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1.
Abstract

Plantar flexion and knee extension fatigue patterns elicited by 25 serial isometric contractions were assessed on eight female distance runners. Fiber type composition of the vastus lateralis and gastrocnemius muscles was examined by a needle biopsy technique. Two different isometric exercise regimens were administered: 10-sec contractions separated by 5-sec intertrial rest (10:5) designed to elicit a rapid rate of fatigue, and 10-sec contractions separated by 20-sec intertrial rest (10:20) designed to induce less fatigue. No fatigue pattern was found for the 10:20 regimen which was consistent with previous data on male distance runners but unlike male power athletes who did exhibit significant fatigue. Significant fatigue decrements were found for the 10:5 knee extension (55.7%) and plantar flexion (75.8%) conditions. Fiber type composition and fatigue decrements did not correlate. Knee extension and plantar flexion maximum strength correlated significantly with the amount of fatigue induced with r's of .82 and .83, respectively. For each separate muscle group, maximum isometric strength was a better predictor of fatigability than fiber type composition. Even though differences in maximal strength and muscle mass existed between knee extension and plantar flexion muscle groups, elicited fatigue curves were similar in pattern differing only in absolute level. High versus low strength classification analysis showed similar knee extension but dissimilar plantar flexion fatigue patterns. Results suggest that the role of fiber type composition, muscle mass, and maximum strength level as they influence local muscular fatigue patterns must be elucidated for each muscle group separately.  相似文献   

2.
运动性肌肉疲劳的表面肌电非线性信号特征   总被引：13，自引：3，他引：10  
王健  方红光  杨红春 《体育科学》2005,25(5):39-43,64
研究目的在于探讨不同强度等长运动诱发肌肉疲劳过程中s EMG非线性信号变化特征及其与肌肉运动耐力的关系。10名青年大学生志愿者参加本次实验。采用4 0 %、6 0 %和80 %MVC强度的等长运动试验诱发肱二头肌疲劳,同步采集该肌肉s EMG信号并进行非线性C(n)和% DET和线性MPF分析。研究发现1)肌肉疲劳过程中s EMG信号的MPF和C(n)呈单调递减型变化,而% DET呈单调递增型变化;2 )不同强度运动负荷诱发肌肉疲劳过程中MPF、C(n)和% DET变化率具有明显的运动强度依赖性并与肌肉耐力运动成绩高度相关;3)以% DET变化率反映运动性肌肉疲劳的敏感度明显高于MPF和C(n)。  相似文献   

3.
Abstract

The purpose of the study was to investigate the effect of a 2-min. isometric exercise training program on force and fatigue in a skeletal muscle. The subjects (N=60) were divided into two equal groups, control and experimental. The control group was tested twice, once at the beginning of the experiment and again after 20 days. The subjects in the experimental group were tested before embarked on a 20-day period of isometric training. held the tension for 2 min. in the morning and again in the afternoon. Periodic tests were on the 5th, 10th, 15th, and 20th days. Large gains of initial strength were recorded on the 5th day. Isometric training continued beyond five days produced no significant gains in initial strength althoughe was a significant increase in isometric endurance. Isometric exercise continued longer than 15 days resulted in a significant decrease in initial strength and isometric endurance.  相似文献   

4.
Abstract

The aim of this study was to examine the time-course of and the relationships between muscle oxygenation, blood volume and myoelectrical manifestations during isometric exercise in children. Twelve healthy children aged 12.5 ± 1.2 years (mean ± s) performed an isometric knee extension at 50% of their maximal voluntary contraction (MVC) until exhaustion to assess endurance time (limit time, T lim). Changes in muscle oxygenation and blood volume were assessed by near infrared spectroscopy (NIRS). The root mean square (RMS) amplitude and the mean power frequency (MPF) from electromyogram (EMG) signals were obtained, as NIRS parameters, from the vastus lateralis. Mean T lim was 117 ± 34 s. The muscle oxygenation and blood volume curves decreased immediately at the beginning of exercise. Maximal deoxygenation occurred at 50% T lim, and fell by 76.9% from the resting value. Similarly, minimal blood volume was observed at 50% T lim; it reached a plateau that lasted until the end of exercise. The kinetics of the MPF and RMS curves were inversely related to time. At the last set of exercises (after 75% T lim), a steeper RMS curve and an abrupt decrease in the MPF curve were observed. Significant correlations (r) between muscle oxygenation, blood volume, root mean square amplitude and mean power frequency were observed, which ranged from 0.72 to 0.99. These findings suggest that the fatigue resulting from sustained isometric exercise is related to a decrease in oxygenation and blood volume.  相似文献   

