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1.
Abstract

Muscle fiber type composition in the vastus lateralis and knee extension isometric strength fatigue patterns were assessed in eight endurance-trained and eight power-trained males. Two different 25-trial isometric contraction exercise regimens were administered: a 10-second contraction, 5-second intertrial rest condition designed to induce a fast rate of fatigue and a 10-second contraction, 20-second intertrial rest condition designed to induce a slower rate of fatigue. The power group fatigued almost four times faster than the endurance group in the 10:5 exercise condition. In the 10:20 exercise condition, the endurance group showed no fatigue pattern while the power group had a significant strength decrement of 32%. In both exercise conditions, the power group exhibited more complex fatigue patterns in terms of statistically significant trend components. Maximum isometric strength correlated positively with slow twitch (ST) percent number in power (r = .80) and endurance (r = .48) groups, but negatively with linear trend coefficients in endurance (r = -.62) and power (r = -.80) groups. Maximum isometric strength also correlated higher with fatigue curve trend coefficients than did muscle fiber type composition. Thus, a faster rate of fatigue was associated with higher maximum isometric strength and with higher ST percent number and area. Since maximum isometric strength correlated with body weight (r = .86 for groups combined), both maximum isometric strength and muscle mass appear to be more important determinants of knee extension isometric strength fatigue patterns than muscle fiber type composition.  相似文献   

2.
To evaluate the effect of concurrent augmented feedback on isometric force output during familiar and unfamiliar muscle movements, 18 men and 21 women, 18 to 23 years of age, completed two isometric exercises: flexion of the thumb (a familiar muscle movement) and abduction of the fifth digit (an unfamiliar movement). The exercises consisted of 10 maximum voluntary isometric contractions lasting 10 s each and separated by 10-s intertrial rest intervals. Concurrent visual feedback was provided during alternate contractions. The order of exercises and trials for feedback was randomly assigned and balanced over subjects. Peak force output during abduction of the fifth digit was significantly (p less than or equal to .01) greater with (4.4 +/- 0.29 kg) than without feedback (4.1 +/- 0.26 kg). Feedback did not influence (p greater than .05) peak force output during thumb flexion (23.2 +/- 1.09 kg vs 22.5 +/- 1.05 kg). Muscular fatigue was more pronounced during thumb flexion without feedback (18.4 +/- 1.17%) than when feedback was provided (11.8 +/- 1.36%). These data suggest that fatigue may increase the effect of feedback on force generation during familiar muscular movements. To obtain maximal isometric force measures during strength testing, augmented feedback should be provided.  相似文献   

3.
Abstract

To evaluate the effect of concurrent augmented feedback on isometric force output during familiar and unfamiliar muscle movements, 18 men and 21 women, 18 to 23 years of age, completed two isometric exercises: flexion of the thumb (a familiar muscle movement) and abduction of the fifth digit (an unfamiliar movement). The exercises consisted of 10 maximum voluntary isometric contractions lasting 10 s each and separated by 10-s intertrial rest intervals. Concurrent visual feedback was provided during alternate contractions. The order of exercises and trials for feedback was randomly assigned and balanced over subjects. Peak force output during abduction of the fifth digit was significantly (p ≤ .01) greater with (4.4 ± 0.29 kg) than without feedback (4.1 ± 0.26 kg). Feedback did not influence (p > .05) peak force output during thumb flexion (232 ±1.09 kg vs 22.5± 1.05 kg). Muscular fatigue was more pronounced during thumb flexion without feedback (18.4 ± 1.17%) than when feedback was provided (11.8 ±136%). These data suggest that fatigue may increase the effect of feedback on force generation during familiar muscular movements. To obtain maximal isometric force measures during strength testing, augmented feedback should be provided.  相似文献   

4.
The purpose of this study was to investigate possible footfall pattern changes in habitual forefoot runners over a prolonged, exhaustive run. A prolonged run was performed to exhaustion in 14 habitual forefoot runners. Vertical ground reaction forces (VGRFs) and kinematics were collected at the beginning and end of the run. Ankle plantar flexor torque and triceps surae electromyographic activity were measured during pre- and post-run isometric contractions. By run’s end, there was an increase in VGRF loading rate and impact peak magnitude, greater dorsiflexion at foot contact and greater knee flexion angle throughout stance. Ankle plantar flexor torque decreased significantly from pre- to post-run tests. This was accompanied by a decrease in the integrated electromyographic activity (iEMG) output for the lateral and medial gastrocnemius. There were significant changes in landing mechanics for forefoot runners that indicate a transition towards more midfoot footfall patterns. A contributing factor may be ankle plantar flexor muscle fatigue that, at touchdown, is exposed to exaggerated eccentric loading. These findings suggest that a forefoot running pattern may become difficult to maintain in longer endurance events, and thus runners should pay attention to this in training to improve performance and mitigate potential injury.  相似文献   

