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.     

The effect of elevating the heels on spinal kinematics and kinetics during the back squat in trained and novice weight trainers

ABSTRACT

This research assessed the influence of various heel elevation conditions on spinal kinematic and kinetic data during loaded (25% and 50% of body weight) high-bar back squats. Ten novice (mass 67.6 ± 12.4 kg, height 1.73 ± 0.10 m) and ten regular weight trainers (mass 66.0 ± 10.7 kg, height 1.71 ± 0.09 m) completed eight repetitions at each load wearing conventional training shoes standing on the flat level floor (LF) and on an inclined board (EH). The regular weight training group performed an additional eight repetitions wearing weightlifting shoes (WS). Statistical parametric mapping (SPM1D) and repeated measures analysis of variance were used to assess differences in spinal curvature and kinetics across the shoe/floor conditions and loads. SPM1D analyses indicated that during the LF condition the novice weight trainers had greater moments around L4/L5 than the regular weight trainers during the last 20% of the lift (P < 0.05), with this difference becoming non-significant during the EH condition. This study indicates that from a perspective of spinal safety, it appears advantageous for novice weight trainers to perform back squats with their heels slightly elevated, while regular weight trainers appear to realize only limited benefits performing back squats with either EH or WS.     

Disruption of splicing-regulatory elements using CRISPR/Cas9 to rescue spinal muscular atrophy in human iPSCs and mice

We here report a genome-editing strategy to correct spinal muscular atrophy (SMA). Rather than directly targeting the pathogenic exonic mutations, our strategy employed Cas9 and guide-sgRNA for the targeted disruption of intronic splicing-regulatory elements. We disrupted intronic splicing silencers (ISSs, including ISS-N1 and ISS + 100) of survival motor neuron (SMN) 2, a key modifier gene of SMA, to enhance exon 7 inclusion and full-length SMN expression in SMA iPSCs. Survival of splicing-corrected iPSC-derived motor neurons was rescued with SMN restoration. Furthermore, co-injection of Cas9 mRNA from Streptococcus pyogenes (SpCas9) or Cas9 from Staphylococcus aureus (SaCas9) alongside their corresponding sgRNAs targeting ISS-N1 into zygotes rescued 56% and 100% of severe SMA transgenic mice (Smn^−/−, SMN2^tg/−). The median survival of the resulting mice was extended to >400 days. Collectively, our study provides proof-of-principle for a new strategy to therapeutically intervene in SMA and other RNA-splicing-related diseases.     

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。     

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。     

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.     

髓鞘内不同浓度甘丙肽拮抗剂对屈肌运动的相反效应

目的 :了解脊髓中不同剂量甘丙肽拮抗剂M35和M40对甘丙肽抑制屈肌运动作用的影响。方法 :电刺激小腿腹神经引起小腿屈肌收缩时 ,观察髓鞘内联合注入甘丙肽和不同浓度拮抗剂时屈肌张力的改变。结果注入0 0 1、 0 0 3及 0 1μmol/LM35时 ,0 1μmol/L甘丙肽对屈肌张力抑制率从 - 2 9 2 %改变至± 15 1%、 - 2 5 %及 -17 8% ;但 1及 3μmol/L的M35使甘丙肽抑制率分别增强至 - 5 1 9%及 - 6 5 6 %。而给于 0 0 1及 0 0 3μmol/LM40时 ,甘丙肽抑制率增至 - 5 6 7%及 - 41 6 % ,0 3、 1及 3μmol/LM40使甘丙肽抑制率分别改变为 - 6 8%、 +12 2 %及 +30 4%。结论　低浓度M35为甘丙肽拮抗剂 ,高浓度M35有甘丙肽激动剂作用 ;低浓度M40为甘丙肽激动剂 ,高浓度M40有甘丙太拮抗剂效应。脊髓神经元可能存在不同甘丙肽亚型受体。     

增龄骨骼肌的机能特征及运动的其影响(综述)

骨骼肌在增龄或衰老时结构与生理机能发生一系列的变化。增龄骨骼肌的主要特征表现为肌肉萎缩、运动单位重建、绝对力量与单位面积的肌力下降 ,同时肌肉的最大输出功率与持续输出功率也下降。增龄骨骼肌与年轻骨骼肌相比更容易收缩时发生损伤且恢复较慢。同时某些运动可对增龄骨骼肌的结构与机能的变化施加一定的影响。