Fatigue reduces the complexity of knee extensor torque during fatiguing sustained isometric contractions     

《European Journal of Sport Science》2013,13(10):1349-1358

Abstract

The temporal structure, or complexity, of muscle torque output reflects the adaptability of motor control to changes in task demands. This complexity is reduced by neuromuscular fatigue during intermittent isometric contractions. We tested the hypothesis that sustained fatiguing isometric contractions would result in a similar loss of complexity. To that end, nine healthy participants performed, on separate days, sustained isometric contractions of the knee extensors at 20% MVC to task failure and at 100% MVC for 60?s. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling were quantified by calculating approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Global, central and peripheral fatigue were quantified using maximal voluntary contractions (MVCs) with femoral nerve stimulation. Fatigue reduced the complexity of both submaximal (ApEn from 1.02?±?0.06 to 0.41?±?0.04, P?<?0.05) and maximal contractions (ApEn from 0.34?±?0.05 to 0.26?±?0.04, P?<?0.05; DFA α from 1.41?±?0.04 to 1.52?±?0.03, P?<?0.05). The losses of complexity were accompanied by significant global, central and peripheral fatigue (all P?<?0.05). These results demonstrate that a fatigue-induced loss of torque complexity is evident not only during fatiguing intermittent isometric contractions, but also during sustained fatiguing contractions.  相似文献   

Effects of flexibility and strength training on peak hamstring musculotendinous strains during sprinting     

Xianglin Wan  Shangxiao Li  Thomas M. Best  Hui Liu  Hanjun Li  Bing Yu 《运动与健康科学(英文)》2021,10(2):222

BackgroundHamstring injury is one of the most common injuries in sports involving sprinting. Hamstring flexibility and strength are often considered to be modifiable risk factors in hamstring injury. Understanding the effects of hamstring flexibility or strength training on the biomechanics of the hamstring muscles during sprinting could assist in improving prevention strategies and rehabilitation related to these injuries. The purpose of this study was to determine the effects of altering hamstring flexibility or strength on peak hamstring musculotendinous strain during sprinting.MethodsA total of 20 male college students (aged 18–24 years) participated and were randomly assigned to either a flexibility intervention group or a strength intervention group. Each participant executed exercise training 3 times a week for 8 weeks. Flexibility, sprinting, and isokinetic strength testing were performed before and after the 2 interventions. Paired t tests were performed to determine hamstring flexibility or strength intervention effects on optimal hamstring musculotendinous lengths and peak hamstring musculotendinous strains during sprinting.ResultsParticipants in the flexibility intervention group significantly increased the optimal musculotendinous lengths of the semimembranosus and biceps long head (p ≤ 0.026) and decreased peak musculotendinous strains in all 3 bi-articulate hamstring muscles (p ≤ 0.004). Participants in the strength-intervention group significantly increased the optimal musculotendinous lengths of all 3 hamstring muscles (p ≤ 0.041) and significantly decreased their peak musculotendinous strain during sprinting (p ≤ 0.017).ConclusionIncreasing hamstring flexibility or strength through exercise training may assist in reducing the risk of hamstring injury during sprinting for recreational male athletes.  相似文献   

男子健美运动员Heath-Carter体型特征及与肌力的相关性     

井兰香 《哈尔滨体育学院学报》2020,(2):23-28

目的:计算健美运动员Heath-Carter体型三因子值,统计三因子与肌肉力矩及输出功率的相关性,并分析影响因素。方法:确定60名男子健美运动员的体型类型;测量上、下肢及躯干肌的峰值屈、伸力矩;分别以2.5、5、7.5、10、12.5、15%体重比递增负荷完成自行车蹬车运动,记录每种负荷下的最大输出功率。结果:健美运动员体型三因子平均值为4.40-7.21-1.31(0.31-1.07-0.12),坐标值为(-3.11,8.61),属于远离外因子、偏内胚层的中胚层类型。肌肉力矩和输出功率均与内因子不相关,与中因子呈正相关,与外因子呈负相关。结论:中、外因子影响肌肉力矩和功率输出,对肌肉造型起主要作用。由于内因子值较高且与肌肉收缩能力并不相关,提示不宜将健美训练作为减脂的主要手段。  相似文献   