5.
Attaching elastic tubes (ETs) to resistance training machines can affect the exercise load profile. The purpose of this study was to assess the training effects of added ETs, which were strategically attached to provide additional loads only during the deceleration phase of the knee extension exercise. Twenty-two healthy participants, assigned to either an experimental group (with ETs) or a control group (without ETs), participated in a 12-week strength-training program using a knee extension exercise machine. The acceleration effects were quantified and a method of attaching the ETs to the knee extension machine was developed. The effects of the added ETs were analysed by testing dynamic and isometric maximum contractions at four knee flexion angles (10°, 30°, 50°, and 80°). Analyses of covariance with the initial values as the covariate were used to examine the ET effects. A greater increase in isometric maximum strength was found in the experimental group than in the control group at knee flexion angles of 10° [effect size (ES) = 2.25] and 30° (ES = 1.18). No significant difference in the dynamic maximum strength was found between the groups. The use of ETs increased strength at smaller knee flexion angles with quadriceps that were relatively short.  相似文献   

6.
Abstract

Two matched groups of 10 subjects each were employed to assess possible central facilitation effects over 4 weeks of training. Each of the 12 training sessions consisted of 20 trials of maximum isometric wrist flexion for 5 sec. with a 30-sec. rest period between trials. Two experimental conditions were used. On alternate sessions condition one consisted of 20 trials with odd-numbered trials being unilateral and even-numbered trials being simultaneous bilateral efforts. Condition two consisted of the first 15 trials being unilateral and the last 5 trials simultaneous bilateral. The right limb in Group I and the left limb in Group II constituted the criterion measures. Central facilitation effects due to simultaneous bilateral isometric wrist contractions were: (a) not present initially and (b) not elicited through the 4 weeks of training. The finding held for both dominant and nondominant limbs and for fatigued and nonfatigued states.  相似文献   

7.
目的:明确BTE PrimusRS系统测评下肢肌群极限功率与肌耐力的测量模式选取与参数设置;并测量青年男性髋伸、膝伸与踝跖屈肌群极限功率与肌耐力。方法:40名男大学生,在BTE PrimusRS系统等张模式下,阻力矩50%等长峰值力矩(The Isometric Peak Torque,IPT)。IPT重复3次,时间3 s,间歇5 s,非爆发式静力性测量模式;等张极限功率(The Isotonic Peak Power,IPP)重复3次,时间10 s,间歇15 s,尽最快速度完成;等张极限肌耐力(The Isotonic Peak Endurance,IPE)测试要求运动幅度(90°或90°以内)与动作频率(60次/min)一定,持续运动至疲劳。结果:青年男性髋伸、膝伸与踝跖屈肌群IPT为198.56(24.53)、166.45(27.53)、154.90(25.17)N.m;IPP为161.21(28.57)、74.43(16.12)、74.62(19.91)W;IPE总功为6 460.69(2 521.18)、1 407.28(456.93)、2 259.56(771.88)J。结论:BTE PrimusRS系统能以等张模式精确测评下肢单关节肌群IPP与IPE,阻力矩为非爆发式静力性测量模式50%IPT。青年男性髋伸、膝伸与踝跖屈肌群IPT、IPP、IPE测试结果完善了人体单关节肌群生物力学特征基础参数库。  相似文献   

8.
The aim of this study was to determine whether there are differences in the fatigability of plantar flexor muscles during sustained submaximal contractions in prepubertal boys and girls. Fifteen boys (age 10.0 +/- 1.0 years) and 15 girls (age 9.8 +/- 0.9 years) participated in the study. The fatigue protocol consisted of a 10 min isometric plantar flexion at 20% of the maximal voluntary contraction. Immediately after this, five maximal isometric contractions were performed with a 3 min interval between contractions. During the experiment, electromyograms of the agonist muscles soleus and medial gastrocnemius and antagonist tibialis anterior were recorded. We observed no differences between the sexes (P < 0.05) in the decrease in torque or in the recovery rate after the fatigue protocol. Nor were there any differences between the sexes (P < 0.05) in agonist or antagonist muscle activation during the fatigue protocol and recovery period. The results indicate that there are no differences in fatigability between prepubertal boys and girls during submaximal sustained contractions, probably because the agonist and antagonist muscles were activated similarly in both sexes.  相似文献   

