Changes In Muscle Physiology Research Articles

Control of Skeletal Muscle Cell Growth and Size Through Adhesion GPCRs.

Skeletal muscle homeostasis is regulated by a constant influx of chemicals and exposure to mechanical stimuli. A number of key signaling pathways that translate these stimuli into changes in muscle physiology have been established. The GPCR family known as adhesion GPCRs (aGPCRs) has largely elusive roles in skeletal muscle biology; however, their unique capacity to activate adhesion and G protein signaling pathways makes them an attractive point of investigation. The skeletal muscle myofiber contains a highly organized cytoarchitecture to ensure contractile function. This requires intricate interactions with components of the extracellular matrix (ECM) surrounding each fiber. aGPCRs possess extended N-termini known to interact with ECM proteins and complexes suggesting a compatible role in skeletal muscle biology. Furthermore, recent work demonstrated the involvement of certain aGPCRs in whole muscle hypertrophy and differentiation of muscle progenitor cells. Signaling pathways downstream of aGPCRs are still incompletely understood; however, initial findings show involvement of the Gα12/13 subunit signaling to the pro-anabolic Akt/mTOR pathway. Together, this chapter will review the emerging role of aGPCRs in skeletal muscle biology and putative mechanism(s) employed to regulate skeletal muscle growth.

Using skin temperature and muscle thickness to assess muscle response to strength training

ABSTRACT Introduction: Several studies already reported the response of many biomarkers after strength training, but studies using low cost diagnostic imaging tools are rare. Objective: To evaluate the usage of skin temperature and muscle thickness (MT) to monitor muscle response (until 96 hours after) to high-intensity strength training. Methods: This is a short-term longitudinal study with 13 trained, healthy male volunteers. Volunteers performed five sets of biceps bi-set exercise with their dominant arm with dumbbells, with load of 70% of one-repetition maximum (1RM). The ultrasound (US) and thermal images were acquired before and immediately after the last set, 24, 48, 72 and 96 hours after exercise. Results: The analysis was divided in two stages: acute muscle response (until 24 hours after training) and delayed muscle response (from 24 to 96 hours after training). The elbow flexors thickness showed the peak value immediately after the last set of training. Skin temperature (on elbow flexors) and the elbow flexors thickness grew continuously from 24 to 96 hours after strength training. There is a high correlation (r=0.941, p=0.017) between skin temperature and muscle thickness from the end of exercise until 96 hours after strength training. Conclusions: The US images showed high sensibility for muscle physiological changes on the first 24 hours after exercise. On the other hand, the thermal images had higher sensibility for muscle physiological changes than US images from 24 to 96 hours after training.

Fibre type composition in the lumbar perivertebral muscles of primates: implications for the evolution of orthogrady in hominoids

The axial musculoskeletal system is important for the static and dynamic control of the body during both locomotor and non-locomotor behaviour. As a consequence, major evolutionary changes in the positional habits of a species are reflected by morpho-functional adaptations of the axial system. Because of the remarkable phenotypic plasticity of muscle tissue, a close relationship exists between muscle morphology and function. One way to explore major evolutionary transitions in muscle function is therefore by comparative analysis of fibre type composition. In this study, the three-dimensional distribution of slow and fast muscle fibres was analysed in the lumbar perivertebral muscles of two lemuriform (mouse lemur, brown lemur) and four hominoid primate species (white-handed gibbon, orangutan, bonobo, chimpanzee) in order to develop a plausible scenario for the evolution of the contractile properties of the axial muscles in hominoids and to discern possible changes in muscle physiology that were associated with the evolution of orthogrady. Similar to all previously studied quadrupedal mammals, the lemuriform primates in this study exhibited a morpho-functional dichotomy between deep slow contracting local stabilizer muscles and superficial fast contracting global mobilizers and stabilizers and thus retained the fibre distribution pattern typical for quadrupedal non-primates. In contrast, the hominoid primates showed no regionalization of the fibre types, similar to previous observations in Homo. We suggest that this homogeneous fibre composition is associated with the high functional versatility of the axial musculature that was brought about by the evolution of orthograde behaviours and reflects the broad range of mechanical demands acting on the trunk in orthograde hominoids. Because orthogrady is a derived character of euhominoids, the uniform fibre type distribution is hypothesized to coincide with the evolution of orthograde behaviours.

