Force development of fast and slow skeletal muscle at different muscle lengths

Abstract

It is known that the behavior of fast and slow skeletal muscles differs, but a comparison between fast and slow muscles with different stimulation patterns at various muscle lengths is lacking. The twitch, tetanus, and double pulse responses with a number of interval times have been investigated for a fast (EDL) and a slow (soleus) muscle of the rat at three muscle lengths (in vivo, at 37 degrees C, pentobarbital sodium anesthesia). The twitches of EDL and soleus change with muscle length, but the relative form of the ascending phase is independent of muscle length. The tetanus amplitude is independent of the muscle length over a considerable length range below the optimum twitch length. The form of the ascending phases of EDL-tetanus and double pulse responses (with certain interval times between the stimuli) varies with muscle length in contrast with the comparable soleus force patterns. The maximum slope in the descending phase of all contraction patterns decreases with increasing muscle length above the optimum twitch length.

Additional in-series compliance reduces muscle force summation and alters the time course of force relaxation during fixed-end contractions

“…Relative to the rise time of force in the presence of additional series elastic compliance, half-relaxation time was also less sensitive to step increases in initial fibre bundle length. The decay of twitch force has been shown previously to be more sensitive to initial muscle length than that of the rise time of force (Close, 1964;Wallinga-de Jonge et al, 1980). We suggest that the amplitude of active shortening permitted under the compliant conditions in the present study may have limited the influence of initial length on relaxation kinetics.…”

“…When values of force summation reported in the literature for animal (Ranatunga, 1977;Wallinga-de Jonge et al, 1980;Parmiggiani and Stein, 1981) and, specifically, human muscles (Duchateau and Hainaut, 1986;Baudry et al, 2005) are considered, the reduction in relative force summation owing to additional series elastic compliance was small. This finding may be due, in part, to the animal model selected.…”

Effects of series elastic compliance on muscle force summation and the rate of force rise

“…These same factors have been shown to also influence the twitch:tetanus ratio (Ranatunga, 1977;Stein and Parmiggiani, 1981;Moore and Stull, 1984), which appears to be inversely related to doublet force summation (Duchateau and Hainaut, 1986a). Differences in doublet force summation between fast and slow twitch muscle (Ranatunga, 1977;Wallinga-de Jonge et al, 1980) may be well explained by fibre-type-specific sarcoplasmic reticulum Ca 2+ kinetics (Baylor and Hollingworth, 2003;Barclay, 2012) and contractile apparatus Ca 2+ sensitivity (Stephenson and Williams, 1985).…”

“…The activation dynamics of muscle, especially the kinetics of sarcoplasmic Ca 2+ release and reuptake (Duchateau and Hainaut, 1986b;Barclay, 2012), are likely important determinants of force generation in response to consecutive stimuli. Indeed, doublet force summation is influenced by factors that alter the Ca 2+ sensitivity of the contractile apparatus Williams, 1982, 1985;Sweeney and Stull, 1990), including muscle length (Wallinga-de Jonge et al, 1980;Mela et al, 2002), muscle temperature (Ranatunga, 1977) and post-activation potentiation (Baudry et al, 2005). These same factors have been shown to also influence the twitch:tetanus ratio (Ranatunga, 1977;Stein and Parmiggiani, 1981;Moore and Stull, 1984), which appears to be inversely related to doublet force summation (Duchateau and Hainaut, 1986a).…”

Low-frequency fatigue, post-tetanic potentiation and their interaction at different muscle lengths following eccentric exercise

“…It was hypothesised that PTP can (partly) compensate for LFF. Because potentiation (when expressed as potentiated force relative to non-potentiated force) is muscle length dependent, being higher at short muscle lengths (Rassier and MacIntosh, 2002;Roszek et al, 1994;Wallinga-de Jonge et al, 1980), we investigated how the extent of LFF was expressed across different muscle lengths both in a potentiated and a nonpotentiated condition.…”