Human vastus lateralis and soleus muscles display divergent cellular contractile properties

Abstract

The purpose of this study was to investigate potential differences in single-fiber contractile physiology of fibers with the same myosin heavy chain isoform (MHC I and MHC IIa) originating from different muscles. Vastus lateralis (VL) and soleus biopsies were obtained from 27 recreationally active females (31 Ϯ 1 yr, 59 Ϯ 1 kg). A total of 943 single fibers (MHC I ϭ 562; MHC IIa ϭ 301) were isolated and examined for diameter, peak tension (Po), shortening velocity (Vo), and power. The soleus had larger (P Ͻ 0.05) fibers (MHC I ϩ18%; MHC IIa ϩ19%), higher MHC I Vo (ϩ13%), and higher MHC I Po (ϩ18%) compared with fibers from the VL. In contrast, fibers from the VL had higher (P Ͻ 0.05) specific tension (MHC I ϩ18%; MHC IIa ϩ20%), and MHC I normalized power (ϩ25%) compared with the soleus. There was a trend for MHC IIa soleus fibers to have higher Vo [MHC IIa ϩ13% (P ϭ 0.058)], whereas VL MHC IIa fibers showed a trend for higher normalized power compared with soleus fibers [MHC IIa ϩ33% (P ϭ 0.079)]. No differences in absolute power were detected between muscles. These data highlight muscle-specific differences in single-fiber contractile function that should serve as a scientific basis for consideration when extending observations of skeletal muscle tissue from one muscle of interest to other muscles of origin. This is important when examining skeletal muscle adaptation to physical states such as aging, unloading, and training. skeletal muscle; muscle plasticity APPLICATION OF THE NEEDLE biopsy technique has allowed scientists to better characterize human skeletal muscle over the course of the last four decades (2, 3). Some of the more commonly investigated muscles include the gastrocnemius, deltoid, vastus lateralis, and soleus. From this research the functional diversity of skeletal muscle has been well documented. For instance, the three primary myosin heavy chain (MHC) isoforms identified in human skeletal muscle (30) (i.e., MHC I, MHC IIa, and MHC IIx) display contrasting metabolic (27a) and contractile properties (5). Consequently, whole muscle, which is composed of multiple MHC isoforms, has the ability to perform within a functional continuum influenced by relative fiber-type distribution. Although fiber-type distribution can substantially vary between muscles from an individual (19) (e.g., soleus and vastus lateralis), little is known about the functional differences that may exist within a fiber-type population from different muscles of origin (4).Physical activity has repeatedly been shown to induce alterations in single muscle fiber contractile physiology (11,15,20,31,34,36,40). Therefore, two leg muscles with distinctly different daily loading demands (9), much like the vastus lateralis and soleus, could have disparate contractile profiles. To our knowledge, only two human single-fiber studies have made a direct functional comparison between fibers containing the same MHC isoform obtained from different muscles (17,41). While the original inquiry did not detect differences between vastus lateralis and...

Influence of tracer selection on protein synthesis rates at rest and postexercise in multiple human muscles

“…The difference in muscle tissue fluid enrichment between these two muscles may be specific to endurance-trained athletes, as we have recently reported no muscle specific differences in sedentary, untrained subjects (26). Although the mixed muscle protein FSR was not different between the vastus lateralis and soleus muscles in the current study, these muscles display divergent fiber type composition (24), metabolic capacity (27), contractile properties (28), and response to exercise (13). Collectively, these factors highlight the heterogeneity between human muscles and warrant the need to use caution when interpreting and extrapolating muscle based studies in humans.…”

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“…Clinically meaningful changes in muscle strength were especially evident at the anterior thigh level (8/11 vs. 7/11 at posterior thigh vs. 4/11 at legs). In all three segments, patients with clinically meaningful improvements also showed greater changes in muscle mass following exercise (Luden et al 2008). Whatever the mechanism, the selective improvement of the anterior thigh has a dramatic clinical impact, since the quadriceps femuris is the main muscle involved in standing and walking (Jankowska et al 2008;Gerrits et al 2009).…”

Concurrent Exercise on a Gravity-Independent Device during Simulated Microgravity

“…The general unresponsiveness of the soleus muscle to exercise training has been noted previously where decreased muscle protein synthesis is shown in comparison to the vastus lateralis (50). This response may be due to the high percentage of type I fibers that comprise the soleus (~65% type I MHC mRNA) versus the vastus lateralis (~30% type I MHC mRNA) although single-fiber differences have been found when comparing fibers of the same MHC isoform (33). MHC I and MHC IIa fibers of the soleus were reported to have larger fiber diameters but lower specific tension than those found in the vastus lateralis (33).…”

“…This response may be due to the high percentage of type I fibers that comprise the soleus (~65% type I MHC mRNA) versus the vastus lateralis (~30% type I MHC mRNA) although single-fiber differences have been found when comparing fibers of the same MHC isoform (33). MHC I and MHC IIa fibers of the soleus were reported to have larger fiber diameters but lower specific tension than those found in the vastus lateralis (33). Regardless of the apparent mRNA differences in expression, no change in muscle CSA as measured by histological staining was seen with the vastus lateralis or soleus with 10 days of ULLS or ULLS+EX (data not shown).…”