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1.
Objective: The acute responses to resistance training (RT) between males and females are poorly understood, especially from a neural perspective. Therefore, we aimed to compare the corticospinal and intracortical responses during fatigue and recovery following RT.

Methods: Twenty-two participants (12M, 10F) completed one-session of RT (3?×?12 repetition maximum) unilateral leg extensions with 60?s recovery. Single- and paired-pulse transcranial magnetic stimulation measured changes in the motor-evoked potential (MEP), corticospinal silent period (CSP), CSP/MEP ratio, and intracortical facilitation/inhibition (ICF, SICI). The maximal compound wave (MMAX) measured peripheral excitability of the rectus femoris (RF) and maximal voluntary isometric contraction (MVIC) neuromuscular function of the leg extensors. Measures were taken immediately post, 30?min, 1 and 6?h post-training.

Results: A significantly greater increase in MEP/MMAX ratio (p?=?.005) was observed for females immediately post-training compared to males. While no sex differences in MEP/MMAX ratio was observed at 30?min and 1?h post-training, a greater MEP/MMAX ratio for males was observed at 30?min (p?p?=?.003). CSP trended to decrease for males compared to females immediately post-training (d?=?1.93). MVIC was decreased post-training for males; 14.22% and females; 14.16% (P?MAX reduced at 30?min for both groups (P?P?>?.05).

Conclusion: The net output of corticospinal excitability is similar between males and females during fatigue. However, the mechanism in which this is modulated (increased MEP, decreased CSP) appears to be sex-specific.  相似文献   

2.
Surface electromyographic (EMG) signals were recorded from the hamstring muscles during six sets of submaximal isokinetic (2.6 rad x s(-1)) eccentric (11 men, 9 women) or concentric (6 men, 4 women) contractions. The EMG per unit torque increased during eccentric (P < 0.01) but not during concentric exercise. Similarly, the median frequency increased during eccentric (P < 0.01) but not during concentric exercise. The EMG per unit torque was lower for submaximal eccentric than maximum isometric contractions (P < 0.001), and lower for submaximal concentric than maximum isometric contractions (P < 0.01). The EMG per unit torque was lower for eccentric than concentric contractions (P < 0.05). The median frequency was higher for submaximal eccentric than maximum isometric contractions (P < 0.001); it was similar, however, between submaximal concentric and maximum isometric contractions (P = 0.07). Eccentric exercise resulted in significant isometric strength loss (P < 0.01), pain (P < 0.01) and muscle tenderness (P < 0.05). The greatest strength loss was seen 1 day after eccentric exercise, while the most severe pain and muscle tenderness occurred 2 days after eccentric exercise. A lower EMG per unit torque is consistent with the selective recruitment of a small number of motor units during eccentric exercise. A higher median frequency during eccentric contractions may be explained by selective recruitment of fast-twitch motor units. The present results are consistent with the theory that muscle damage results from excessive stress on a small number of active fibres during eccentric contractions.  相似文献   

3.
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.  相似文献   

4.
Surface electromyographic (EMG) signals were recorded from the hamstring muscles during six sets of submaximal isokinetic (2.6 rad s -1 ) eccentric (11 men, 9 women) or concentric (6 men, 4 women) contractions. The EMG per unit torque increased during eccentric (P < 0.01) but not during concentric exercise. Similarly, the median frequency increased during eccentric (P < 0.01) but not during concentric exercise. The EMG per unit torque was lower for submaximal eccentric than maximum isometric contractions (P < 0.001), and lower for submaximal concentric than maximum isometric contractions (P < 0.01). The EMG per unit torque was lower for eccentric than concentric contractions (P < 0.05). The median frequency was higher for submaximal eccentric than maximum isometric contractions (P < 0.001); it was similar, however, between submaximal concentric and maximum isometric contractions (P = 0.07). Eccentric exercise resulted in significant isometric strength loss (P < 0.01), pain (P < 0.01) and muscle tenderness (P < 0.05). The greatest strength loss was seen 1 day after eccentric exercise, while the most severe pain and muscle tenderness occurred 2 days after eccentric exercise. A lower EMG per unit torque is consistent with the selective recruitment of a small number of motor units during eccentric exercise. A higher median frequency during eccentric contractions may be explained by selective recruitment of fast-twitch motor units. The present results are consistent with the theory that muscle damage results from excessive stress on a small number of active fibres during eccentric contractions.  相似文献   

