ObjectiveThis study aims to compare the effects of linear periodization (LP) and undulating periodization (UP) resistance training on athletic ability, body composition, blood lipid, and blood glucose.MethodsWe searched PubMed, Embase, Scopus, and Web of Science to collect relevant studies comparing the health-promoting effects of LP and UP up to July 20th, 2025. Two authors independently extracted and coded the data. The TESTEX Scale was employed to assess the quality of included studies. Egger’s test and sensitivity analysis were conducted to evaluate the robustness of results. Subsequent subgroup analyses were carried out based on participants’ age, sex, training duration, and obesity status.ResultsA total of 29 studies met the inclusion criteria. The results showed that LP and UP had comparable effects on enhancing athletic capacity, improving body composition, and regulating blood glucose and insulin resistance. Further subgroup analysis indicated that UP was superior to LP in increasing lean body mass among obese individuals and achieving short-term weight loss goals. In contrast, LP was more appropriate for long-term weight loss. The sole study involving only males suggested that UP was more effective than LP in reducing insulin resistance in men.ConclusionLP and UP demonstrated similar effects on enhancing athletic capacity, improving body composition, and regulating blood glucose and insulin resistance. UP was superior to LP in improving body composition among obese individuals and attaining short-term weight loss goals. Training load regiment can be prescribed according to specific objectives in practical applications.

Introduction:Knee injuries are highly prevalent among athletes. Following a knee injury, athletes may experience minor disruptions to their competition and training schedules, or in severe cases, the injury may even jeopardize their athletic careers. Incorporating targeted knee injury prevention training into routine training is thus critical for mitigating knee injury risk. Aim:This meta-analysis aimed to investigated whether exercise-based preventive training influences the incidence of knee injuries in athletes. Exploratory and prespecified subgroup analyses were concurrently performed to identify potential factors influencing the effectiveness of preventive training programs. Method:This study adopted a systematic review and meta-analysis design. A systematic literature search was performed across four electronic databases: PubMed, Embase, Web of Science, and Cochrane Library. The main search terms included "Athletes," "Knee Injuries," "Prevention and Control," and "Random Allocation." Results:A total of 10 studies, involving 15,296 participants, were included in this meta - analysis. The groups that received preventive training showed a significantly lower incidence of knee injuries (overall; RR = 0.68, 95% CI: 0.51-0.92, p = 0.011) and anterior cruciate ligament injuries (RR = 0.43, 95% CI: 0.25-0.74, p = 0.002). Subgroup analysis also revealed several group differences; however, these findings should be interpreted with caution due to the small sample size. The overall heterogeneity of the results was high, and the sources of heterogeneity could not be identified. Conclusion:Exercise-based injury-prevention training (such as strength, balance, and plyometric training) can reduce the incidence of knee injuries. Systematic review registration number:PROSPERO (registration no. CRD42024543884).

BackgroundBeta-alanine is widely used as an ergogenic aid in sports nutrition, yet most evidence comes from male or mixed-sex samples. Its effects in women therefore remain unclear. This systematic review and meta-analysis examined the effects of beta-alanine supplementation on exercise performance and related outcomes in women.MethodsThis review followed PRISMA 2020 guidelines and was registered in PROSPERO (CRD420261362733). PubMed, Web of Science, Scopus, the Cochrane Library, and Embase were searched from inception to April 30, 2026. Randomized controlled studies in women comparing beta-alanine with placebo or control were included. Outcomes included time to exhaustion (TTE), maximal or peak oxygen uptake, peak power, anaerobic performance, and body fat percentage. RoB 2 and GRADE were used to assess risk of bias and certainty of evidence, respectively. Random-effects meta-analyses were conducted using standardized mean differences with 95% confidence intervals.ResultsTwelve reports from 11 independent randomized controlled trials involving 312 women were included. Beta-alanine supplementation showed a pooled effect in favor of TTE (8 studies, N = 187; SMD = 0.49, 95% CI 0.20 to 0.79; p = 0.001; I2 = 0%). For the remaining outcomes, pooled estimates were imprecise, with 95% confidence intervals including trivial and, where applicable, potentially meaningful effects. Moreover, certainty of evidence was very low for all outcomes after downgrading for risk of bias, imprecision, and publication bias; peak power and anaerobic performance were additionally downgraded for indirectness.ConclusionBeta-alanine supplementation may improve TTE in trials conducted in women, but current evidence does not support clear pooled effects on peak power, anaerobic performance, VO₂max and VO₂peak, or body fat percentage. Overall, these findings suggest an outcome-specific response pattern, although confidence in the evidence remains limited because of the small evidence base and very low certainty across outcomes.Systematic review registrationhttps://www.crd.york.ac.uk/PROSPERO/view/CRD420261362733, identifier PROSPERO (CRD420261362733).

