Mixed
High-intensity dynamic exercise (>70% VO2max) causes a net loss of muscle protein due to increased amino acid oxidation and breakdown, whereas resistance exercise primarily stimulates protein synthesis post-exercise but also elevates breakdown.
If you do very intense cardio (like sprinting or heavy cycling), your body may break down muscle protein for fuel. If you lift weights, your body tries to build muscle after the workout, but it also breaks down protein at the same time. To grow, you need to eat enough protein to tip the balance toward building.
if the exercise is intense enough, there is a net loss of muscle protein (as a result of decreased protein synthesis, increased breakdown, or both)... Resistance exercise causes little change in amino acid oxidation but probably depresses protein synthesis and elevates breakdown acutely.
Why this rating
Based on a comprehensive review of metabolic studies.
Source
P<scp>ROTEIN AND</scp> A<scp>MINO</scp> A<scp>CID</scp> M<scp>ETABOLISM</scp> D<scp>URING AND</scp> A<scp>FTER</scp> E<scp>XERCISE AND THE</scp> E<scp>FFECTS OF</scp> N<scp>UTRITION</scp>
Michael J. Rennie et al. · Annual Review of Nutrition · 2000
DOI 10.1146/annurev.nutr.20.1.457
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