9.
Abstract

Three experimental groups of 45 S's each were given 30 repeated isometric wrist flexion trials. Each trial consisted of a maximal 5-sec. effort followed by a rest period of 5,10, or 20 sec. In each recuperation group S's were divided into subgroups representing high, middle, and low levels of absolute strength. The data were analyzed by an analysis of variance of trends allowing statistical tests for best fitting trend components and trend differences between subgroups. Low level of strength groups always demonstrated a fatigue pattern significantly different from high and middle levels. High and middle levels displayed similar patterns differing only on absolute level of strength. Caution isefore indicated in definition and magnitude assessment of derived curve components based upon composite fatigue curves secured on unknown levels of strength. It seems unlikely that the same factors responsible for muscular fatigue can be operating in the same manner at different levels of isometric strength.  相似文献   

10.
The objective of this study was to determine whether sprint performance is related to the mechanical (elongation - force relationship of the tendon and aponeurosis, muscle strength) and morphological (fascicle length, pennation angle, muscle thickness) properties of the quadriceps femoris and triceps surae muscle - tendon units. Two groups of sprinters (slow, n = 11; fast, n = 17) performed maximal isometric knee extension and plantar flexion contractions on a dynamometer at 11 different muscle - tendon unit lengths. Elongation of the tendon and aponeurosis of the gastrocnemius medialis and the vastus lateralis was measured using ultrasonography. We observed no significant differences in maximal joint moments at the ankle and knee joints or morphological properties of the gastrocnemius medialis and vastus lateralis between groups (P > 0.05). The fast group exhibited greater elongation of the vastus lateralis tendon and aponeurosis at a given tendon force, and greater maximal elongation of the vastus lateralis tendon and aponeurosis during maximum voluntary contraction (P < 0.05). Furthermore, maximal elongation of the vastus lateralis tendon and aponeurosis showed a significant correlation with 100-m sprint times (r = -0.567, P = 0.003). For the elongation - force relationship at the gastrocnemius medialis tendon and aponeurosis, the two groups recorded similar values. It is suggested that the greater elongation of the vastus lateralis tendon and aponeurosis of the fast group benefits energy storage and return as well as the shortening velocity of the muscle - tendon unit.  相似文献   

11.
Abstract

Twenty-seven male subjects performed two 5-min bouts of rhythmic, isometric elbow flexion and two similar bouts of knee extension at a rate of 30 maximal contractions per min. Exponential analyses revealed that the pattern of fatigue for each limb followed a single component curve of the form: Yt = a0e ?Kot + c. An analysis of variance comparing the results from the two limbs revealed that (a) the strength scores for the leg were significantly (p < .05) higher than those for the arm throughout the exercise bouts; (b) both limbs experienced a significant strength decrement; and (c) there was significant interaction between trials and limbs. It appeared that the greater loss of strength by the knee extensors was reponsible for this interaction. It was concluded that during a rhythmic, all-out task, the rates of fatigue experienced by the two muscle groups tend to differ, with the elbow flexors fatiguing more rapidly initially but reaching a plateau at a relatively higher level than the knee extensors.  相似文献   

12.
主动肌和拮抗肌功能转变瞬间的肌电平均功率频率变化   总被引：2，自引：1，他引：1  
目的:通过对主动肌和拮抗肌功能转变瞬间肌电平均功率频率的观察,探讨中枢控制因素在决定MPF变化中的独立性作用.方法:10名健康男性志愿者在完成60%MVC强度的疲劳性等长屈肘运动负荷试验后,瞬间转变肌肉工作性质,完成60%MVC强度的疲劳性等长伸肘运动,分别记录肱二头肌和肱三头肌的sEMG信号,观察两次疲劳试验以及瞬间转变过程中肌电MPF等sENG指标变化.结果:等长屈肘和等长伸肘快速转变的瞬间,主动肌和拮抗肌MPF等各项sEMG信号分析指标均发生了显著性改变,表现出明显的跃变现象;无论是转变之前,还是转变之后的等长疲劳试验过程中,主动肌与拮抗肌的MPF、C(n)和%DEF均表现出类似的变化规律,而拮抗肌AEMG则维持相对恒定.结论:中枢运动控制是导致疲劳过程中MPF单调递减变化的独立性作用因素,其可能的作用机制是CNS将主动肌与拮抗肌作为一组控制肌群实施同步控制.  相似文献   

