Kinematic and electromyographic comparisons between chin-ups and lat-pull down exercises

The purpose of this study was to compare kinematics and muscle activity between chin-ups and lat-pull down exercises and between muscle groups during the two exercises. Normalized electromyography (EMG) of biceps brachii (BB), triceps brachii (TB), pectoralis major (PM), latissimus dorsi (LD), rectus abdominus (RA), and erector spinae (ES) and kinematics of back, shoulder, and seventh cervical vertebrae (C7) was analysed during chin-ups and lat-pull down exercises. Normalized EMG of BB and ES and kinematics of shoulder and C7 for chin-ups were greater than lat-pull down exercises during the concentric phase (p < 0.05). For the eccentric phase, RA during lat-pull down exercises was greater than chin-ups and the kinematics of C7 during chin-ups was greater than lat-pull down exercises (p < 0.05). For chin-ups, BB, LD, and ES were greater than PM during the concentric phase, whereas BB and LD were greater than TB, and LD was greater than RA during the eccentric phase (p < 0.05). For lat-pull down exercise, BB and LD were greater than PM, TB, and ES during the concentric phase, whereas LD was greater than PM, TB, and BB during the eccentric phase (p < 0.05). Subsequently, chin-ups appears to be a more functional exercise.     

Reliability of EMG normalisation methods for upper-limb muscles

Abstract

The study investigated different electromyographic (EMG) normalisation methods for upper-limb muscles. This assessment aimed at comparing the EMG amplitude and the reliability of EMG values obtained with each method. Eighteen male tennis players completed isometric maximal voluntary contractions and dynamic strength exercises (push-ups and chin-ups) on three separate test sessions over at least 7 days. Surface EMG activity of nine upper body muscles was recorded. For each muscle, an analysis of variance for repeated measures was used to compare maximal EMG amplitudes between test conditions. The intra-class correlation coefficient, the coefficient of variation and the standard error of measurement were calculated to determine the EMG reliability of each condition. On the basis of a compromise between maximal EMG amplitude and high reliability, the chin-ups appeared to be the optimal normalisation method for M. latissimus dorsi, M. posterior deltoid, M. biceps brachii, M. flexor carpi radialis and M. extensor carpi radialis. The push-ups seemed relevant to normalise M. anterior deltoid and M. triceps brachii activity, while isometric maximal voluntary contraction remained the most appropriate method for M. pectoralis major and M. middle deltoid. Thus, original methods are proposed to normalise EMG signal of upper-limb muscles.     

Electromyographic Study of Selected Muscles Involved in Movements of Upper Arm at Scapulohumeral Joint

Abstract

This article presents an investigation, by means of electromyography, of the functions of the biceps brachii, the deltoideus, the latissimus dorsi, the pectoralis major, the serratus anterior, the cleido mastoideus, the teres major, the trapezius, and the triceps brachii (long head) in movements of the upper arm and the shoulder girdle at scapulo-humeral, acromioclavicular, and sternoclavicular joints. The procedure for collecting the data was established on the basis of records taken on twelve subjects; and the findings that are reported were based on 20 complete sets taken on five subjects.     

运动性肌肉疲劳过程中主动肌与拮抗肌sEMG相干性分析

目的:通过静态疲劳负荷实验过程中主动肌与拮抗肌sEMG的相干性分析探索运动性肌肉疲劳过程中中枢神经系统对主动肌与拮抗肌共神经输入(common neural inputs)同步支配的变化特征。方法:以10名健康男性青年志愿者为研究对象,记录受试者以50%MVC负荷强度静态屈肘运动诱发肌肉疲劳过程中主动肌肱二头肌与拮抗肌肱三头肌的sEMG,为考查疲劳因素对相干性分析结果的影响作用,对记录的sEMG按运动持续时间平均分为两段,分别对两段sEMG进行相干性分析处理。结果:在疲劳负荷实验过程中,肱二头肌与肱三头肌MF指标随运动持续时间表现出显著性的单调递减变化趋势。从相干性分析结果看,在beta频段和gamma频段内,运动后半段肱二头肌与肱三头肌sEMG相干函数值要明显小于运动前半段,而tremor频段内无显著性差异。结论:在50%MVC静态负荷屈肘运动致肌肉疲劳过程中,随着负荷运动持续时间的增加,中枢神经系统对主动肌肱二头肌与拮抗肌肱三头肌共神经输入同步支配下降,这可能是由于主动肌与拮抗肌脊髓运动神经元兴奋性及运动皮层对脊髓运动神经元激活能力随疲劳发展的下降不同步性及为维持既定的收缩负荷,中枢神经系统对主动肌与拮抗肌运动单位的募集策略采取不同的调节方式造成的。     

