Muscle Fatigue

The investigators describe their multifaceted approach to the study of the relationship between whole-body vibration and low back pain. In vivo experiments, using percutaneous pin-mounted accelerometers have shown that the natural frequency is at 4·5 Hz. The frequency response was affected by posture, seating, and seat-back inclination. The response appears to be largely determined by the rocking of the pelvis. Electromyographic studies have shown that muscle fatigue occurs under whole body vibration. After whole body vibration exposure the muscle response to a sudden load has greater latency. Vehicle driving may be a reason for low back pain or herniated nucleus pulposus. Prolonged seating exposure, coupled with the whole body vibration should be reduced for those recovering from these problems. Vibration attenuating seats, and correct ergonomic layout of the cabs may reduce the risks of recurrence.

The neural and muscular changes during fatigue produced in repeated submaximal static contractions of knee extensors were measured. Three groups of differently adapted male subjects (power-trained, endurance-trained and untrained, 15 in each) performed the exercise that consisted of 10 trials of submaximal static contractions at the level of 40% of maximal voluntary contraction (MVC) force till exhaustion with the inter-trial rest intervals of 1 min. MVC force, reaction time and patellar reflex time components before and after the fatiguing exercise and following 5, 10 and 15 min of recovery were recorded. Endurance-trained athletes had a significantly longer holding times for all the 10 trials compared with power-trained athletes and untrained subjects. However, no significant differences in static endurance between power-trained athletes and untrained subjects were noted. The fatigue test significantly prolonged the time between onset of electrical and mechanical activity (electromechanical delay) in voluntary and reflex contractions. The electromechanical delay in voluntary contraction condition for power-trained and untrained subjects and in reflex condition for endurancetrained subjects had not recovered 15 min after cessation of exercise. No significant changes in the central component of visual reaction time (premotor time of MVC) and latency of patellar reflex were noted after fatiguing static exercise. It is concluded, that in this type of exercise the fatigue development may be largely owing to muscle contractile failure.

Many studies have reported prolonged force deficits after a bout of resistance training. However there is a dearth of in formation on the neuromuscular mechanisms underlying these deficits. This shldy examined whether an acute bout of resistance training had prolonged detrimental effects on muscle activation and excitation-contraction coupling. Two groups of 16 subjects each were tested before resistance ex ercise and at 1, 3, 5, and 7 days postexercise. A dynamic group was tested for concentric and eccentric 1 repetition maximum and 3-methylhistidine (3-MH). An isometric group was tested for maximal vohmtary contraction, muscle inactivation, relative fatigue, and evoked twitch properties. Both groups experienced similar increases in pain, limb cir cumference, and decreased range of motion between 1 and 3 days postexercise. Decrements occurred with eccentric strength, maximal voluntary contraction, muscle inactiva tion, relative fatigue, twitch amplihlde, and increases in 3 MH. Although muscle damage-induced characteristics (pain, swelling, range of motion, 3-MH) were not correlated with neuromuscular impairments (muscle activation, force output), disruption of excitation-contraction coupling may have contributed to decrements in fatigue. . The effect of muscle damage on strength and fatigue deficits. J. Strength Condo Res. 15 : 255-263. 2001.

