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1.
Abstract

Non-local muscle fatigue has been demonstrated with unilateral activities, where fatiguing one limb alters opposite limb forces. Fewer studies have examined if non-local fatigue occurs with unrelated muscles. The purpose of this study was to investigate if knee extensors fatigue alters elbow flexors force and electromyography (EMG) activity. Eighteen males completed a control and fatiguing session (randomised). Blood lactate was initially sampled followed by three maximal voluntary contractions (MVC) with the elbow flexors and two with the knee extensors. Thereafter, subjects either sat (control) or performed five sets of bilateral dynamic knee extensions to exhaustion using a load equal to the dominant limb MVC (1-min rest between sets). Immediately afterwards, subjects were assessed for blood lactate and unilateral knee extensors MVC, and after 1 min performed a single unilateral elbow flexor MVC. Two minutes later, subjects performed 12 unilateral elbow flexor MVCs (5 s contraction/10 s rest) followed by a third blood lactate test. Compared to control, knee extensor force dropped by 35% (p < 0.001; ES = 1.6) and blood lactate increased by 18% (p < 0.001; ES = 2.8). Elbow flexor forces were lower after the fatiguing protocol only during the last five MVCs (p < 0.05; ES = ～0.58; ～5%). No changes occurred between conditions in EMG. Elbow flexor forces significantly decreased after knee extensors fatigue. The effect was revealed during the later stages of the repeated MVCs protocol, demonstrating that non-local fatigue may have a stronger effect on repeated rather than on single attempts of maximal force production.  相似文献   

2.
Abstract

Match-induced fatigue of knee muscle strength and agonist-antagonist strength-ratios may affect both performance and risk of injury in soccer players. Once explosive tasks are imperative in soccer as well as hamstring strain injuries occur during high-velocity moments, rapid force capacity of this muscle group is especially important. This study evaluated the effect of match-induced fatigue on knee muscle strength and strength-ratio parameters after a single professional soccer match. Male professional soccer players (n?=?16; 24.2?±?3.9 years) were tested before and after a soccer match (56.2?±?22.6?min of playing) for knee flexors (hamstring) and extensors (quadriceps) isometric peak torque (MVC) and rate of torque development (RTD) – as well as the hamstring-to-quadriceps ratio (H:Q) – at 30° of knee flexion. Knee injuries often occur at this joint angle, which is common in sprinting, pivoting, sidecutting, and jumping. Match-induced fatigue caused a left shift in the knee extensors torque-time curve with no significant change in both early (i.e. 0–50?ms) and late (i.e. 0–200?ms) RTD, and a right shift in the knee flexors torque-time curve with a decrease in early RTD (～16%, p?=?.029) and late RTD (～11%, p?=?.011). Knee extensors and knee flexors peak torque remained unchanged (p?>?.05). Early RTD H:Q decreased by～24% (p?=?.027), while late RTD H:Q and MVC H:Q remained unchanged (p?>?.05). In conclusion, match-induced fatigue impaired the ability to rapidly produce force at an angle where injuries are most susceptible to occur. Important information is missed if only the traditional H:Q is considered.  相似文献   

3.
Abstract

In the present study, we examined the relationships between muscle volume and joint torque for the elbow flexors and extensors in young and elderly individuals, with the aim of evaluating age effects on these relationships. The participants were 45 young (27 men and 18 women aged 20–37 years) and 51 elderly (19 men and 32 women aged 60–77 years) individuals. The joint torques developed during isometric maximal voluntary elbow flexion and extension were measured using a torque meter. The muscle volumes of the elbow flexors and extensors were determined by magnetic resonance imaging. For the elbow flexors, joint torque was significantly correlated with muscle volume in both young and elderly individuals (r=0.564–0.872). There were also significant correlations between muscle volume and joint torque for the elbow extensors in elderly men and women as well as in young men and women (r=0.715–0.826). None of the y-intercepts of the regression lines between muscle volume and joint torque were significantly different from zero. Furthermore, no significant age or gender effects on the joint torque per muscle volume of the elbow flexors and extensors were observed. The present results suggest that muscle volume is a main determinant of joint torque regardless of age and gender, for both muscle groups.  相似文献   

