The effect of induced alkalosis and submaximal cycling on neuromuscular response during sustained isometric contraction

Abstract

The aim of this study was to determine if inducing metabolic alkalosis would alter neuromuscular control after 50 min of standardized submaximal cycling. Eight trained male cyclists (mean age 32 years, s = 7; [Vdot]O_2max 62 ml · kg^?1 · min^?1, s = 8) ingested capsules containing either CaCO₃ (placebo) or NaHCO₃ (0.3 g · kg^?1 body mass) in eight doses over 2 h on two separate occasions, commencing 3 h before exercise. Participants performed three maximal isometric voluntary contractions (MVC) of the knee extensors while determining the central activation ratio by superimposing electrical stimulation both pre-ingestion and post-exercise, followed by a 50-s sustained maximal contraction in which force, EMG amplitude, and muscle fibre conduction velocity were assessed. Plasma pH, blood base excess, and plasma HCO₃ were higher (P < 0.01) during the NaHCO₃ trial. After cycling, muscle fibre conduction velocity was higher (P < 0.05) during the 50-s sustained maximal contraction with NaHCO₃ than with placebo (5.1 m · s^?1, s = 0.4 vs. 4.2 m · s^?1, s = 0.4) while the EMG amplitude remained the same. Force decline rate was less (P < 0.05) during alkalosis-sustained maximal contraction and no differences were shown in central activation ratio. These data indicate that induced metabolic alkalosis can increase muscle fibre conduction velocity following prolonged submaximal cycling.     

Indirect evidence of human skeletal muscle damage and collagen breakdown after eccentric muscle actions

Indirect markers of muscle damage and collagen breakdown were recorded for up to 9 days after a bout of concentric, followed by a bout of eccentric, muscle actions. Nine untrained participants performed two bouts of 50 maximum effort repetitions on an isokinetic dynamometer (angular velocity 1.05 rad.s-1, range of motion 1.75 rad). An initial concentric bout of muscle actions was followed by an eccentric bout 21 days later, using the same knee extensors. Concentric actions induced no changes in maximum voluntary isometric contraction force (MVC),nor induced any changes in the serum enzyme activities of creatine kinase, a lactate dehydrogenase isoenzyme (LDH-1), or alkaline phosphatase. Similarly, concentric actions induced no change in markers of collagen breakdown,namely plasma hydroxyproline and serum type 1 collagen concentration.In contrast,eccentric actions induced a 23.5 ± 19.0% (mean ± s) decrease in MVC immediately post-exercise (P< 0.05), and increased the serum enzyme activities of creatine kinase and LDH-1 to 486 ± 792 and 90 ± 11 IU.l-1 respectively on day 3 post-exercise, and to 189 ± 159 and 96 ±13 IU.l-1 respectively on day 7 post-exercise (all P < 0.05). Eccentric actions induced no significant changes in plasma hydroxyproline, but increased collagen concentration on days 1 and 9 post-exercise (48.6% and 44.3% increases above pre-exercise on days 1 and 9 respectively; both P < 0.05). We conclude that eccentric but not concentric actions may result in temporary muscle damage, and that collagen breakdown may also be affected by eccentric actions. With caution, indices of collagen breakdown may be used to identify exercise-induced damage to connective tissue.     

Soccer

Many studies try to understand fundamental soccer skills, most focusing on kicking. However, a full picture of an efficient kick remains incomplete owing to constraints of test designs and difficulties that arise in synchronizing and analyzing information generated by multiple assessment techniques. Previous scientific studies may be generally categorized as: two‐dimensional kinematic analysis using high‐speed cameras, muscle activity studies using electromyog‐raphy, three‐dimensional analysis of the kicking‐leg using a partial‐body model, and kinetic studies using force measurements and modelling. No existing inquiries have used full‐body three‐dimensional motion capture and modelling to examine kicking. The current study remedies this deficiency and defines a full‐body model capable of revealing more detailed characteristics of kicking. Additionally, it reveals effects of long‐term training by comparing novices with skilled athletes and explores new parameters that have potential to aid quantitative evaluations of skill. Results show effective upper‐body movement to be a key factor in creating better initial conditions for a more explosive muscle contraction during kicking. It permits a more powerful quasi whip‐like movement of the kicking leg. Finally, the timely change of distance between the kick‐side hip and the non‐kick‐side shoulder provides a quantitative means of measuring kick quality.     

