Aim: Inspiratory muscle (diaphragm) function declines with age, contributing to exercise intolerance and impaired airway clearance. Studies of diaphragm dysfunction in rodents have focused on moderate aging (similar to 24 months); thus, the impact of advanced age on the diaphragm and potential mechanisms of dysfunction are less clear. Therefore, we aimed to define the effects of advanced age on the mechanics, morphology, and global and redox proteome of the diaphragm.Methods: We studied diaphragm from young (6 months) and very old male mice (30 months). Diaphragm function was evaluated using isolated muscle bundles. Proteome analyses followed LC-MS/MS processing of diaphragm muscle.Results: Advanced aging decreased diaphragm peak power by similar to 35% and maximal isometric specific force by similar to 15%, and prolonged time to peak twitch tension by similar to 30% (P < 0.05). These changes in contractile properties were accompanied, and might be caused by, decreases in abundance of calsequestrin, sarcoplasmic reticulum Ca2+-ATPase, sarcalumenin, and parvalbumin that were revealed by our label-free proteomics data. Advanced aging also increased passive stiffness (P < 0.05), which might be a consequence of an upregulation of cytoskeletal and extracellular matrix proteins identified by proteomics. Analyses of cysteine redox state indicated that the main diaphragm abnormalities with advanced aging are in metabolic enzymes and mitochondrial proteins.Conclusion: Our novel findings are that the most pronounced impact of advanced aging on the diaphragm is loss of peak power and disrupted cysteine redox homeostasis in metabolic enzymes and mitochondrial proteins.