间断性短臂离心机+Gz暴露联合运动锻炼对心血管自主神经调节功能的影响

目的 利用短臂离心机进行梯度G值联合运动负荷锻炼,观察间断性锻炼3周后人体心血管自主神经调节功能的变化.方法 8名健康青年男性间断进行离心机梯度G值(1～2 G)暴露联合30 W运动负荷锻炼,每天30 min,持续3周.记录心电图和逐跳连续血压,运用自回归谱分析法得到心率变异性(HRV)与收缩压变异性功率谱.锻炼前后进行头高位倾斜联合下体负压测试,观察立位应激时心血管功能变化.结果 在卧位休息时,锻炼3周后被试者HRV的低频与高频比值较锻炼前显著下降(P＜0.05),收缩压变异性的低频功率较锻炼前显著增加(P＜0.05).在头高位倾斜联合下体负压实验时,锻炼后被试者心率较锻炼前显著下降(P＜0.05),总外周阻力显著增加(P＜0.05),每搏量呈增加的趋势.结论 离心机+Gz暴露联合30 W运动锻炼3周可以增加平卧位心脏迷走神经与外周血管交感神经活动水平,增强立位应激时血压调节能力,提高了心血管功能储备.     

Development and Application of SAC-Ⅲ Human Short-arm Centrifuge

目的 研制一种新型短臂离心机(SAC-Ⅲ)并观察其应用效果.方法 SAC-Ⅲ型短臂离心机由电源、操作控制系统、声像监控系统、脚踏阻力锻炼及做功计量系统、电控静音刹车系统、工作转臂及支承结构等部件组成.通过电源系统,使工作转臂绕支撑装置作圆周运动,产生人工重力.选取16名男性志愿者,在SAC-Ⅲ型短臂离心机上人工重力暴露,分析在1G,2G和3G作用下心率和呼吸等生理参数的变化.结果 利用SAC-Ⅲ型短臂离心机,与基础值相比,心率和呼吸率1G暴露时呈增加趋势,2G暴露时显著增加(P＜0.05),3G暴露时进一步增加(P＜0.01).结论 在SAC-Ⅲ型短臂离心机暴露时,心率和呼吸率的变化表明其能有效模拟人工重力作用,可作为飞行人员抗荷生理训练设备或航天员对抗失重生理影响的有力措施.     

三周间断性短臂离心机+Gz暴露和运动负荷对人体心功能的影响

目的 利用短臂离心机进行梯度G值暴露联合运动负荷锻炼,观察间断性锻炼3周后人体心脏收缩、泵血功能的变化.方法 8名健康青年男性间断进行梯度G值(1-2 G)离心机+Gz暴露联合30 W运动负荷锻炼,每天30 min,持续3周.采用心电机械图法和阻抗法测量锻炼前后心脏的收缩功能与泵血功能.结果 锻炼2周后被试者左室射血时间(LVET)及射血分数(EF)较锻炼前显著增加(P<0.05).心率(HR)、射血前期(PEP)与LVET比值(PEP/LVET)显著下降(P<0.05);锻炼3周后,LVET及EF进一步增加(P<0.01),HR及PEP/LVET进一步下降(P<0.05),同时PEP下降达到差异显著性,每搏量(SV)和总外周阻力(TPR)显著增加(P<0.05).结论 3周间断性离心机+Gz暴露联合运动负荷锻炼可显著增强心脏收缩与泵血功能.     