Objective:To systematically evaluate cluster structure training (CS) and traditional training (TS) in enhancing athletes' motor abilities and explore sport-specific effects. Methods:Systematic searches of PubMed, Embase, Cochrane, and Web of Science (inception to March 2025). Quality was assessed using TESTEX, with meta-analyses calculating SMD (P < 0.05) and subgroup analyses by sport. Results:A total of 11 studies were included, showing that CS outperformed TS in improving athletes' sprint ability (SMD = -0.32, 95% CI: [-0.56, -0.07], P = 0.012), explosive power (SMD = 0.39, 95% CI: [0.10, 0.68], P = 0.009) with significant differences. Subgroup analysis further revealed sport-specific effects: CS was more effective than TS in enhancing maximum strength (SMD = 0.30, 95% CI: [0.01, 0.59], P = 0.043), explosive power (SMD = 0.96, 95% CI: [0.26, 1.65], P = 0.007), and sprint ability (SMD = -0.65, 95% CI: [-1.15, -0.16], P = 0.009) in volleyball athletes, as well as peak power in soccer athletes (SMD = 0.68, 95% CI: [0.01, 1.36], P = 0.047). Conclusion:CS benefits volleyball and soccer, where explosive power is key. Coaches should tailor CS to sports' energy demands and work-rest ratios. Clinical Trial Registration:https://www.crd.york.ac.uk/PROSPERO/home, identifier CRD420251015968.

Background: This study aims to elucidate the causal effect of physical activity (PA) at different times of day on the risk of cardiovascular diseases, including subtypes of stroke, heart failure, atherosclerosis (AS), myocardial infarction, hypertension, and peripheral artery disease. Methods: Two-sample univariable and multivariable Mendelian randomization were conducted. Genetic instruments for total PA and PA across twelve 2-hour intervals were derived from UK Biobank. Summary-level data for outcomes were obtained from large consortia. We estimated causal effects using inverse variance weighted, MR-Egger, and weighted median methods. Sensitivity analyses were also conducted. Results: Multivariable Mendelian randomization revealed independent protective effects of PA during 6 AM to 8 AM, 10 AM to 12 PM, and 4 PM to 6 PM on total and ischemic stroke. In contrast, the effect in protecting total, ischemic and large artery stroke were detected for PA during 6 PM to 8 PM in univariable MR. PA during 2 AM to 4 AM and 10 AM to 12 PM had directly protective effect of total AS, and PA during 2 PM to 4 PM for coronary AS, while univariable MR results indicated PA during 8 PM to 10 PM and 6 PM to 8 PM decreased the risk of cerebral and coronary AS, respectively. PA during 2 PM to 4 PM exhibited a total but not a direct effect of reducing risk of total and essential hypertension. No robust causal associations were observed for heart failure, myocardial infarction, or peripheral artery disease. Conclusion: This study provides evidence that PA during specific periods is causally associated with the risk of stroke, AS, and hypertension. These findings suggest that the timing of PA should be considered for the prevention of cardiovascular diseases.

