Tuesday, February 17, 2009

Performance Research for February: Protein Synthesis and Exercise Round 1

The balancing act between protein synthesis and breakdown: exercise as a model to understand the molecular mechanisms regulating muscle mass.

Rasmussen BB, Richter EA.
No Abstracts available.

Making room for protein in approaches to muscle recovery from endurance exercise.

Rodriguez NR.

No Abstracts available.

Human muscle protein synthesis and breakdown during and after exercise.

Kumar V, Atherton P, Smith K, Rennie MJ. The University of Nottingham.

Skeletal muscle demonstrates extraordinary mutability in its responses to exercise of different modes, intensity and duration, which must involve alterations of muscle protein turnover, both acutely and chronically. Here we bring together information on the alterations in the rates of synthesis and degradation of human muscle protein by different types of exercise and the influences of nutrition, age and sexual dimorphism. Where possible we summarize the likely changes in activity of signalling proteins associated with control of protein turnover. Exercise of both the resistance and non-resistance types appears to depress muscle protein synthesis (MPS) and muscle protein breakdown (MPB) during exercise, whereas both are elevated after exercise in the fasted state, when net muscle protein balance remains negative.

Positive net balance is achieved only when amino acid availability is increased, thereby raising MPS markedly. Such post-exercise increases in amino acids are less important for inhibiting MPB than insulin, the secretion of which is stimulated most by glucose availability, without itself stimulating MPS. Exercise training appears to increase basal muscle protein turnover, with differential responses of the myofibrillar and mitochondrial protein fractions to acute exercise in the trained state.

CONCLUSION: Ageing reduces the responses of myofibrillar protein and anabolic signalling to resistance exercise. There appear to be few if any differences in the response of young women and young men to acute exercise, although there are indications that in older women the responses may be blunted more than in older men.

My Notes: Excellent info if you are looking at the effects of exercise and protein!

Nutritional and Contractile Regulation of Human Skeletal Muscle Protein Synthesis and mTORC1 Signaling.

Drummond MJ, Dreyer HC, Fry CS, Glynn EL, Rasmussen BB. University of Texas Medical Branch.

In this review we discuss current findings in the human skeletal muscle literature describing the acute influence of nutrients (leucine-enriched essential amino acids in particular) and resistance exercise on muscle protein synthesis and mTORC1 signaling. We show that essential amino acids and an acute bout of resistance exercise independently stimulate human skeletal muscle protein synthesis. It also appears that ingestion of essential amino acids following resistance exercise leads to an even larger increase in the rate of muscle protein synthesis as compared to the independent effects of nutrients or muscle contraction.

Until recently the cellular mechanisms responsible for controlling the rate of muscle protein synthesis in humans were unknown. In this review we highlight new studies in humans that have clearly shown the mTORC1 signaling pathway is playing an important regulatory role in controlling muscle protein synthesis in response to nutrients and/or muscle contraction.

CONCLUSION: We propose that essential amino acid ingestion shortly following a bout of resistance exercise is beneficial in promoting skeletal muscle growth and may be useful in counteracting muscle wasting in a variety of conditions such as aging, cancer cachexia, bedrest/physical inactivity, and perhaps during rehabilitation following trauma or surgery.

My Notes: All the meat heads in the room nod your heads---protein post training is good. Nothing new there. If you are lifting and not taking in protein post training, get to it!

Age-related differences in the dose-response relationship of muscle protein synthesis to resistance exercise in young and old men.

Kumar V, Selby A, Rankin D, Patel R, Atherton P, Hildebrandt W, Williams J, Smith K, Seynnes O, Hiscock N, Rennie MJ. University of Nottingham, School of Graduate Entry Medicine and Health, City Hospital, Uttoxeter Road, Derby, DE22 3DT, UK.

We investigated how myofibrillar protein synthesis (MPS) and muscle anabolic signalling were affected by resistance exercise at 20-90% of 1 repetition maximum (1 RM) in two groups (25 each) of post-absorptive, healthy, young (24 +/- 6 years) and old (70 +/- 5 years) men with identical body mass indices (24 +/- 2 kg m(-2)). We hypothesized that, in response to exercise, anabolic signalling molecule phosphorylation and MPS would be modified in a dose-dependant fashion, but to a lesser extent in older men. Vastus lateralis muscle was sampled before, immediately after, and 1, 2 and 4 h post-exercise.

MPS was measured by incorporation of [1,2-(13)C] leucine (gas chromatography-combustion-mass spectrometry using plasma [1,2-(13)C]alpha-ketoisocaparoate as surrogate precursor); the phosphorylation of p70 ribosomal S6 kinase (p70s6K) and eukaryotic initiation factor 4E binding protein 1 (4EBP1) was measured using Western analysis with anti-phosphoantibodies. In each group, there was a sigmoidal dose-response relationship between MPS at 1-2 h post-exercise and exercise intensity, which was blunted (P < style="font-weight: bold;">

CONCLUSION: The results suggest that in the post-absorptive state: (i) myofibrillar protein synthesis is dose dependant on intensity rising to a plateau at 60-90% 1 repetition maximum; (ii) older men show anabolic resistance of signalling and myofibrillar protein synthesis to resistance exercise.

My Notes: More data showing a difference in older folks.