APPROACH:
Prior to the start of bed rest, subjects will follow a schedule of resistance and aerobic exercise training five days per week to familiarize themselves with the equipment and protocols. These exercise sessions will be individualized based on fitness and comfort level with the equipment. The goal of the pre-bed rest training period is to “ramp-up” the subjects to the full integrated resistance and aerobic training prescription and identify loads and speed settings for the in-bed rest training sessions. The subject will also perform a stretching exercise regimen during exercise sessions, with the aid of an exercise physiologist.

During bed rest, subjects will perform supine resistance training and continuous and interval aerobic exercise six days per week. The resistance exercise and continuous aerobic exercise that occur on the same day will be separated by at least 4 hours. Resistance exercise sessions will be performed using an in-house designed squat machine and modified commercial off-the-shelf (COTS) equipment. The resistance training sessions will consist of a variety of squat, heel raise, leg press and leg curl exercises. The aerobic exercise sessions will be completed using a supine cycle ergometer and vertical treadmill. At least two-thirds of the aerobic exercise sessions will be performed on the treadmill.

Resistance Exercise Sessions:
First 27 subjects: Resistance exercise will be performed three days per week, every other day using a prone leg curl, horizontal leg press, and horizontal squat machine (i.e. HEF). A standard warm-up protocol will be conducted for the lower body prior to exercise. The resistance exercise sessions will consist of a variety of squat, hamstring curl, heel raise and leg press exercises. The protocol will vary so that a “HEAVY,” “MEDIUM,” and “LIGHT” day of exercise will be performed during the week. The pre-bed rest exercise sessions will be used to familiarize the subjects with the exercise equipment, teach subjects proper form, and determine individualized loads to be used during bed rest. The in-bed rest sessions will be performed to maintain muscular strength and function during bed rest.

Last 8 subjects: Squat exercises previously performed on the Horizontal Squat Device will now be performed on the M-MED. Leg press, heel raise and hamstring curl previously performed on their specific devices will now be performed on the M-MED.

Aerobic Exercise Sessions:
First 27 subjects: Aerobic exercise sessions will be completed on the supine cycle ergometer and the Standalone Zero-Gravity Locomotion Simulator (sZLS). A minimum of two-thirds of the total aerobic sessions will be performed on the sZLS and the balance will be performed on the cycle ergometer. For some subjects, the sZLS or the supine cycle may not be suitable for all aerobic protocols due to fitness levels or comfort levels. In these situations the Exercise Physiology researchers will coordinate with the bed rest schedulers to meet the subject’s needs.

During the pre-bed rest and bed rest phases, the continuous aerobic exercise sessions will be performed on the same day as the resistance training sessions and will be separated by at least 4 hours. Interval aerobic exercise sessions will be performed three times per week on non-resistance exercise days.

Last 8 subjects: Rowing exercise will replace the running and cycling exercises currently performed on the sZLS and supine cycle. Rowing will be performed as interval and continuous sessions.

RESULTS:
This study is currently in progress. Results will be at the conclusion of the study.

Ploutz-Snyder LL, Downs M, Ryder J, Hackney K, Scott J, Buxton R, Goetchius E, and Crowell B. Integrated resistance and aerobic exercise protects fitness during bed rest. Medicne and Science in Sports and Exercise. 2014. February; 46(2):358-68. []

Exercise

Magnetic resonance imaging (MRI)

Musculoskeletal physiology

Oxygen consumption

Ultrasonography

Actin filament density

Cross Sectional Area leg

Dystrophin dystroglycan complex

Fiber ATPase

Fiber cross bridge stiffness

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