ContextAnterior cruciate ligament (ACL) injuries are prevalent in sports and often require surgical intervention followed by rehabilitation. Several rehabilitation methods have been used for patients after ACL surgery.ObjectiveThis study aimed to assess the overall efficacy of exercise therapy in improving outcomes for patients following ACL surgery using a systematic review and meta-analysis of randomized controlled trials (RCTs).Data sourcesPubMed, Web of Science, Embase, and the Cochrane Library were searched for randomized controlled trials published from 1 January 2000 to 30 August 2024. Study quality was assessed using the Cochrane Risk-of-Bias tool.Study selectionA total of 11 randomized controlled trials (whole-body vibration training = 4, core-stability training = 2, strength training = 3, blood flow restriction training = 1, and aquatic training = 1) involving 552 anterior cruciate ligament surgery patients were included.Data extractionTwo researchers individually screened the key information for each eligible study and evaluated the quality of the studies. Any dispute was discussed by a third researcher.ResultsCompared with conventional therapy, exercise therapy significantly reduced pain scores (mean difference: −0.53, 95% CI: −0.82 to −0.24, and p < 0.001) and improved muscle strength (flexion: 13.76 and extension: 12.46) and knee function (effect size: 2.06 and p = 0.001). Secondary outcomes, although less pronounced, also demonstrated improvement.LimitationThe sources of heterogeneity among the included studies were not fully identified, particularly concerning variations in exercise protocols or patient characteristics. Additionally, the therapeutic effects of specific exercise modalities (e.g., strength training versus aquatic training) were not directly compared.ConclusionExercise therapy is effective in reducing pain, enhancing muscle strength, and improving knee function in ACL surgery patients. These findings underscore the importance of integrating tailored exercise therapies into rehabilitation programs.Systematic review registration numberhttps://www.crd.york.ac.uk/PROSPERO/, identifier registration number. CRD42023476653.

BackgroundExternalizing problem behaviors can significantly and negatively impact adolescents’ learning, daily life, and future socialization. While physical exercise is believed to inhibit adolescents’ externalizing problem behaviors, the extent of its effect and the mediating mechanisms remain unclear.MethodsThis study is based on data from the 2018 China Family Panel Studies (CFPS). The CFPS project employed the Externalizing Problem Behaviors Scale (EPBS), the Rosenberg Self-Esteem Scale (RSES), and the Self-Control Scale (SCS) to measure adolescents’ externalizing problem behaviors, self-esteem, and self-control. Additionally, physical exercise was measured by collecting data on the time and frequency of adolescents’ physical exercise. Parent-child relationships were evaluated using a composite variable that included four dimensions: frequency of quarrels, frequency of heart-to-heart talks, parental awareness of their children’s whereabouts, and children’s trust in their parents. Based on data collection and variable construction, this study employed multiple linear regression, propensity score matching, and quantile regression to analyze the impact of physical exercise on adolescents’ externalizing problem behaviors and the heterogeneity of these effects. Additionally, the Bootstrap mediation effect test was employed to explore the mediating roles of parent-child relationships, self-esteem, and self-control in this process.ResultsThe analysis demonstrates that physical exercise significantly inhibits adolescents’ externalizing problem behaviors (β = −0.095, p < 0.01), although the effect varies significantly among different populations. Compared to males (β = −0.077, p < 0.1), rural residents (β = −0.065, p > 0.1), individuals with poorer family economic status (β = −0.080, p < 0.1), and those with more severe problem behaviors (τ = 0.75, β = −0.086, p < 0.05), physical exercise yields a more pronounced inhibitory effect on females (β = −0.113, p < 0.01), urban residents (β = −0.134, p < 0.01), individuals with better family economic status (β = −0.115, p < 0.01), and those with milder problem behaviors (τ = 0.25, β = −0.112, p < 0.01). Furthermore, through enhancements in parent-child relationships (CI: -0.015; -0.002), self-esteem (CI: -0.019; -0.003), and self-control (CI: -0.055; -0.025), physical exercise indirectly mitigates adolescents’ externalizing problem behaviors.ConclusionPhysical exercise significantly reduces adolescents’ externalizing problem behaviors, with effects differing across various groups. Parent-child relationships, self-esteem, and self-control mediate this relationship, underscoring the positive influence of exercise on adolescent behavior.

BACKGROUND:In contemporary society, physical appearance significantly influences individuals' social interactions and career achievements. Although some studies suggest that physical exercise may positively impact physical appearance, most rely on subjective self-assessment data. In contrast, third-party evaluations are widely regarded as more objective and reliable. Thus, this study aims to explore the effects of physical exercise on physical appearance, as assessed by third-party evaluations, and to examine its heterogeneity. METHODS:This study utilized third-party physical appearance evaluation data from 25,460 respondents in the 2018 China Family Panel Studies (CFPS) and assessed the impact of physical exercise on physical appearance using multiple linear regression and instrumental variable analysis. Furthermore, the heterogeneity in the effects of physical exercise was investigated using subgroup regression and quantile regression analyses. RESULTS:The findings indicate that physical exercise substantially enhances physical appearance, with its effects varying significantly across different populations. Specifically, women, urban residents, and those with lower appearance scores experience more pronounced enhancement from physical exercise compared to men, rural residents, and those with higher scores. Additionally, the effect of age on the impact of physical exercise on appearance exhibits an inverted U-shaped relationship. Middle-aged adults (40-59 years) experience the most significant improvements, while benefits are lower for adolescents (10-20 years), young adults (20-39 years), and older adults (60-80 years). CONCLUSIONS:This study systematically reveals the positive impact of physical exercise on physical appearance, demonstrating that regular exercise can significantly enhance individual appearance scores. This finding contributes to a broader understanding of the multifaceted benefits of physical exercise.

