Mechanism by which static exercise improves insulin resistance in skeletal muscle of type 2 diabetes / 中国组织工程研究

BACKGROUND:Skeletal muscle insulin resistance is the key pathological link of type 2 diabetes.Static exercise can effectively improve skeletal muscle insulin resistance,but the mechanism remains unclear. OBJECTIVE:To explore the mechanism of static exercise on insulin resistance in the skeletal muscle of type 2 diabetic mice based on the phosphatidyl inositol 3-kinase(PI3K)/protein kinase B(AKT)/glucose transporter(GLUT4)signaling pathway. METHODS:After 1 week of adaptive feeding,7 out of 40 C57BL/6 mice were randomly selected as blank group and fed common diet,while the other mice were fed high-fat diet and taken to prepare type 2 diabetes models through the low-dose streptozotocin intraperitoneal injection.Twenty-four mice were successfully modeled and they were randomly divided into model group(n=8),metformin group(n=8)and static exercise group(n=8),which continued to be fed high-fat diet.The metformin group was given 200 mg/kg metformin dissolved in normal saline(2 ml/kg)by gavage,once a day,for 6 weeks.The static exercise group was given normal saline daily by gavage and carried out static exercise,30 minutes a day,6 days per week.The model group was given the same dose of normal saline daily by gavage without exercise intervention.After the intervention,the fasting blood glucose of each group was detected,the intraperitoneal glucose tolerance test was performed,and the area under the glycemic curve was calculated.Glycosylated hemoglobin,serum insulin,insulin resistance index were detected by ELISA.Total cholesterol,triglyceride,high-density lipoprotein,low-density lipoprotein were detected using biochemical methods.The mRNA expression levels of PI3K,AKT and GLUT4 in the gastrocnemius of mice were detected by real-time quantitative PCR.Morphological changes of the gastrocnemius were observed by hematoxylin-eosin staining,and the cross-sectional area of muscle fibers was calculated. RESULTS AND CONCLUSION:Compared with the blank group,fasting blood glucose,glycosylated hemoglobin,area under the glycemic curve,insulin resistance index,total cholesterol,triglyceride and low-density lipoprotein levels were significantly increased in the model group(P<0.01,P<0.05).Whereas,these indicators were significantly lower in the static exercise and metformin group than the model group(P<0.01,P<0.05).Compared with the blank group,serum insulin and high-density lipoprotein levels were significantly declined in the model group(P<0.01)and the mRNA expression of PI3K,AKT and GLUT4 in the gastrocnemius of mice were also significantly reduced(P<0.01).These indicators were significantly elevated in the metformin group and static exercise group compared with the blank group(P<0.01).Compared with the blank group,the muscle fibers in the model group were disordered,and the muscle cells atrophied and the muscle fiber gap widened.The cross-sectional area of muscle fibers was significantly decreased in the model group compared with the blank group(P<0.01).Compared with the model group,atrophy of the gastrocnemius fibers and muscle fiber space were improved in the static exercise group and the metformin group,and the cross-sectional area of muscle fiber was significantly increased in both groups(P<0.01).These findings indicate that static resistance training may promote glucose uptake and utilization by up-regulating the expression of PI3K,AKT and GLUT4 mRNA in skeletal muscle tissue,thereby improving the morphology and function of skeletal muscle tissue,alleviating insulin resistance and regulating glucose homeostasis.

Effects of isometric resistance training on blood pressure and physical fitness of men

Abstract AIMS The present study aimed to investigate the effects of whole body isometric resistance training (IRT) on blood pressure (BP), strength and aerobic fitness. We also analyzed whether the effects of whole body isometric training compares to whole body dynamic resistance training (DRT). METHODS Twenty-nine pre-hypertensive sedentary males, aged between 40 and 60 years were divided into three groups: IRT (n = 10), DRT (n = 9), and Control (n = 10). Both programs involved whole body resistance training, and occurred for 12 weeks, three times/week, at an intensity of 60% of a dynamic one repetition maximum test (1RM). Before and after 12 weeks, 24 hours blood pressure monitoring, 1RM strength and aerobic fitness were assessed. RESULTS IRT reduced diastolic BP values during a 24-hour period and daytime. There was also a decrease in mean BP values during daytime (P<0.05). No interaction between time and group in systolic BP, diastolic BP, mean BP, heart rate and arterial stiffness index were observed (P>0.05). IRT increased strength and aerobic fitness when compared to Control group. However, these changes were lower than DRT regarding strength (DRT: ∆ = 43.1±10.6% vs. IRT: ∆ = 24.1±7.1% vs. CON: Δ = 4.2±11.5%; P<0.05) and aerobic fitness (DRT: ∆ = 22.9±10.7% vs. IRT: ∆ = 12.9±6.1% vs. CON: Δ = -2.1±7.4%; P<0.01). CONCLUSION Whole body IRT reduced diastolic BP and mean BP, however, the decrease was not different for the DRT group. IRT also increased strength and aerobic fitness, nevertheless, these changes were lower than after DRT.