5.
Abstract

Knee extension isokinetic peak torque was assessed at angular velocities of 0, 30, 180, and 240[ddot]/sec, and isokinetic endurance was assessed by 50 consecutive contractions at 180[ddot]/sec in eight college age men. Also, muscle fiber type of the vastus lateralis was determined and related to isokinetic strength and fatigability. To determine the influence of initial strength on isokinetic endurance the 50 serial isokinetic contractions were assessed after subjects performed two bicycle exercise regimens designed to affect initial strength levels. Neither isokinetic peak torques (made relative to MVC or per Kg of body weight) nor the amount of strength loss over the 50 contractions correlated with fiber type. The peak torques at 180[ddot]/sec at the start of the 50 contractions differed over the three conditions (unfatigued and after the two bicycle exercise regimens), however, the amount of of strength loss over the 50 trials was similar for the three conditions. Also, the patterns of the three isokinetic fatigue curves were remarkably similar. Thus, the initial strength level across the treatments did not affect the rate of fatigue. However, when the treatment conditions were examined separately, the amount of strength loss over the 50 trials correlated significantly with initial strength. Thus, factors other than, or in addition to, fiber type and initial strength level must influence the rate of isokinetic fatigue.  相似文献   

6.
Abstract

The research was undertaken to determine if an increase in the duration of a sustained voluntary isometric contraction is more closely related to changes in cardiovascular endurance or changes in strength. Subjects (N = 24) were tested before and after a training program to determine their endurance (oxygen consumption) and strength. The training program consisted of one daily sustained voluntary isometric contraction of the left forearm flexors at a prescribed percentage of the subject's maximum isometric strength. When the mean duration of contractions for each group showed a significant increase, training ceased.

The groups which trained with contractions of 50, 75, and 100 percent of a maximum voluntary contraction showed significant increases in strength, but not in endurance. The group which trained with a 25 percent contraction increased significantly in endurance, but not in strength. The increased duration of contractions at percentages greater than or equal to 50 percent of a maximum voluntary contraction appeared to be due to increased strength. Hence, measuring cardiovascular endurance by the duration of a sustained voluntary isometric contraction at percentages greater than 25 percent seems unjustified.  相似文献   

7.
Abstract

Congestive heart failure (CHF) patients experience reduced muscle fatigue resistance and exercise capacity. The aim of this study was to assess whether skeletal muscle in CHF patients has a normal training response compared to healthy subjects. We compared the effect of one-legged knee extensor (1-KE) endurance training in CHF patients (n=10), patients with coronary artery disease (CAD, n=9) and healthy subjects (n=13). The training response was evaluated by comparing trained leg and control leg after the training period. The fall in peak torque during 75 maximal 1-KE isokinetic contractions revealed that CHF patients were less fatigue resistant than healthy subjects in the control leg, but not in the trained leg. Peak power and peak oxygen uptake during dynamic 1-KE exercise was ~10–16% higher in trained leg than control leg. This training response was not significant different between groups. Muscle biopsies of vastus lateralis showed that fibre type composition was not different between trained leg and control leg. Capillary density was 6.5% higher in trained leg than control leg when all groups were pooled. In conclusion, the more fatigable skeletal muscle of CHF patients responds equally to endurance training compared to skeletal muscle of CAD patients and healthy subjects.  相似文献   