Cognitive ability plays a crucial role in adolescents’ academic performance and subsequent career development. Although previous studies have demonstrated that physical activity, self-education expectations, and learning behaviors positively affect the cognitive development of adolescents, the extent of their influence and their mediating roles require further elucidation. This study is based on tracking survey data from 2,688 adolescents in Chinese households collected in 2018. Multiple linear regression, Propensity Score Matching, and Quantile regression were employed to analyze the impact and heterogeneity of physical activity on adolescents’ cognitive ability. Furthermore, the Bootstrap mediation test was used to explore the mediating roles of self-education expectations and learning behaviors in this process. The results indicate the following: Physical activity significantly promotes adolescents’ cognitive ability; for those with poorer cognitive ability, it exerts a greater impact. Moreover, in addition to its direct effects, physical activity indirectly enhances adolescents’ cognitive ability through the mediation of three factors (self-education expectations, learning behaviors, self-education expectations and learning behaviors). These discoveries offer significant insights into diverse strategies for developing cognitive ability in adolescents, contributing to both theoretical research and practical interventions.

从管理模式、竞赛体系、学训安排、人才出路、师资力量、家校联动、经费支持、科学研究、硬件设施9 个方面,全面分析日本东京都校园足球特点,认为:东京都校园足球实行制度化管理,教育部门与足协之间职责明确、通力合作;打造类型多样、参与面广、衔接合理的赛事体系;尊重学生运动爱好,开展多种运动项目教学,组建俱乐部集中训练;足球队员接受完整的文化教育,融入社会各行各业;得益于自身良性循环系统,校园足球师资队伍"数量足、质量高";建立良好的家校联动机制,形成教育合力;教学训练依靠教育专项经费,竞赛依靠足协经费和市场赞助;根据日本球员身体特点,研究适合自身的战术体系;硬件设施条件一般,基本满足学训需要.我国校园足球取得了长足发展,进步有目共睹,但面临"体育系统弱教育"与"教育系统弱体育"导致的校园足球发展难题.借鉴日本成功范式,提出发展我国校园足球的启示:全面深化学校体育改革,丰富校园体育活动,用自然分流的方式让学生参与所爱的运动项目(包括足球);加强足球科学研究,提高学训效果,提升竞赛观赏性;教育系统和体育系统要加强体制改革,创新联合机制,勇于破除制约校园足球发展的利益藩篱;"校园"彰显教育,"足球"象征体育,发展校园足球应遵循教育规律和体育规律.

ABSTRACT Introduction In recent years, there have been a number of reforms in table tennis, trends in technology development, and demands on the part of athletes to improve their competitive ability and prevent injuries. Objective Evaluate the effect of abdominal core strength training on ball control stability in table tennis players. Methods By random sampling and grouping method, the national top-level table tennis players were divided into an experimental group and a control group (17 boys in each group and seven girls in each group); the experiment lasted for one week, during which the athletes in the experimental group performed abdominal core strength training, while the athletes in the control group performed regular training. Results There was no significant difference in the longitudinal comparison of the control group before and after the experiment (P>0.05), and there was a very significant difference in the horizontal comparison between the two groups after the experiment (P<0.01). Conclusion Abdominal core strength training has a positive effect on improving the technical stability of table tennis players. Core strength can improve the athlete’s attack speed and recovery. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

为了研究校园足球政策供给的协同状况,以2009—2021年国务院及各部委发布的53项校园足球相关政策为样本,采用文本分析法,基于"时间-主体-工具"三维分析框架,对政策的演变史、政策制定主体和政策工具使用类型等多个维度进行了计量分析.研究表明,我国校园足球政策连续性较好,但与时代发展目标的协同性不强;政策制定主体联动性有所提高,但多元治理主体的全面协同仍然不足;政策工具类型的使用比较全面,但不同类型组合的协同性不高,环境型政策过溢,供给型性政策不足,需求型政策匮乏.为了提高政策的执行效果,应该对校园足球政策体系的协同性进行优化,主要路径包括:加强政策与时代目标的协同以完成新阶段的新使命;深化政策决策主体间的协同以提高政策执行效果;提高政策工具组合的协同以完善政策工具使用结构.