5.
The aim of this study was to examine the metabolic demand and extent of muscle damage of eccentric cycling targeting knee flexor (FLEX) and knee extensor (EXT) muscles. Methods: Eight sedentary men (23.3?±?0.7?y) underwent two eccentric cycling sessions (EXT and FLEX) of 30?min each, at 60% of the maximum power output. Oxygen consumption (VO2), heart rate (HR) and rated perceived exertion (RPE) were measured during cycling. Countermovement and squat jumps (CMJ and SJ), muscle flexibility, muscle soreness and pain pressure threshold (PPT) of knee extensor and flexor muscles were measured before, immediately after and 1–4 days after cycling. Results: FLEX showed greater VO2 (+23%), HR (+14%) and RPE (+18%) than EXT. CMJ and SJ performance decreased similarly after cycling. Muscle soreness increased more after EXT than FLEX and PPT decreased in knee extensor muscles after EXT and decreased in knee flexor muscles after FLEX. Greater loss of muscle flexibility in knee flexor muscles after FLEX was observed. Conclusion: Eccentric cycling of knee flexor muscles is metabolically more demanding than that of knee extensors, however muscle damage induced is similar. Knee flexors experienced greater loss of muscle flexibility possibly due to increased muscle stiffness following eccentric contractions.  相似文献   

6.
Abstract

Fifteen highly skilled sprinters were filmed while running at maximum velocity. The results were digitized and computer processed with interest focused on the muscle moments generated about the hip, knee, and ankle of the ground leg. Muscle activity about the hip consisted of extensor (concentric) dominance from foot descent, through foot strike, and into mid-support. Muscle dominance shifted to the hip flexors (eccentric) during mid-support and continued through takeoff. Muscle dominance at the knee demonstrated a pattern of flexor (eccentric, then concentric) dominance from foot descent through foot strike and into mid-support. Knee extensors (eccentric, then concentric) then achieved dominance through takeoff. During the later stages of takeoff, the dominance decreased or reversed briefly to flexor (eccentric) activity prior to a period of minimal activity following the toe-off position. From a period of minimal activity prior and subsequent to ground contact, the plantar flexors (eccentric, then concentric) of the foot were dominant throughout the ground phase. Qualitatively, the unexpected knee flexor dominance during foot strike was generated to limit the braking action created during this portion of ground contact. The unanticipated hip flexor dominance during takeoff served to rotate the upper body forward and into the approaching air phase. In addition, both of these actions allowed efficient use of the two-joint muscles of the leg during the critical phases of ground contact. Finally, the minimizing or reversing of the knee extensor dominance during the later stages of takeoff served to protect the joint from injury. Quantitatively, the magnitude of hip extensor/knee flexor activity during foot strike was significantly related (r = .70, p = .01) to the prior occurrences of related leg injury in the subjects.  相似文献   

7.
This study compared the muscular activation of the pectoralis major, anterior deltoid and triceps brachii during a free-weight barbell bench press performed at 0°, 30°, 45° and –15° bench angles. Fourteen healthy resistance trained males (age 21.4 ± 0.4 years) participated in this study. One set of six repetitions for each bench press conditions at 65% one repetition maximum were performed. Surface electromyography (sEMG) was utilised to examine the muscular activation of the selected muscles during the eccentric and concentric phases. In addition, each phase was subdivided into 25% contraction durations, resulting in four separate time points for comparison between bench conditions. The sEMG of upper pectoralis displayed no difference during any of the bench conditions when examining the complete concentric contraction, however differences during 26–50% contraction duration were found for both the 30° [122.5 ± 10.1% maximal voluntary isometric contraction (MVIC)] and 45° (124 ± 9.1% MVIC) bench condition, resulting in greater sEMG compared to horizontal (98.2 ± 5.4% MVIC) and –15 (96.1 ± 5.5% MVIC). The sEMG of lower pectoralis was greater during –15° (100.4 ± 5.7% MVIC), 30° (86.6 ± 4.8% MVIC) and horizontal (100.1 ± 5.2% MVIC) bench conditions compared to the 45° (71.9 ± 4.5% MVIC) for the whole concentric contraction. The results of this study support the use of a horizontal bench to achieve muscular activation of both the upper and lower heads of the pectoralis. However, a bench incline angle of 30° or 45° resulted in greater muscular activation during certain time points, suggesting that it is important to consider how muscular activation is affected at various time points when selecting bench press exercises.  相似文献   