8.
A well-documented observation after eccentric exercise is a reduction in maximal voluntary force. However, little is known about the ability to maintain maximal isometric force or generate and maintain dynamic peak power. These aspects of muscle function were studied in seven participants (5 males, 2 females). Knee extensor isometric strength and rate of fatigue were assessed by a sustained 60 s maximal voluntary contraction at 80 degrees and 40 degrees knee flexion, corresponding to an optimal and a shortened muscle length, respectively. Dynamic peak power and rate of fatigue were assessed during a 30 s Wingate cycle test. Plasma creatine kinase was measured from a fingertip blood sample. These variables were measured before, 1 h after and 1, 2, 3 and 7 days after 100 repetitions of the eccentric phase of the barbell squat exercise (10 sets x 10 reps at 80% concentric one-repetition maximum). Eccentric exercise resulted in elevations in creatine kinase activity above baseline (274+/-109 U x l(-1); mean +/- s(x)) after 1 h (506+/-116 U x l(-1), P < 0.05) and 1 day (808+/-117 U x l(-1), P < 0.05). Isometric strength was reduced (P < 0.05) for 7 days (35% at 1 h, 5% at day 7) and the rate of fatigue was lower (P < 0.05) for 3 days at 80 degrees and for 1 day at 40 degrees. Wingate peak power was reduced to a lesser extent (P < 0.05) than isometric strength at 1 h (13%) and, although the time course of recovery was equal, the two variables differed in their pattern of recovery. Eccentrically exercised muscle was characterized by an inability to generate high force and power, but an improved ability to maintain force and power. Such functional outcomes are consistent with the proposition that type II fibres are selectively recruited or damaged during eccentric exercise.  相似文献   

9.
The purpose of this study was to explore the dose–response relationship between exercise and cognitive performance using an acute bout of isometric exercise. University students (N = 55) were randomly assigned to control, 30%, 50% and 70% of maximum voluntary handgrip contraction groups. Participants performed a modified Stroop task before and after completion of an isometric handgrip endurance trial at their assigned exercise intensity. Ratings of perceived exertion (RPE) and forearm muscle activation (EMG) showed linear trends of progressively greater RPE and muscle activation at greater exercise intensity levels. Regression analysis showed significant (P < .05) linear degradations in frequency of errors on the Stroop task with increasing exercise intensity. We conclude that performing isometric exercise until exhaustion is associated with reduced cognitive performance and that higher intensity isometric exercise leads to greater performance impairments in a linear dose–response manner.  相似文献   

10.
This study investigated the acute effects of Kinesio taping (KT) on muscular power, strength, endurance, and self-perceived fatigue level. This is a randomized, partial double-blind, crossover trial. Eighteen healthy adults (7 males [23.86?±?1.68 years] and 11 females [24.82?±?3.71 years]) were enrolled in this study. All subjects underwent three different trials which included no tap (NT), placebo tap (PT), and KT. Idividuals were assessed for peak and mean power, muscular strength and endurance, and self-perceived fatigue after each condition. The results revealed no significant differences in all variables (p?>?0.05) except muscular endurance (F?=?5.775, p?=?0.007). Muscular endurance in the NT (58.28?±?12.18?reps/min) condition was significantly higher than that in the KT (52.83?±?11.76?reps/min) condition. These results suggest that KT on rectus femoris and the patella of the lower limb does not improve muscular function and self-perceived fatigue level. KT is unlikely to enhance exercise performance capacity in healthy adults.  相似文献   

11.
叶伟  王健  刘加海 《体育科学》2004,24(9):19-23,66
应用非线性动力学的方法，研究最大和60％MVC强度肱二头肌静态疲劳负荷及其恢复期表面肌电信号复杂度变化规律，探讨肌肉疲劳过程中sEMG信号变化的可能原因和机制。结论：sEMG信号Lempel—Ziv复杂度反映了神经活动策略和神经肌肉功能状态的变化。运动负荷诱发肱二头肌静态疲劳过程中sEMG信号复杂度随运动负荷时间延长而减小，恢复期sEMG信号复杂度和MVC均随恢复时间的延长以相似的模式快速恢复，提示，sEMG信号复杂度可以用于肌肉功能状态恢复的评价。  相似文献   

