We examine the following muscle parameters: mass, cross-sectional area, force, twitch and tetanus relaxation, force-frequency relationships, fatiguability, force loss following eccentric contractions, and stiffness.
To assess mass, cross-sectional area, force, twitch and tetanus relaxation, force-frequency relationships, and fatiguability, we used a set of male and female 129/ReJ mice divided into two age groups: adult (2 6 months of age) and aged (20 22 months of age).
Each point represents a single bundle calcium transient plotted against the corresponding force, either twitch or tetanus (at 10 Hz).
Figure 2 depicts the alterations in contractile force and twitch kinetics that occur during the transition from 1 to 4 Hz.
Consistent with maximal specific force measurements, twitch force was modestly decreased in Mbnl1+ /ΔE3 / Mbnl2 GT2/GT2 animals, with intermediate and maximal reduction in this series being observed in Mbnl1 ΔE3/ΔE3 and Mbnl1 ΔE3/ΔE3/mice3 ΔE2 mice, respectively (Pt decreased 26.2% and 29.3% compared to wild type mice for Mbnl1 ΔE3/ΔE3 and Mbnl1 ΔE3/ΔE3/mice3 ΔE2 mice, respectively).
There was no statistically significant difference between groups in peak twitch force, time to peak twitch tension (TPT), one-half relaxation time (1/2RT) or maximum rate of force development during a twitch (dPt/d t) of TA muscles in situ (data not shown).
Twitch kinetics (time to peak twitch force, half-relaxation time, and twitch-to-tetanus ratio) were significantly lower in the extraocular muscles than in the EDL muscle bundles.
Time-to-peak-twitch force, half-relaxation time, maximum twitch force and maximum tetanic force were determined.
Half-relaxation time was measured from the peak of twitch force to the point where twitch tension fell to half of its peak value.
During recovery, the 20 50 Hz ratios, muscle forces and twitch CTs and ½ RTs returned to pre-exposure/baseline levels.