Angle-specific knee muscle torques of ACL-reconstructed subjects and determinants of functional tests after reconstruction     

Özge Çınar-Medeni  Gulcan Harput  Gul Baltaci 《Journal of sports sciences》2019,37(6):671-676

The purposes of this study were to analyse (a) if “angle-specific” (AS) flexor and extensor torques were different between ACL-reconstructed and uninvolved limbs, (b) the difference in peak torque occurrence angles for concentric and eccentric knee flexor and extensor torques between involved and uninvolved limbs and (c) if AS concentric and eccentric knee flexor and extensor torques are determinants of performance in the “single-leg hop test” (SLHT) and “vertical jump and reach test” (VJRT) in ACL-reconstructed legs. Twenty-seven male ACL-reconstructed volunteers were included in the study. Isokinetic knee muscle strength, SLHT and VJRT were performed 6 months after ACL reconstruction. No difference was found in extremity and knee joint angle interaction for concentric and eccentric flexor and extensor torques (p > 0.05). Peak torque occurrence angles were not different between involved and uninvolved limbs (p > 0.05). In involved extremities, concentric knee extensor strength at 90° was a determinant of SLHT performance (R² = 0.403, p < 0.05), and concentric knee extensor strength at 60° was a determinant of VJRT (R² = 0.224, p < 0.05). Assessment of AS concentric knee extensor strength at 60° and 90° might be important, because these were determinants of functional test performance.  相似文献   

举重运动员等动肌力特征的分析与研究   总被引：1，自引：0，他引：1  

张前锋 《广州体育学院学报》2012,32(1):86-89

本研究利用CYBEX-6000型测力系统,对国家举重队和广东省举重队部分运动员的等动肌力特征进行分析和研究,综合归纳出举重运动员等动肌力的总体规律特征,提出针对性的建议.  相似文献   

生酮饮食对体重管理、肌肉合成以及运动表现的影响          下载免费PDF全文

康杰 《体育科研》2018,(1):1-16

自20世纪20年代以来,极低碳水化合物饮食或生酮饮食疗法被应用于癫痫的治疗,甚至在某些情况下能够完全取代药物治疗。1970年以后,这种饮食疗法作为一种肥胖治疗手段而被广泛知晓 。生酮饮食（Ketogenic Diets,KD）是指碳水化合物减少（通常小于20 g/d或低于每天摄入总能量的5%）而蛋白质和脂肪含量相对增加的饮食。目前认为这三大营养物质的重排可以诱导生理性酮症,进而减轻体重。近年来,许多运动员也希望通过生酮饮食减脂以取得更好的运动表现。尽管生酮饮食在体重管理方面作用显著,但它是否能够维持或提高体能表现仍不明确。文章讨论了生酮饮食的代谢效应和潜在风险,以及近期关于生酮饮食对体重减轻、肌肉合成和运动表现影响的研究进展。  相似文献   

Short- and long-term reliability of leg extensor power measurement in middle-aged and older adults     

Christopher Hurst  Alan M Batterham  Kathryn L Weston  Matthew Weston 《Journal of sports sciences》2018,36(9):970-977

Muscular power is important for maintaining physical functioning with aging. Proper quantification of the reliability of muscular power tests is crucial to inform monitoring of individuals and sample size planning for interventional studies. This study evaluated short- and long-term reliability of leg extensor power measurement in 72 adults (age 62.7 ± 8.6 years). Participants completed four repeat trials on the Nottingham leg extensor power rig, with a further trial twelve weeks later. Mean change, typical error, and intraclass correlation coefficients (ICC) were calculated. For short-term reliability, mean change in power output was trivial after two trials (1.2–4.8%). Typical errors were small following four trials in the dominant leg of males (10.9–5.8%), three in the non-dominant leg of males (9.9–6.2%) and the dominant leg of females (10.0–9.6%) and two in the non-dominant leg in females (8.3%). Intraclass correlation coefficients (ICCs) were very high (0.88–0.96). For long-term reliability, mean change remained trivial (1.0–2.5%), typical errors remained small (5.8–8.6%), and ICCs very high (0.94–0.96). The leg extensor power rig is a reliable method for assessing lower body muscular power, both short- and long-term, with only minimal habituation effects.  相似文献   