4.
The aim of this study was to assess the effect of a unilateral anterior cruciate ligament reconstruction (ACLR) on maximum voluntary contraction (MVC) and explosive strength of both the involved limb and the uninvolved limb. Nineteen male athletes completed a standard isometric testing protocol 4 months post-ACLR, while 16 healthy participants served as a control group (CG). The explosive strength of the knee extensors and flexors was assessed as RFD obtained from the slope of the force–time curves over various time intervals. Both muscle groups of the involved limb had significantly lower MVC compared to the uninvolved. The involved limb also had significantly lower RFD in the late phase of contraction (140–250 ms) for both knee extensors and flexors (P < 0.05). There was no difference in MVC between the uninvolved limb and the CG. However, RFD of the uninvolved limb was lower compared to CG for both knee extensors (0–180 ms; P < 0.01) and flexors (0–150 ms; P < 0.05). ACLR leads to lower MVC and explosive strength of the involved limb. As a consequence of potential crossover (presumably neural-mediated) effects, explosive strength deficits could be bilateral, particularly in the early phase of the contraction (<100 ms).  相似文献   

5.
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   

6.
Abstract

In this study, we examined the effects of time-of-day-specific strength training on maximum strength and electromyography (EMG) of the knee extensors in men. After a 10-week preparatory training period (training times 17:00–19:00 h), 27 participants were randomized into a morning (07:00–09:00 h, n = 14) and an evening group (17:00–19.00 h, n = 13). Both groups then underwent 10 weeks of time-of-day-specific training. A matched control group (n = 7) completed all testing but did not train. Unilateral isometric knee extension peak torque (MVC) and one-repetition maximum half-squat were assessed before and after the preparatory training and after the time-of-day-specific training at times that were not training-specific (between 09:00 and 16:00 h). During training-specific hours, peak torque and EMG during MVC and submaximum isometric contraction at 40% MVC were assessed before and after the time-of-day-specific training. The main finding was that a significant diurnal difference (P < 0.01) in peak torque between the 07:00 and 17:00 h tests decreased after time-of-day-specific training in the morning group but not in the evening or control groups. However, the extent of this time-of-day-specific adaptation varied between individuals. Electromyography during MVC did not show any time-of-day-specific adaptation, suggesting that peripheral rather than neural adaptations are the main source of temporal specificity in strength training.  相似文献   

7.
Abstract

The degree of contribution to performance of the vertical jump by leg components plantar flexors, knee extensors, and hip extensors was determined experimentally and tested by analysis of covariance. One control and four experimental groups from 100 college men at Brigham Young University were randomly assigned to varying muscle strengthening programs for 8 weeks. Initial and final vertical jump tests and strength measures were administered. Gains in the vertical jump significant beyond the .05 level were registered by experimental groups which strengthened knee and/or hip extensors. Control and plantar flexor strengthening groups did not register significant jump gains. Each experimental group registered significant isotonic strength gains in the programed muscle groups.  相似文献   

8.
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   

9.
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   

10.
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11.
Abstract

Aim: To investigate the effect of different water immersion (WI) treatments on recovery from intermittent shuttle running exercise in comparison to an ecologically relevant control.

Methods: Forty males performed 90 minutes intermittent shuttle running, following which they were assigned to either: (1) 12-min standing WI at 12°C; (2) 12-min standing WI at 35°C; (3) 2-min seated WI at 12°C; (4) an ecologically relevant control consisting of 12 minutes walking at 5 km h?1. Muscle soreness, maximal voluntary contraction (MVC) of the knee flexors and extensors, hop distance, creatine kinase activity and myoglobin concentration were measured before exercise and in the 168 hours following the intervention. Between-group differences, time effects and interaction effects were investigated by mixed-model ANOVA.

