Described herein are compounds that comprise a carrier residue that is or is an analog of carnitine, an optional linker group, and a residue of a protease inhibitor comprising an aldehyde group or acetal derivatives of the aldehyde group, and pharmaceutical compositions and kits thereof. The compounds, compositions, and kits are useful for treating muscle disorders in animals and humans that result from the undesired activity of biological proteases. The compounds of the invention are particularly effective as calpain inhibitors, and can be used to treat the resulting muscular disorders, exemplified by Duchenne or Becker muscular dystrophy.