Whole-body vibration effects on the muscle activity of upper and lower body muscles during the baseball swing in recreational baseball hitters

The purpose of this study was to evaluate the effects of whole-body vibration (WBV) on the muscle recruitment of selected upper and lower body muscles during the baseball swing. Participants were recreationally trained males (n = 16, 22 +/- 2 years, 181.4 +/- 7.4 cm, 84.7 +/- 9.0 kg), with previous baseball experience. Subjects participated in three randomized sessions on separate days, consisting of three sets of five swings offa hitting tee. Exercises (upper and lower body dynamic and static movements) with or without WBVexposure were performed between swing sets. During each swing, the gastrocnemius, biceps femoris, gluteus maximus, pectoralis major, latissimus dorsi, and triceps brachii were evaluated for electromyographic (EMG) activity. EMG values were normalized to EMG measured during maximal voluntary isometric contraction. Statistical analysis revealed no significant differences in EMG activity across the three treatments. In addition, the results displayed a specific muscle recruitment order during the swing, starting with the lower body followed by the upper body muscles. This study was the first to report the recruitment order during the baseball swing. Although acute exposure to WBV did not significantly alter the muscle recruitment, these results may prove useful for practitioners looking to enhance baseball swing performance.     

我国优秀男子拳击运动员后手直拳击打环节相关肌群的EMG特征及其运动学分析

目的:研究我国优秀男子拳击运动员后手直拳出拳击打环节相关肌群的sEMG特征及其相应的运动学变化,为拳击专项力量训练提供参考.方法:通过表面肌电和三维红外高速摄像系统同步测试方法,采集6名高水平男子拳击运动员后手直拳出拳击打环节表面肌电和运动学的相关数据.结果:1)出拳击打环节,肌肉活动顺序为:腓肠肌→股二头肌→三角肌前束→肱三头肌→肱二头肌长头→肱桡肌.2)击打过程中三角肌前束、肱二头肌和肱三头肌肉在相应时间位置上出现明显的预激活和共收缩现象.3)肌肉做功百分比排序为:三角肌前束＞肱三头肌＞股二头肌＞腓肠肌＞肱桡肌＞肱二头肌长头,aEMG计算结果与肌肉做功百分比保持相一致的趋势.4)肩关节、上臂环节质心和拳心速度的峰值在击打过程中呈现次序性.结论:拳击后直拳出拳击打环节所选肌肉活动呈现从下肢向上肢激活的次序性.击打过程中三角肌前束、肱二头肌和肱三头肌肉在相应时间位置上出现的预激活和共收缩现象可能是反映运动员技术水平和特点的指标.在肌肉做功百分比和aEMG方面,三角肌前束、肱三头肌和股二头肌在动作过程中表现出相对重要的地位.上肢相关肌群的活动次序与肩关节、上臂环节质心和拳心速度变化的时序性有着合理的解剖学相关,是产生上肢开放链鞭打动作的根本原因.     

The acute effects of bodyweight suspension exercise on muscle activation and muscular fatigue

This investigation examined effects of two exercise modes (barbell, BB; bodyweight suspension, BWS) on muscle activation, resistance load, and fatigue. During session one, nine resistance-trained males completed an elbow flexion one-repetition maximum (1RM). During sessions two and three, subjects completed standing biceps curls to fatigue at 70% 1RM utilizing a randomized exercise mode. Surface electromyography (sEMG) recorded muscle activation of the biceps brachii, triceps brachii, anterior deltoid, posterior deltoid, rectus abdominis, and erector spinae. BWS resistance load was measured using a force transducer. Standing maximal voluntary isometric contractions of the elbow flexors recorded at 90° were used to determine the isometric force decrement and rate of fatigue (ROF) during exercise. sEMG and resistance load data were divided into 25% contraction duration bins throughout the concentric phase. BWS resulted in a 67.7?±?7.4% decline in resistance load throughout the concentric phase (p?≤?0.05). As a result, BB elicited higher mean resistance loads (31.4?±?4.0?kg) and biceps brachii sEMG (84.7?±?27.8% maximal voluntary isometric contractions, MVIC) compared with BWS (20.4?±?3.4?kg, 63.4?±?21.6% MVIC). No difference in rectus abdominis or erector spinae sEMG was detected between exercise modes. Isometric force decrement was greater during BWS (?21.7?±?7.0?kg) compared with BB (?14.9?±?4.7?kg); however, BB (?3.0?±?0.8?kg/set) resulted in a steeper decline in ROF compared with BWS (?1.7?±?0.6?kg/set). The variable resistance loading and greater isometric force decrement observed suggest that select BWS exercises may resemble variable resistance exercise more than previously considered.     