12.
Twelve endurance athletes and six power athletes performed fatiguing isokinetic knee flexions/extensions. Isokinetic torque was recorded during the exercise. Isometric torque, cortisol and lactate responses, electromyographic (EMG) mean power frequency, average rectified value, and conduction velocity were analysed before and after the isokinetic exercise to determine correlations between electrophysiological variables and mechanical performances and/or blood concentrations of biomarkers in the two groups of athletes. The EMG variables were estimated from signals recorded from the vastus lateralis in both voluntary and electrically elicited isometric contractions. Power athletes recorded higher values than endurance athletes for the following variables: pre-exercise isometric maximal voluntary contraction (MVC), isokinetic MVC, rate of mechanical fatigue during isokinetic contractions, pre - post exercise variations and recovery times of conduction velocity and mean power frequency, and lactate concentrations. Moreover, conduction velocity overshooting was observed in endurance athletes during the recovery phase after exercise. The correlation analyses showed that the higher the rate of mechanical fatigue, the higher the lactate production and the reduction in conduction velocity due to the exercise.  相似文献   

13.
The aim of this study was to determine the effects of a single bout of endurance exercise on subsequent strength performance. Eight males with a long history of resistance training performed isokinetic, isometric and isotonic leg extension strength tests 8 and 32 h after 50 min of cycle ergometry at 70-110% of critical power. The participants also completed a control condition in which no cycling was performed. Plasma lactate and ammonia were measured before and immediately after each strength test. Isokinetic, isometric and isotonic leg extension torques were not significantly different 8 or 32 h after endurance exercise compared with the control condition (P > 0.05). A large (50.3%), but not statistically significant, increase in plasma ammonia was evident during the strength tests performed 8 h after endurance exercise, while a significant (P < 0.05) increase in ammonia was also seen 32 h after endurance exercise. No significant changes in plasma ammonia were evident in the control condition. Our results suggest that leg extension strength was not compromised by an earlier bout of endurance cycling. However, metabolic activity during the strength tests might have been altered by the preceding bout of endurance exercise.  相似文献   

14.
Abstract

This study aimed to examine the effects of application of kinaesthetic tapes on plantarflexor muscle performance. We hypothesised that taping of the triceps surae muscle would improve plantarflexor muscle strength and endurance with no significant effect on drop jump performance. Using a repeated-measures design, all performance measures were obtained in 24 volunteers on two separate occasions: without tapes and after application of kinaesthetic tapes. Performance tests included measurements of isometric plantarflexor muscle strength and the associated electromyographic activity of the gastrocnemius muscle, an isokinetic fatigue resistance test (30 contractions at 180° · s?1) and assessments of drop jump performance. The taping-intervention was associated with an increase in gastrocnemius electromyographic activity. However, significant increases in isometric strength were only found at fully dorsiflexed ankle positions (+12% at ?20°). Strength gains were negatively correlated to baseline strength (r = ?.58). The intervention did not affect the results of the isokinetic fatigue and drop jump tests. The application of kinaesthetic tapes over the triceps surae muscle promotes an increase in isometric strength and gastrocnemius muscle activity. Our data suggest that these effects are joint-angle dependent and more prominent in weaker individuals. By contrast, the taping-intervention improves neither drop jump performance nor muscular endurance.  相似文献   

15.
‘A tribute to Dr J. Rogge’ aims to systematically review muscle activity and muscle fatigue during sustained submaximal quasi-isometric knee extension exercise (hiking) related to Olympic dinghy sailing as a tribute to Dr Rogge’s merits in the world of sports. Dr Jacques Rogge is not only the former President of the International Olympic Committee, he was also an orthopaedic surgeon and a keen sailor, competing at three Olympic Games. In 1972, in fulfilment of the requirements for the degree of Master in Sports Medicine, he was the first who studied a sailors’ muscle activity by means of invasive needle electromyography (EMG) during a specific sailing technique (hiking) on a self-constructed sailing ergometer. Hiking is a bilateral and multi-joint submaximal quasi-isometric movement which dinghy sailors use to optimize boat speed and to prevent the boat from capsizing. Large stresses are generated in the anterior muscles that cross the knee and hip joint, mainly employing the quadriceps at an intensity of 30–40% maximal voluntary contraction (MVC), sometimes exceeding 100% MVC. Better sailing level is partially determined by a lower rate of neuromuscular fatigue during hiking and for ≈60% predicted by a higher maximal isometric quadriceps strength. Although useful in exercise testing, prediction of hiking endurance capacity based on the changes in surface EMG in thigh and trunk muscles during a hiking maintenance task is not reliable. This could probably be explained by the varying exercise intensity and joint angles, and the great number of muscles and joints involved in hiking.