The aim of this study was to determine morphological and functional changes of the elbow extensor muscles in response to a 12-week self-perceived maximal resistance training (MRT). Twenty-one healthy sedentary young men were engaged in elbow extensor training using isoacceleration dynamometry for 12 weeks with a frequency of five sessions per week (five sets of ten maximal voluntarily contractions, 1-min rest period between each set). Prior to, at 6 weeks and after the training, a series of cross-sectional magnetic resonance images of the upper arm were obtained and muscle volumes were calculated. Maximal and endurance strength increased (P<0AE01) by 15% and 45% at 6 weeks, and by 29% and 70% after 12 weeks compared with baseline values, while fatigue rate of the elbow extensors decreased by 67%. The volume of triceps brachii increased in both arms (P<0AE01) by 4% at 6 weeks, and by 8% after 12 weeks compared with baseline values (right armfrom 487AE4 ± 72AE8 cm 3 to 505AE8 ± 72AE3 cm 3 after 6 weeks and 525AE3 ± 73AE7 cm 3 after 12 weeks; left arm -from 475AE3 ± 79AE1 cm 3 to 493AE2 ± 72AE7 cm 3 after 6 weeks and 511AE3 ± 77AE0 cm 3 after 12 weeks). A high correlation was found between maximal muscle strength and muscle volume prior (r 2 = 0AE62) and after (r 2 = 0AE69) the training (P£0AE05). A self-perceived MRT resulted in an increase in maximal and endurance strength. Morphological adaptation changes of triceps brachii as a result of 12-week specific strength training can explain only up to 26% of strength gain.

Recent evidence suggests that musculoskeletal disorders (MSDs) may be the result of a fatigue failure process in affected tissues. This paper describes a new low back exposure assessment tool (the Lifting Fatigue Failure Tool [LiFFT]), which estimates a &quot;daily dose&quot; of cumulative loading on the low back using fatigue failure principles. Only three variables are necessary to derive the cumulative load associated with a lifting task: the weight of the load, the maximum horizontal distance from the spine to the load, and the number of repetitions for tasks performed during the workday. The new tool was validated using two existing epidemiological databases: the Lumbar Motion Monitor (LMM) database, and a database from a U.S. automotive manufacturer. The LiFFT cumulative damage metric explained 92% of the deviance in low back disorders (LBDs) in the LMM database and 72-95% of the deviance in low back outcomes in the automotive database (depending on the outcome measure). Thus,...

These experiments tested the hypothesis that short-term endurance exercise training would rapidly improve (within 5 days) the diaphragm oxidative/antioxidant capacity and protect the diaphragm against contraction-induced oxidative stress. To test this postulate, male Sprague-Dawley rats (6 weeks old) ran on a motorized treadmill for 5 consecutive days (40-60 min x day(-1)) at approximately 65% maximal oxygen uptake. Costal diaphragm strips were excised from both sedentary control (CON, n=14) and trained (TR, n=13) animals 24 h after the last exercise session, for measurement of in vitro contraction properties and selected biochemical parameters of oxidative/antioxidant capacity. Training did not alter diaphragm force-frequency characteristics over a full range of submaximal and maximal stimulation frequencies (P &gt; 0.05). In contrast, training improved diaphragm resistance to fatigue as contraction forces were better-maintained by the diaphragms of the TR animals during a submaxim...

Fatigue Pro®le, a new numerical method for characterising fatigue in isokinetic cycle ergometry is presented and compared with the conventional fatigue index (FI). The new method describes the temporal development of muscle fatigue based on the decline of peak power output throughout a whole trial. The advantage of this method is demonstrated by the analysis of two 25 s maximum trials, separated by 90 s recovery, performed by a well-trained athlete at a pedal frequency of 120 revolutions per minute. A fourth degree polynomial was ®tted to model the peak power data. Using the polynomial model coecients the ®rst derivative represented the rate of changing peak power which represented the Fatigue Pro®le. The conventional FI was calculated as A35 Ws A1 and A32 Ws A1 for trials 1 and 2 respectively, indicating minor dierences in fatigue between trials. In contrast the Fatigue Pro®le revealed important numeric and temporal dierences between the trials. For trial 1 a maximum rate of peak power decline of A65 Ws A1 was reached at approximately 6 s into the trial. In marked contrast, in trial 2, maximum rate of peak power decline (A146 Ws A1) occurred immediately. The Fatigue Pro®le approach allows the characterisation of the temporal development of fatigue under dierent experimental conditions and in combination with other techniques may yield further insight into the underlying mechanisms of fatigue.

