Received March 14, 2004
Revised May 19, 2004
Accepted after revision June 10, 2004

¹ University of Alberta

^* To whom correspondence should be addressed. E-mail: tputman{at}ualberta.ca.

	Abstract

The present study investigated the reliability (Rab) of isometric measures of time-to-peak tension (TTP), half rise time (RT), half fall-time (FT), twitch force (TWf) and tetanic force (TETf) and the sag ratio as applied to slow soleus (SOL), and the fast-twitch extensor digitorum longus (EDL) and medial gastrocnemius (MG) muscles of the rat hindlimb. In addition, the relationship of each individual isometric measure was examined with regard to the pattern of MHC isoform expression. Measures of TTP, RT, FT and the sag ratio were negatively correlated with MHCIId/x and MHCIIb (P < 0.0001), and positively correlated with MHCI (P < 0.0001). TWf and TETf were negatively correlated with MHCI content (P < 0.0001) and positively with MHCIId/x (P < 0.0001) and MHCIIb (P < 0.001). Comparisons of isometric measures using a Students' t-test revealed that they were not different between the right and left legs; all measures displayed high correlations between the left and right legs (r = 0.71 to 0.85, P < 0.0001). In contrast to standard tests of statistical significance, these functional measures exhibited a considerable range of Rab when individual muscles were studied in only one hindlimb. When averaged across all muscles, however, the FT, RT, TWf and TTP measures possessed high overall reliability; measures of TETf and sag ratio were moderately reliable. The results of this study show that the isometric measures studied possess significant predictive value with regard to MHC isoform content; the left and right legs are interchangeable but display a considerable range of reliability when only on hindlimb is studied.

Key Words: Muscle, Muscle contraction, Myosin