HP动作对抗推拉效应的离心机训练方法

目的 建立飞行员做HP动作对抗推拉效应(push-pull effect,PPE)的离心机训练方法. 方法 依据实际空战机动飞行中记录的推拉动作(push-pull maneuver,PPM)飞行参数,在载人离心机常规训练的基础上增加HP动作对抗PPE训练.受试者为6名飞行员.训练分3日进行,第1日采用预编程模式,飞行员穿抗荷服训练HP动作,载荷为+Gz增长率和下降率均为3 G/s、峰值分别为3、5、6、7G各持续10 s的曲线.第2日采用预编程模式,载荷为一组-1Gz持续5 s与+Gz分别为3、5、6、7G各持续10 s,G值增长率为2 G/s,下降率为1 G/s的PPM曲线,飞行员在-1Gz时采用HP动作的呼吸方式呼吸,从-1Gz向+Gz开始转换时即做较用力的HP动作,并随着+Gz的增加逐渐加大用力程度.第3日采用闭环模式,进行+3、+5、+8 Gz各持续10 s的HP与PHP动作训练.记录飞行员的+Gz耐力、心率(heart rate,HR)、呼吸率(breathing rate,BR)、双腿蹬力(muscular force of legs,F1egs)等指标的变化,并采用SPSS 10.0统计软件对数据进行自身对照t检验或重复测量的方差分析. 结果 第1日,6名飞行员采用HP动作,均完成了+7 Gz持续10 s离心机训练,其中1名飞行员因曾患椎间盘突出,退出后续训练.第2日,5名飞行员均完成了HP动作对抗PPE训练,通过了-1Gz持续5 s,至+3、+5、+6、+7 Gz持续10s的PPM训练.第3日,5名飞行员均完成了HP与PHP动作+8 Gz持续10 s训练.随+Gz值的增加,Flegs明显高于前一次+Gz暴露时(F=127.047～322.488,P＜0.01),HR、BR均显著高于+1 Gz安静时(P＜0.01).各+Gz暴露时的Flegs、HR、BR在3个训练日之间无显著差异;-1Gz暴露时的HR、BR均显著高于+1 Gz安静时(P＜0.01).飞行员主诉HP动作对抗PPE的离心机训练明显提高了对抗PPE的能力和信心. 结论 采用本研究建立的HP动作对抗PPE的离心机训练方法,能够显著提高飞行员对抗PPE的能力.     

±Gx或±Gy与+Gz复合作用对人体抗荷耐力的影响

目的观察受试者暴露于±Gx或±Gy与+Gz复合离心机加速度作用下,复合加速度对人体抗荷耐力的影响和相关生理变化。方法分别测定6名受试者在单独+Gz作用,以及+2.5 Gx/+Gz、-1Gx/+Gz、+2 Gy/+Gz,-1 Gy/+Gz复合加速度作用时的基础+Gz耐力,观察加速度耐力情况和相关生理变化。三轴向加速度增长率均为1 G/s,峰值作用时间10 s。加速度作用过程中,受试者采用HP动作的呼吸方式,但呼气不用力,不收紧上身和腿部肌肉。结果 -1 Gy/+Gz、-1 Gx/+Gz的复合作用对基础+Gz耐力没有显著影响;+2 Gy/+Gz的复合作用时基础+Gz耐力增加(0.54±0.10)G(P0.01);+2.5 Gx/+Gz的复合作用时基础+Gz耐力增加(0.63±0.31)G(P0.01);心率、呼吸率与对照相比均无显著差异。±Gy/+Gz暴露时会出现不对称的视力丧失,+2.5 Gx/+Gz作用时,受试者感觉眼球前凸、压迫眼睑,眼睛有充血感。结论在采用HP动作呼吸方式的条件下,-1 Gy/+Gz、-1 Gx/+Gz复合作用对基础+Gz耐力无显著影响,+2 Gy/+Gz、+2.5 Gx/Gz的复合作用能够增加+Gz耐力。     

SAC-Ⅲ短臂离心机的研制与应用研究

目的研制一种新型短臂离心机(SAC-Ⅲ)并观察其应用效果。方法 SAC-Ⅲ型短臂离心机由电源、操作控制系统、声像监控系统、脚踏阻力锻炼及做功计量系统、电控静音刹车系统、工作转臂及支承结构等部件组成。通过电源系统,使工作转臂绕支撑装置作圆周运动,产生人工重力。选取16名男性志愿者,在SAC-Ⅲ型短臂离心机上人工重力暴露,分析在1 G,2 G和3 G作用下心率和呼吸等生理参数的变化。结果利用SAC-Ⅲ型短臂离心机,与基础值相比,心率和呼吸率1 G暴露时呈增加趋势,2 G暴露时显著增加(P<0.05),3 G暴露时进一步增加(P<0.01)。结论在SAC-Ⅲ型短臂离心机暴露时,心率和呼吸率的变化表明其能有效模拟人工重力作用,可作为飞行人员抗荷生理训练设备或航天员对抗失重生理影响的有力措施。     

