Contraction force generated by tarsal joint flexion and extension in dogs with golden retriever muscular dystrophy

Force generated due to torque caused by tarsal joint flexion and extension was measured noninvasively at 3, 4.5, 6, and 12 months of age in dogs with the Duchenne homologue, golden retriever muscular dystrophy (GRMD). Absolut e and body-weight-corrected GRMD twitch and tetanic force values were lower than normal at all ages (P < 0.01 for most). Tarsal flexion and extension were differentially affected. Flexion values were especially low at 3 month s, whereas extension was affected more at later ages. Several other GRMD fi ndings differed from normal. The twitch/tetany ratio was generally lower; p ost-tetanic potentiation for flexion values was less marked; and extension relaxation and contraction times were longer. The consistency of GRMD value s was studied to determine which measurements will be most useful in evalua ting treatment outcome. Standard deviation was proportionally greater for G RMD versus normal recordings. More consistent values were seen for tetany v ersus twitch and for flexion versus extension. Left and right limb tetanic flexion values did not differ in GRMD; extension values were more variable. These results suggest that measurement of tarsal tetanic force should be m ost useful to document therapeutic benefit in GRMD dogs, (C) 1999 Elsevier Science B.V. All rights reserved.