Muscle Protein Breakdown After Resistance Exercise

O n training forums, there are questions and recommendations on the amount and timing of protein intake. Much of it, I take to be hearsay, speculative and anecdotal.

The findings in the study below, indicate that muscle protein breakdown and synthesis does NOT occur 60 minutes after resistance exercise. It appears to start 180 minutes or more after exercise.

Much of the talk and recommendations of taking high protein shakes and meals immediately before, during and after a workout, seem to be unfounded and misplaced.




Free Amino Acid Pool And Muscle Protein Balance After Resistance Exercise.


Pitkanen HT1, Nykanen T, Knuutinen J, Lahti K, Keinanen O, Alen M, Komi PV, Mero AA.

Abstract

PURPOSE
The aim of this study was to assess the effects of a resistance exercise session (RES) on free amino acid concentrations and protein synthesis and breakdown of the vastus lateralis (VL) muscle during recovery in male subjects.

METHODS
Both the exercise group (EG) and the control group (CG) consisted of six healthy physically active men. On the experiment day in fasting conditions, a stable isotopic tracer of L-[ring-2H(5)] phenylalanine was infused and EG started a heavy 50-min hypertrophic RES for lower extremities after 55 min of infusion. At the same time, CG was at rest. During recovery of 195 min after RES, several blood samples were drawn from the femoral artery (FA) and the femoral vein (FV) and muscle samples from the VL muscle. The enrichment was analyzed by GC/MS and leg muscle amino acid kinetics determined by three-pool compartment model between FA, FV, and VL.

RESULTS
During recovery at 60 min after RES, there was no difference in muscle protein synthesis or muscle protein breakdown between the groups, but at 195 min, both muscle protein synthesis (P < 0.05) and muscle protein breakdown (P < 0.05) were increased in EG compared with CG. The protein net balance was negative and similar in both groups. Simultaneously in serum concentrations, there was a decrease in leucine (P < 0.05) associated with an increase in aspartate (P < 0.05). Furthermore, the exercise-induced increase in alanine concentration decreased both in serum and muscle.

CONCLUSION
In fasting conditions, protein net balance is negative and RES induces an increase in muscle protein synthesis and breakdown at 195 min but not yet at 60 min of recovery.

PMID: 12750588 [PubMed - indexed for MEDLINE]

http://www.ncbi.nlm.nih.gov/pubmed/12750588