8.
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.  相似文献   

9.
跳远起跳肌肉专项能力生物力学研究   总被引：3，自引：0，他引：3  
王琨  魏文仪 《体育科学》2005,25(1):42-45
运用生物力学理论和实验研究方法 ,对跳远运动员起跳过程中起跳腿肌肉群表现出的专项能力特点进行研究。结果表明 ,髋关节伸肌群离心收缩能力对起跳十分重要 ;起跳表现出“前支撑蹬伸”特征 ;起跳过程中膝关节伸肌群的主动向心收缩能力对人体产生必要制动和适宜的腾起垂直速度具有重要意义 ;起跳初始阶段 (起跳过程 8%的时间里 )膝关节产生较大的屈肌力矩 ,即表现出膝关节屈肌群的主动收缩。  相似文献   

10.
篮、排球运动员下肢3关节肌等速测试的对比研究   总被引：32，自引：3，他引：29  
虞重干  郭权 《体育科学》2000,20(1):73-75,88
用Cybex等速测力系统对篮排球运动员进行了下肢3关节力量测试,结果表明两项目运动员下肢3关节肌力的主要差别在于膝关节伸肌离心收缩能力和膝关节屈肌向心收缩能力,在运动实践中可能表现为在起跳过程中的缓冲能力的差异。  相似文献   

11.
Fatigue represents a reduction in the capability of muscle to generate force. The aim of the present study was to establish the effects of exercise that simulates the work rate of competitive soccer players on the strength of the knee extensors and knee flexors. Thirteen amateur soccer players (age 23.3+/-3.9 years, height 1.78+/-0.05 m, body mass 74.8+/-3.6 kg; mean+/-s) were tested during the 2000-2001 soccer season. Muscle strength of the quadriceps and hamstrings was measured on an isokinetic dynamometer. A 90 min soccer-specific intermittent exercise protocol, incorporating a 15 min half-time intermission, was developed to provide fatiguing exercise corresponding in work rate to a game of soccer. The exercise protocol, performed on a programmable motorized treadmill, consisted of the different intensities observed during soccer match-play (e.g. walking, jogging, running, sprinting). Muscle strength was assessed before exercise, at half-time and immediately after exercise. A repeated-measures analysis of variance showed significant reductions (P < 0.001) in peak torque for both the quadriceps and hamstrings at all angular velocities (concentric: 1.05, 2.09, 5.23 rad x s(-1); eccentric: 2.09 rad x s(-1)). The peak torque of the knee extensors (KE) and knee flexors (KF) was greater before exercise [KE: 232+/-37, 182+/-34, 129+/-27, 219+/-41 N x m at 1.05, 2.09 and 5.23 rad x s(-1) (concentric) and 2.09 rad x s(-1) (eccentric), respectively; KF: 126+/-20, 112+/-19, 101+/-16, 137+/-23 N x m] than at half-time (KE: 209+/-45, 177+/-35, 125+/-36, 214+/-43 N x m; KF: 114+/-31, 102+/-20, 92+/-15, 125+/-25 N x m) and greater at half-time than after exercise (KE: 196+/-43, 167+/-35, 118+/-24, 204+/-43 N x m; KF: 104+/-25, 95+/-21, 87+/-13, 114+/-27 N x m). For the hamstrings:quadriceps ratio, significant changes were found (P < 0.05) for both legs, the ratio being greater before than after exercise. For fast:slow speed and left:right ratios, no significant changes were found. We conclude that there is a progressive reduction in muscle strength that applies across a range of functional characteristics during exercise that mimics the work rate in soccer.  相似文献   

