Key result
In rat skeletal muscle, peak developed tension for double-pulse contractions occurred at Lo-TET + 0.1 mm, making them more suitable for setting experimental length than twitch contractions.
Double-pulse contractions are more suitable than twitch contractions for setting optimal muscle length in experimental studies of skeletal muscle.
Answers are grounded in this paper and cite their sources.
Supports double-pulse over twitch for length setting in rat muscle experiments; leaves open translation to other models or cardiac tissue.
The length dependence of force development of mammalian skeletal muscles was evaluated during twitch, double-pulse, and tetanic contractions, and the relation between muscle length and the time-dependent characteristics of twitch and double-pulse contractions were determined. In situ isometric contractions of the rat gastrocnemius muscle were analyzed at seven different lengths, based on a reference length at which the maximal response to double-pulse contractions occurred (Lopt-2P). Twitch and double-pulse contractions were analyzed for developed tension (DT), contraction time (tC), average rate of force development (DT-tC(-1)), half-relaxation time (t50%R), peak rate of relaxation (DT x dtmin(-1)), and 90%-relaxation time (t90%R). Considering the length at which maximal tetanic DT occurred to be the optimal length (Lo-TET), the peak DT for twitch contractions and double-pulse contractions was observed at Lo-TET + 0.75 mm (p < 0.05) and Lo-TET + 0.1 mm (p > 0.05), respectively. When measured at the length for which maximal twitch and double-pulse contractions were obtained, tetanic DT was 95.2 +/- 3 and 99.0 +/- 2% of the maximal value, respectively. These observations suggest that double-pulse contractions are more suitable for setting length for experimental studies than twitch contractions. Twitch and double-pulse contraction tC were 15.53 +/- 1.14 and 25.0 +/- 0.6 ms, respectively, at Lopt-2P, and increased above Lopt-2P and decreased below Lopt-2P. Twitch t50%R was 12.18 +/- 0.90 ms at Lopt-2P, and increased above Lopt-2P and below Lopt-2P. Corresponding changes for double-pulse contractions were greater. Stretching the muscle leads to slower twitch contractions and double-pulse contractions, but the mechanisms of this change in time course remain unclear.
No takes yet. Share an insight, caveat, or question.
Rassier et al. (2002) studied this question. Double-pulse contractions vs. Twitch contractions was evaluated on Length dependence of force development. In rat skeletal muscle, peak developed tension for double-pulse contractions occurred at Lo-TET + 0.1 mm, making them more suitable for setting experimental length than twitch contractions.
Synapse has enriched 10 related papers. Consider them for comparative context: