Logistic risk model for the unique effects of inherent aerobic capacity on +Gz tolerance before and after simulated weightlessness

D. A. Ludwig, V. A. Convertino, D. J. Goldwater, H. Sandler

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


Small sample size (n < 10) and inappropriate analysis of multiviariate data have hindered previous attempts to describe which physiologic and demographic variables are most important in determining how long humans can tolerate acceleration. Data from previous centrifuge studies conducted at NASA/Ames Research Center, utilizing a 7-14 d bed rest protocol to simulate weightlessness, were included in the current investigation. After review, data on 25 women and 22 men were available for analysis. Study variables included gender, age, weight, height, percent body fat, resting heart rate, mean arterial pressure, V̇O2 max, and plasma volume. Since the dependent variable was time to greyout (failure), two contemporary biostatistical modeling procedures (proportional hazard and logistic discriminant function) were used to estimate risk, given a particular subject's profile. After adjusting for pre-bed-rest tolerance time, none of the profile variables remained in the risk equation for post-bed-rest tolerance greyout. However, prior to bed rest, risk of greyout could be predicted with 91% accuracy. All of the profile variables except weight, MAP, and those related to inherent aerobic capacity (V̇O2 max, percent body fat, resting heart rate) entered the risk equation for pre-bed-rest greyout. A cross-validation using 24 new subjects indicated a very stable model for risk prediction, accurate within 5% of the original equation. The result for the inherent fitness variables is significant in that a consensus as to whether an increased aerobic capacity is beneficial or detrimental has not been satisfactorily established. We conclude that tolerance to +Gz acceleration before and after simulated weightlessness is independent of inherent aerobic fitness.

Original languageEnglish (US)
Pages (from-to)1057-1061
Number of pages5
JournalAviation Space and Environmental Medicine
Issue number11
StatePublished - Dec 1 1987

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health


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