Age-related decreases in motor unit discharge rate and force control during isometric plantar flexion

Aging is related to multiple changes in muscle physiology and function. Previous findings concerning the effects of aging on motor unit discharge rate (DR) and fluctuations in DR and force are somewhat contradictory. Eight YOUNG and nine OLD physically active males performed isometric ramp (RECR) and isotonic (ISO) plantar flexions at 10 and 20% of surface EMG at MVC. Motor unit (MU) action potentials were recorded with intramuscular fine-wire electrodes and decomposed with custom build software “Daisy”. DR was lower in OLD in RECR-10% (17.9%, p<0.001), RECR-20% (15.8%, p<0.05), ISO-10% (17.7%, p<0.01) and ISO-20% (14%, n.s.). In YOUNG force fluctuations were smaller at ISO-10% (72.1%, p<0.001) and ISO-20% (55.2%, p<0.05) which were accompanied with a slight increase in DR variation (n.s.). The observed lower DR in OLD is in line with earlier findings in small distal muscles. Also the larger force fluctuation in OLD was in line with previous studies with smaller hand muscles. These findings suggest that the age-related changes in MU control do exist also in large leg extensors that play an important role in human locomotion and balance control.

Muscle Functional MRI as an Imaging Tool to Evaluate Muscle Activity

Muscle functional magnetic resonance imaging (mfMRI) is an innovative technique that offers a noninvasive method to quantify changes in muscle physiology following the performance of exercise. The mfMRI technique is based on signal intensity changes due to increases in the relaxation time of tissue water. In contemporary practice, mfMRI has proven to be an excellent tool for assessing the extent of muscle activation following the performance of a task and for the evaluation of neuromuscular adaptations as a result of therapeutic interventions. This article focuses on the underlying mechanisms and methods of mfMRI, discusses the validity and advantages of the method, and provides an overview of studies in which mfMRI is used to evaluate the effect of exercise and exercise training on muscle activity in both experimental and clinical studies.

Scientific Basis of Minimally Invasive Spine Surgery

Literature review. To describe the scientific basis of minimally invasive spine surgery as it relates to posterior lumbar surgery. Minimally invasive spine (MIS) surgery is predicated on several basic principles: (1) avoid muscle crush injury by self-retaining retractors; (2) do not disrupt tendon attachment sites of key muscles, particularly the origin of the multifidus muscle at the spinous process; (3) use known anatomic neurovascular and muscle compartment planes; and (4) minimize collateral soft tissue injury by limiting the width of the surgical corridor. Literature review. The conventional midline posterior approach for lumbar decompression and fusion violates these key principles of MIS surgery. The tendon origin of the multifidus muscle is detached, the surgical corridor is exceedingly wide, and significant muscle crush injury occurs through the use of powerful self-retaining retractors. The combination of these events leads to well-described changes in muscle physiology and function. MIS surgery is performed using table-mounted tubular retractors that focus the surgical dissection to a narrow corridor directly over the surgical target site. The path of the surgical corridor is selected on the basis of anatomic planes, specifically avoiding injury to the musculotendinous complex and the neurovascular bundle. With these relatively simple modifications to surgical technique, significant improvements in intraoperative blood loss, postoperative pain, surgical morbidity, return of function, among others, have been achieved. However, MIS techniques remain technically demanding and a significant complication rate has been observed during the initial learning curve of the procedures.

Effect of Transportation and Low Voltage Electrical Stimulation on Meat Quality Characteristics of Omani Sheep

The aim of this study was to determine the effects of road transportation during the hot season (36 oC) and low voltage electrical stimulation on meat quality characteristics of Omani sheep. Twenty intact male sheep (1-year old) were divided into two equal groups: 3 hrs transported or non-transported. The transported group was transferred to the slaughterhouse the day of slaughter in an open truck covering a distance of approximately 300 km. The non-transported group was kept in a lairage of a commercial slaughterhouse with ad libitum feed and water for 3 days prior to slaughter. Blood samples were collected from the animals before loading and prior to slaughter in order to assess their physiological response to stress in terms of hormonal levels. Fifty percent of the carcasses from each group were randomly assigned to low voltage (90 V) at 20 min postmortem. Muscle ultimate pH, expressed juice, cooking loss percentage, WB-shear force value, sarcomere length, myofibrillar fragmentation index and colour L*, a*, b* were measured on samples from Longissimus dorsi muscles collected 24 hrs postmortem at 2-4 oC. The transported sheep had significantly (P&lt;0.05) higher cortisol adrenaline, nor-adrenaline, and dopamine levels than the non-transported group. Muscles from electrically-stimulated carcasses had significantly (P&lt;0.05) lower pH values, longer sarcomere length, lower shear force value, higher expressed juice, myofibrillar fragmentation index and L* values than those from non-stimulated ones. Transportation significantly influenced meat quality characteristics of the Longissimus dorsi muscle. Muscle ultimate pH and shear force values were significantly higher, while CIE L*, a*, b*, expressed juice and cooking loss were lower in transported than non-transported sheep. This study indicated that pre-slaughter transportation at high ambient temperatures can cause noticeable changes in muscle physiology in sheep. Nevertheless, meat quality of transported sheep can be improved by electrical stimulation post-slaughter.

