Naturligtvis individuellt, menju äldre man blir, desto större aminosyreresistens utvecklas. Det anabola gensvaret på aminosyreintag, och därmed också styrketräning+aminosyreintag, blir mindre, och så även den hypertrofiska responsen. Muskulaturen förlorar sin kapacitet för proteinsyntes med åren. Jämför man 20-åringar med 70-åringar är gensvaret sämre hos dom senare.
Citat:
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we set out to test this by examining the responses to oral essential amino acids in a group of young, healthy (28-year-old) men and a group of healthy, elderly (70-year-old) men who had similar lean body masses as a percentage of their body weight (∼80% on average) but who had different leg muscle masses, the elderly subjects showing a slight decrement from 20 to 16% of body weight. We studied these subjects under conditions in which we clamped the secretion of insulin at postabsorptive values (i.e. fasting). We were pleased to discover that our hypothesis was supported. There were no decrements of muscle protein synthesis in the basal state but elderly men appeared to be less able to take advantage of essential amino acids in stimulating muscle protein synthesis. Indeed, the extent on their inability to do so was reflected in the fact that, paradoxically, they had more amino acid in the blood after ingestion of the oral essential amino acid than the younger subjects. When we related the response of muscle protein synthesis not to the dose given but to the availability of amino acids in the plasma (in fact the area under the curve of leucine concentration versus time), the differences between the young and the old subjects were exacerbated. Thus, it appeared that the elderly subjects exhibited what might be called ‘amino acid resistance’ of muscle (Cuthbertson et al. 2005). The elderly subjects did have slightly less muscle and also slightly less capacity for protein synthesis within them (indicated by the RNA : DNA ratio), so that the efficiency of protein synthesis, i.e. protein synthesis per unit RNA, was substantially less. The major mechanistic differences appeared to lie in the anabolic signalling pathways in the young and old subjects. We found that the total amounts of anabolic signalling proteins were diminished in the elderly subjects, and in addition their responsiveness in terms of phosphorylation of the proteins after essential amino acid ingestion was markedly less. Thus, the responsiveness and the sensitivity of the response were both diminished in the elderly subjects. Note that these effects were entirely to do with the responses to essential amino acids, since we had taken insulin responsiveness out of the equation by using the insulin clamp.
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Rennie MJ. Exp Physiol. 2005 Jul;90(4):427-36.
Eftersom gruppen i den här studien var strax under 70 och inte uppvisade några sådana tecken, så kanske... 70? Omkring där.