Comparison of Electrocardiographic Criteria for Identifying Left Ventricular Hypertrophy in Athletes from Different Sports Modalities

OBJECTIVES: In athletes, isolated electrocardiogram high voltage criteria are widely used to evaluate left ventricular hypertrophy, but positive findings are thought to represent normal electrocardiogram alterations. However, which electrocardiogram criterion can best detect left ventricular hypertrophy in athletes of various sport modalities remains unknown. METHODS: Five electrocardiogram criteria used to detect left ventricular hypertrophy were tested in 180 male athletes grouped according to their sport modality: 67% low-static and high-dynamic components and 33% high-static and high-dynamic components of exercise. The following echocardiogram parameters are the gold standard for diagnosing left ventricular hypertrophy: left ventricular mass index ≥134 g.m-2, relative wall thickness ≥0.42 mm, left ventricular diastolic diameter index ≥32 mm.m-2, septum wall thickness ≥13 mm, and posterior wall thickness ≥13 mm. Results for the various criteria were compared using the kappa coefficient. Significance was established at p<0.05. RESULTS: Fifty athletes (28%) presented with left ventricular hypertrophy according to electrocardiogram findings, with the following sensitivities and specificities, respectively: 38-53% and 79-83% (Perugia), 22-40% and 89-91% (Cornell), 24-29% and 90% (Romhilt-Estes), 68-87% and 20-23% (Sokolow-Lyon), and 0% and 99% (Gubner). The Perugia and Cornell criteria had higher negative predictive values for the low-static and high-dynamic subgroup. Kappa coefficients were higher for Romhilt-Estes, Cornell and Perugia criteria than for Sokolow-Lyon and Gubner criteria. CONCLUSION: All five evaluated criteria are inadequate for detecting left ventricular hypertrophy, but the Perugia, Cornell and Romhilt-Estes criteria are useful for excluding its presence. The Perugia and Cornell criteria were more effective at excluding left ventricular hypertrophy in athletes involved in a sport modality with low-static and high-dynamic component predominance.

Anticipation of exercise and response in skin and muscle sympathetic nerve activity / 体力科学

A study was conducted to determine whether anticipation of exercise alters the responses of sympathetic nerve activity to muscle contraction. Sympathetic nerve activity leading to the skin (SSA) and muscle (MSA) was recorded from the tibial nerve in the left and right legs using tungsten microelectrodes. Heart rate and blood pressure (oscillometric method) were also measured during the experiment. Seven healthy subjects, who gave informed consent, participated in the experiment. They were asked to exert a static handgrip (SHG) for 2 min at a tension of 30% of maximal voluntary handgrip. Two different situations were set before the commencement of exercise. One was that after several minutes of controlled rest, a countdown was started 2 min before the exercise, and then the handgrip was applied (Cond. 1) . The other was that a preparation time of between 7 and 5 min was set prior to the handgrip exercise while no information regarding the starting time of exercise was given to the subjects (Cond. 2) . SSA for 30 s just before the exercise was increased in comparison with the control value at rest in Cond. 1, but not in Cond. 2. There was no difference in the SSA response patterns to SHG between the two conditions. Before the commencement of SHG, MSA did not alter from the control value at rest in either condition. The magnitudes of the increase in MSA during SHG were almost identical under both conditions. Heart rate for 30s before SHG in Cond. 1 was increased significantly from the control value, whereas there was no significant change in Cond. 2. The magnitude of the heart rate response to SHG was the same in both conditions. The mean blood pressure showed no significant change before SHG, but increased significantly during SHG in both conditions. The increases in SSA and heart rate prior to the commencement of exercise may be related to the anticipatory response to the exercise, although this response was not significant in MSA. These results confirm that anticipation of exercise increases sympathetic outflow to the skin. This may be advantageous in adapting the body to exercise.

Thermographic observations of the skin related with the arm exercise / 体力科学

To visualize skin temperatures during the dynamic and static arm exercises, a monochromatic thermograph was used.<BR>The thermoviewer JTG system presented a 5-monochromatic step-thermal display in centaral temperatures of 34.5 or 34.0°C and a temperature range of 2°C. The temperature resolving power of the system was 0.2°C. A 35 mm camera was used to take a synchronous thermogram of 2 sec scanning time.<BR>The experiments were carried out in August in an experimental room with an air temperature of 27.3±0.6°C, and a relative humidity of 50.5±4.3%.<BR>The skin temperatures of the forearm, upper arm and chest for five male subjects (18-25 yr) were observed before, during and after 5 min exercise on an arm ergometer at work intensities of 0, 2, 3 and 4 kg (dynamic exercise : a rate of 40 contractions/min as timed with a metoronome) .<BR>The following results were obtained.<BR>1) Changes in skin temperatures were observed in detail and over a wide area during the dynamic and static exercises.<BR>2) The upper arm skin temperature increased as soon as that of the shoulder fell immediately after the beginning of dynamic exercise.<BR>3) The decrease in skin temperatures on the chest, shoulder and upper arm appeared with static exercise.<BR>4) The fall in skin temperature increased and spread from forearm toward chest with the incresse in static work intensity.

EFFECTS OF STATIC EXERCISE AND DYNAMIC EXERCISE ON SYSTOLIC TIME INTERVALS (STI) IN CHILDREN / 中国运动医学杂志

The purpose of this study was to investigate STI changes resulting from static and dynamic exercises in boys, 9-10 years old, so as to reveal the effects of physical work of different types and loads on the heart function.Our research showed that the effects of static load and dynamic load on STI in children were different. After dynamic exercise all items of STI changed significantly and PEP/LVET decreased significantly. No PEP change was found after static exercises (50% and 80% max load). Static exercise of 50% max load resulted in no IVCT change, but static exercise of 80% max load resulted in very significant change of IVCT, and the longest recovery period was found afterwards. Thus, 80% static exercise would result in a heavy, transient heart load in children.Our research also showed that the changes of HR?systolic blood pressure?LVET after dynamic load and static load were significantly different indicating that oxygen consumption in heart muscles was higher during dynamic exercise and the effect of dynamic exercise on heart was stronger.