Evolution of contractile and elastic properties of rat soleus muscle fibres under unloading conditions

Abstract

S U M M A R YRats were submitted to 14 days of hindlimb suspension in order to examine the contractile and elastic properties of the soleus muscles under disuse conditions. The calcium/strontium activation properties, the maximal shortening velocity ( V J , as well as the time behaviour of force transients following quick releases and the T, curves characterizing the active part of the s8eries elastic elements, were determined on single chemically skinned fibres. After the functional measurements, the fibres were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis in order to analyse both the myosin heavy (MHC) and light (MLC) chain isoforms. According to the MHC and MLC composition, two groups of fibres were defined after hindlimb suspension: a group of slow fibres expressing the slow set of both MHC and MLC isoforms, and a group of fast fibres coexpressing the slow and fast MHC and MLC isoforms with a predominant expression of the fast ones. For the first group, the contractile as well as the elastic properties were found to be close to those of control slow soleus fibres. For the second group, both contractile and elastic properties were modified insofar as they became close to those found in a fast muscle such as the extensor digitorum longus. We suggested that between the two populations found in the soleus muscle after hindlimb suspension the modifications in the contractile properties, as well as the alterations in the elastic characteristics, were concomitant to the changes in both MHC and MLC compositions.

Effects of Hypodynamia-Hypokinesia on the Muscle Spindle Discharges of Rat Soleus Muscle

“…A decrease in the stiffness of isolated soleus muscle (Canon and Goubel 1995) and in Achilles tendon stiffness (Almeïda-Silveira et al 2000) was observed after 3 wk of unloading. The results obtained by Canon and Goubel (1995) were confirmed by Toursel et al (1999) on isolated skinned fibers of rat soleus muscle. Moreover, the passive tension of in situ rat soleus muscle increased after 7 and 14 days of whole body suspension (Gillette and Fell 1996).…”

“…These fibers are less stiff than the slow type I fibers (Petit et al 1990). After HH, in rat soleus muscle, Toursel et al (1999) also reported an increase in the compliance on a population of hybrid fast fibers, which coexpressed the MHC IIA and MHC I isoforms (MHC IIA Ͼ MHC I). Moreover, Miller et al (2001) have demonstrated that HH induced a shift in the relative proportion of collagen isoform (type I to III) in the soleus muscle in relation to the fiber type transition (slow to fast).…”

Effect of strength training on musculotendinous stiffness in elderly individuals

“…Unfortunately, no one has raised the question of investigating changes in the stiffness properties of muscle fibres following high-intensity resistance training in elderly individuals. Nevertheless, it is well known that muscle fibres, which have different contractile properties such as unloaded shortening velocity, may well also have different stiffness properties (Toursel et al 1999). In fact, according to Toursel et al (1999), fast-twitch fibres may have a bigger unloaded shortening velocity and may be less stiff than slow-twitch fibres.…”

Changes in muscle and joint elasticity following long-term strength training in old age

“…Unfortunately, no one has raised the question of investigating changes in the stiffness properties of muscle fibres following training in old age. Nevertheless, it is well known that muscle fibres, which have different contractile properties, may well also have different stiffness properties (Toursel et al 1999). In fact, according to Toursel et al (1999) type IIa fibres may have a bigger specific force and may be less stiff than type I fibres.…”