阻力训练及超等长阻力训练对下肢肌肉活性和力量的影响

目的:观察阻力训练和超等长阻力训练后下肢肌肉力量变化,比较肌肉激活模式的不同.方法:将16名男性篮球运动员随机分成两组,分别实施8周下肢阻力训练和超等长阻力训练.采用3-D测力台测试训练前、后最大随意收缩值,用表面肌电记录训练前、后6次重复训练动作的胫骨前肌、腓肠肌外侧头、股直肌、股外侧肌、股二头肌的激活信号,计算积分肌电值和髋、膝、踝关节周围拮抗肌共激活.结果:两组下肢肌肉力量均显著提高,阻力训练组效果较明显.超等长阻力训练组肌肉活性显著高于阻力训练组.训练后超等长阻力训练组肌肉活性出现适应性变化,髋、踝关节拮抗肌共激活显著升高,膝关节拮抗肌共激活训练前、后没有显著性差异.阻力训练组训练前、后肌肉活性及拮抗肌共激活没有显著变化.结论:超等长阻力训练有助于提高肌肉间协调性,可以优化肌肉动作的运动策略.     

钾钠离子与骨骼肌疲劳的关系研究进展

骨骼肌的收缩能力是影响机体运动能力的重要因素。肌膜内外离子的运动,决定着体内生物电的变化。剧烈运动时,由于代谢产物堆积、酸碱平衡失调等因素,可使形成生物电的主要离子K^＋,Na^＋浓度发生变化,特别是K^＋浓度变化尤为突出,近而影响膜电位,最终使肌肉兴奋性下降,运动能力降低,出现疲劳。基于K^＋,Na^＋与骨骼肌疲劳之间存在重要关系,本文就近年来国内外钾、钠离子方面的研究做一综述。     

浑圆桩练习增进健康效果的实验分析及推广建议

目的：探索浑圆桩练习对人体健康的促进作用。方法：以30名大学生为研究对象，进行为期4个月的站桩练习，分别于站桩前、站桩过程中、站桩结束2个月对测试者的部分生理指标进行测量，并进行比较分析。结果：浑圆桩练习有助于人体大脑产生α波；能够有效改善颈部和腰部的生理弯曲，使之趋于正常并得以保持；能够有效增进肌肉力量、柔韧性和骨密度，但站桩结束2个月后，力量和柔韧性有所降低。结论：浑圆桩练习可有效增进人体健康。建议：应完善组织机构建设，加大宣传推广力度，做好辅导和创新工作，推动站桩健身活动的发展。     

间歇运动降低炎症和蛋白泛素化降解改善心梗导致的大鼠骨骼肌萎缩

摘要：目的：探讨间歇运动及间歇运动联合TNF-α抑制剂Etanercept对心梗大鼠骨骼肌MuRF1和Smyd1表征的影响及炎症水平与骨骼肌功能改善的关系。方法：雄性3月龄SD大鼠70只,随机分为假心梗组(S)、心梗组(MI)、心梗+间歇运动组(ME)、心梗+ Etanercept组(MIT)、心梗+生理盐水组(MIS)、心梗+间歇运动+ Etanercept组(MET)、心梗+间歇运动+生理盐水组(MES),每组10只。采用左冠状动脉结扎法制备心梗模型,S组只在心脏相同位置穿线不结扎。ME组、MET组和MES组术后1周采用大鼠跑台进行间歇运动干预。其中MIT组和MET组于术前3 d腹腔注射Etanercept(1.2 μg/g)1次,术后i.p. 1次/3 d×4周,MIS组和MES组注射定量生理盐水作为参照。各组训练结束后次日腹腔麻醉,测定心脏功能,之后冰浴条件下快速剥离并切取胫骨前肌,入甲醛固定或液氮冷藏备用。胫骨前肌重量/胫骨长度比值测定骨骼肌质量变化,免疫荧光测定骨骼肌HSP70和骨架蛋白Myosin表达变化及细胞横截面积,RT-qPCR测定骨骼肌MuRF1和MAFbx mRNA基因表达变化,Western Blot测定骨骼肌MuRF1、MAFbx、Smyd1、HSP90、TNF-α、NF-κB(pp65)、IL-6、IL-10、HSP70、Myosin和α-actinin蛋白表达变化,糜蛋白酶活性试剂盒检测骨骼肌蛋白酶体活性变化。结果：心梗导致大鼠骨骼肌质量系数、细胞横截面积、细胞骨架蛋白Myosin和α-actinin及肌纤维生成关键因子Smyd1表达显著降低（P<0.01）,MuRF1、MAFbx、TNF-α、IL-6、NF-κB（pp65）和伴侣分子HSP90表达显著升高（P<0.01）,间歇运动或Etanercept干预以及二者联合干预均可显著提高心梗大鼠骨骼肌质量系数、细胞横截面积、IL-10、Myosin、α-actinin和Smyd1蛋白表达（P<0.05, P<0.01）,降低MuRF1、MAFbx、TNF-α、IL-6、NF-κB（pp65）和HSP90水平（P<0.05, P<0.01）;心梗大鼠骨骼肌的细胞浆和细胞核MuRF1蛋白表达显著升高（P<0.05, P<0.01）,糜蛋白酶活性增加（P<0.01）,间歇运动可进一步升高其胞浆和胞核HSP70表达（P<0.01）,降低MuRF1蛋白表达、细胞浆/细胞核HSP70比值和糜蛋白酶活性（P<0.05, P<0.01）,且机体炎症水平与细胞浆/细胞核HSP70比值呈显著正相关（P<0.01）。结论：间歇运动或Etanercept干预或二者的共同干预均可显著提高心梗大鼠骨骼肌质量、骨架蛋白和Smyd1的表达,增加细胞横截面积,降低MuRF1、MAFbx和HSP90的表达,改善骨骼肌功能。     