人力短臂离心机训练后心血管功能的改变

目的 观察人力短臂离心机训练后心血管功能的改变，探讨人力短臂离心机的训练效果。方法 9名健康男性青年利用人力短臂离心机进行训练，转速为30-34r／min，持续时间为5min，1次／d，连续训练7d。测量心血管功能的变化。结果 人力短臂离心机训练3d后，心率显著降低(P＜0．05)，左室射血时间(LVET)显著延长(P＜0．01)；训练7d后，心率进一步降低(P＜0．01)，左室射血时间显著延长(P＜0．05)，每搏量显著增加(P＜0．05)。结论 人力短臂离心机连续训练7d后可明显改善心脏泵血功能。     

中等水平+Gz暴露对飞行员尿微量白蛋白、尿α1微球蛋白及尿常规检测指标的影响

目的 观察中等水平+Gz暴露对飞行员尿微量白蛋白(MA)、尿α1微球蛋白(α1M)及尿常规10项检测指标的影响.方法 33名歼击机飞行员接受离心机基础+Gz耐力检查,最高加速度暴露水平为+4.25 G/10 s,观察10名飞行员+Gz暴露后2 h和23名飞行员+Gz暴露后24 h尿液指标中MA、α1M和尿常规10项指标的变化情况.结果 离心机检查前,33名飞行员尿液指标检测结果均正常.离心机检查完毕所有飞行员均无明显不适主诉.离心机检查后2 h有1名飞行员尿MA高于正常值,1名飞行员尿α1M高于正常值,次日复查正常,尿常规10项检测结果均正常,但+Gz暴露后2 h尿比重略有减小(t=4.129,P＜0.01),pH值略有增加(t=6.530,P＜0.01).离心机检查后24 h,有1名飞行员尿MA升高,1名飞行员尿α1M升高,1名飞行员尿常规10项检测检出少量红细胞,+Gz暴露后24 h尿比重及pH值与暴露前比较差异不显著.与离心机检查前比较,检查后2 h、24 h尿MA和口lM均无明显差异(t=1.616、0.376、0.640、0.422,P＞0.05).结论 中等水平+Gz暴露对少部分飞行员肾功能指标有轻微影响,个别人员可出现短暂异常,应注意加强+Gz暴露后飞行员肾功能的监测和保护.     

+G_z负荷下动物心率变化特点及指标选取方法的探讨

用大白鼠和家兔对+Gz负荷下心率的变化规律进行了实验研究。指出,同心率可作为运动负荷的指标一样,在一定的G值范围内,可作为+Gz负荷强度的指标。用负荷心率曲线时间积分的增量(△St)作指标,能更灵敏地反映负荷及心脏代偿情况。对用心率作为动物G耐力耐受终点指标进行了探讨,以心功能衰竭期心率曲线的拐点处心率为依据,提出大白鼠宜取心率降至负荷前的68％(或2/3);家兔可取3/4为指标。并指出,由于耐受终点心率呈右偏态分布,不能求均值。     