优秀乒乓球运动员肘关节等动屈伸运动时拮抗肌共激活现象研究

目的:研究优秀乒乓球运动员和普通在校大学生肘关节拮抗肌活动在等动屈伸过程中的差异。方法:以8名优秀乒乓球运动员和8名普通高校大学生为研究对象,利用Biodex等动测试仪和Noraxon表面肌电仪记录上肢肘关节等动屈伸过程中作为拮抗肌的肱二头肌和肱三头肌的力量特征和表面肌电信号特征。肘关节伸肌和屈肌分别在最大等长收缩、15°/s、30°/s、60°/s、120°/s、180°/s、240°/s条件下进行3次最大等动离心屈伸运动。以标准化的均方根振幅(RMS)和标准化的峰值力矩作为评价指标。结果:对于大学生和优秀乒乓球运动员来说,随着肘关节速度的增加,两组受试者的屈伸肌力矩都呈下降趋势,大学生表现为速度大于60°/s时伸肌力矩大于屈肌力矩(P<0.05),优秀乒乓球运动员表现为伸肌力矩低于屈肌力矩,但没有统计学差别(P>0.05)。大学生和优秀乒乓球运动员都表现为在向心收缩时不同速度下随着主动肌力矩下降,拮抗肌激活水平表现为逐渐增高,且所有线性拟合系数r2>0.7。优秀乒乓球运动员拮抗肌肱三头肌的激活水平(在MVC时:10.1%±5.2%,240°/s时:15.1%±6.6%)要显著低于普通高校大学生(MVC时:29.3%±8.8%,240°/s时:38.0%±15.1%)。而作为拮抗肌的肱二头肌激活水平在普通大学生和优秀乒乓球运动员之间没有统计学差异(P>0.05)。优秀乒乓球运动员拮抗肌/主动肌肌电活动比要显著低于普通大学生(P<0.05)。结论:与普通大学生相比,优秀乒乓球运动员肘关节拮抗肌肱三头肌的激活水平要更低,这可能是优秀乒乓球运动员对肘关节周围肌肉进行长期训练的结果。而两者拮抗肌肱二头肌激活水平没有统计学差异,其原因可能是由于两者在日常活动中肱二头肌作为拮抗肌经常为了克服地心引力受到同样的刺激造成的。     

Isometric training with maximal co-contraction instruction does not increase co-activation during exercises against external resistances

Abstract

The present investigation verified that strength is improved by a training programme consisting of repetitions of maximal isometric voluntary co-contractions without increasing co-activations during contractions against external resistances. Ten participants performed 12 training sessions (four sets of 6 × 4 second maximal isometric co-contraction of the elbow flexor and extensors, 3 days a week for 4 weeks). Surface electromyograms of triceps and biceps brachii were collected during maximal voluntary isometric elbow flexion and extension against a force transducer. Maximal voluntary isometric force increased significantly after training, by 13.8 ± 6.0% (extension) and 9.6 ± 9.5% (flexion), but the observed increases in EMG of agonist muscles during maximal voluntary contraction were not significant. No significant changes in the levels of co-activation of the elbow flexors and extensors were observed. No significant change was observed for all the parameters in a control group of ten participants. These results indicated that the strength improvements after co-contraction training occur without increases in co-activation level.     

