Tetanic force, corrected for body weight (N/kg), generated by tarsal joint flexors (left) and extensors (right) from normal dogs and GRMD dogs at 3, 4.5, 6, and 12 months of age. Values for GRMD dogs are lower (P<.01 for all) than those of normal dogs at all ages. However, the differential between GRMD and normal dogs differs. Flexion values are especially low at 3 months, whereas extension is affected more at later ages. (From Kornegay JN, Bogan DJ, Bogan JR, et al. Contraction force generated by tibiotarsal joint flexion and extension in dogs with golden retriever muscular dystrophy. J Neurol Sci 1999;166:119; with permission.)