短臂离心机重力暴露及有氧运动对心血管功能的影响

目的 观察利用短臂离心机单纯人工重力暴露、单纯有氧运动锻炼、人工重力暴露联合有氧运动锻炼3种锻炼方案对心血管功能及心脏自主神经调节功能的影响.方法 将24名健康青年男性志愿者随机分为3组:单纯人工重力暴露组、单纯有氧运动锻炼组及人工重力暴露联合运动锻炼组,每组8人.单纯人工重力暴露组进行间断梯度G值(1～2 G)离心机锻炼,单纯有氧运动锻炼组进行40 W的有氧运动负荷锻炼,人工重力暴露联合有氧运动锻炼组则进行间断梯度G值(1～2 G)离心机暴露,同时进行40 W运动锻炼,每天30 min,持续1周.采集心电图和逐跳连续血压,分析心率变异性与收缩压变异性功率谱.采用心电机械图法和阻抗法测量锻炼前后心脏的收缩与泵血功能.结果 人工重力暴露联合有氧运动锻炼组1周后受试者心率较锻炼前显著下降,且有统计学意义(P＜0.05),每搏量、左室射血时间及血压变异性低频功率较锻炼前显著增加,且有统计学意义(P＜0.05),而其他两组以上参数无显著变化.结论 1周人工重力暴露联合40 W有氧运动负荷锻炼可显著增强心脏泵血功能及自主神经调节功能.上述参数的明显改善可能得益于人工重力与有氧运动的复合作用. Abstract： Objective To investigate the changes of cardiovascular function and cardiovascular autonomic nervous regulation caused by short arm centrifuge exposure (SAC), aerobic exercise (EX),or their combination (SAC+ EX).Methods Twenty-four healthy male subjects were randomly and averagely divided into 3 groups that executed SAC, EX and SAC+ EX respectively.Subjects in SAC group experienced 1-2 G centrifuge training while EX group merely performed aerobic exercise with 40 W-load.In SAC+ EX group, subjects performed 40 W-load exercise for 30 min when they exposed on centrifuge once a day for 1 week.Electrocardiogram, continue blood pressure were monitored and used for HR variation and systolic blood pressure variation spectrum a(n)alysis.The training caused changes on systole and blood-pumping functions were got by analyzing mechanical-cardiogram and impedance-cardiogram.Results Analysis showed that 1-week SAC+EX training improved subjects' cardiac pumping function and cardiovascular autonomic nervous modulation, which associated with significant decreased heart rate (P＜0.05) and significant increased stroke volume (SV), left ventricular ejection time (LVET) and lower frequency (0.04-0.15 Hz) of arterial pressure spectral power (P＜0.05) as compared with those in other 2 groups.Conclusions 1-week SAC+40 W-load EX training could significantly improve cardiac pumping function, cardiac vagal modulation and peripheral smooth muscle vascular tone.Such combined action promotes the changes.However,alternative SAC or EX training is not sufficient enough to induce similar alterations.     

Acceleration effects on manual performance with isometric and displacement joysticks

BACKGROUND: We have shown before that novice human subjects produce exaggerated isometric forces when exposed to three times normal terrestrial acceleration (+3 Gz), and that this deficit is compensated by intensive training in +3 Gz. We now investigate whether training in normal terrestrial gravity (normal G) is also effective. We further examine whether subjects in +3 Gz produce not only exaggerated forces, but also exaggerated hand displacements. METHODS: Experiments were conducted in the stationary (normal G) or rotating (+3 Gz) gondola of a man-rated centrifuge. With their dominant hand, subjects produced either forces using an isometric joystick, or hand displacements using a regular joystick. Response directions and magnitudes were prescribed visually. In practice trials, subjects received continuous visual feedback about their performance, while in test trials they did not. RESULTS: Subjects produced exaggerated forces in +3 Gz, whether or not they previously practiced the task in normal G. In contrast, subjects did not produce exaggerated hand displacements in +3 Gz. DISCUSSION: Exaggerated force production in +3 Gz is not overcome by task practice in normal G, as opposed to task practice in +3 Gz. This might be an indication that pilot training should contain extended practice of force production during phases of increased gravity (+Gz) to avoid motor deficits during flight maneuvers inducing +Gz. Furthermore, the control of isometric and regular joysticks seems to be based on partly distinct neural mechanisms, with different +Gz dependence. Thus, against the background of motor performance during +Gz, regular sticks might be favorably compared to isometric sticks in high-performance aircrafts.     

+Gz重复暴露后兔颈椎间盘BMP表达和影像学改变

目的：探讨＋Gz重复暴露对兔颈椎影像学和椎间盘骨形态发生蛋白（BMP）表达的影响。方法：15只兔随机分为对照组、＋G2暴露1d组、2周组、4周组、6周组。每组3只。＋Gz暴露组兔每天连续5次暴露于＋6Gz、持续45s，中间间歇5min。各组动物均于实验前后颈椎侧位拍片作自身对比，实验结束后气栓法处死并取颈椎做BMP免疫组化分析。结果：X线片显示对照组、＋Gz暴露1d组及2周组兔颈椎无明显变化，而＋Gz暴露4周组和6周组兔颈椎均出现显著退行性改变。对照组、＋Gz暴露1d、2周和4周组兔颈椎间盘未见BMP阳性细胞表达，＋Gz暴露6周组兔颈椎间盘的纤维环中可见少量散在分布的BMP阳性表达的软骨细胞。结论：＋6Gz重复暴露4周和6周可引起兔颈椎发生退行性改变和椎间盘BMP的表达。     

