We examined whether O2 saturation in several leg muscles changes as exercise intensity increases. Twelve healthy young males performed 20 W/min ramp bicycle exercise until exhaustion. Pulmonary O2 uptake (VO 2) was monitored continuously during the experiments to determine peak oxygen uptake. Muscle O2 saturation (SmO2) was also monitored continuously at the belly of the vastus lateralis (VL), rectus femoris, vastus medialis, biceps femoris, gastrocnemius lateralis, gastrocnemius medialis, and tibialis anterior by near-infrared spatial resolved spectroscopy. Although the VL muscle mainly contributes during cycling exercise, deoxygenation was enhanced not only in the VL muscle but also in the other thigh muscles and lower leg muscles with increased exercise intensity. Furthermore, SmO2 response during ramp cycling exercise differed considerably between leg muscles.