When active skeletal muscle is stretched, it generally responds with a contraction which resists the stretch. This response is termed the muscle stretch reflex. The size (gain) and timing (phase) of the response has been found to depend on many factors including the characteristics of the applied stretch, the muscle contraction level and the subject's intention. Investigations of this stretch reflex have often involved stretches to muscle which contained frequencies either beyond the range of voluntary movement or else which could be consciously tracked. This study sought to characterise the frequency response of the stretch reflex, in terms of its gain and phase, under a variety of conditions while using stretches to the muscle which were relevant to voluntary movement, yet which were too irregular to be tracked. The types of stretch which satisfied these criteria had first to be determined by an investigation of tracking performance under different conditions of peripheral feedback. Having established the types of stretch which could be used to guarantee reflex rather than voluntary responses, the stretch reflex was investigated using stretches of different amplitude and bandwidth and spanning the full range of contraction level. Research was also undertaken to determine whether the gain and phase of the reflex response could be decoupled from the background contraction level of the muscle and to examine any associated effects on the mechanical properties of the limb. Explanatory models for some of these reflex responses were developed. An interaction between normal physiological tremor and the stretch reflex response was also investigated.

The present study investigated the hypothesis that maximal voluntary contractions (MVC) peak torque, VJ, muscle tenderness, and plasma creatine activity would be significantly less for the condition that subjects were exposed to hypoxic (H) condition for 4 hours after eccentric exercise compared with the normoxic (N) condition.

Thesis (M.S.E.S.)--University of Toledo, 2005. / Typescript. "Submitted as partial fulfillment of the requirements for the Master of Science degree in Exercise Science." Bibliography: leaves 71-87.

The goals of this research were to a) characterize the protein-function relationships of skeletal muscle single fibers from the mouse hindlimb b) examine mouse-strain related differences in myosin heavy chain composition (MHC) and single fiber contractile function, and c) quantify changes in fiber size and contractile function in response to 7 days of non-weight bearing. This research is significant because mechanistic approaches to understanding relationships between muscle protein expression, contractile function, and mechanical loading will likely benefit from a transition from the traditional laboratory rat to genetically modified mouse models. The methods used in this research feature an in vitro skinned-fiber preparation and single-fiber gel electrophoresis. Hindlimb muscles of mice were excised, and dissected into smaller bundles from which single muscle fibers were isolated. Single fibers were placed in skinning solution that permeabilized the fiber's membrane. The ends of skinned single muscle segments were attached to stainless steel troughs, which were connected to an isometric force transducer and a direct-current position motor. This system allowed the measurement of the fiber's cross-sectional area (CSA), peak isometric force (P���), and unloaded maximal shortening velocity (V���) during maximal Ca�����-activating. The identification of the fiber's MHC content was subsequently achieved by electrophoresis of a sample of each fiber segment. The results showed that the C57BL/6 mouse soleus muscle contains a MHC composition (20% type I) that is dramatically different than the ICR and CBA/J mouse strains (50% type I, respectively). Type I fibers from the C57BL/6 mouse had V��� that was 25% lower than type I fibers from ICR and CBA/J mice. Following 7 days of hindlimb suspension (HS) all strains experienced significant soleus muscle and single-fiber atrophy and decreases in the absolute and specific (force/fiber CSA) of type I and II fibers. However, type I fibers from C57BL/6 mice showed no change in V��� whereas type I fibers from ICR and CBA/J showed increased V���. In conclusion, this research demonstrates that unlike the rat and human models of non-weight bearing, mouse soleus type I and II fibers are equally affected by HS with respect to decreases in fiber CSA and force. However, type I fiber V��� was elevated only in mouse strains with solei containing at least 50% type I MHC. These findings challenge the current view that non-weight bearing affects slow fibers more than fast fibers, and suggests that changes in single fiber contractile function with HS may be influenced in part by the MHC distribution of the muscle. / Graduation date: 2003

