Relatively low levels of reactive oxygen species (ROS) produced inside resting skeletal muscles play important functions in cell signaling. When ROS production increases to levels beyond the buffering capacity of muscle antioxidant systems, a state of oxidative stress develops, which leads to skeletal muscle contractile dysfunction. A clear association between oxidative stress and depressed skeletal muscle performance has been described in several acute and chronic conditions, such as systemic inflammation and chronic obstructive lung diseases. The observation that the levels of oxidant-derived posttranslational protein modifications, including protein carbonylation, are elevated inside skeletal muscle fibers when oxidative stress develops suggest that these modifications play important roles in regulating muscle function. This proposal is supported by recent studies that unveiled that several myofilament (myosin heavy chain and actin), mitochondrial (aconitase, creatine kinase), and cytosolic (enolase, aldolase and glyceraldehyde 3-phosphate dehydrogenase and carbonic anhydrase III) proteins are carbonylated inside skeletal muscle fibers in many animal models of muscle dysfunction, and in humans with impaired skeletal muscle contractility. However, the functional importance of carbonylation in determining the function of muscle-specific proteins and the precise contribution of carbonylation-induced dysfunction of these proteins to overall muscle contractile deficit in various pathologies remain to be determined.