A. Experimental Approach
In this proposal we ask for support to test, experimentally, the effects of intermittent +Gz training on, cardiovascular function and aerobic performance. The goals of the proposed research will be achieved by conducting a pilot study investigating the physiological responses to both passive and active hypergravity training.
Phase I. Effects of Hypergravity Training (HGT)
Overview: In Phase I subjects will undergo exercise-coupled hypergravity training (HGTX), defined as a subject working at 70% of VO2max, 5 days/week, for 45-min/day, at 2.5 +Gz for 28 days (see Table 2 for protocol summary). We will investigate the effects of HGTX on cardiovascular function and aerobic performance and compare these effects to subjects undergoing similar +Gz loads passively and to subjects undergoing similar levels of aerobic training on an upright cycle ergometer. For the purposes of this proposal, the +Gz loading conditions are in reference to the foot since this represents the loading conditions on the pedal that the knee extensors and plantar flexor muscles must work against. To achieve 2.5 +Gz at the feet, the subject will rotate at 38 RPM.
Hypotheses:
The Phase I study will test the following hypotheses:
Hypothesis I: HGTX and HGTP will enhance carotid sinus baroreflex function and orthostatic tolerance.
Hypothesis II: Under similar training regimes, HGTX will enhance aerobic performance compared to standard upright bicycle ergometry.
Specific Aims: obtaining the following will test the hypotheses:
a. Determine the effects of +Gz training on aerobic performance.
b. Determine the effects of +Gz exercise training on the baroreflex sensitivity.
c. Determine the effects of +Gz training on orthostatic tolerance.
d. Determine the effects of =Gz training on autonomic function
Physiological Assessment for all Subjects:
The following physiological information will be measured for each subject in Phase I of the proposed research; VO2 max, arterial baroreflex function, heart rate variability and orthostatic tolerance.
Experimental Design:
30 male subjects ranging from 21-45 yrs of age will be recruited to participate in this study.
All subjects will be initially screened using a medical history, motion sickness questionnaire, physical examination and electrocardiogram. Subjects will be excluded if: i) they have any health problem (e.g., cardiovascular) that would be adversely affected by Space Cycle activity; and ii) they cannot tolerate Space Cycle activity. All subjects will sign an informed consent document approved by the Institutional Review Board at the University of California Irvine Medical Center. Human subjects and training periods will be coordinated and supervised by the General Clinical Research Center (GCRC), Specialized Human Performance Laboratory (SHPL). This subunit (SHPL) is one of seven funded by the National Institutes of Health (NIH) and National Center for Research Resources (NCRR). The facility is a 4500 sq ft site in the new Hewitt Science Building at the UCI School of Medicine and is also located at the UCI Medical Center in Orange, Ca. The laboratory has state of the art equipment designed to facilitate exercise components for research. For all subjects, initial baseline measurements will be made at the GCRC. These include a VO2max determination, baroreflex function and orthostatic tolerance testing. Following all baseline determinations, the subjects will be randomly assigned into one of three groups, standard exercise training (ET), passive hypergravity training (HGTP) and exercise-coupled hypergravity training (HGTX). Each group will consist of 7 males. For the ET and HGTX groups, endurance training will consist of bicycle ergometry, 5 days/week at 70% of VO2max for 45-min per training session. The HGTX group will be exposed to a +Gz at the feet of 2.5 G, which translates into a rotational rate of 38 RPM. Concurrently, the HGTP group will be exposed 5 days/week, 45-min duration, to the same G-loading as the HGTX group, but will not conduct any endurance training.
