In the present study 23 participants completed three months of supervised aerobic exercise training of one leg (training period 1) followed by 9 months of rest before 12 of the participants completed a second exercise training period (training period 2) of three months of both legs. Skeletal muscle biopsies have been collected before and after the training periods. We have compared trained leg with untrained leg and studied gene and isoform expression. Additional samples included in this study has been previously submitted (GEO accession number GSE58387 and GSE60590). Overall design: Analyze of transcriptome in skeletal muscle biopsy samples in response to exercise training in 23 participants in total (in addition to data previously submitted GEO accession number GSE58387 and GSE60590). Biopsy is collected from skeletal muscle before and after training period.