Exercise　training　can　mitigate　symptoms　of　claudication　(walking-induced　muscle　pain)　in　patients　with　peripheral　artery　disease　(PAD).　One　adaptive　response　enabling　this　improvement　is　enhanced　muscle　oxygen　metabolism.　To　explore　this　issue,　we　used　arterial-occlusion　diffuse　optical　spectroscopy　(AO-DOS)　to　measure　the　effects　of　exercise　training　on　the　metabolic　rate　of　oxygen　(MRO2)　in　resting　calf　muscle.　Additionally,　venous-occlusion　DOS　(VO-DOS)　and　frequency-domain　DOS　(FD-DOS)　were　used　to　measure　muscle　blood　flow　(F)　and　tissue　oxygen　saturation　(StO(2)),　and　resting　calf　muscle　oxygen　extraction　fraction　(OEF)　was　calculated　from　MRO2,　F,　and　blood　hemoglobin.　Lastly,　the　venous/arterial　ratio　(gamma)　of　blood　monitored　by　FD-DOS　was　calculated　from　OEF　and　StO(2).　PAD　patients　who　experience　claudication　(n　=　28)　were　randomly　assigned　to　exercise　and　control　groups.　Patients　in　the　exercise　group　received　3　months　of　supervised　exercise　training.　Optical　measurements　were　obtained　at　baseline　and　at　3　months　in　both　groups.　Resting　MRO2,　OEF,　and　F,　respectively,　increased　by　30%　(12%,　44%)　(p　＜　0.001),　17%　(6%,　45%)　(p　=　0.003),　and　7%　(0%,　16%)　(p　=　0.11),　after　exercise　training　(median　(interquartile　range)).　The　pre-exercise　gamma　was　0.76　(0.61,　0.89);　it　decreased　by　12%　(35%,　6%)　after　exercise　training　(p　=　0.011).　Improvement　in　exercise　performance　was　associated　with　a　correlative　increase　in　resting　OEF　(R　=　0.45,　p　=　0.02).