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January 16, 2002

Muscle Protein Synthesis in Younger and Older Men—Reply

Author Affiliations

Stephen J.LurieMD, PhD, Senior EditorIndividualAuthor

JAMA. 2002;287(3):317-318. doi:10.1001/jama.287.3.313

In Reply: We disagree with Dr Yarasheski and colleagues that collecting 2 muscle samples from the same leg was responsible for our inability to detect differences between young and older men in the muscle protein fractional synthesis rate (FSR), since the second biopsy was taken approximately 7 to 8 cm from the first. Moreover, unlike previous studies, we used independent measures of muscle protein synthesis based on A-V balance and tissue free phenylalanine enrichment, which confirmed the FSR results. Finally, whereas by normalizing our results by total leg volume we probably overestimated the amount of muscle in older men, this would cause an underestimation (rather than an overestimation, as suggested) of protein synthesis per unit of muscle volume. Since technical problems cannot explain the differences between our results and those from the 4 studies cited by Yarasheski et al, it is pertinent to examine the differences in experimental design between the various studies.