The effects of maximal and submaximal arm crank ergometry and cycle ergometry on postural sway

Abstract

This study aimed to determine whether arm crank ergometry (ACE) disturbed postural sway to the same extent as cycle ergometry (CE). Nine healthy, none specifically trained adults undertook posturographic tests before and after five separate exercise trials consisting of: two incremental exercise tests to exhaustion for ACE and CE to examine postural sway responses to maximal exercise and to determine peak power output (W_max); two subsequent tests of 30 min duration for ACE and CE at a relative workload corresponding to 50% of the ergometer-specific W_max (ACE_rel; 53 ± 8 W and CE_rel; 109 ± 16 W). A final CE trial was performed at the same absolute power output (CE_abs) as the submaximal ACE trial to match absolute exercise intensity (i.e., 53 ± 8 W). The centre of pressure (COP) displacement was recorded using a force platform before, immediately after exercise and during a 30-min recovery period. ACE had no effects on postural sway (P > 0.05). An increase in mediolateral COP displacement was observed following maximal CE only (P = 0.001), while anteroposterior COP displacement and COP path length increased following maximal and submaximal CE (P < 0.05). These differences in postural sway according to exercise mode likely stem from the activity of postural muscles when considering that CE recruits lower limb muscles involved in balance. This study provides evidence of an exercise mode which does not elicit post-exercise balance impairments, therefore possesses applications to those at an increased risk of falling.     

Anthropometrics and electromyography as predictors for maximal voluntary isometric arm strength

BackgroundMuscular strength can be conceptually determined by two components: muscle activation and size. Muscle activation by the central nervous system can be measured by surface electromyography (sEMG). Muscular size reflects the amount of contractile protein within a skeletal muscle and can be estimated by anthropometric measurements. The purpose of this study was to determine the relative contributions of size parameters and muscle activation to the prediction of maximal voluntary isometric elbow flexion strength.MethodsA series of anthropometric measurements were taken from 96 participants. Torque and root-mean-square (RMS) of the sEMG from the biceps brachii were averaged across three maximal voluntary isometric contractions. A multiple linear regression analysis was performed based on a Pearson's correlation matrix.ResultsBody weight (BW) accounted for 39.1% and 27.3% in males and females, respectively, and was the strongest predictor of strength for males. Forearm length (L3) was the strongest predictor of strength in females (partial R² = 0.391). Elbow circumference (ELB) accounted for a significant (p < 0.05) amount of variance in males but not females. The addition of sEMG RMS as a third variable accounted for an average of 10.1% of the variance excluding the equation of BW and L3 in females. The strongest prediction equation included BW, L3, and ELB accounting for 55.6% and 58.5% of the variance in males and females, respectively.ConclusionAnthropometrics provide a strong prediction equation for the estimation of isometric elbow flexion strength. Muscle activation, as measured by sEMG activity, accounted for a significant (p < 0.05) amount of variance in most prediction equations, however, its contribution was comparable to an additional anthropometric variable.     

