each subject. Sensitivities and specificities of proposed occipital condyle-C1 interval cutoffs of 2 and 3 SDs above the mean and previously published occipital condyle-C1 interval cutoffs for atlanto-occipital injury were then calculated on the basis of occipital condyle-C1 interval measurements for each subject.RESULTS:An occipital condyle-C1 interval 2 SDs above the age-specific mean has a sensitivity of 50% and specificity of 89%–100%, depending on the age group. An occipital condyle-C1 interval 3 SDs above the age-specific mean has a sensitivity of 50% and a specificity of 95%–100%. A 4.0-mm occipital condyle-C1 interval has a sensitivity of 36% and a specificity of 100% in all age groups. A 2.5-mm occipital condyle-C1 interval has a sensitivity of 93% and a specificity of 18%–100%.CONCLUSIONS:Occipital condyle-C1 interval widening cutoffs used to establish atlanto-occipital injury lack both sensitivity and specificity in children and young teenagers. MR imaging is necessary to establish a diagnosis of atlanto-occipital injury in children and young teenagers when the appropriate mechanism of injury is present.

This is the second part of a 2-part study assessing the occipital condyle-C1 interval (CCI) in the pediatric population. Part 1 of the study established the normative values of the CCI for 7 pediatric age groups based on 124 patients who were imaged for indications other than trauma or developmental anomaly.¹ Part 2 of this study aimed to determine the utility of applying age-specific abnormal CCI cutoff values to detect atlanto-occipital injury.Prior studies have found that the CCI is a sensitive and specific marker for atlanto-occipital dislocation (AOD).^2,3 Pang et al² found a CCI cutoff of 4 mm to be 100% sensitive and specific for AOD in the pediatric population. Gire et al³ found a CCI cutoff of 2.5 mm for both the adult and pediatric populations to have a sensitivity of 100% and a specificity of 84% for AOD. These values assume that the CCI joint-space measurement is unchanged throughout childhood and early adolescence; this assumption is contrary to the findings in Part 1 of our study. Because we have evaluated pediatric subjects with trauma suspected of having AOD with concordant MR imaging evidence of atlanto-occipital injury, it has been our experience that the CCI joint space is not consistently widened in cases of atlanto-occipital injury. The purpose of this study was to determine the sensitivity and specificity for detection of atlanto-occipital injury by using age-specific abnormal CCI cutoff values derived from Part 1 of this study as well as the prior proposed abnormal cutoff values of 4 and 2.5 mm.     

Cardiac response to whole-body heating.

Changes in ventricular function, as described by systolic time interval analysis, have been studied during heat stress and the time course of these changes, as well as changes in heart rate, have been investigated. Seven male and female subjects, 22-35 years of age, immersed their lower legs in water 42-44 degrees C for 30 min; their trunks and upper legs were enclosed in nonpermeable plastic to prevent evaporative heat loss. Total beat interval (R-R), left ventricular ejection time (LVET), pre-ejection period (PEP), arterial blood pressure, and oral temperature were monitored periodically during heating and recovery (post-hearing) periods. The stress induced significant (p less than 0.05) decreases in R-R and LVET by 5 min of heating which continued decreasing throughout the 30-min heating period. Heart rate accelerated from 72 up to 97 beats/min. LVET's during heat stress were shorter than those at similar resting heart rates. R-R and LVET were increased significantly by 1-min recovery but had not returned to preheating levels at 15 min. PEP, on the other hand, was not reduced until 15 min of heating, and did not start to recover until 3 min post-heating, after which it reached values exceeding control. A small increase in systolic blood pressure was maintained throughout heating and remained at 15 min recovery. Oral temperature increased approximately 1 degree C during the heating procedure; 50% of this was dissipated by 15 min recovery. Results are consistent with a two-stage cardiac response to heat-vagal withdrawal followed by a strong sympathetic outflow to the heart affecting both inotropic and chronotropic characteristics.     

Post-exercise heart rate variability of endurance athletes after different high-intensity exercise interventions

Methodological problems have limited the number of studies on heart rate variability (HRV) dynamics immediately after exercise. We used the short-time Fourier transform method to study immediate (5 min) and slow (30 min) recovery of HRV after different high-intensity exercise interventions. Eight male athletes performed two interval interventions at 85% and 93% (IV₈₅ and IV₉₃) and two continuous interventions at 80% and 85% (CO₈₀ and CO₈₅) of the velocity at VO_2max (vVO_2max). We found no increase in high frequency power (HFP), but low frequency (LFP) and total power (TP) increased ( P <0.05) during the first 5 min of the recovery after each intervention. During the 30-min recovery, HFP, LFP and TP (1) increased slowly toward resting values, but HFP remained lower ( P <0.01) than at rest, (2) were lower ( P <0.05) after IV₉₃ and CO₈₅ when compared with IV₈₅ and CO₈₀, respectively and (3) were lower ( P <0.01) after CO₈₅ when compared with IV₈₅. HRV recovery was detected during the immediate recovery after interventions. Increased exercise intensity resulted in lower HRV both in interval and in continuous interventions. In addition, when interval and continuous interventions were performed at a similar workload, HRV was lower after continuous intervention.     

Transient and maintained changes of the spontaneous occipital EEG during acute systemic hypoxia

BACKGROUND: It has been reported that during systemic hypoxia the spectral power of spontaneous EEG (closed eyes) increases, except for the power in the alpha band, which decreases. HYPOTHESIS: It is surmised that after a sudden decrease in inspired oxygen, the EEG parameters and SaO2 show similar temporal characteristics. METHODS: Normobaric acute hypoxia in 14 healthy subjects was evoked by breathing a hypoxic gas. Frequency spectra were calculated from occipital recordings and quantified together with the parameters of the spectral alpha peak. RESULTS: During the first 20 min of exposure, SaO2 decreases exponentially. With eyes open, the frequency bands show a transient increase in power (110-160%). The peak-time of the transient is shorter for the alpha and beta1 bands (4.5 min) than for the delta2 and theta bands (7 min). After the transient, the bands reach sustained power levels ca. 65% higher than the control value. The frequency of the alpha peak decreases with 0.61 +/- 0.16 Hz (mean +/- SE). In contrast to the eyes-closed condition, the peak amplitude increases (41 +/- 12%). CONCLUSIONS: During systemic hypoxia many characteristics of the spontaneous EEG with open eyes differ from those under normoxia, and alpha activity deviates strongly from that during hypoxia with closed eyes. During the first 20 min of exposure changes in power are most prominent and do not follow the change of SaO2. Monitoring total EEG power with open eyes, SaO2 and respiration gives a good impression of the hypoxia-related neurophysiological state of the subject.