12.
Electromyographic analysis of repeated bouts of eccentric exercise   总被引：1，自引：0，他引：1  
The repeated bout effect refers to the protective effect provided by a single bout of eccentric exercise against muscle damage from a similar subsequent bout. The aim of this study was to determine if the repeated bout was associated with an increase in motor unit activation relative to force production, an increased recruitment of slow-twitch motor units or increased motor unit synchronization. Surface electromyographic (EMG) signals were recorded from the hamstring muscles during two bouts of submaximal isokinetic (2.6 rad x s(-1)) eccentric (11 men, 9 women) or concentric (6 men, 4 women) contractions separated by 2 weeks. The EMG per unit torque and median frequency were analysed. The initial bout of eccentric exercise resulted in strength loss, pain and muscle tenderness, while the repeated eccentric bout resulted in a slight increase in strength, no pain and no muscle tenderness (bout x time effects, P < 0.05). Strength, pain and tenderness were unaffected by either bout of concentric exercise. The EMG per unit torque and median frequency were not different between the initial and repeated bouts of eccentric exercise. The EMG per unit torque and median frequency increased during both bouts of eccentric exercise (P < 0.01) but did not change during either concentric bout. In conclusion, there was no evidence that the repeated bout effect was due to a neural adaptation.  相似文献   

13.
Previous studies analysing electromyograms (EMGs) from indwelling electrodes have indicated that fast-twitch motor units are selectively recruited for low-intensity eccentric contractions. The aim of this study was to compare the frequency content of surface EMGs from quadriceps muscles during eccentric and concentric contractions at various contraction intensities. Electromyograms were recorded from the rectus femoris, vastus lateralis and vastus medialis muscles of 10 men during isokinetic (1.05 rad x s(-1)) eccentric and concentric knee extension contractions at 25%, 50%, 75% and 100% of maximal voluntary contraction (MVC) for each contraction mode. Additionally, isometric contractions (70 degrees) were performed at each intensity. The mean frequency and root mean square (RMS) of the surface EMG were computed. Mean frequency was higher for eccentric than concentric contractions at 25% (P < 0.01), 50% (P < 0.01) and 75% (P < 0.05) but not at 100% MVC. It increased with increasing contraction intensity for isometric (P < 0.001) and concentric (P < 0.01) contractions but not for eccentric contractions (P = 0.27). The EMG amplitude (RMS) increased with increasing contraction intensity similarly in each contraction mode (P < 0.0001). Higher mean frequencies for eccentric than concentric contractions at submaximal contraction intensities is consistent with more fast-twitch motor units being active during eccentric contractions.  相似文献   

14.
Abstract

This study investigated the effects of knee localised muscle damage on running kinematics at varying speeds. Nineteen young women (23.2 ± 2.8 years; 164 ± 8 cm; 53.6 ± 5.4 kg), performed a maximal eccentric muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60 rad · s-1. Lower body kinematics was assessed during level running on a treadmill at three speeds pre- and 48 h after. Evaluated muscle damage indices included isometric torque, muscle soreness and serum creatine kinase activity. The results revealed that all indices changed significantly after exercise, indicating muscle injury. Step length decreased and stride frequency significantly increased 48 h post-exercise only at the fastest running speed (3 m · s-1). Support time and knee flexion at toe-off increased only at the preferred transition speed and 2.5 m · s-1. Knee flexion at foot contact, pelvic tilt and obliquity significantly increased, whereas hip extension during stance-phase, knee flexion during swing-phase, as well as knee and ankle joints range of motion significantly decreased 48 h post-exercise at all speeds. In conclusion, the effects of eccentric exercise of both knee extensors and flexors on particular tempo-spatial parameters and knee kinematics of running are speed-dependent. However, several pelvic and lower joint kinematics present similar behaviour at the three running speeds examined. These findings provide new insights into how running kinematics at different speeds are adapted to compensate for the impaired function of the knee musculature following muscle damage.  相似文献   

15.
短跑途中跑支撑阶段支撑腿关节肌肉生物力学特性的研究   总被引：5，自引：1，他引：4  
采用测力、测角加速度和多机多分辨拍摄技术对短跑途中跑支撑阶段肌肉动力学特征进行关节内力矩的计算与分析。研究表明，运动员踝关节跖屈肌的最大力矩与跑的速度呈显著相关；膝关节的伸肌在接近一半的支撑时间内是做离心收缩，离心收缩肌力矩的峰值要高于向心收缩的肌力矩峰值，离地前20％时刻膝关节屈肌起重要作用；髋关节在支撑阶段存在关节屈伸肌群交替工作，在着地后瞬间有较大的屈肌力矩，在离地前髋关节伸肌起重要作用，支撑阶段下肢关节肌肉快速退让性的离心收缩与主动收缩起同样重要的作用。  相似文献   

