Short-arm (1.9 m) +2.2 Gz acceleration: Isotonic exercise load-O-2 uptake relationship

Background: The deconditioning syndrome from prolonged bed rest (BR) or spa ceflight includes decreases in maximal oxygen uptake ((V) over dot o(2)max) , muscular strength and endurance, and orthostatic tolerance. In addition t o exercise training as a countermeasure, +Gz (head-to-foot) acceleration tr aining on 1.8-2.0 m centrifuges can ameliorate the orthostatic and accelera tion intolerances induced by BR and immersion deconditioning. Purpose: Stud y A was designed to determine the magnitude and linearity of the heart rate (HR) response to human-powered centrifuge (HPC) acceleration with supine e xercise vs. passive (no exercise) acceleration. Study B was designed to tes t the hypothesis that moderate +Gz acceleration during exercise will not af fect the respective normal linear relationships between exercise load and ( V) over dot o(2)max, HR, and pulmonary ventilation ((V) over dot EBTPS). St udy C: TO determine if these physiological responses from the HPC runs (exe rcise + on-platform acceleration) will be similar to those from the exercis e + 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 a t 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 sta tions. A (V) over dot o(2)max test and submaximal exercise runs occurred un der three conditions: (EXA) exercise ton-platform cycle at 42%, 61%, 89% an d 100% ((V) over dot o(2)max) with no acceleration; (HPC) exercise + accele ration via the chain drive at 25%,50%, and 100% Gzmax (35%, 72% and 100% (V ) over dot o(2)max); and (EXA) exercise (on-platform cycle at 42%, 61%, 89% , and 100% (V) over dot o(2)max) with acceleration performed via the off-pl atform cycle operator at +2.2 +/- 0.2 Gz [50% of max (rpm) G]. Results: Stu dy A: Mean (+/-SE) Amax was 43.7 +/- 1.3 rpm ((X) over bar = +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) over bar HR on G z levels indicated explained variances (r(2)) of 0.88 (exercise) and 0.96 ( passive). The (X) over bar exercise HR of 107 +/- 4 (25%), to 189 +/- 13 (1 00%) 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 d ifferences in (V) over dot o(2), HR or (V) over dot EBTPS at the submaximal or maximal levels between the EX and EXA runs. Mean (+/-SE) (V) over dot o (2)max 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) over dot o(2) (p = 0.45 ), HR (p < 0.08), (V) over dot EBTPS (p = 0.28), Or the RE (p = 0.15) when the exercise load was (V) over dot o(2)max. Conclusion: Addition of + 2.2 G z acceleration does not significantly influence levels of oxygen uptake, he art rate, or pulmonary ventilation during submaximal or maximal cycle ergom eter leg exercise on a short-arm centrifuge.