+Gz暴露对大鼠大脑皮层HSP70蛋白表达的影响

目的：观察＋Gz暴露对大鼠大脑皮层HSP70蛋白表达水平的影响，探讨＋Gz暴露致脑损伤的机理。方法：100只SD大鼠随机分为对照组，＋2Gz暴露组，＋6Gz暴露组，＋10Gz暴露组，各组在G暴露后的6h、1、2．4、6d处死，免疫组织化学方法观察大鼠脑皮层HSP70蛋白表达情况，并对结果进行统计分析。结果：3个＋Gz暴露组的HSP70蛋白表达水平均显著高于对照组；不同G值之间的比较表明，＋6Gz组HSP70蛋白表达水平最高，＋10Gz组最低。结论：＋Gz暴露对大鼠大脑皮层HSP70蛋白表达水平有显著影响。     

正、负加速度交替急性大鼠脑组织NO、NOS及血浆ET的含量变化

目的：研究正、负加速度交替暴露后急性大鼠脑组织一氧化氮（NO）、一氧化氮合酶（NOS）及血浆内皮素（ET）的含量变化，探讨正、负加速度交替暴露后，易发生加速度引起意识丧失（G-indnced less of consciousness,G-LOC)的机制。方法：30只雄性Wistar大鼠随机分成3组：对照组、正加速（ Gz）组和正、负加速度（ Gz和-Gz）交替组。于暴露后即翔麻醉采血、取脑。测定脑组织NO、NOS及血浆中ET的含量。结果： Gz组和 Gz、-Gz交替组与对照组比较，脑组织中的NO、NOS及血浆中ET的含量增多，有显著性差异； Gz、-Gz交替组与 Gz组比较，脑组织中的NO、NOS及血浆中ET的含量增多，有差异性。结论： Gz、-Gz交替暴露和单纯 Gz、-Gz暴露均可使脑组织中的NO、NOS及血浆中ET的含量增多；且 Gz、-Gz交替暴露增多明显。说明 Gz、-Gz交替暴露对大脑所致损伤程度更重。     

Hemodynamic responses to seated and supine lower body negative pressure: comparison with +Gz acceleration.

Hemodynamic changes between upright and supine lower body negative pressure (LBNP) to levels of -70 mm Hg were compared in 8 subjects (5 males, 3 females) and correlated with their findings during simulated Shuttle reentry acceleration with a slow onset rate of 0.002 G/s (1,020 s to peak +2 Gz) and during gradual onset exposures (0.03 G/s) to +3 Gz and +4 Gz. Six of the 8 subjects were able to tolerate 2 min at peak +2 Gz, 2-5 min at +3 Gz, and 1-2 min at +4 Gz. Heart rate (HR) at any given level of upright LBNP regularly exceeded supine levels. HR change at -50 mm Hg in upright subjects (+47.7 bpm from 74.1 +/- 1.9 (M +/- S.E.) bpm, control) was 2.6 times greater than in supine subjects (+18.3 bpm from 64.8 +/- 2.8 bpm, control). HR values at -40 mm Hg supine (73.7 +/- 2.6) matched seated upright pre-LBNP control levels (74.1 +/- 1.9 bpm), while values at -70 mm Hg supine (102.5 +/- 4.4 bpm) were not significantly different from those at -40 mm Hg upright (103.1 +/- 4.0 bpm). Peak HR during +3 Gz (145.8 +/- 7.7 bpm) and +4 Gz (152.3 +/- 6.5 bpm) significantly exceeded recorded supine and upright LBNP levels, whereas values at +2 Gz (104.8 +/- 5.5 bpm) closely matched those at -40 mm Hg upright (103.1 +/- 4.0 bpm) and -70 mm Hg supine (102.5 +/- 4.4 bpm). Supine LBNP HR changes in this relatively small group of subjects closely matched those previously reported in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)     