目的:探讨高温、常湿环境下,激活后增强(PAP)诱导训练负荷以及间歇时间对短跑运动员垂直爆发力、水平爆发力以及水平加速的影响.方法:选取11名一级、6名二级男子短跑运动员,测试其诱导训练前后垂直纵跳(CMJ)、立定跳远(SLJ)、10码跑(TYR)成绩(温度＞32℃,相对湿度＜60％).诱导训练负荷(L)分别为1×4×90％1RM、1×6×85％1RM、1×8×80％1RM、1×10×75％1RM(组数×次数×％1RM),间歇时间(T)分别为3 min、6 min、9 min、12 min.结果:诱导训练后的T3min测试成绩均低于基准成绩(Pre);T6min 3项测试成绩提高幅度最大,CMJ测试在T6min与1×10X75％1RM组合时提高6.1％(P＜0.05),SLJ与TYL测试最佳成绩在T6min与1×4×90％1RM组合时,成绩分别提高2.4％、1.5％;CMJ与SLJ测试的T9min成绩与Pre相比有所提高,但无显著性差异(P＞0.05),TYR测试T9min成绩呈下降趋势,但无显著性差异(P＞0.05);T12min测试成绩均低于Pre(P＞0.05).结论:在高温环境下,间歇时间对PAP存在显著影响,负荷对PAP无显著性影响;75％～90％1RM均能产生PAP,T6min对运动表现影响最大,产生的PAP效应最佳;诱导训练后过短或过长时间的间歇均不会提高运动表现.

目的:评估中国足协U23政策对适龄球员竞技表现及其比赛结果的影响.方法:采用符号分析、逐步判别模型、有序逻辑回归模型等方法,对2017—2018赛季均出场的34名U23球员的上场参数与竞技表现进行研究.结果:与2017赛季相比,U23球员在2018赛季的进攻类与防守类变量均未发生显著性变化(P>0.05);U23球员出场的位置、射正、进球以及解围等指标与比赛结果为弱正相关关系;其中后三者对比赛结果呈正向影响;U23球员上场时间与上场时间节点影响比赛胜负概率,但程度较弱且无统计学意义;射正、进球以及解围三项运动表现指标对比赛胜负概率影响显著.结论:U23政策的变更调整对年轻球员的配额保护执行效果与预期目标背道而驰,没有显著提升其竞技表现;教练员应对U23时采用的"少上场、晚上场"策略不会对比赛胜负产生显著影响,但U23球员关键竞技指标可以在一定程度上影响比赛胜负的概率.

以全面质量管理理论为基础形成的职业足球俱乐部青少年球员培训绩效评估工具已广泛应用于比利时的职业足球俱乐部青少年球员培训绩效评估中.比利时体育行业协会通过"IK Gym"体操俱乐部的全面质量管理体系实现了对其培训质量的管理与评估.而在足球运动技能培训方面,培训质量管理与绩效评估的典范当属"Foot PASS"绩效评估系统,该系统是当前国际上较权威的青少年足球培训的全面质量管理与绩效评估工具.该绩效评估系统成为比利时足球协会管理职业足球俱乐部青少年球员培训工作的有效手段.基于以上,构建中国职业足球俱乐部青少年足球运动员培训质量标准与绩效评估指标体系,以期为中国足球协会及其职业足球俱乐部完善青少年足球运动员培训质量管理制度与绩效考核制度提供理论参考.

