Concurrent exercise and muscle protein synthesis: implications for exercise countermeasures in space.

Area of Science:

• Exercise Physiology
• Muscle Metabolism
• Space Medicine

Background:

• Long-duration space missions require exercise countermeasures, often combining aerobic and resistance training.
• Despite resistance exercise's effectiveness in preventing muscle loss in microgravity simulations, astronauts experience muscle atrophy.
• Earth-based studies indicate concurrent training may blunt muscle hypertrophy and strength gains compared to resistance training alone.

Purpose of the Study:

• To investigate whether performing aerobic exercise before resistance exercise attenuates the acute anabolic response in human skeletal muscle.
• To determine the impact of pre-exercise aerobic activity on myofibrillar protein synthesis rates following resistance exercise.

Main Methods:

• Myofibrillar protein synthesis rates were measured in 12 healthy adults using [2H5]phenylalanine incorporation.
• Muscle samples were analyzed after a resistance exercise protocol (leg press and extension).
• The protocol was repeated with a preceding 90-minute strenuous aerobic cycling session.

Main Results:

• Myofibrillar protein synthesis rates were not significantly different between resistance exercise alone and concurrent exercise.
• The rate following resistance exercise was 0.092 ± 0.006% per hour.
• The rate following concurrent exercise was 0.100 ± 0.007% per hour.

Conclusions:

• The acute anabolic response to resistance exercise is not suppressed by preceding aerobic exercise.
• This suggests that other mechanisms may be responsible for the blunted muscle adaptations observed with chronic concurrent training.
• Findings have implications for optimizing exercise countermeasures for astronauts during long space missions.