Upper limb and trunk muscle activity patterns during seated and standing cycling

The objective of this study is to clarify the functional roles of upper limb muscles during standing and seated cycling when power output increases. We investigated the activity of seven upper limb and trunk muscles using surface electromyography (EMG). Power outputs ranged from ~100–700 W with a pedalling frequency of 90 revolution per minute. Three-dimensional handle and pedal forces were simultaneously recorded. Using non-negative matrix factorisation, we extracted muscle synergies and we analysed the integrated EMG and EMG temporal patterns. Most of the muscles showed tonic activity that became more phasic as power output increased. Three muscle synergies were identified, associated with (i) torso stabilisation, (ii) compensation/generation of trunk accelerations and (iii) upper body weight support. Synergies were similar for seated and standing positions (Pearson’s r > 0.7), but synergy #2 (biceps brachii, deltoidus and brachioradialis) was shifted forward during the cycle (~7% of cycle). The activity levels of synergy #1 (latissimus dorsi and erector spinae) and synergy #2 increased markedly above ~500 W (i.e., ~+40–70% and +130–190%) and during periods corresponding to ipsi- and contralateral downstrokes, respectively. Our study results suggest that the upper limb and trunk muscles may play important roles in cycling when high power outputs are required.     

Influence of short-term inertial training on swimming performance in young swimmers

The aim of this study was to evaluate the influence of dry-land inertial training (IT) on muscle force, muscle power, and swimming performance. Fourteen young, national-level, competitive swimmers were randomly divided into IT and control (C) groups. The experiment lasted four weeks, during which time both groups underwent their regular swimming training. In addition, the IT group underwent IT using the Inertial Training Measurement System (ITMS) three times per week. The muscle groups involved during the upsweep phase of the arm stroke in front crawl and butterfly stroke were trained. Before and after training, muscle force and power were measured under IT conditions. Simultaneously with the biomechanical measurements on the ITMS, the electrical activity of the triceps brachii was registered. After four weeks of training, a 12.8% increase in the muscle force and 14.2% increase in the muscle power (p?<?.05) were noted in the IT group. Moreover, electromyography amplitude of triceps brachii recorded during strength measurements increased by 22.7% in the IT group. Moreover, swimming velocity in the 100?m butterfly and 50?m freestyle improved significantly following the four weeks of dry-land IT (?1.86% and ?0.76%, respectively). Changes in the C group were trivial. Moreover, values of force and power registered during the ITMS test correlated negatively with the 100?m butterfly and 50?m freestyle swimming times (r value ranged from ?.80 to ?.91). These results suggest that IT can be useful in swimming practice.     

Upper limb muscle fatigue during prolonged Boccia games with underarm throwing technique

This study investigated the acute fatigue pattern in neuromuscular activity after a simulated Boccia game and the effect of fatigue pattern on sport performance. Nine elite Boccia athletes were tested before, during, and after a simulated game. Maximum ball speed was captured with video, and the target hitting rate and rating of perceived exertion (RPE) score were collected and analyzed. Electromyography signals from the upper trapezius, anterior deltoid, posterior deltoid, biceps brachii, triceps brachii, and wrist extensor muscles were collected by surface electrode and were evaluated with mean power frequency (MPF). Only the upper trapezius muscle showed fatigue as demonstrated by a reduction of MPF of 8% (p = 0.027) when comparing the first and last throws in a simulated game. Subjective RPE score increased during the game (118%, p = 0.004), and sports performance in terms of maximum ball speed (-12%, p = 0.004) and target hitting rate (-25%, p = 0.004) also deteriorated. In conclusion, fatigue on the upper trapezius muscle was demonstrated in elite Boccia athletes following a prolonged Boccia game and may have affected Boccia performance. Preventative measures against upper trapezius muscle fatigue and endurance training for synergists of the upper trapezius muscle may be considered in future studies.     

Effects of latissimus dorsi length on shoulder flexion in canoeists,swimmers, rugby players,and controls

BackgroundShoulder flexion requires an optimal length of the latissimus dorsi muscle in order to allow full lateral rotation of the humerus and upward scapular rotation. If shoulder flexion (in an externally rotated position) is restricted, this may predispose the individual to shoulder pathology. Sports such as swimming and canoeing have increased shoulder injuries and require high levels of latissimus dorsi muscle activity, which may create muscle hypertrophy and increased stiffness, resulting in a loss of muscle length. The objective of this study was to investigate if differences are present in shoulder flexion in internally and externally rotated positions across different sports (swimming, canoeing, and rugby) and a non-sporting control group.MethodsOne hundred subjects (40 physically active controls, 25 professional Rugby Union players, 20 elite, national-level canoeists (slalom), and 15 elite, national-level swimmers) participated in this study. Shoulder flexion range of motion was measured using a standard goniometer, with the arm elevated in either full external or internal rotation.ResultsA significant difference in shoulder flexion range was observed between canoeists and swimmers, canoeists and controls, rugby players and canoeists, rugby players and swimmers, and controls and swimmers in the external rotation position (p < 0.017), but not between controls and rugby players (p = 0.12). For the internal rotation position, swimmers significantly differed from canoeists, rugby players, and controls (p < 0.017), but there were no significant differences between rugby players, canoeists, and controls (p > 0.07).ConclusionThis study found that the length of the latissimus dorsi differs between sports and controls in accordance with the specific physical demands of their sport.     