The repeatability of subjective and objective assessments of neck muscle fatigue is very important with regard to the clinical applicability of these methods.To establish between-days reliability, 33 healthy volunteers performed a 60% maximum voluntary isometric contraction test from a standing position in all neck movements. Cervical muscle fatigue was assessed on three separate occasions from the spectral (median frequency, MF) and amplitude (root mean square, RMS) analysis of the electromyogram (EMG) signal recorded from the cervical paraspinal group, splenius capitis, levator scapulae and sternocleidomastoid. Subjective assessment of fatigue was rated by employing the Borg scale. Intraclass correlation coefficient ICC(1,1), standard error of measurement (SEM), smallest detectable difference (SDD) indices and Pearson’s correlation co-efficient were calculated for the analysis of the results.Normalised median frequency (MF) slope had low repeatability and large between-day error (ICC(1,1) = 0.28–0.61; SEM = 0.33–0.60%/s; SDD = 132.7–703.2%) for the protagonist muscles of each movement. Initial median frequency (IMF) had moderate to good reliability and small error (ICC(1,1) = 0.64–0.81; SEM = 2.8–8.8 Hz; SDD = 19.9–38.5%). The RMS slope yielded also poor repeatability. The Borg assessment was more reliable than the EMG estimate though variability between sessions was still quite high (SDD = 29.2–136.5%). No correlation was found between the EMG and Borg assessment of neck muscle fatigue (r = −0.01–0.39).The protocol used for assessing neck muscle fatigue proved to be reliable only for the IMF but the clinical usefulness of this measure remains questionable. The lack of correlation between objective and subjective estimation of neck muscle fatigue was possibly a consequence of the poor measurement repeatability. Further research is needed to identify the factors responsible for these results on neck area.

The influence of psychosocial components on back and abdominal endurance tests in patients with persistent non-specific low back pain should be investigated to ensure the correct interpretation of these measures. Three-hundred and thirty-two patients (291 men and 41 women) from 19 to 63 years performed an abdominal and back muscle endurance test after completing some psychosocial questionnaires. During the endurance tests, surface electromyography signals of the internal obliques, the external obliques, the lumbar multifidus and the iliocostalis were recorded. Patients were dichotomized as underperformers and good performers, by comparing their real endurance time, to the expected time of endurance derived from the normalized median frequency slope. Independent t-tests were performed to examine the differences on the outcome of the questionnaires. In the back muscle endurance test, the underperformers had significantly lower (p < 0.05) scores on some of the physical subscales of the SF-36. The underperformers group of the AE test scored significantly higher on the DRAM MZDI (p = 0.018) and on the PCS scale (p = 0.020) and showed also significantly lower scores on the SF-36 (p < 0.05). Back muscle endurance tests are influenced by physical components, while abdominal endurance tests seem influenced by psychosocial components.

Repetitive motion-induced fatigue not only alters local motion characteristics but also provokes global reorganization of movement. However, the three-dimensional (3D) characteristics of these reorganization patterns have never been documented in detail. The goal of this study was to assess the effects of repetitive reaching-induced arm fatigue on the whole-body, 3D biomechanical task characteristics. Healthy subjects (N = 14) stood and performed a continuous reaching task (RRT) between two targets placed at shoulder height to fatigue. Whole-body kinematic (Vicon Ó ), kinetic (AMTI Ó force platforms) and electromyographic (EMG, Noraxon Ó ) characteristics were recorded. Maximal voluntary isometric efforts (MVIE) of the shoulder and elbow were measured pre-and post-RRT. Post-RRT shoulder elevation MVIE was reduced by 4.9 ± 8.3% and trapezius EMG amplitude recorded during the RRT increased by 46.9 ± 49.9% from the first to last minute of the RRT, indicating that arm fatigue was effectively induced. During fatigued reaching, subjects elevated their shoulder (11.7 ± 10.5 mm) and decreased their average shoulder abduction angle by 8.3 ± 4.4°. These changes were accompanied by a lateral shift of the body's center of mass towards the non-reaching arm. These findings suggest a compensatory strategy to decrease the load on the fatigued shoulder musculature.