The first goal of this study was to understand the role of calpains in skeletal muscle protein degradation in cultured cells. We have developed a genetic approach to inhibit endogenous calpain activity through over-expressing dominant negative m-calpain (DN), antisense m-calpain (AS) and calpastatin inhibitory domain (CID). We observed that, under conditions of accelerated degradation (serum withdrawal), inhibition of m-calpain through DN-m-calpain over-expression caused a 30% inhibition of total protein degradation whereas CID over-expression reduced degradation by 63%. These constructs did not significantly affect degradation in the presence of serum. These data indicate that calpains participate in the accelerated degradation associated with serum withdrawal. Inhibition of calpain also stabilized nebulin, a major structural protein of the sarcomere. These observations indicate that calpains play significant roles in muscle protein turnover. Finally, over-expression of antisense m-calpain caused a transient reduction in m-calpain concentration after which normal m-calpain concentration was quickly re-established. These observations indicate that m-calpain is a short half-life protein in muscle cells. The second goal of this study is to investigate the role of calpain in the mediation of PARP protein level in differentiating myoblasts. Poly(ADP-ribosyl)ation, catalyzed by PARP, is involved in various physiological events, such as DNA excision repair, DNA recombination, DNA replication, cell differentiation, cell growth and transformation, and apoptosis. A protease participating in PARP turnover could be a significant regulator to the events which PARP is involved. A relationship between apoptosis and myofibrillar protein degradation via a common protease might suggest the basis for muscle wasting and atrophy which characterize in many muscle diseases. We established a genetic approach to inhibit endogenous calpain activity through over-expressing calpastatin inhibitory domain (CID). We observed that (1) inhibition of calpain activity increased PARP concentration when post-confluent myoblasts were cultured with 2% HS medium, an inducer of differentiation and (2) inhibition of calpain activity prevented PARP degradation induced by A23187 and etoposide in differentiating myoblasts. These data demonstrate that calpain is involved in regulation of PARP in cultured cells. / Graduation date: 1998

Vertebrate development requires the activity of multiple members of the myocyte enhancer factor 2 (mef2) gene family for muscle cell specification and subsequent differentiation. Additionally, it is thought that several muscle-specific functions of MEF2 family proteins require binding additional co-factors including members of the Transcription Enhancing Factor-1 (TEF-1) and Vestigial-like protein families. In Drosophila there is a single mef2 (Dmef2) gene as well single homologues of TEF-1 and vestigial-like; sd and vg, respectively. To help clarify the role(s) of these factors, we examined the requirements for Vg and Sd during Drosophila muscle specification. Analysis of loss of Vg or Sd function mutations confirms that both are required for muscle differentiation, as loss of sd or vg leads to a reproducible loss of a subset of cardiac or somatic muscle cells in developing embryos. However, the requirement for Sd or Vg is cell specific, as over-expression of each of these proteins in other muscle cells also has a deleterious effect on muscle differentiation. Finally, I determined that Sd, Vg and Dmef2 can interact directly. Thus, the muscle specific phenotypes associated with loss or ectopic Vg or Sd expression may be a consequence of alternative binding of Vg and Sd to Dmef2 to form alternative protein complexes that modify Dmef2 activity. The somatic muscles of Drosophila develop in a complex pattern that is repeated in each embryonic hemi-segment. Initial communication between somatic muscles and the epidermal tendon cells is critical for formation of this muscle pattern. However, later establishment of attachments between longitudinal muscles at the segmental borders is largely independent of the muscle-epidermal attachment signals, and relatively little is known about how this event is regulated. Here I show that expression of the transcription factor Vg is required in ventral longitudinal muscles (VL1-4) to make them competent to form stable inter-muscular attachments. Further, the cell-specific differentiation events induced by Vg in two muscles fated to form attachments appear to be coordinated by Drosophila Epidermal Growth Factor (DER) signalling. / Molecular Biology and Genetics