Highlights

  • Dr Jacques Rogge, former president of the International Olympic Committee and Olympic Finn sailor, was the first to study muscle activity during sailing using invasive needle EMG to obtain his Master degree in Sports Medicine at the Ghent University.

  • Hiking is a critical bilateral and multi-joint movement during dinghy racing, accounting for >60% of the total upwind leg time. Hiking generates large stresses in the anterior muscles that cross the knee and hip joint.

  • Hiking is considered as a quasi-isometric bilateral knee extension exercise. Muscle activity measurements during sailing, recorded by means of EMG, show a mean contraction intensity of 30-40% maximal voluntary contraction with peaks exceeding 100%.

  • Hiking performance is strongly related to the development of neuromuscular fatigue in the quadriceps muscle. Since maximal strength is an important determinant of neuromuscular fatigue during hiking, combined strength and endurance training should be incorporated in the training program of dinghy sailors.

  相似文献   

16.
Abstract

Elite badminton requires muscular endurance combined with appropriate maximal and explosive muscle strength. The musculature of the lower extremities is especially important in this context since rapid and forceful movements with the weight of the body are performed repeatedly throughout a match. In the present study, we examined various leg-strength parameters of 35 male elite badminton players who had been performing resistance exercises as part of their physical training for several years. The badminton players were compared with an age-matched reference group, the members of whom were physically active on a recreational basis, and to the same reference group after they had performed resistance training for 14 weeks. Maximal muscle strength of the knee extensor (quadriceps) and flexor muscles (hamstrings) was determined using isokinetic dynamometry. To measure explosive muscle strength, the contractile rate of force development was determined during maximal isometric muscle contractions. In general, the badminton players showed greater maximal muscle strength and contractile rate of force development than the reference group: mean quadriceps peak torque during slow concentric contraction: 3.69 Nm · kg?1, s=0.08 vs. 3.26 Nm · kg?1, s=0.8 (P<0.001); mean hamstring peak torque during slow concentric contraction: 1.86 Nm · kg?1, s=0.04 vs. 1.63 Nm · kg?1, s=0.04 (P<0.001); mean quadriceps rate of force development at 100 ms: 24.4 Nm · s?1·kg?1, s=0.5 vs. 22.1 Nm·s?1 · kg?1, s=0.6 (P<0.05); mean hamstring rate of force development at 100 ms: 11.4 Nm · s?1·kg?1, s=0.3 vs. 8.9 Nm · s?1 · kg?1, s=0.4 (P<0.05). However, after 14 weeks of resistance training the reference group achieved similar isometric and slow concentric muscle strength as the badminton players, although the badminton players still had a higher isometric rate of force development and muscle strength during fast (240° · s?1) quadriceps contractions. Large volumes of concurrent endurance training could have attenuated the long-term development of maximal muscle strength in the badminton players. The badminton players had a higher contractile rate of force development than the reference group before and after resistance training. Greater explosive muscle strength in the badminton players might be a physiological adaptation to their badminton training.  相似文献   

17.
Laser sailors have to tolerate fatiguing contractions of the lower-body muscles for prolonged periods. The aims of the present study were (1) to evaluate the difference between top-ranked and club sailors, in their capacity to resist fatigue during sustained isometric and maximal power exercise, and (2) to examine the relationships between the above parameters and performance on a Laser simulator and competitive racing performance according to the national ranking list. Eight Greek nationally ranked Laser sailors were compared with eight club sailors. Each sailor performed: (a) an effort to the limit of tolerance on the Laser simulator, (b) an effort to the limit of tolerance of isometric endurance for the right leg on an isokinetic dynamometer, and (c) a Wingate test of maximal lower-body anaerobic power on a cycle ergometer. In the nationally ranked sailors, isometric endurance time (mean 160 s, s = 50) and endurance time on the Laser simulator (1381 s, s = 1354) were significantly (P < 0.05) longer than in the club sailors (101 s, s = 29 and 565 s, s = 367, respectively), whereas the final minute heart rate (in both groups: 149 beats . min(-1), s = 22) and the mean arterial pressure (nationally ranked sailors: 129 mmHg, s = 16; club sailors: 120 mmHg, s = 21) on the Laser simulator were not different between groups. During the Wingate test, the nationally ranked sailors had a significantly lower index of fatigue (42%, s = 5) than the club sailors (49%, s = 6). Isometric endurance time was significantly correlated with the Wingate index of fatigue (r = -0.73; P < 0.001). The nationally ranked sailors' mean and maximal anaerobic powers were significantly correlated with their national ranking positions (r = -0.83 and -0.71, respectively). It is suggested that isometric endurance and anaerobic power are well-developed in Laser class sailors and may influence their sailing performance. Furthermore, compared with club sailors, the nationally ranked sailors are able to sustain the same intensity of lower-limb isometric contractions for much longer with similar cardiovascular responses.  相似文献   