García-López, D., J.A. de Paz, E. Moneo, R. Jiménez-Jiménez, G. Bresciani, and M. Izquierdo. Effects of short vs. long rest period between sets on elbow-flexor muscular endurance during resistance training to failure. J. Strength Cond. Res. 21(4):1320Res. 21(4): -1324Res. 21(4): . 2007.-This study aimed to examine shortterm resistance training effects of resting period length between sets on maximal number of repetitions and mean velocity over a moderate-intensity (60% of the maximum voluntary isometric contraction [MVIC]) set to failure on elbow-flexor muscles. The MVIC and surface electromyographic activity (sEMG) were also measured. Twenty-one untrained subjects were divided into 3 groups: short rest between sets (1 minute; SR), long rest between sets (4 minutes; LR), and nontraining control group (CG). The SR and LR performed 3 sets to failure in an arm-curl machine, 2 days per week for 5 weeks, with moderate loads (60-75% of the MVIC). The LR completed a significantly higher (31.6%, p Ͻ 0.05) total training volume than the SR. Both training groups enhanced the maximal number of repetitions to failure, with no significant differences in the magnitude of gains. The posttraining average velocity achieved by the SR at 40, 50, 60, 70, 80, and 90% of the total number of repetitions completed was significantly higher (p Ͻ 0.05) than the corresponding average velocity achieved on pretraining conditions, whereas no significant differences were observed in the LR. No significant changes in the MVIC or sEMG were observed in any group. We conclude that short-term elbow-flexor resistance training to failure, allowing 1 or 4 minutes of rest between sets, induces similar gains concerning local muscular endurance. Nevertheless, only the SR training approach reduced the rate of decline in the average repetition velocity during a set to failure. This can be of some importance in sport modalities in which not only the maximal number of repetitions (e.g., muscle endurance), but also a greater maintenance of high repetition velocities, may be critical for performance.

Stout, J.R., J.T. Cramer, M. Mielke, J. O'Kroy, D.J. Torok, and R.F. Zoeller. Effects of twenty-eight days of betaalanine and creatine monohydrate supplementation on the physical working capacity at neuromuscular fatigue threshold. J. Strength Cond. Res. 20(4):928-931. 2006.-The purpose of this study was to examine the effects of 28 days of beta-alanine (b-Ala) and creatine monohydrate (CrM) supplementation on the onset of neuromuscular fatigue by using the physical working capacity at neuromuscular fatigue threshold (PWC FT ) test in untrained men. Fifty-one men (mean age Ϯ SD ϭ 24.5 Ϯ 5.3 years) volunteered to participate in this 28-day, double-blind, placebocontrolled study and were randomly assigned to 1 of 4 groups: placebo (PLA; 34 g dextrose; n ϭ 13), CrM (5.25 g CrM plus 34 g dextrose; n ϭ 12), b-Ala (1.6 g b-Ala plus 34 g of dextrose; n ϭ 12), or b-Ala plus CrM (CrBA; 5.25 g CrM plus 1.6 g b-Ala plus 34 g dextrose; n ϭ 14). The supplement was ingested 4 times per day for 6 consecutive days, then twice per day for 22 days before posttesting. Before and after the supplementation, subjects performed a continuous incremental cycle ergometry test while a surface electromyographic signal was recorded from the vastus lateralis muscle to determine PWC FT . The adjusted mean posttest PWC FT values (covaried for pretest PWC FT values) for the b-Ala and CrBA groups were greater than those for the PLA group (p Յ 0.05). However, there were no differences between the CrM vs. PLA, CrBA vs. b-Ala, CrM vs. b-Ala, or CrM vs. CrBA groups (p Ͼ 0.05). These findings suggested that b-Ala supplementation may delay the onset of neuromuscular fatigue. Furthermore, there appeared to be no additive or unique effects of CrM vs. b-Ala alone on PWC FT .