为提高我国青少年足球运动员训练的科学化水平,对足球训练实践领域的训练理论与模式进行梳理,并辩证分析了不同训练理论、模式的价值、局限性及其应用策略.研究表明,当前足球训练实践的指导理论主要有行为主义理论和建构主义理论,分别对应形成了"直接式"与"情景式"两种训练模式.前者主要利用生物体的条件反射进行强化,对运动员掌握规范与娴熟的技术以及固定战术套路效果显著,但不利于运动员在复杂情景下的整体竞技能力及应变能力培养;后者主要利用运动员的主观能动性,对运动员的认知能力进行干预,对培养运动员的复杂战术能力与决策能力效果显著,但会降低技术学习的效率.因此,教练员在设计训练时,要根据训练目标、训练内容以及训练对象的水平灵活选择,.为不同性质的训练主题匹配合适的训练模式,以提高训练的针对性.

采用内容分析法,构建集"政策工具-政策制定主体-时间数量"一体化的校园足球三维分析框架,对2009—2018年国务院以及各部委发布的校园足球相关政策进行计量分析,并构建了我国校园足球政策的协同模型.研究表明,校园足球政策制定主体以单一部门为主,联合部门发文量较少,政策制定主体协同度仍需提升.在政策工具的使用上存在较大差异,政府偏向于环境型政策的使用,供给型政策比例有待提高,需求型政策相对匮乏.随着校园足球的深入发展,应该进一步提高政策制定主体的协同性,适当调整环境型政策工具,增加税收金融类;合理匹配供给型政策工具,加强校园足球的推动力;增加需求型政策工具,提高校园足球的拉动力.

Various factors of campus football policy implementation are analyzed by using literature research, logic analysis and other methods and combined with a series of policy documents and social environment of campus football, the Sabatir and Mazmanian policy implementation model.The study believes that the problem of campus football in China is complicated, the policy system is imperfect, the shortage of teachers and the lack of funds for implementation, the lack of linkage between the implementing agencies and the unclear responsibility, which makes low motivation and low recognition of the target groups, coupled with the unfavorable policy enforcement environment, and the supervision mechanism.And the evaluation system is not perfect, leading to policy implementation block.Therefore, we should change the ideological concepts of the target group, stimulate the internal motivation of the target group, clarify the implementation goals of the campus football policy, improve the supporting measures for policies, broaden the implementation resources of the policy, strengthen cooperation between the various executive departments, and establish a supervision system, improve the policy implementation mechanism and optimize the policy implementation environment.Thereby the efficiency of campus football policy implementation can be improved.

了解中学生逃避体育锻炼行为现状,构建并检验中学生逃避体育锻炼行为理论模型,以480名中学生为研究对象,对中学生逃避体育行为现状进行分析,通过分层回归、结构方程模型等方法对自主支持、自主动机、计划行为、自我效能、逃避意图与逃避行为的关系进行研究.结果发现,体育活动等级低于19分的学生占52.10%,逃避体育锻炼行为者中女生占56.40%,高于男生;逃避体育锻炼行为者的自主支持、相对自主动机指数、计划行为变量、自我效能感均低于坚持者,而逃避意图与逃避行为均高于坚持者;上述变量均能显著预测逃避意图与逃避行为,其中主观规范与主观行为控制感2个变量对逃避意图的影响最大;建立的逃避行为路径模型分别能够解释逃避意图的40%(男)和37%(女),能够解释逃避行为的9%(男)和14%(女),多群组分析表明模型不存在性别差异.结果说明:中学生群体存在较为严重的逃避体育锻炼行为,逃避群体中女性比例高于男性,建立的模型能够在一定程度上解释中学生逃避体育锻炼行为的成因.

This paper presents a time‐frequency analysis technique to assess quadriceps femoris muscle fatigue induced by cyclic dynamic contraction .10 male college students were selected to perform cycle ergometer experiment with 1 to 5 step increasing load from 50w to 200w + .The last 5 seconds sEMG signals during each load was acquired and then contraction section was cut out for time‐frequency analysis .Choi‐Williams distribution was used to obtain instantane‐ous power spectrum density and then to compute the instantaneous mean frequency (IMNF) and instantaneous median frequency (IMDF) .The results show that both IMNF and IMDF de‐creased approximately linearly with the increasing load after three load level ,and combined with the characteristics of that integrated EMG ( iEMG ) increased with the increasing load simulta‐neously ,which can identify fatigue degree induced by increasing different cycling loads .It was demonstrated that IMNF outperforms IMDF in computation efficiency so that it can be com‐bined with iEMG to form a united parameters which can assess muscle fatigue during cyclic dy‐namic contraction .