Aerobic fitness: II. Orthostasis and V̇O(2peak) following head-down tilt

J. W. Williamson, X. Shi, J. J. Chen, C. G. Crandall, W. G. Squires, L. P. Krock, P. B. Raven

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

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 (V̇O(2peak)) during upright bicycle ergometry and tolerance time during 70° head-up tilt (HUT) were compared within and between groups before and after 4 h of -6° head-down tilt (HDT). Eight ET subjects with a mean V̇O(2peak) of 61.7 ± 1.6 ml · kg-1 · min-1 were matched for age, height, and weight with eight UT subjects (V̇O(2peak) = 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 < 0.03. Reductions in V̇O(2peak) 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 < 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 V̇O(2peak) and the change in OT time, r = -0.74, P < 0.01. The decrease in OT was also significantly correlated to the PV decrease, r = 0.59, P < 0.04. The UT subjects had significantly augmented pressor responses to HUT manifested by the increases in both HR and MAP following HDT. However, after HDT, the ET subjects failed to demonstrate an immediate increase in HR with the initiation of HUT. These data suggest that ET individuals may experience a greater PV loss than UT individuals following acute simulation of microgravity. The greater reduction in PV may also explain the greater reductions in both V̇O(2peak) and OT experienced by the ET subjects following 4 h of HDT.

Original languageEnglish (US)
Pages (from-to)999-1006
Number of pages8
JournalMedicine and Science in Sports and Exercise
Volume24
Issue number9
StatePublished - 1992

Fingerprint

Head-Down Tilt
Dizziness
Plasma Volume
Head
Weightlessness Simulation
Oxygen
Ergometry
Exercise Tolerance
Weights and Measures

Keywords

  • DECONDITIONING
  • ENDURANCE EXERCISE TRAINING
  • HEAD-DOWN TILT
  • ORTHOSTASIS
  • PEAK OXYGEN UPTAKE

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Public Health, Environmental and Occupational Health
  • Physical Therapy, Sports Therapy and Rehabilitation

Cite this

Aerobic fitness : II. Orthostasis and V̇O(2peak) following head-down tilt. / Williamson, J. W.; Shi, X.; Chen, J. J.; Crandall, C. G.; Squires, W. G.; Krock, L. P.; Raven, P. B.

In: Medicine and Science in Sports and Exercise, Vol. 24, No. 9, 1992, p. 999-1006.

Research output: Contribution to journalArticle

Williamson, JW, Shi, X, Chen, JJ, Crandall, CG, Squires, WG, Krock, LP & Raven, PB 1992, 'Aerobic fitness: II. Orthostasis and V̇O(2peak) following head-down tilt', Medicine and Science in Sports and Exercise, vol. 24, no. 9, pp. 999-1006.
Williamson, J. W. ; Shi, X. ; Chen, J. J. ; Crandall, C. G. ; Squires, W. G. ; Krock, L. P. ; Raven, P. B. / Aerobic fitness : II. Orthostasis and V̇O(2peak) following head-down tilt. In: Medicine and Science in Sports and Exercise. 1992 ; Vol. 24, No. 9. pp. 999-1006.
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