Cluster analysis tests the importance of myogenic gene expression during myofiber XXXX in @entity1 .

@entity1 @entity9171 @entity1184 @entity442
We applied K-means cluster analysis to test the hypothesis that muscle-specific factors known to modulate protein synthesis and satellite cell activity would be differentially expressed during progressive resistance training (PRT, 16 wk) in 66 @entity1 subjects experiencing extreme, modest, and failed myofiber @entity1184 . Muscle mRNA expression of IGF-I isoform Ea (IGF-IEa), mechanogrowth factor ( @entity442 , IGF-IEc), myogenin, and @entity9171 were assessed in muscle biopsies collected at baseline (T1) and 24 h after the first (T2) and last (T3) loading bouts from previously untrained subjects clustered as extreme responders (Xtr, n=17), modest responders (Mod, n=32), and nonresponders (Non, n=17) based on mean myofiber @entity1184 . Myofiber growth averaged 2,475 microm2 in Xtr, 1,111 microm2 in Mod, and -16 microm2 in Non. Main training effects revealed increases in all transcripts (46-83%, P<0.005). For the entire cohort, IGF-IEa, @entity442 , and myogenin mRNAs were upregulated by T2 (P<0.05), while @entity9171 did not increase significantly until T3 (P<0.001). Within clusters, @entity442 and myogenin upregulation was robust in Xtr (126% and 65%) and Mod (73% and 41%) vs. no changes in Non. While significant in all clusters by T3, IGF-IEa increased most in Xtr (105%) and least in Non (44%). Although @entity9171 expression increased overall, no changes within clusters were detected. We reveal for the first time that @entity442 and myogenin transcripts are differentially expressed in subjects experiencing varying degrees of PRT-mediated myofiber @entity1184 . The data strongly suggest the load-mediated induction of these genes may initiate important actions necessary to promote myofiber growth during PRT, while the role of @entity9171 is less clear.