13.
This study quantified lower-limb strength decrements and assessed the relationships between strength decrements and performance fatigue during simulated basketball. Ten adolescent, male basketball players completed a circuit-based, basketball simulation. Sprint and jump performance were assessed during each circuit, with knee flexion and extension peak concentric torques measured at baseline, half-time, and full-time. Decrement scores were calculated for all measures. Mean knee flexor strength decrement was significantly (P < 0.05) related to sprint fatigue in the first half (R = 0.65), with dominant knee flexor strength (R = 0.67) and dominant flexor:extensor strength ratio (R = 0.77) decrement significantly (P < 0.05) associated with sprint decrement across the entire game. Mean knee extensor strength (R = 0.71), dominant knee flexor strength (R = 0.80), non-dominant knee flexor strength (R = 0.75), mean knee flexor strength (R = 0.81), non-dominant flexor:extensor strength ratio (R = 0.71), and mean flexor:extensor strength ratio (R = 0.70) decrement measures significantly (P < 0.05) influenced jump fatigue during the entire game. Lower-limb strength decrements may exert an important influence on performance fatigue during basketball activity in adolescent, male players. Consequently, training plans should aim to mitigate lower-limb fatigue to optimise sprint and jump performance during game-play.  相似文献   

14.
A single bout of eccentric exercise induces a protective adaptation against damage from a repeated bout. The aim of this study was to determine whether this repeated bout effect is due to a change in the length-tension relationship. Twelve individuals performed an initial bout of six sets of 10 eccentric quadriceps contractions and then performed a repeated bout 2 weeks later. Eccentric contractions were performed on an isokinetic dynamometer at 1.04 rad x s(-1) with a target intensity of 90% of isometric strength at 70 degrees of knee flexion. Isometric strength and pain were recorded before and after both eccentric bouts and on each of the next 3 days. Isometric strength was tested at 30 degrees, 50 degrees, 70 degrees, 90 degrees and 110 degrees of knee flexion. On the days following the initial bout, there was a significant loss of isometric strength at all knee flexion angles except 110 degrees (bout x angle: P < 0.01). On day 2, strength averaged 86% of baseline for 30-90 degrees and 102% of baseline for 110 degrees. Strength loss and pain after the initial bout was contrasted by minimal changes after the repeated bout (pain: P < 0.001; strength: P < 0.01). The repeated bout effect was associated with a rightward shift in the length-tension curve; before the repeated bout, isometric strength was 6.8% lower at 30 degrees and 13.6% higher at 110 degrees compared with values before the initial bout (bout x angle: P < 0.05). Assuming that torque production at 110 degrees occurs on the descending limb of the length-tension curve, the increase in torque at 110 degrees may be explained by a longitudinal addition of sarcomeres. The addition of sarcomeres would limit sarcomere strain for subsequent eccentric contractions and may explain the repeated bout effect observed here.  相似文献   

15.
Abstract

Thirty male subjects were given 20 trials of isometric wrist flexion on each arm. Each trial consisted of 5 sec. of maximum exertion followed by a 30 sec. rest period. Subjects were ranked on the basis of the first two trials for each of the limbs and divided into three groups of 10 subjects each representing high, middle, and low levels of strength.

Analysis of variance of the fatigue curve trends suggested that: (a) there is no biologically fixed and constant absolute critical intensity level of isometric muscular tension which occludes intramuscular circulation, and (b) different levels of strength possess dissimilar local circulatory efficiency and/or tolerance to fatigue products.  相似文献   

16.
The purpose of this study was to investigate the effects of using an internal versus external focus of attention during resistance training on muscular adaptations. Thirty untrained college-aged men were randomly assigned to an internal focus group (INTERNAL) that focused on contracting the target muscle during training (n?=?15) or an external focus group (EXTERNAL) that focused on the outcome of the lift (n?=?15). Training for both routines consisted of 3 weekly sessions performed on non-consecutive days for 8 weeks. Subjects performed 4 sets of 8–12 repetitions per exercise. Changes in strength were assessed by six repetition maximum in the biceps curl and isometric maximal voluntary contraction in knee extension and elbow flexion. Changes in muscle thickness for the elbow flexors and quadriceps were assessed by ultrasound. Results show significantly greater increases in elbow flexor thickness in INTERNAL versus EXTERNAL (12.4% vs. 6.9%, respectively); similar changes were noted in quadriceps thickness. Isometric elbow flexion strength was greater for INTERNAL while isometric knee extension strength was greater for EXTERNAL, although neither reached statistical significance. The findings lend support to the use of a mind–muscle connection to enhance muscle hypertrophy.  相似文献   

