Axial Stress Provides a Lower Bound on Shear Wave Velocity in Active and Passive Muscle

ABSTRACTUltrasound shear wave elastography can be used to characterize mechanical properties of unstressed tissue by measuring shear wave velocity (SWV), which increases with increasing tissue stiffness. Measurements of SWV have often been assumed to be directly related to the stiffness of muscle. Some have also used measures of SWV to estimate stress, since muscle stiffness and stress covary during active contractions. However, few have considered the direct influence of muscle stress on SWV, independent of the stress-dependent changes in muscle stiffness, even though it is well known that stress alters shear wave propagation. The objective of this study was to determine how well the theoretical dependency of SWV on stress can account for measured changes of SWV in passive and active muscle. Data were collected from six isoflurane-anesthetized cats; three soleus muscles and three medial gastrocnemius muscles. Muscle stress and stiffness were measured directly along with SWV. Measurements were made across a range of passively and actively generated stresses, obtained by varying muscle length and activation, which was controlled by stimulating the sciatic nerve. Our results show that SWV depends primarily on the stress in a passively stretched muscle. In contrast, the SWV in active muscle is higher than would be predicted by considering only stress, presumably due to activation-dependent changes in muscle stiffness. Our results demonstrate that while SWV is sensitive to changes in muscle stress and activation, there is not a unique relationship between SWV and either of these quantities when considered in isolation.

CHANGE OF IMMUNOLOGICAL RESISTANCE AND BIOCHEMICAL PROCESSES IN PERIPHERAL BLOOD LYMPHOCYTES IN ACTION STRESS

The aim of the study was to study changes in immunological reactivity and biochemical processes in peripheral blood lymphocytes in Pakistani students under the action of muscle stress. To achieve this goal, the states of the immune, lipid peroxidation and antioxidant systems and energy metabolism were studied in 30 students from South Asia under the influence of muscle stress. The state of cellular, humoral and nonspecific phagocytic immunity was determined in all students before and 1, 2 and 3 days after the stress of muscle load. The research results show that the state of the immune system after muscle stress was characterized by phase changes in the parameters of cellular, humoral and nonspecific phagocytic immunity with a restoration or increase in indicators at the end of the observation. An increase in the activity of enzymes of energy metabolism in peripheral blood lymphocytes after stress of muscular load on days 2 and 3 after ensures the processes of successful adaptation. The state of lipid peroxidation and the antioxidant system in peripheral blood lymphocytes under muscle stress reflects the stress of the organism's adaptive reactions with the development of lipid hyperperoxidation under conditions of increased energy costs.

Continuous Protein Supplementation Reduces Acute Exercise-Induced Stress Markers in Athletes Performing Marathon

The aim of this study was to determine the changes in endurance performance and metabolic, hormonal, and inflammatory markers induced by endurance stress (marathon race) in a combined strategy of training and dietary protein supplementation. The study was designed as a randomised controlled trial consisting of regular endurance training without and with a daily intake of a soy protein-based supplement over a three-month period in 2 × 15 (10 males and 5 females per group) endurance-trained adults. Body composition (body mass, BMI, and fat mass) was determined, and physical fitness was measured by treadmill ergometry at baseline and after 3 months of intervention; changes in exercise-induced stress and inflammatory markers (CK, myoglobin, interleukin-6, cortisol, and leukocytes) were also determined before and after a marathon competition; eating behaviour was documented before and after intervention by a three-day diet diary. Although no significant influence on endurance performance was observed, the protein supplementation regime reduced the exercise-induced muscle stress response. Furthermore, a protein intake of ≥20% of total energy intake led to a lower-level stress reaction after the marathon race. In conclusion, supplementary protein intake may influence exercise-induced muscle stress reactions by changing cellular metabolism and inflammatory pathways.