18.
The aim of this study was to determine the effects of a single bout of endurance exercise on subsequent strength performance. Eight males with a long history of resistance training performed isokinetic, isometric and isotonic leg extension strength tests 8 and 32 h after 50 min of cycle ergometry at 70-110% of critical power. The participants also completed a control condition in which no cycling was performed. Plasma lactate and ammonia were measured before and immediately after each strength test. Isokinetic, isometric and isotonic leg extension torques were not significantly different 8 or 32 h after endurance exercise compared with the control condition ( P > 0.05). A large (50.3%), but not statistically significant, increase in plasma ammonia was evident during the strength tests performed 8 h after endurance exercise, while a significant ( P ? 0.05) increase in ammonia was also seen 32 h after endurance exercise. No significant changes in plasma ammonia were evident in the control condition. Our results suggest that leg extension strength was not compromised by an earlier bout of endurance cycling. However, metabolic activity during the strength tests might have been altered by the preceding bout of endurance exercise.  相似文献   

19.
Abstract

This study investigated the influence of dehydration during soccer-type intermittent exercise on isokinetic and isometric muscle function. Eight soccer players performed two 90-min high-intensity intermittent shuttle-running trials without (NF) or with (FL) fluid ingestion (5 ml · kg?1 before and 2 ml · kg?1 every 15 min). Isokinetic and isometric strength and muscular power of knee flexors and knee extensors were measured pre-exercise, at half-time and post-exercise using isokinetic dynamometry. Sprint performance was monitored throughout the simulated-soccer exercise. Isokinetic knee strength was reduced at faster (3.13 rad · s?1; P = 0.009) but not slower (1.05 rad · s?1; P = 0.063) contraction speeds with exercise; however, there was no difference between FL and NF. Peak isometric strength of the knee extensors (P = 0.002) but not the knee flexors (P = 0.065) was significantly reduced with exercise with no difference between FL and NF. Average muscular power was reduced over time at both 1.05 rad · s?1 (P = 0.01) and 3.14 rad · s?1 (P = 0.033) but was not different between FL and NF. Mean 15-m sprint time increased with duration of exercise (P = 0.005) but was not different between FL and NF. In summary, fluid ingestion during 90 min of soccer-type exercise was unable to offset the reduction in isokinetic and isometric strength and muscular power of the knee extensors and flexors.  相似文献   

20.
Purpose: Exercise limitation in recipients of lung transplant may be a result of abnormalities in the skeletal muscle. However, it is not clear whether these abnormalities are merely a reflection of the changes observed in the pretransplant condition. The purpose of this paper was to compare thigh muscle volume and composition, strength, and endurance in lung transplant recipients to people with chronic obstructive pulmonary disease (COPD).Methods: Single lung transplant recipients (n=6) and people with COPD (n=6), matched for age, sex, and BMI participated in the study. Subjects underwent MRI to determine muscle size and composition, lower extremity strength testing and an isometric endurance test of the quadriceps.Results: Lung transplant recipients had similar muscle volumes and intramuscular fat infiltration of their thigh muscles and similar strength of the quadriceps and hamstrings to people with COPD who had not undergone transplant. However, quadriceps endurance tended to be lower in transplant recipients compared to people with COPD (15 ± 7 seconds in transplant versus 31 ± 12 seconds in COPD, p = 0.08).Conclusions: Recipients of lung transplant showed similar changes in muscle size and strength as people with COPD, however muscle endurance tended to be lower in people with lung transplants. Impairments in muscle endurance may reflect the effects of immunosuppressant medications on skeletal muscle in people with lung transplant.Key Words: lung transplant, muscle function, MRI  相似文献   

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