β and γ-Sarcoglycans are Decreased in the Detrusor Smooth Muscle Cells of the Partially Obstructed Rabbit Bladder

We evaluated and quantified the levels of sarcoglycans present in the detrusor muscle layer of rabbits with partial bladder outlet obstruction. Rabbits underwent surgery, as previously described, to partially obstruct the urethra. One, 3, 7 and 14 days after obstruction the detrusor muscle layer was dissected free of the remaining bladder tissue and extracted with detergent to isolate the transmembrane components of the dystroglycan-glycoprotein complex. Several components of the dystroglycan-glycoprotein complex were characterized and quantified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis several bands were noted on gels with a molecular weight (43 and 35 kDa, respectively) corresponding to beta and gamma-sarcoglycan. As obstruction progressed longitudinally, the levels of beta and gamma-sarcoglycan showed progressive decrease at the protein level with beta-sarcoglycan levels recovering at later time points. Bladders with a functional physiology that showed more advanced symptoms of dysfunction had a greater decrease in beta and gamma-sarcoglycan protein. The levels of beta and gamma-sarcoglycan progressively change with obstruction with greater changes occurring in the levels of gamma-sarcoglycan. It is likely that alterations in the dystroglycan-glycoprotein complex are responsible for some of the changes in muscle physiology that occur as a consequence of obstruction.

Generation and phenotypic characterization of a galanin overexpressing mouse

In most parts of the peripheral nervous system galanin is expressed at very low levels. To further understand the functional role of galanin, a mouse overexpressing galanin under the platelet-derived growth factor-B was generated, and high levels of galanin expression were observed in several peripheral tissues and spinal cord. Thus, a large proportion of neurons in autonomic and sensory ganglia were galanin-positive, as were most spinal motor neurons. Strong galanin-like immunoreactivity was also seen in nerve terminals in the corresponding target tissues, including skin, blood vessels, sweat and salivary glands, motor end-plates and the gray matter of the spinal cord. In transgenic superior cervical ganglia around half of all neuron profiles expressed galanin mRNA but axotomy did not cause a further increase, even if mRNA levels were increased in individual neurons. In transgenic dorsal root ganglia galanin mRNA was detected in around two thirds of all neuron profiles, including large ones, and after axotomy the percentage of galanin neuron profiles was similar in overexpressing and wild type mice. Axotomy reduced the total number of DRG neurons less in overexpressing than in wild type mice, indicating a modest rescue effect. Aging by itself increased galanin expression in the superior cervical ganglion in wild type and transgenic mice, and in the latter also in preganglionic cholinergic neurons projecting to the superior cervical ganglion. Galanin overexpressing mice showed an attenuated plasma extravasation, an increased pain response in the formalin test, and changes in muscle physiology, but did not differ from wild type mice in sudomotor function. These findings suggest that overexpressed galanin in some tissues of these mice can be released and via a receptor-mediated action influence pathophysiological processes.

Electromyographic activity of the human extensor carpi ulnaris muscle changes with exposure to repetitive ulnar deviation.

With little known about the changes in muscle physiology due to repetitive work during an 8 h workday, our objective was to quantify the changes in muscle activity due to this type of work. Using a repeated measurements design, 13 healthy women participated in three conditions, each lasting 2 days: a control condition where they remained inactive, and two repetitive work conditions involving repeated ulnar deviation of the wrist at 20 and 25 repetitions a minute at workloads which they themselves had deemed acceptable for 8 h through a psychophysical protocol. Electromyographic (EMG) activity of the extensor carpi ulnaris muscle was recorded during voluntary isometric contractions (20% and 60% maximal voluntary contraction) eight times throughout the work and control days at 0, 2, 4.25, 6.75, 8, 9, 10, and 11 h. The amplitude of the EMG signal was lower on workdays compared to the control days. Although power was significantly reduced in all spectrum bands of the EMG power spectra, the reductions were not uniform across the entire frequency range, giving rise to different shapes of the EMG power spectra. Initial median frequency of the EMG signal showed no change between the control and workdays (P = 0.51); however, the decline of the median frequency with respect to time over the course of each isometric contraction was steeper during workdays compared to control days (P = 0.003). These changes suggest that the muscles are in an early stage of fatigue when working for an 8 h day.