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We investigated the effects of acute and chronic repeated-sprint exercise (RSE) on the skeletal muscle messenger RNA (mRNA) expression and protein abundance/phosphorylation associated with mitochondrial biogenesis.Ten healthy young adults (seven males, three females) performed the RSE trial, comprising three sets of 5 × 4-s maximal sprints on a nonmotorized treadmill, with a 20-s recovery between sprints and 4.5 min between sets. After 4 wk of repeated-sprint training, three times per week, participants repeated the RSE. A vastus lateralis muscle biopsy was obtained at rest, immediately after, and 1 and 4 h after RSE, before and after training. Venous blood lactate and glucose were measured at rest and during recovery. Real-time reverse transcriptase polymerase chain reaction and Western blot techniques were used to measure mRNA expression and protein abundance, respectively.Acute RSE increased the phosphorylation of acetyl-CoA carboxylase (86%, effect size (ES) = 1.4 ± 0.8, P < 0.001) and Ca2+ calmodulin-dependent protein kinase II (69%, ES = 0.7 ± 0.6). Peroxisome proliferator–activated receptor γ coactivator 1α (PGC-1α; 208%, ES = 1.5 ± 0.7, P < 0.001) and nuclear respiratory factor 1 (92%, ES = 0.7 ± 0.8) mRNA expression was increased after RSE. Four weeks of training increased the abundance of PGC-1α protein at rest (33%, ES = 0.9 ± 0.7).Both acute and chronic RSE, despite only 60 s and 12 min of exercise, respectively, altered the molecular signaling associated with mitochondrial adaptations and PGC-1α mRNA expression in skeletal muscle. However, the small-to-moderate changes in resting PGC-1α protein abundance after training, together with the absence of changes in aerobic fitness, require further research to understand the functional significance of PGC-1α in response to RSE.