Force generation and the ability of the heart muscle to contract and correspondingly to beat depends upon multiple interactions between myosin and actin-tropomyosin-troponin, the key proteins of the contractile apparatus. The myosin molecule consists of two heavy chains and two types of light chains, two essential (ELC) and two regulatory (RLC) light chains. We hypothesize that mutations in myosin ELC may affect the ability of myosin to bind to actin, thus producing structurally and/or functionally abnormal sarcomeres effecting heart muscle contraction and relaxation. We believe that this pathological process underlies the basis of Familial Hypertrophic Cardiomyopathy (FHC), a genetic disorder caused by mutations in the genes encoding the major myofilament proteins, including the myosin ELC. I have investigated the effects of two FHC ELC mutations, A57G and E143K, on the actin-myosin interaction and generation of contractile force. Here, I show evidence that mutations in the ELC may cause disruptions in sarcomeric structure which then may cause abnormal muscle contraction and lead to compensatory hypertrophy.

Muscle strain injuries affect a wide range of physically active people around the world and are reaching epidemic proportions. Despite the variety of treatment options available in rehabilitation, there are no clear guidelines for electrical stimulation that provide effective reproducible results that address the underlying cause of these injuries. For instance, electrotherapy is inefficient at stimulating muscles, because of imprecise parameters and an ability to target particular muscles. The difference between this study and previous research is the precise delivery of electrical stimulation (intramuscular) at two different frequencies (2 Hz and 50 Hz) and comparing it a control group. Objective: To determine the difference on muscle strength and functional status between three treatments modalities for sub acute and chronic hamstring strains. Design: A randomized experimental design was used to compare the effects of low (2 Hz), high (50 Hz) and no-electrical (control) intramuscular stimulation on muscle strength and mental and functional status (AMSMC HEALTH STATUS INDEX). Each group consisted of 18 subjects. Main Outcome: The difference in treatment modalities was evaluated by comparing the muscle strength test (Biodex Dynamometer) results and the AMSMC HEALTH STATUS INDEX results in pretest and post-test conditions. Results: The AMSMC HEALTH STATUS INDEX, but not muscle strength test (Biodex), changed significantly after 2-Hz electrical intramuscular stimulation (pre-test µ = 66.56, Std= 11.92, post-test µ= 92.89, Std= 6.25), whereas no statistically significant changes in health status index and muscle strength test occurred with 50-Hz (pre-test = 69.22, Std= 11.31, post-test µ= 70.22, Std= 12.27)) and no-electrical stimulation groups (pre-test µ= 69.11, post-test µ= 73.39, Std= 13.18).

Understanding the regulatory mechanisms controlling utrophin A expression at the sarcolemma of dystrophic muscles will facilitate the development of therapeutic strategies to ameliorate the pathophysiological features of Duchenne Muscular Dystrophy (DMD). The main goal of this study was to characterize the regulation of utrophin A IRES activity using a transgenic mouse model expressing the utrophin A 5’UTR bicistronic reporter and to identify trans-acting factors that could mediate IRES activity and endogenous expression of utrophin A. We found that utrophin A IRES activity is specifically expressed in skeletal muscles. Moreover, we identified eEF1A2 as a muscle-specific trans-acting factor that can interact with utrophin A and mediate IRES-dependent translation of utrophin A. Finally, we showed that eEF1A2 mediates endogenous utrophin A expression and localization in skeletal muscle. Identifying pharmacological compounds that would specifically target eEF1A2 and increase endogenous levels of utrophin A expression could serve as a drug-based therapy to treat DMD.

Since a significantly greater percentage of body weight is supported by the non-paretic limb following stroke, a greater amount of fatigue may be present during daily activities. This may affect the ability of these individuals to maintain a stable upright posture. The presence of falls following a stroke has been attributed in part to this asymmetrical stance post-stroke. Therefore the purpose of this study was to assess the effect of quadriceps muscle fatigue on bi-pedal posture in individuals who had a stroke and an age-matched control group. Although individuals after stroke displayed greater postural sway under the paretic limb than the non-paretic limb or control subjects, results of this study show that sustaining an isometric knee extension of the non-paretic limb induces changes in postural control for individuals after stroke, but that these changes do not markedly differ from those of healthy age-matched controls.