Study protocol, implementation, and verification of a short versatile upright exercise regime during 5 days of bed rest

Objectives: This work provides a reference for future papers originating from this study by providing basic results on body mass, urine volume, and hemodynamic changes to 5 days of bed rest (BR) and by describing acute cardio-respiratory/mechanographic responses to a short versatile upright exercise battery. Methods: Ten male subjects (mean±SEM age: 29.4±1.5 years; height: 178.8±1.5 cm; body mass: 77.7±1.5 kg) performed, in random order, 5 days of 6° head-down tilt (HDT) BR with no exercise (CON), or BR with daily 25 minutes of quiet upright standing (STA) or upright locomotion replacement training (LRT). Results: Plasma volume, exercise capacity and orthostatic tolerance decreased similarly between interventions following 5 days of BR. Upright heart rate during LRT and STA increased throughout BR; from 137±4 bpm to 146±4 bpm for LRT (P<0.01); and from 90±3 bpm to 102±6 bpm (P<0.001) for STA. Conclusion: the overall similarity in the response to BR, and increase in upright heart rate during the LRT sessions suggest early and advancing cardiovascular deconditioning during 5 days of BR bed rest, which was not prevented by the versatile exercise regime.