The respiratory and limb skeletal muscles become weakened in sepsis, congestive heart failure, and other inflammatory diseases. A potential mediator of muscle weakness is tumor necrosis factor (TNF)-α, a cytokine that can stimulate muscle wasting and also can induce contractile dysfunction without overt catabolism. This study addressed the latter process. Murine diaphragm and limb muscle (flexor digitorum brevis [FDB]) preparations were used to determine the relative sensitivities of these muscles to TNF-α. Intact muscle fibers were isolated from FDB and microinjected with indo-1 to measure changes in sarcoplasmic calcium regulation. We found that TNF-α depressed tetanic force of the diaphragm and FDB to comparable degrees across a range of stimulus frequencies. In isolated muscle fibers, TNF-α decreased tetanic force without altering tetanic calcium transients or resting calcium levels. We conclude that (1) TNF-α compromises contractile function of diaphragm and limb muscle similarly, and (2) TNF-α decreases force by blunting the response of muscle myofilaments to calcium activation.