古典式摔跤运动员提抱技术的腰背表面肌电分析研究

通过解剖学动作分析、表面肌电测试法,对古典式摔跤运动员使用提抱技术时的表面肌电进行实验测试,分析古典式摔跤运动员使用提抱技术的腰背肌肉协同变化过程。结果显示：1）在使用跪撑提抱技术时腰背肌肉中背阔肌做功百分比最高,平均为350k;2）主动肌的激活顺序为竖脊肌、背阔肌,肩胛提肌;3）在提抱技术中拮抗肌发挥着重要作用,且高水平运动员在提抱技术发力阶段;拮抗肌放电量与主动肌放电量有同步明显上升趋势;4）运动员应加强主动肌与拮抗肌的快速力量、反应力量和力量耐力训练,特别是针对性地进行专项力量训练。     

System approach to games and competitive playing

Abstract

The force enhancement of muscle twitch contraction after a maximal voluntary contraction (MVC) has been defined as post-activation potentiation. However, the effects of post-activation potentiation on ballistic movements have not been studied extensively, or the underlying neurophysiologycal mechanism. In the current study, we examined post-activation potentiation and spinal H-reflex excitability in the soleus muscle. Mechanical power during explosive ballistic plantar flexions was measured in 14 males before and after 5 s, 4 min, and 10 min of isometric conditioning (EPF_pre, EPF_5s, EPF_4min, EPF_10min, respectively). Four sessions corresponding to four different protocols of isometric conditioning were conducted. The protocols were different in the intensity (10% vs. 100% of MVC) and duration (7 vs. 10 s) of the isometric conditioning. The results showed a significant enhancement in mechanical power in EPF_4min compared with EPF_pre, only when the isometric conditioning was performed at 100% of MVC for 10 s. No significant changes were observed in the H-related parameters (e.g amplitude, threshold, H/M ratio) after the isometric conditioning. Our results show that to obtain a post-activation potentiation during explosive ballistic movements, the intensity and duration of the isometric conditioning must be controlled. Moreover, the improvement in mechanical power is not related to spinal H-reflex excitability.     

浙江省优秀青年男子排球运动员强攻扣球手臂挥摆动作运动学与表面肌电学分析

目的:探讨青年男子排球运动员强攻扣球技术动作的关键;方法:使用两台高速摄像机和表面肌电仪对7名青年男子排球运动员强攻扣球手臂挥摆动作进行运动学和表面肌电学同步分析;结果:运动员在引臂后拉期主要由三角肌前束和三角肌后束完成,在甩臂击打期和击打作用期,肱三头肌、背阔肌、前臂屈腕的这些主动肌的电活动明显增强,起拮抗作用的肱二头肌和前臂伸腕肌群的电活动也非常强烈,而且,在各个阶段每对主动肌/拮抗肌表现为较好的协调性;背弓角为130.2°±4.7°、挥臂角为113.2°±6.1°、最后出手球速为23.5±0.7 m/s;背弓角,挥臂角与最后出手球速的相关系数r分别为-0.512(P<0.05)和0.484(P<0.05);结论:在强攻扣球手臂挥摆过程中,扣球臂的拮抗肌发挥着重要作用,起跳后挥臂的背弓角和挥臂角是影响最后出手球速的主要因素。     

Muscle activity and accuracy of performance of the smash stroke in badminton with reference to skill and practice