Comparison of Effect of Piperine and Capsaicin with Tabata Exercise on Changes in Serum Nitric Oxide and Creatine Kinase of Kung Fu Boys

Introduction: Tabata exercise programs can produce free radicals and muscle soreness and herbal supplements may be helpful as mediators in response to oxidative damage and muscle stress. Therefore, the purpose of this study was to compare the effects of these two supplements with Tabata exercise activity on nitric oxide and creatine kinase enzyme. Methods: The research was a quasi-experimental one and the participants were boys practicing Kung Fu. Among them, 33 boys (19-25 years old) were selected as a research sample by obtaining written consent and were randomly divided into three groups: Tabata exercise, Tabata exercise + capsaicin, Tabata exercise + piperine). During the eight weeks of piperine and capsaicin supplementation, all three groups participated in a Tabata training protocol. After the last session, blood sampling was taken in two basic stages immediately.The results were compared with one-way analysis of variance and Bonferroni test in the inferential section and SPSS version 16 software. Results: Creatine kinase activity in the two groups of supplement + exercise compared to the exercise group had a significant decrease (p = 0.004) and nitric oxide (p = 0.001) in the two groups of supplement + exercise compared to the exercise group had a significant increase. These changes were more pronounced in the Tabata exercise group with capsaicin supplementation. This significance was confirmed by Bonferroni test. There was no significant difference between the two groups of Tabata exercise and capsaicin and peprin consumption. Conclusion: Both piperine and capsaicin supplements decreased creatine kinase activity and increased nitric oxide. These two supplements were able to reduce some of the oxidative damage and muscle stress resulting from exercise by different mechanisms.

Changes in Muscle Stress and Sarcomere Adaptation in Mice Following Ischemic Stroke

While abnormal muscle tone has been observed in people with stroke, how these changes in muscle tension affect sarcomere morphology remains unclear. The purpose of this study was to examine time-course changes in passive muscle fiber tension and sarcomeric adaptation to these changes post-ischemic stroke in a mouse model by using a novel in-vivo force microscope. Twenty-one mice were evenly divided into three groups based on the time point of testing: 3 days (D3), 10 days (D10), and 20 days (D20) following right middle cerebral artery ligation. At each testing time, the muscle length, width, and estimated volume of the isolated soleus muscle were recorded, subsequently followed by in-vivo muscle tension and sarcomere length measurement. The mass of the soleus muscle was measured at the end of testing to calculate muscle density. Two-way ANOVA with repeated measures was used to examine the differences in each of the dependent variable among the three time-point groups and between the two legs. The passive muscle stress of the impaired limbs in the D3 group (27.65 ± 8.37 kPa) was significantly lower than the less involved limbs (42.03 ± 18.61 kPa; p = 0.05) and the impaired limbs of the D10 (48.92 ± 14.73; p = 0.03) and D20 (53.28 ± 20.54 kPa; p = 0.01) groups. The soleus muscle density of the impaired limbs in the D3 group (0.69 ± 0.12 g/cm3) was significantly lower than the less involved limbs (0.80 ± 0.09 g/cm3; p = 0.04) and the impaired limbs of the D10 (0.87 ± 0.12 g/cm3; p = 0.02) and D20 (1.00 ± 0.14 g/cm3; p < 0.01) groups. The D3 group had a shorter sarcomere length (2.55 ± 0.26 μm) than the D10 (2.83 ± 0.20 μm; p = 0.03) and D20 group (2.81 ± 0.15 μm; p = 0.04). These results suggest that, while ischemic stroke may cause considerable changes in muscle tension and stress, sarcomere additions under increased mechanical loadings may be absent or disrupted post-stroke, which may contribute to muscle spasticity and/or joint contracture commonly observed in patients following stroke.

Coupling to substrate adhesions drives the maturation of muscle stress fibers into myofibrils within cardiomyocytes

Focal adhesions have been known to be involved in the assembly of sarcomere-containing myofibrils for decades. Here, we define several molecular players required for the connection between adhesions and myofibrils and show that the strength of this connection positively correlates with myofibril maturation.