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Publication Abstracts

Short-Arm (1.9 m) +2.2 Gz Acceleration: Isotonic Exercise Load-O2 Uptake Relationship

John E. Greenleaf, Ph.D., Jennifer L. Chou, M.A., Natalie J. Stad, M.A., Georges P.N. Leftheriotis, M.D., Naomi F. Arndt, M.Eng.Sc., Catherine G. R. Jackson, Ph.D., Shawn R. Simonson, Ed.D, and Paul R. Barnes, Ph.D.
Aviat Space Environ Med 1999; 70:1173-82

Abstract

Background: The deconditioning syndrome from prolonged bed rest (BR) or spaceflight includes decreases in maximal oxygen uptake (V(dot)O2max), muscular strength and endurance, and orthostatic tolerance. In addition to exercise training as a countermeasure, +Gz (head-to-foot) acceleration training on 1.8-2.0 m centrifuges can ameliorate the orthostatic and acceleration intolerances induced by BR and immersion deconditioning. Purpose: Study A was designed to determine the magnitude and linearity of the heart rate (HR) response to human-powered centrifuge (HPC) acceleration with supine exercise vs. passive (no exercise) acceleration. Study B was designed to test the hypothesis that moderate +Gz acceleration during exercise will not affect the respective normal linear relationships between exercise load and V(dot)O2max, HR, and pulmonary ventilation (V(dot)EBTPS). Study C: To determine if these physiological responses from the HPC runs (exercise + on-platform acceleration) will be similar to those from the exercise + off-platform acceleration responses. Methods: In Study A, four men and two women (31-62 yr) were tested supine during exercise + acceleration and only passive acceleration at 100% [maximal acceleration (rpm) = Amax] and at 25%, 50%, and 75% of Amax. In Studies B and C, seven men (33 ± SD 7 yr) exercised supine on the HPC that has two opposing on-platform exercise stations. A V(dot)O2max test and submaximal exercise runs occurred under three conditions: (EX) exercise (on-platform cycle at 42%, 61%, 89% and 100% V(dot)O2max) with no acceleration; (HPC) exercise + acceleration via the chain drive at 25%,50%, and 100% Gzmax (35%, 72% and 100% V(dot)O2max); and (EXA) exercise (on-platform cycle at 42%, 61%, 89%, and 100% V(dot)O2max) with acceleration performed via the off-platform cycle operator at +2.2 ± 0.2 Gz [50% of max (rpm) G]. Results: Study A: Mean (±SE) Amax was 43.7 ± 1.3 rpm (X(overbar)= +3.9 ± 0.2, range = 3.3 to 4.9 Gz). Amax run time for exercise +acceleration was 50-70 s, and 40-70 s for passive acceleration. Regression of X(overbar) HR on Gz levels indicated explained variances (r2) of 0.88 (exercise) and 0.96 (passive). The X(overbar) exercise HR of 107 ± 4 (25%), to 189 ± 13 (100%) bpm were 43-50 bpm higher (p < 0.05) than comparable passive HR of 64 ± 2 to 142 ± 22 bpm, respectively. Study B: There were no significant differences in V(dot)O2, HR or V(dot)EBTPS at the submaximal or maximal levels between the EX and EXA runs. Mean (±SE) V(dot)O2max for EX was 2.86 ± 0.12 L · min-1 (35 ± 2 ml · min-1 · kg-1) and for EXA was 3.09 ± 0.14 L · min-1 (37 ± 2 ml·min-1 · kg-1). Study C: There were no significant differences in the essentially linear relationships between the HPC and EXA data for V(dot)O2 (p = 0.45), HR (p < 0.08), V(dot)EBTPS (p = 0.28), or the RE (p = 0.15) when the exercise load was % V(dot)O2max. Conclusion: Addition of + 2.2 Gz acceleration does not significantly influence levels of oxygen uptake, heart rate, or pulmonary ventilation during submaximal or maximal cycle ergometer leg exercise on a short-arm centrifuge.

Keywords: maximal work capacity, centrifugation, exercise-acceleration, passive acceleration heart rate, pulmonary ventilation

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Table of Contents for Volume 70, Number 12 of the ASME journal.