Partial least squares based identification of Duchenne muscular dystrophy specific genes

Large-scale parallel gene expression analysis has provided a greater ease for investigating the underlying mechanisms of Duchenne muscular dystrophy (DMD). Previous studies typically implemented variance/regression analysis, which would be fundamentally flawed when unaccounted sources of variability in the arrays existed. Here we aim to identify genes that contribute to the pathology of DMD using partial least squares (PLS) based analysis. We carried out PLS-based analysis with two datasets downloaded from the Gene Expression Omnibus (GEO) database to identify genes contributing to the pathology of DMD. Except for the genes related to inflammation, muscle regeneration and extracellular matrix (ECM) modeling, we found some genes with high fold change, which have not been identified by previous studies, such as SRPX, GPNMB, SAT1, and LYZ. In addition, downregulation of the fatty acid metabolism pathway was found, which may be related to the progressive muscle wasting process. Our results provide a better understanding for the downstream mechanisms of DMD.     

Rate of Force Development in the Handgripping Muscles by Females as a Function of Fatigue Level

Abstract

Twenty-eight young, adult women were tested for maximum voluntary contraction (MVC) of the grip flexors and were then given five fatigue trials in which the task was to maintain a maximum isometric contraction until the strength level had been degraded to either 80%, 60%, or 40% MVC. At that time, the subject relaxed and within one second was commanded to generate a single contraction as rapidly and forcefully as possible. Testing was also conducted in the nonfatigued state (1.00 MVC). Forces were determined at 4, 8, 16, 32, 64, 128, 256, 512, and 1,024 msec following the initial deflection of the pen from the baseline. Normalized force values were calculated by dividing the force expressed at the various time intervals by the maximum force generated under that condition at 1,024 msec. For both absolute and normalized rate of force development, the highest rate was attained between 32–64 msec. During that time period, the rate of absolute force development was reduced 10% at the 80% MVC level, 30% at 60% MVC, and 53% at 40% MVC. There was a definite pattern of depressed rate of absolute force development up to 256 msec at the higher fatigue levels. For normalized force, fatiguing a muscle to 80% MVC had no effect except at 64 msec where a greater percentage of maximal force was attained than at 1.00 MVC. Beyond that level of fatigue, however, normalized force tended to be adversely affected as fatigue progressed. The time required to develop either 50% or 70% of maximal force was significantly longer for the 40% MVC level than for the remaining conditions. In addition, the time necessary to develop 70% of maximal force was longer for the 60% MVC fatigue level than for the 80% MVC level.     

Effect of time on biomechanics during exercise on the functional re-adaptive exercise device

ABSTRACT

Mechanistic studies of the Functional Re-adaptive Exercise Device (FRED) have shown it automatically recruits Lumbar Multifidus (LM) and Transversus Abdominis (TrA) – two deep-spinal muscles that are atrophied and show altered motor control in low back pain (LBP). No studies have investigated the time required to familiarise to FRED exercise, which is required to inform future FRED based clinical trial protocols. This study therefore determined the effect of time, during FRED exercise, on biomechanical outcome measures, to establish the familiarisation period, and assess for loss of technique throughout a ten minute trial. A cohort comparison study of 148 participants, 70 experiencing low back pain, had lumbopelvic kinematics, exercise frequency and movement variability measured during a 10 minute trial. Magnitude-based inference was used to assess for familiarisation, using plots of variation over time with familiarised reference ranges. The no pain group took 170 seconds, and the back pain group took 150 seconds, to familiarise. A familiarisation period of at least 170 seconds (2.8 minutes) is recommended. This justifies, and provides a familiarisation time for use of the FRED as a motor control intervention.     