+Gz作用下兔心脏功能的改变

为观察＋Ｇｚ作用下兔心脏功能的改变，７只新西兰兔经麻醉后依次分别暴露于＋２、＋４和＋６Ｇｚ，峰值持续时间为３０ｓ，增长率为１Ｇ／ｓ，每次暴露后恢复时间为１５ｍｉｎ。记录左心室内压、左心室内压变化速率、心电图等的变化。在＋２、＋４和＋６Ｇｚ作用下，左心室内压峰值较暴露前对照值分别降低６２．９６％（Ｐ＜０．０１）、６３．３４％（Ｐ＜０．０１）及８２．０１％（Ｐ＜０．０１），左心室内压最大上升速率分别降低５８．４６％（Ｐ＜０．０１）、５３．５９％（Ｐ＜０．０１）及６３．０６％（Ｐ＜０．０１），左心室舒张末压分别降低６７．７８％（Ｐ＞０．０５）、３３２．７４％（Ｐ＜０．０１）及５００．５４％（Ｐ＜０．０１）。除ＰｖＣＯ２在＋６Ｇｚ作用后即刻显著升高外（Ｐ＜０．０５），其余动、静脉血气结果在＋Ｇｚ作用后即刻较暴露前对照值均无显著性变化。＋Ｇｚ作用可引起兔心脏泵血功能显著降低。     

＋Gz作用下兔颅内压的改变

采用侧脑室插管法记录颅内压的技术，观察不同Ｇ值水平及增长率的＋Ｇｚ作用下兔颅内压变化。结果表明：（１）在增长率和峰值作用时间恒定量，麻醉兔在＋３、＋５及＋７Ｇｚ作用下，颅内压降低。随Ｇ值增加，颅内压负值亦随之增大，呈显著负相关。     

Acceleration in other axes affects +Gz tolerance: dynamic centrifuge simulation of agile flight

BACKGROUND: Modern, thrust-vectored jet aircraft have the capability of developing multi-axis accelerations, especially during the performance of "supermaneuvers." These "agile" aircraft are capable of unconventional flight. The human consequences of this agile flight environment are unknown. METHODS: This multi-axis acceleration environment was studied on the Dynamic Environment Simulator gimbaled centrifuge. There were nine relaxed, unprotected subjects who were exposed to either lateral (+/- 1, +/- 2 Gy), transverse chest-to-back (+1, 2.5, or 4 Gx), or back-to-chest (-1 Gx) sustained acceleration. Positive C (+Gz) acceleration was then added beginning at 1.0 Gz by gradual onset (0.1 Gz x s(-1)) until the subjects lost nearly all of their vision. Baseline +Gz-only relaxed tolerances were measured before and after all combined Gy/Gz and Gx/Gz exposures. Heart rate, percent cerebral oxygen saturation, and cerebral blood volumes were collected during each exposure. RESULTS: Adding moderate transverse (+Gx) acceleration significantly reduced +Gz tolerance. Relaxed, unprotected +Gz tolerance was reduced approximately 0.25 G when 1.0 or 2.5 Gx was added to the increasing +Gz exposure. Adding moderate lateral Gy significantly increased +Gz tolerance. Relaxed, unprotected +Gz tolerance was increased approximately 0.5 G when +2 Gy or -2 Gy was added to the -Gz exposure. The decrease in cerebral blood volume was significantly less when +Gz was added to -1 Gx compared with the addition of +Gz to +Gx. CONCLUSIONS: Multi-axis sustained accelerations, such as those experienced during thrust-vectored aircraft maneuvers, can either enhance or reduce the +Gz tolerance of the pilot depending on the direction of the net gravitoinertial force. Gy acceleration in conjunction with Gz acceleration can enhance G tolerance. Gx acceleration in addition to Gz acceleration can reduce G tolerance.     

Isometric force production in experienced fighter pilots during +3 Gz centrifuge acceleration

INTRODUCTION: Previously, we have shown that na?ve subjects produce exaggerated isometric forces when exposed to increased acceleration (+Gz) for the first time. The present study investigates whether +G,-experienced PA-200 Tornado pilots show similar deficits. METHODS: Experiments were conducted in the stationary (+1 Gz) or rotating (+3 Gz) gondola of a human-rated centrifuge. With their dominant hand, seven pilots produced visually prescribed forces of specific direction and magnitude using an isometric joystick. In practice trials, subjects received continuous visual feedback about their performance, while in test trials they did not. RESULTS: Peak forces during test trials were significantly higher in +3 Gz than in +1 Gz, although this increase of about 25% referring to the +1 Gz value was somewhat smaller in pilots than in nonpilot controls (increase of about 36%). DISCUSSION: Since pilots' responses were exaggerated in +3 Gz, it seems that frequent exposure to varying +Gz levels is not sufficient for a profound adaptation of force-producing mechanisms to +3 Gz. In consequence, pilots' performance on isometric tasks could be compromised during flight maneuvers in +Gz.