Purpose: Exercise prescriptions for spaceflight include aerobic and resistive countermeasures, yet few studies have evaluated their combined effects on exercise responses after real or simulated microgravity. We hypothesized that upright aerobic capacity (V˙O2pk) is protected during a 60-d bed rest (BR) in which intermittent (40%-80% pre-BR V˙O2pk) aerobic exercise (supine treadmill exercise against lower body negative pressure) was performed 2-4 d·wk−1 and resistive exercise (inertial flywheel exercises) was performed 2-3 d·wk−1. Further, we hypothesized that ingestion of an amino acid supplement that was shown previously to counteract muscle atrophy, would reduce the decline in V˙O2pk in nonexercising subjects during BR.
Methods: Twenty-four healthy women (8 nonexercise controls (CON), 8 exercisers (EX), and 8 nonexercisers with nutritional supplementation (NUT)) underwent a 20-d ambulatory baseline period, 60 d of 6° head-down tilt BR, and 21 d of ambulatory recovery. V˙O2pk was measured pre-BR and on the third day of recovery from BR (R3).
Results: In the EX group, V˙O2pk (mean ± SE) was not different from pre-BR (−3.3 ± 1.2%) on R3, although it decreased significantly in the CON (−21.2 ± 2.1%) and NUT (−25.6 ± 1.6%) groups.
Conclusions: These results indicate that alternating aerobic and resistive exercise on most days during prolonged microgravity simulated by BR is sufficient to preserve or allow quick recovery of upright aerobic capacity in women but that a nutritional supplementation alone is not effective.