Stephen J.LurieMD, PhD, Senior EditorIndividualAuthor
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.
Volpi E, Rasmussen BB, Sheffield-Moore M, Wolfe RR. Muscle Protein Synthesis in Younger and Older Men—Reply. JAMA. 2002;287(3):317-318. doi:10.1001/jama.287.3.313