Fig. 3

Global mRNA expression and transcriptome profiles in response to low and moderate volume resistance training. The amounts of muscle tissue used during cDNA synthesis varied over the course of the study and between volume conditions (a low-volume, LOW; moderate-volume, MOD). Library sizes increased during the course of the intervention, with a tendency towards a greater increase in the low-volume condition (b). Difference in library sizes between volume conditions when expressed per-unit tissue weight were diminished, though increases from baseline were maintained (c). The tissue offset-normalized model identified 21 genes with higher expression in the moderate volume condition (d, e), ten of which was shared with the effective library-size normalized model at week 2 (e), and none of which was shared with the naïve model. No volume-dependent differences were found at Week 12 using the tissue-offset model. At this time point, library-size and naïve models both showed a marked skew towards augmented expression in the low-volume condition. At Week 2, functional annotation identified gene sets relating to extracellular matrix in response to higher training volume (tissue-offset model, orange and purple circles, f), all of which were more highly expressed in MOD, indicated by the positive enrichment score. Orange circles denote gene sets that were identified from rank-based enrichment tests based on the full data set. Purple circles denote gene categories that were also identified using over-representation analysis (ORA). Normalization strategies had global effects on enrichment analyses using rank tests, assessed using fold-changes and minimum significant differences scores (not shown), illustrated with the tissue-offset model leading to marked increases in genes associated with the “Collagen containing extracellular matrix” gene set (g) as well as a shift in the full distribution of Log2 fold-changes between volume conditions towards MOD (shown as density curves). Black bars represent genes that belong to the gene set identified as enriched (g). Genes symbols indicate genes identified as differentially expressed in each normalization scenario