Results: The shuttle running exercise induced an increase in muscle soreness (1, 24, 48 and 72 hours post-intervention) creatine kinase activity and myoglobin concentration (post-exercise and 1, 24 and 48 hours post-intervention), and reduced MVC of the knee extensors (11% reduction at 24 hours, remaining reduced at 48 and 72 hours), flexors (24% reduction at 24 hours, remaining reduced at 24, 48, 72 and 168 hours), and hop distance (24 and 48 hours). However, no between-group differences or interaction effects were evident for any of these parameters.

Conclusion: The WI protocols investigated were not better than light exercise in facilitating recovery from shuttle running exercise. Future studies examining the efficacy of WI as a recovery intervention should include a representative control condition to increase their relevance to sporting populations.  相似文献   

12.
Abstract

This study investigated whether hot pack treatment could provide prophylactic effects on muscle damage induced by eccentric exercise of the wrist extensors. Twenty-eight healthy men (age 21±1 years, weight 65±16 kg, height 171±6 cm) were randomly placed into hot pack (n = 14) and control (n = 14) groups. All participants performed an exercise consisting of 300 maximal eccentric contractions of the wrist extensors of the non-dominant arm using an isokinetic dynamometer. A hot pack was applied for 20 min to the wrist extensors of the exercised arm before the exercise for the hot pack group. The control group received no treatment before the exercise. Measured variables included pain intensity assessed by a visual analogue scale and a modified Likert's scale, cold thermal pain threshold, pressure pain threshold (PPT), range of motion in active wrist flexion (ROM-AF) and extension (ROM-AE), range of motion in passive wrist flexion (ROM-PF) and extension (ROM-PE), grip strength, and wrist extension strength. Changes in these variables before, immediately after, and 1 to 8 days following the exercise were compared between groups by a two-way repeated measures ANOVA. All outcome measures from both groups (except for the cold thermal pain threshold of the hot pack group) demonstrated a significant change within the first 2–3 days following exercise. Significant differences between groups were only found at a single point in time for PPT, ROM-PF, ROM-PE and ROM-AE, and the changes were smaller for the hot pack group in comparison to the control group. These results suggest that the prophylactic effects of hot pack treatment on eccentric exercise-induced muscle damage of the wrist extensors are limited.  相似文献   

13.
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14.
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   

15.
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.  相似文献   

16.
The hypothesis, that sailing upwind in wind speeds above 12 knots causes fatigue, which manifests as a reduction in exerted hiking strap force and/or maximal isometric voluntary contraction force (MVC) of the knee extensors, was evaluated. Additionally, it was investigated if a relationship exists between maximal exerted hiking force (hMVC) and sailing performance. In part 1 of the study, 12 national level athletes sailed upwind for 2?×?10?min while hiking strap forces were continuously acquired. Before, in between and after sailing periods, the MVC of the knee extensors was measured. In part 2 of the study, hMVC was measured dry land in a hiking bench and correlated with the overall results at a national championship. Hiking strap force decreased from the first to the last minute in both 10?min sailing periods (430?±?131 vs. 285?±?130?N, P?<?.001 and 369?±?74 vs. 267?±?97 N, P?<?.001, respectively), but MVC was similar before, between and after the two 10?min sailing periods (878?±?215 vs. 852?±?202 vs. 844?±?211 130?N). In part 2, a significant positive correlation (r2?=?0.619, P?<?.01) was observed between hMVC and regatta results. In conclusion, upwind sailing in wind speeds above 12 knots causes sailing-specific fatigue as evidenced by a marked reduction in exerted hiking strap force. However, MVC of the knee extensors was not compromised ～45?s after hiking was terminated. Additionally, sailing performance is related to maximal hiking force.  相似文献   

17.
目的研究篮球运动员下肢膝关节肌力在疲劳状态下的变化,以便加强容易疲劳肌群的力量训练。方法研究选择高水平女篮11名运动员为受试者,采用等速肌力测试系统测定膝关节正常状态和疲劳状态下的屈伸肌力及做功情况。结果篮球运动员在运动中更容易导致屈肌产生疲劳,左侧下肢膝关节屈肌的总功力量存在明显差异性。结论篮球运动更容易引起膝关节屈肌产生疲劳,加强屈肌的肌肉力量训练对提高篮球运动员专项力量将有很大帮助。  相似文献   

