From a cell signaling perspective, short-duration intense muscular work is typically associated with resistance training and linked to pathways that stimulate growth. However, brief repeated sessions of sprint or high-intensity interval exercise induce rapid phenotypic changes that resemble traditional endurance training. We tested the hypothesis that an acute session of intense intermittent cycle exercise would activate signaling cascades linked to mitochondrial biogenesis in human skeletal muscle. Biopsies (vastus lateralis) were obtained from six young men who performed four 30-s "all out" exercise bouts interspersed with 4 min of rest (<80 kJ total work). Phosphorylation of AMP-activated protein kinase (AMPK; subunits alpha1 and alpha2) and the p38 mitogen-activated protein kinase (MAPK) was higher (P <or= 0.05) immediately after bout 4 vs. preexercise. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) mRNA was increased approximately twofold above rest after 3 h of recovery (P <or= 0.05); however, PGC-1alpha protein content was unchanged. In contrast, phosphorylation of protein kinase B/Akt (Thr(308) and Ser(473)) tended to decrease, and downstream targets linked to hypertrophy (p70 ribosomal S6 kinase and 4E binding protein 1) were unchanged after exercise and recovery. We conclude that signaling through AMPK and p38 MAPK to PGC-1alpha may explain in part the metabolic remodeling induced by low-volume intense interval exercise, including mitochondrial biogenesis and an increased capacity for glucose and fatty acid oxidation.