17.
目的:通过对湖南师范大学9名北狮运动员双侧膝关节屈伸肌群进行等速测试,为揭示该项运动膝关节肌群收缩的生物力学特性提供实验依据。方法:采用BIODEX SYSTEM 3等速测试系统对湖南师范大学北狮运动员膝关节屈伸肌群进行等速测试,测试指标为峰力矩、相对峰力矩、屈伸肌峰力矩比、平均功率及做功疲劳度。结果:1)北狮运动员双侧膝关节屈伸肌峰力矩和相对峰力矩随测试速度的增加呈递减趋势;2)狮头狮尾屈伸肌群峰力矩比值和做功疲劳度无显著性差异;3)狮头狮尾左右膝关节同一肌群峰力矩无显著性差异。结论:舞狮运动员膝关节肌群峰力矩变化随测试速度的增加而减少,平均功率呈现随运动速度的增加而增加,到达一定速度后随速度的增加而减少的特征。  相似文献   

18.
The neural mechanisms explaining strength increase following mental training by motor imagery (MI) are not clearly understood. While gains are mostly attributed to cortical reorganization, the sub-cortical adaptations have never been investigated. The present study investigated the effects of MI training on muscle force capacity and the related spinal and supraspinal mechanisms. Eighteen young healthy participants (mean age: 22.5?±?2.6) took part in the experiment. They were distributed into two groups: a control group (n?=?9) and an MI training group (n?=?9). The MI group performed seven consecutive sessions (one per day) of imagined maximal isometric plantar flexion (4 blocks of 25 trials per session). The control group did not engage in any physical or mental training. Both groups were tested for the isometric maximal plantar flexion torque (MVC) and the rate of torque development (RTD) before and after the training session. In addition, soleus and medial gastrocnemius spinal and supraspinal adaptations were assessed through the recording of H-reflexes and V-waves, with electrical stimulations of the posterior tibial nerve evoked at rest and during MVC, respectively. After one week, only the MI training group increased both plantar flexion MVC and RTD. The enhancement of muscle torque capacity was accompanied by significant increase of electromyographic activity and V-wave during MVC and of H-reflex at rest. The increased cortical descending neural drive and the excitability of spinal networks at rest could explain the greater RTD and MVC after one week of MI training.  相似文献   

19.
Abstract

Sixty-two elite adolescent (age: 16.39 ± 1.62 yrs) female track and field athletes volunteered to be measured isokinetically for peak torque of the leg flexors and extensors. The sample included 16 throwers, 11 jumpers, 12 middle-distance runners (> 400 m), and 23 sprinters. A Cybex II isokinetic dynamometer was used to measure dominant leg strength at 180°/sec. One-way ANOVA revealed significant between group differences for absolute flexion and extension (Nm), extension/body weight (Nm/Kg), and extension/lean body weight (Nm/Kg). Scheffe post-hoc comparisons showed that, for absolute leg extension strength, throwers were stronger than middle-distance runners (by 54.4%), sprinters (35.6%), and jumpers (23.6%). For absolute leg flexion movements, throwers were stronger than middle distance runners (37.4%) and sprinters (32.1%). Jumpers had greater extension peak torque values than middle-distance runners relative to body weight (14.0%), and throwers were stronger than middle-distance runners for extension/lean body weight (14.9%)). No other comparisons were significant. However, when strength was expressed relative to body weight or lean body weight, there were few differences between events for flexion or extension. Given that absolute strength scores were correlated with body weight and lean body weight, peak torque/body weight or peak torque/lean body weight may be more sensitive than absolute values as indicators of underlying factors (such as training status or fiber type composition) responsible for the differences in muscular strength between groups.  相似文献   

20.
Lower limb isometric strength is a key parameter to monitor the training process or recognise muscle weakness and injury risk. However, valid and reliable methods to evaluate it often require high-cost tools. The aim of this study was to analyse the concurrent validity and reliability of a low-cost digital dynamometer for measuring isometric strength in lower limb. Eleven physically active and healthy participants performed maximal isometric strength for: flexion and extension of ankle, flexion and extension of knee, flexion, extension, adduction, abduction, internal and external rotation of hip. Data obtained by the digital dynamometer were compared with the isokinetic dynamometer to examine its concurrent validity. Data obtained by the digital dynamometer from 2 different evaluators and 2 different sessions were compared to examine its inter-rater and intra-rater reliability. Intra-class correlation (ICC) for validity was excellent in every movement (ICC > 0.9). Intra and inter-tester reliability was excellent for all the movements assessed (ICC > 0.75). The low-cost digital dynamometer demonstrated strong concurrent validity and excellent intra and inter-tester reliability for assessing isometric strength in the main lower limb movements.  相似文献   

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