The aims of this study were to establish the temporal-spatial relationship between muscle activity and the smash stroke of skilled badminton players and to assess performance accuracy using the ellipse of constant distance. We recorded the surface electromyographic (EMG) activity of selected superficial muscles of the stroking arm and shoulder--flexor carpi ulnalis, extensor carpi radialis, triceps brachii (lateral head), biceps brachii and trapezius (upper)--during the badminton smash. In the first part of the study, we examined the characteristics of muscle function and performance accuracy of skilled and unskilled individuals during the badminton smash. Five well-trained badminton players and five students with no experience of badminton were asked to smash a shuttle as hard as they could towards a vertical square target 4 m away, repeating the stroke 30 times. In general, the skilled players showed a more constant time from peak electromyographic amplitude to impact. Immediately after impact, the electromyographic activity of the triceps brachii and flexor carpi radialis of the skilled players decreased; in the unskilled participants, however, it continued until well after impact. The area of the ellipse of constant distance and the off-target distance, which were used as indices of performance accuracy, were smaller for the skilled than for the unskilled participants. In the second part of the study, one skilled and one unskilled participant performed 100 trials a day for 6 days. The time from peak electromyographic amplitude to impact in the extensor carpi radialis and flexor carpi ulnalis was more variable in the unskilled than in the skilled participant even after 6 days of practice, but the proximal muscles of the unskilled participant had a similar pattern of activity to that of the skilled player. Thus, controlling the distal muscles appears to be important for achieving accurate performance of the smash in badminton.     

Muscle activity and accuracy of performance of the smash stroke in badminton with reference to skill and practice

The aims of this study were to establish the temporal-spatial relationship between muscle activity and the smash stroke of skilled badminton players and to assess performance accuracy using the ellipse of constant distance. We recorded the surface electromyographic (EMG) activity of selected superficial muscles of the stroking arm and shoulder - flexor carpi ulnalis, extensor carpi radialis, triceps brachii (lateral head), biceps brachii and trapezius (upper) - during the badminton smash. In the first part of the study, we examined the characteristics of muscle function and performance accuracy of skilled and unskilled individuals during the badminton smash. Five welltrained badminton players and five students with no experience of badminton were asked to smash a shuttle as hard as they could towards a vertical square target 4 m away, repeating the stroke 30 times.In general, the skilled players showed a more constant time from peak electromyographic amplitude to impact. Immediately after impact, the electromyographic activity of the triceps brachii and flexor carpi radialis of the skilled players decreased; in the unskilled participants, however, it continued until well after impact. The area of the ellipse of constant distance and the off-target distance, which were used as indices of performance accuracy, were smaller for the skilled than for the unskilled participants. In the second part of the study, one skilled and one unskilled participant performed 100 trials a day for 6 days. The time from peak electromyographic amplitude to impact in the extensor carpi radialis and flexor carpi ulnalis was more variable in the unskilled than in the skilled participant even after 6 days of practice, but the proximal muscles of the unskilled participant had a similar pattern of activity to that of the skilled player. Thus, controlling the distal muscles appears to be important for achieving accurate performance of the smash in badminton.     

The effect of a psyching strategy on neuromuscular activation and force production in strength-trained men

Force and electromyographic (EMG) activity of the biceps and triceps brachii were measured in 15 strength-trained men during maximal isometric action of the forearm flexors, with the elbow at 90 degrees, following 20-s periods of psyching (PSY), reading aloud (RA), and mental arithmetic (MA). Perceived arousal and attentional focus ratings for PSY were greater than those obtained for RA and MA, which were undifferentiated. Perceived effort, biceps and triceps EMG, and maximal force did not differ across conditions. Therefore, in highly trained men under conditions of brief exertion, when the biomechanics of the muscular action were controlled, psyching resulted in a perception of enhanced readiness but did not influence force or muscular activation differently from psychological states that were preceded by distraction.     

Agonist and Antagonist Muscle EMG Activity Pattern Changes with Skill Acquisition

Abstract

The purpose of this research was to investigate the modifications in the control of the biceps brachii (agonist) and triceps brachii (antagonist) muscles during the learning of two elbow flexion tasks in sixteen college-age women. A positioning and a coincidence task were each performed at 40° and 200° per second angular velocity while bipolar surface electrodes recorded the electromyographic (EMG) activity of the muscles involved. Data on the EMG activity, angular kinematics, and timing and angular displacement error were quantified and subjected to statistical analyses. The results of the error analyses indicated that subjects did learn the various tasks over the 120 trials. Because there were no significant changes in the angular velocity patterns over trials, the EMG activity modifications are suggested to reflect differences in the control of the muscles monitored during the movements. In addition, EMG activity pattern modifications which occurred in discrete portions of the movements in both muscles indicate an increased cocontraction of the opposing muscles as subjects learned the tasks. Temporal periods in which modifications were observed appear to represent the critical periods in each movement task.