The purpose of this study was to elucidate the mechanisms underlying low-intensity exercise-induced peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) protein expression in rat skeletal muscles. Rats (5–6 wk old) swam without a load and ran on the treadmill at a speed of 13 m/min, respectively, in two 3-h sessions separated by 45 min of rest. PGC-1α content in epitrochlearis muscle (EPI) was increased by 75 and 95%, immediately and 6 h after swimming, respectively, with no increase in PGC-1α content in the soleus (SOL). After running, PGC-1α content in EPI was unchanged, whereas a 107% increase in PGC-1α content was observed in SOL 6 h after running. Furthermore, in EPI and SOL as well as other muscles (triceps, plantaris, red and white gastrocnemius), PGC-1α expression was enhanced concomitant with reduced glycogen postexercise, suggesting that expression of PGC-1α occurs in skeletal muscle recruited during exercise. PGC-1α content in EPI was increased after 18-h in vitro incubation with 0.5 mM 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and 4 mM caffeine. However, AICAR incubation did not affect PGC-1α content in the SOL, whereas caffeine incubation increased it. These results suggest that exercise-induced PGC-1α expression in skeletal muscle may be mediated by at least two exercise-induced signaling factors: AMPK activation and Ca²⁺ elevation. The number of factors involved (both AMPK and Ca²⁺, or Ca²⁺ only) in exercise-induced PGC-1α expression may differ among muscles.