Short-arm (1.9 m) +2.2 Gz acceleration: Isotonic exercise load-O₂ uptake relationship

Background: The deconditioning syndrome from prolonged bed rest (BR) or spaceflight includes decreases in maximal oxygen uptake (V̇O₂max), 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 V̇O₂max, HR, and pulmonary ventilation (V̇EBTPS). 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 V̇O₂max test and submaximal exercise runs occurred under three conditions: (EX) exercise (on-platform cycle at 42%, 61%, 89% and 100% V̇O₂max) with no acceleration; (HPC) exercise + acceleration via the chain drive at 25%, 50%, and 100% Gzmax (35%, 72% and 100% V̇O₂max); and (EXA) exercise (on-platform cycle at 42%, 61%, 89%, and 100% V̇O₂max) 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 (X̄ = +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 X̄ HR on Gz levels indicated explained variances (r₂) of 0.88 (exercise) and 0.96 (passive). The X 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 V̇O₂, HR or V̇EBTPS at the submaximal or maximal levels between the EX and EXA runs. Mean (±SE) V̇O₂max 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 V̇O₂max (p = 0.45), HR (p < 0.08), V̇EBTPS (p : 0.28), or the RE (p = 0.15) when the exercise load was % V̇O₂max 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.