发展肌肉爆发力的“最大动量训练法”研究

本文是一项实验性研究报告，目的是验证作者提出的“最大动量训练法”设想。作者采用瑞士产Ｋｉｓｔｌｅｒ测力系统，测定了１７名受试者腿部力量训练的动作。根据所获动力学数据确定了受试者所应采用的适宜载荷量；然后对１７名受试者进行了三个月的力量训练。前后的实验材料分析对比得出结论：１．载荷量变化时，人体完成动作时的肌肉输出冲量不同，且存在极值。２．用输出冲量极值点所对应的载荷量来训练肌肉力量，能更有效的发展肌肉的爆发性力量。３．用动力学指标来确定载荷量的方法，较合理的考虑了人体自重、不同练习动作差异、肌肉成分差异和完成动作速度等问题。使力量训练更具有针对性、准确性和实效性。     

耐力运动与高脂饮食对Wistar大鼠骨骼肌线粒体融合分裂蛋白表达的影响研究

目的:观察耐力运动与高脂饮食干预对肥胖大鼠骨骼肌线粒体融合与分裂蛋白表达的影响。方法:48只Wistar大鼠分N组(16只)与H组(32只)普食/高脂饲喂造模8周,随后分为NNC组、NNE组、HHC组、HHE组、HNC组与HNE组,NNC组、NNE组、HNC组与HNE组使用普食饲喂9周,HHC组与HHE组继续使用高脂饲喂9周,NNE组、HHE组与HNE组进行9周耐力运动干预。结果:高脂饲喂后大鼠骨骼肌线粒体融合蛋白MFN1、MFN2表达减少,分裂蛋白FIS1表达增加,耐力运动干预增加了高脂饲喂后大鼠骨骼肌线粒体MFN1、MFN2的表达,降低了DRP1、FIS1的表达。结论:高脂饲喂显著降低了骨骼肌线粒体融合蛋白的表达,增加了分裂蛋白的表达,耐力运动干预显著增加了骨骼肌线粒体融合蛋白的表达,显著降低了HFD干预后骨骼肌线粒体分裂蛋白的表达。     

不同运动水平射击运动员熵值及脑功能变化的研究

目的:研究在同一比赛情况下不同运动水平射击运动员脑α波各阶段熵值、中枢疲劳指数、中枢紧张度等相应的变化规律。方法:采用高级训练状态监控仪,对不同运动水平射击运动员脑α波各阶段熵值、中枢疲劳指数及中枢紧张度进行比较研究。结果:(1)熵值是反映射击运动员竞技能力状态的一个重要指标,它是一个动态的变化过程,运动水平更高的健将级运动员熵值更为稳定,不同运动水平运动员均值不存在差异性;(2)不同级别射击运动员中枢疲劳指数准备阶段、赛前阶段、赛后阶段呈现递增的趋势;(3)运动水平较低运动员赛前阶段中枢紧张度最高。     

现实与理想的张力——基于考试与素质发展关系的中小学考试思路构建

我国中小学考试正处于相当混乱的状况,其原因之一是较长时间以来关于考试与素质发展的关系存在着以下认识误区:不恰当地套用二元对立的思维方式;对考试与素质发展之性质的误解;将局部当作整体;片面地或过高地看待考试的功能。考试与素质发展既有着重要的实质性联系,又有着重要区分,它们之间的关系可概括为局部现实与完满理想的张力关系。基于这种张力关系的考试体系构建的基本思路包括:确立全景发展的理想;充分考虑考试体系构建的有效性;关注和把握考试的局限性。     

THE APPLICATION OF BIODEX TO FUNCTIONAL DIAGNOSIS AND REHABILITATION OF THIGH AND KNEE INJURIES

Forty-two (male 28, female 14) athletes with quadriceps / hamstring strain, or knee injury were the subjects. The strength of knee extensor and nexor were measured on Bodex system before,during, and after rehabilitation. Peak Torque of 60°/sec concentric, 240°/sec concentric, and 60°/sec eccentric contrsction were taken and evaluated using the"Evaluation Scales", and Torque Curves were analysed. The results indicated: except Hamstring /Quadriceps Torque Ratio of 60°/sec concentric contraction of involved side much higher, and Involved/ Uninvolved Torque Ratio lower, the abnormal Torque Curve of quadriceps (60°/sec concentric) may be a good indicator of quadriceps strain, knee sprain, and chronic knee injury. Abnormal Torque Curve might also be used in selecting athletes. When the subjects took part in the rehabilitation program according to the Biodex reports, the results were satisfying.