Specific muscle synergies in national elite female ice hockey players in response to unexpected external perturbation     

Minhee Kim  Yushin Kim  Hyeyoung Kim 《Journal of sports sciences》2018,36(3):319-325

This study aimed to investigate specific muscle synergies in elite ice hockey players indicating highly developed postural control strategies used to restore balance against unexpected external perturbations. Seven elite athletes (EA) on the women’s national ice hockey team and 7 non-athletes (NA) participated in this study. Based on trajectories of centre of mass (COM), analysis periods were divided into an initial phase (a balance disturbance after perturbation onset) and a reversal phase (a balance recovery response), respectively. Muscle synergies were extracted at each phase by using non-negative matrix factorization. k-means cluster analysis was performed to arrange similar muscle synergies in all participants. EA showed significantly shorter recovery period of COM and smaller body sway than NA. In the initial phase, we identified 2 EA-specific synergies related to ankle plantar flexors or neck extensors. In the case of an NA-specific synergy, co-activation of the ankle plantar flexors and dorsiflexors was found. In the reversal phase, no specific muscle synergies were identified. As the results, EA-specific muscle synergies showed low co-activation strategy of agonists and antagonists in ankle and neck extensors. Our results could provide critical information for rehabilitation strategies in athletes requiring high postural stability.  相似文献   

Acupuncture on Intracellular Ionic Distribution inMuscle Injury and Its Mechanism     

QU Zhuqing  LU Dinghou  WANG Yirun 《北京体育大学学报》1995,(Z2)

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A new linearly-combined bi-exponential model for kinetic analysis of the isometric relaxation process of <Emphasis Type="Italic">Bufo gastrocnemius</Emphasis> under electric stimulation in vitro     

Guo R  Li SB  Zhao LN  Zhao YS  Lu W  Yuan P  Deng P  Liao F 《Journal of Zhejiang University. Science. B》2007,8(12):867-874

There was a slow-relaxing tail of skeletal muscles in vitro upon the inhibition of Ca^2＋-pump by cyclopiazonic acid （CPA）. Herein, a new linearly-combined bi-exponential model to resolve this slow-relaxing tail from the fast-relaxing phase was investigated for kinetic analysis of the isometric relaxation process of Bufo gastrocnemius in vitro, in comparison to the single exponential model and the classical bi-exponential model. During repetitive stimulations at a 2-s interval by square pulses of a 2-ms duration at 12 V direct currency （DC）, the isometric tension of Bufo gastrocnemius was recorded at 100 Hz. The relaxation curve with tensions falling from 90% of the peak to the 15th datum before next stimulation was analyzed by three exponential models using a program in MATLAB 6.5. Both the goodness of fit and the distribution of the residuals for the best fitting supported the comparable validity of this new bi-exponential model for kinetic analysis of the relaxation process of the control muscles. After CPA treatment, however, this new bi-exponential model showed an obvious statistical superiority for kinetic analysis of the muscle relaxation process, and it gave the estimated rest tension consistent to that by experimentation, whereas both the classical bi-exponential model and the single exponential model gave biased rest tensions. Moreover, after the treatment of muscles by CPA, both the single exponential model and the classical bi-exponential model yielded lowered relaxation rates, nevertheless, this new bi-exponential model had relaxation rates of negligible changes except much higher rest tensions. These results suggest that this novel linearly-combined bi-exponential model is desirable for kinetic analysis of the relaxation process of muscles with altered Ca2^＋-pumping activity.  相似文献