Fractional synthesis rates (FSR) of skeletal
muscle mitochondrial protein using plasma [13C]KIC
(A) and tissue fluid [13C]leucine
(B) as precursor pool enrichment, and as a percentage of
mixed protein synthesis rates (C) in young, middle-aged, and
old human subjects. Because no gender differences were observed, the
male and female subjects are presented as one group. ∗,
P < 0.05; ∗∗, P < 0.01
versus young.