16.
It is currently unclear how football participation affects knee-joint muscle balance, which is widely considered a risk factor for hamstrings injury. This study compared the angle-specific functional hamstring-to-quadriceps (H:Q) ratio (hamstrings eccentric torque as a ratio of quadriceps concentric torque at the same knee-joint angle) of football players with recreationally active controls. Ten male footballers and 14 controls performed maximal voluntary isometric and isovelocity concentric and eccentric contractions (60, 240 and 400° s?1) of the knee extensors and flexors. Gaussian fitting to the raw torque values was used to interpolate torque values for knee-joint angles of 100–160° (60° s?1), 105–160° (240° s?1) and 115–145° (400° s?1). The angle-specific functional H:Q ratio was calculated from the knee flexors eccentric and knee extensors concentric torque at the same velocity and angle. No differences were found for the angle-specific functional H:Q ratio between groups, at any velocity. Quadriceps and hamstrings strength relative to body mass of footballers and controls was similar for all velocities, except concentric knee flexor strength at 400° s?1 (footballers +40%; P < 0.01). In previously uninjured football players, there was no intrinsic muscle imbalance and therefore the high rate of hamstring injuries seen in this sport may be due to other risk factors and/or simply regular exposure to a high-risk activity.  相似文献   

17.
通过高速摄影、表面肌电图（sEMG）测量以及等速肌力测试等方法对12名体育专业男生进行研究，获取踝关节主要屈伸肌（胫骨前肌和腓肠肌）等速肌力与sEMG之间的关系，以此说明用sEMG来直接评价肌肉用力情况时需进行标准化的必要性及最佳标准化方式。结果表明：相同肌肉收缩过程中，肌力矩值与平均振幅（MA）的变化趋势呈现高度相关，相关系数r在0.6以上；不同收缩形式、不同收缩速度下，均方根振幅（RMS）、积分肌电（iEMG）值会随着收缩速度的增加而减小；跳深动作下肢肌肉sEMG标准化后的值与跳深腾起速度之间均有一定的相关性，标准化后以最大随意等长收缩（MVIC）的标准化值与跳深腾起速度的相关性最高。  相似文献   

18.
Fatigue represents a reduction in the capability of muscle to generate force. The aim of the present study was to establish the effects of exercise that simulates the work rate of competitive soccer players on the strength of the knee extensors and knee flexors. Thirteen amateur soccer players (age 23.3±3.9 years, height 1.78±0.05?m, body mass 74.8±3.6?kg; mean±s) were tested during the 2000–2001 soccer season. Muscle strength of the quadriceps and hamstrings was measured on an isokinetic dynamometer. A 90?min soccer-specific intermittent exercise protocol, incorporating a 15?min half-time intermission, was developed to provide fatiguing exercise corresponding in work rate to a game of soccer. The exercise protocol, performed on a programmable motorized treadmill, consisted of the different intensities observed during soccer match-play (e.g. walking, jogging, running, sprinting). Muscle strength was assessed before exercise, at half-time and immediately after exercise. A repeated-measures analysis of variance showed significant reductions (P?<0.001) in peak torque for both the quadriceps and hamstrings at all angular velocities (concentric: 1.05, 2.09, 5.23 rad?·?s?1; eccentric: 2.09 rad?·?s?1). The peak torque of the knee extensors (KE) and knee flexors (KF) was greater before exercise [KE: 232±37, 182±34, 129±27, 219±41?N?·?m at 1.05, 2.09 and 5.23 rad?·?s?1 (concentric) and 2.09 rad?·?s?1 (eccentric), respectively; KF: 126±20, 112±19, 101±16, 137±23?N?·?m] than at half-time (KE: 209±45, 177±35, 125±36, 214±43?N?·?m; KF: 114±31, 102±20, 92±15, 125±25?N?·?m) and greater at half-time than after exercise (KE: 196±43, 167±35, 118±24, 204±43?N?·?m; KF: 104±25, 95±21, 87±13, 114±27?N?·?m). For the hamstrings?:?quadriceps ratio, significant changes were found (P?<0.05) for both legs, the ratio being greater before than after exercise. For fast?:?slow speed and left?:?right ratios, no significant changes were found. We conclude that there is a progressive reduction in muscle strength that applies across a range of functional characteristics during exercise that mimics the work rate in soccer.  相似文献   

19.
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 x 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 x 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.  相似文献   

20.
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.  相似文献   

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