Macro partitioning
Low muscle glycogen availability during prolonged aerobic exercise increases net skeletal muscle protein degradation and decreases protein synthesis, resulting in a more negative whole-body protein balance compared to high glycogen conditions.
If you are doing long-duration cardio (e.g., >1 hour) and your glycogen stores are low, your body will break down more muscle protein and build less of it. To protect muscle, consider consuming carbohydrates before or during the exercise, or ensure your post-exercise protein intake is sufficient to counteract this increased breakdown.
The net leg protein balance was decreased in the L-CHO group compared with at rest and compared with the H-CHO condition, which was primarily due to an increase in protein degradation... but also due to a decrease in protein synthesis late in exercise.
Why this rating
Randomized crossover design with stable isotope tracers (gold standard for turnover), though small sample size (n=6).
Source
Effect of glycogen availability on human skeletal muscle protein turnover during exercise and recovery
Krista R. Howarth et al. · Journal of Applied Physiology · 2010
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