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To determine whether endurance exercise trained (ET) subjects would experience greater reductions in peak oxygen delivery and orthostatic tolerance (OT) than untrained (UT) subjects, both peak oxygen uptake (VO2peak) during upright bicycle ergometry and tolerance time during 70 degrees head-up tilt (HUT) were compared within and between groups before and after 4 h of -6 degrees head-down tilt (HDT). Eight ET subjects with a mean VO2peak of 61.7 +/- 1.6 ml.kg-1.min-1 were matched for age, height, and weight with eight UT subjects (VO2peak = 38.4 +/- 1.7 ml.kg-1.min-1). Following HDT, decreases in plasma volume (PV) were larger for ET subjects (-3.7 +/- 0.5 ml.kg-1) than for UT subjects (-2.3 +/- 0.3 ml.kg-1), P less than 0.03. Reductions in VO2peak for ET subjects (-5.4 +/- 1.1 ml.kg-1.min-1) were also greater than for UT subjects (-2.4 +/- 0.8 ml.kg-1.min-1), P less than 0.05. The ET (N = 6) subjects also had a significant decrease in OT time (-13.0 +/- 4.2 min) during post-HDT HUT, which was not observed for the UT group (N = 6). A significant inverse correlation was found pre-HDT VO2peak and the change in OT time, r = -0.74, P less than 0.01. The decrease in OT was also significantly correlated to the PV decrease, r = 0.59, P less than 0.04. The UT subjects had significantly augmented pressor responses to HUT manifested by the increases in both HR and MAP following HDT.(ABSTRACT TRUNCATED AT 250 WORDS)
J W Williamson, and
X Shi, and
J J Chen, and
C G Crandall, and
W G Squires, and
L P Krock, and
P B Raven
April 1999,
Hang tian yi xue yu yi xue gong cheng = Space medicine & medical engineering,
J W Williamson, and
X Shi, and
J J Chen, and
C G Crandall, and
W G Squires, and
L P Krock, and
P B Raven
February 1992,
The Physiologist,
J W Williamson, and
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J J Chen, and
C G Crandall, and
W G Squires, and
L P Krock, and
P B Raven
August 2006,
Rossiiskii fiziologicheskii zhurnal imeni I.M. Sechenova,
J W Williamson, and
X Shi, and
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W G Squires, and
L P Krock, and
P B Raven
January 1991,
European journal of applied physiology and occupational physiology,
J W Williamson, and
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C G Crandall, and
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P B Raven
September 2003,
The Journal of physiology,
J W Williamson, and
X Shi, and
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C G Crandall, and
W G Squires, and
L P Krock, and
P B Raven
April 1986,
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J W Williamson, and
X Shi, and
J J Chen, and
C G Crandall, and
W G Squires, and
L P Krock, and
P B Raven
February 1993,
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J W Williamson, and
X Shi, and
J J Chen, and
C G Crandall, and
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L P Krock, and
P B Raven
January 2005,
Pediatric cardiology,
J W Williamson, and
X Shi, and
J J Chen, and
C G Crandall, and
W G Squires, and
L P Krock, and
P B Raven
January 2000,
Pflugers Archiv : European journal of physiology,
J W Williamson, and
X Shi, and
J J Chen, and
C G Crandall, and
W G Squires, and
L P Krock, and
P B Raven
January 2002,
Anesthesia and analgesia,