18.
Abstract

The study examined the acute neuromuscular and metabolic responses and recovery (24 and 48 h) to combined strength and endurance sessions (SEs). Recreationally endurance trained men (n = 12) and women (n = 10) performed: endurance running followed immediately by a strength loading (combined endurance and strength session (ES)) and the reverse order (SE). Maximal strength (MVC), countermovement jump height (CMJ), and creatine kinase activity were measured pre-, mid-, post-loading and at 24 and 48 h of recovery. MVC and CMJ were decreased (P < 0.05) at post-ES and SE sessions in men. Only MVC decreased in ES and SE women (P < 0.05). During recovery, no order differences in MVC were observed between sessions in men, but MVC and CMJ remained decreased. During recovery in women, a delayed decrease in CMJ was observed in ES but not in SE (P < 0.01), while MVC returned to baseline at 24 h. Creatine kinase increased (P < 0.05) during both ES and SE and peaked in all groups at 24 h. The present combined ES and SE sessions induced greater neuromuscular fatigue at post in men than in women. The delayed fatigue response in ES women may be an order effect related to muscle damage.  相似文献   

19.
This study examined whether short-term maximal resistance training employing fast-velocity eccentric knee extensor actions would induce improvements in maximal isometric torque and rate of force development (RFD) at early (<100 ms) and late phases (>100 ms) of rising torque. Twenty healthy men were assigned to two experimental groups: eccentric resistance training (TG) or control (CG). Participants on the TG trained three days a week for a total of eight weeks. Training consisted of maximal unilateral eccentric knee extensors actions performed at 180°s-1. Maximal isometric knee extensor torque (MVC) and incremental RFD in successive 50 ms time-windows from the onset contraction were analysed in absolute terms (RFDINC) or when normalised relative to MVC (RFDREL). After eight weeks, TG demonstrated increases in MVC (28%), RFDINC (0–50 ms: 30%; 50–100 ms: 31%) and RFDREL (0–50 ms: 29%; 50–100 ms: 32%). Moreover, no changes in the late phase of incremental RFD were observed in TG. No changes were found in the CG. In summary, we have demonstrated, in active individuals, that a short period of resistance training performed with eccentric fast-velocity isokinetic muscle contractions is able to enhance RFDINC and RFDREL obtained at the early phase of rising joint torque.  相似文献   

20.
Abstract

The purpose of this study was to determine the effectiveness of a swimming programme and a calisthenics and resistance water training programme, which included aerobic and resistance components, on muscle strength and body weight in postmenopausal women. Both were carried out over a period of 12 months. Ninety-three subjects were randomly assigned to swimming group (SG; n=29), calisthenics and resistance group (CRG; n=34) and control group (CG; n=30). Mean upper-extremities biokinetic force (MF), power (MP) and work (MW) were measured by a biokinetic swim bench (Biometer Swim Bench, Sport Fahnemann). Maximal isometric forces of the trunk flexors (ITF) and knee extensors (IKE) were measured by an isometric strain-gauge dynamometer (T.K.K. 5402, Takei Scientific Instruments Co. Ltd.). Countermovement jump height (CMJ) was evaluated using the Ergojump Bosco System. Energy consumption was measured using a self-administrated food frequency questionnaire (Sanocare Human Systems L.S., Madrid. Spain). Body mass index (BMI) was also measured. CRG improved significantly (p≤0.05) MF increased by 7.92%, MP by 9.08% and MW by 9.3%. SG and CRG demonstrated a significant decrease in BMI (?2.08 and ?2.75% respectively). SG, CRG and CG showed a significant decrease in ITF (?5.07, ?11.34 and ?24.73% respectively) and IKE (?7.99, ?12.77 and ?29.75% respectively). This decrease was significantly greater in CG compared with SG and CRG. There were no significant changes in CMJ in any group. These results indicate that water exercise has significant implications, improving some health-related components of fitness in postmenopausal women.  相似文献   

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