Influence of cold-water immersion on indices of muscle damage following prolonged intermittent shuttle running

Abstract

The aim of this study was to assess the effects of cold-water immersion (cryotherapy) on indices of muscle damage following a bout of prolonged intermittent exercise. Twenty males (mean age 22.3 years, s = 3.3; height 1.80 m, s = 0.05; body mass 83.7 kg, s = 11.9) completed a 90-min intermittent shuttle run previously shown to result in marked muscle damage and soreness. After exercise, participants were randomly assigned to either 10 min cold-water immersion (mean 10°C, s = 0.5) or a non-immersion control group. Ratings of perceived soreness, changes in muscular function and efflux of intracellular proteins were monitored before exercise, during treatment, and at regular intervals up to 7 days post-exercise. Exercise resulted in severe muscle soreness, temporary muscular dysfunction, and elevated serum markers of muscle damage, all peaking within 48 h after exercise. Cryotherapy administered immediately after exercise reduced muscle soreness at 1, 24, and 48 h (P < 0.05). Decrements in isometric maximal voluntary contraction of the knee flexors were reduced after cryotherapy treatment at 24 (mean 12%, s _x  = 4) and 48 h (mean 3%, s _x  = 3) compared with the control group (mean 21%, s _x  = 5 and mean 14%, s _x  = 5 respectively; P < 0.05). Exercise-induced increases in serum myoglobin concentration and creatine kinase activity peaked at 1 and 24 h, respectively (P < 0.05). Cryotherapy had no effect on the creatine kinase response, but reduced myoglobin 1 h after exercise (P < 0.05). The results suggest that cold-water immersion immediately after prolonged intermittent shuttle running reduces some indices of exercise-induced muscle damage.     

Determinants of “optimal” cadence during cycling

Abstract

Cadence is one of the only variables cyclists can adjust to manage their performance and fatigue during an event. Not surprisingly, cadence has received a great deal of attention from the scientific community in an effort to identify the cadence that optimizes power output while minimizing the fatigue that is incurred. The literature appears to present conflicting results with little consensus as regards the optimal pedalling cadence. This is in large part due to the inconsistent definition of the term “optimal” cadence, which has been used to describe energetic cost, muscular stress, and perception of effort. The issue is further confounded by the workload-dependent nature of the “optimal” cadence – that is, at higher power outputs, the optimized cadence is different from that at lower power outputs. Although the optimal cadence is different for energetic, muscular, and perceptual definitions, the curves that describe the effect of changes in cadence on these variables consistently exhibit a J-shaped response. This suggests that there is an underlying principle that is common to each of the definitions. Indeed, it would appear that the response of both the cardio-respiratory system (energetic cost) and the muscular system (muscular stress) is determined by the types of muscle motor units that are recruited during the exercise. Furthermore, although part of the response may be due to the inherent differences in the characteristics between the different motor units, the absolute contraction velocity relative to fibre type optimum may be of greater significance. Even when the power output is increased, the shape of the response curves to changes in cadence remains constant, although the nadir of the curve does shift to the right for increasing power outputs. We propose that the point at which the energetic vs. power and the muscular stress vs. power curves intercept is defined by the cadence at which the perceived effort is minimized (i.e. the preferred cadence). However, cadence fluctuations occur under field conditions that are unrelated to physiological factors and, therefore, the ability to identify an “optimal” cadence is limited to the laboratory environment and specific field conditions.     

Precompetitive anxiety and motor performance: A psychophysiological examination

Male volunteer subjects (27) completed a 5‐week habituation period during which practise was undertaken on three motor performance tests. Tests were of serial reaction time, visuomotor ability and muscular power. Following stabilization of performance subjects entered an experimental period where they performed the tests before an evaluative audience on one occasion, and against a matched opponent, also before an evaluative audience on the final occasion. Preperformance measures were obtained of neuroendocrine activity, anticipatory heart rate and state anxiety. Significant precompeti‐tion elevations in state anxiety, heart rate and adrenaline levels were observed, supporting the notion that the exposure was perceived as stressful by subjects. Significant correlations were obtained between adrenaline levels and both state and trait anxiety scores. Results showed a significant increase in performance compared to habituation levels for all three tests in the audience condition. In the competitive situation against a matched opponent, performance level for the visuomotor and power tests declined significantly compared to the previous session performed before an audience. Serial reaction time performance showed a continuing upward trend, although failing to achieve significance. Changes in performance are discussed with reference to cue‐utilization explanations and broader cognitive resource limitations.