Objective: The usefulness of massage as a recovery method after high-intensity exercise has yet to be established. We aimed to investigate the effects of whole-body massage on heart rate variability (HRV) and blood pressure (BP) after repeated high-intensity cycling exercise under controlled and standardized pretest conditions. Methods: The study included 62 healthy active individuals. After baseline measurements, the subjects performed standardized warm-up exercises followed by three 30-second Wingate tests. After completing the exercise protocol, the subjects were randomly assigned to a massage (myofascial release) or placebo (sham treatment with disconnected ultrasound and magnetotherapy equipment) group for a 40-minute recovery period. Holter recording and BP measurements were taken after exercise protocol and after the intervention. Results: After the exercise protocol, both groups showed a significant decrease in normal-to-normal interval, HRV index, diastolic BP (P N .001), and low-frequency domain values (P = .006). After the recovery period, HRV index (P = .42) and high-frequency (HF) (P = .94) values were similar to baseline levels in the massage group, whereas the HRV index tended (P = .05) to be lower and the HF was significantly (P b .01) lower vs baseline values in the placebo group, which also showed a tendency (P = .06) for HF to be lower than after the exercise. Likewise, diastolic BP returned to baseline levels in the massage group (P = .45) but remained lower in the placebo group (P = .02). Conclusion: Myofascial release massage favors the recovery of HRV and diastolic BP after high-intensity exercise (3 Wingate tests) to preexercise levels.

Despite the wide use of surface electromyography (EMG) recorded during dynamic exercises, the reproducibility of EMG variables has not been fully established in a course of a dynamic leg exercise. The aim of this study was to investigate the reproducibility of eight lower limb muscles activity level during a pedaling exercise performed until exhaustion.Eight male were tested on two days held three days apart. Surface EMG was recorded from vastus lateralis, rectus femoris (RF), vastus medialis, semimembranosus, biceps femoris, gastrocnemius lateral, gastrocnemius medianus and tibialis anterior during incremental exercise test. The root mean square, an index of global EMG activity, was averaged every five crank revolutions (corresponding to about 3 s at 85 rpm) throughout the tests.Despite inter-subjects variations, we showed a high reproducibility of the activity level of lower limb muscles during a progressive pedaling exercise performed until exhaustion. However, RF muscle seemed to be the less reproducible of the eight muscles investigated during incremental pedaling exercise. These results suggest that each subject adopt a personal muscle activation strategy in a course of an incremental cycling exercise but fatigue phenomenon can induce some variations in the most fatigable muscles (RF).

Objectives: Biering-Sorensen test is an isometric back endurance test. Biering-Sorensen test scores have varied in different cultural and occupational groups. The aims of this study were to collect normative data on Biering-Sorensen holding times, to determine the discriminative ability of the Biering-Sorensen test in Turkish coal miners, and to examine the association between Biering-Sorensen test result and functional disability. Methods: One hundred and fifty male coal miners participated in this study. Trunk extensor muscle strength was measured using the Biering-Sorensen test. Oswestry disability index was used to measure the functional disability level of low back pain. Results: The mean Biering-Sorensen holding time for the total subject group was 107.3 AE 22.5 s. The mean time of Biering-Sorensen test of the subjects with and without low back pain were 99.9 AE 19.8 and 128.6 AE 15.2 s, respectively. The difference between the subjects with and without low back pain was statistically significant ( p < 0.001). There was a statistically significant negative correlation between Oswestry functional disability score and Biering-Sorensen holding time (r ¼ À0.824, p < 0.001). Conclusions: Turkish coal miners have low mean back extensor endurance holding times. Biering-Sorensen test had a good discriminative ability in our study group. Trunk muscle strength has a significant effect on the disability level of low back pain. Thus trunk muscle endurance training exercise therapy may be effective for the reduction of disability in patients with low back pain.

The primary aim of this study was to examine central fatigue of the plantar flexor muscle group after prolonged running using the twitch interpolation technique. Eight healthy, habitually active male subjects ran on a motorized treadmill for 2 h at a speed corresponding to 75% of peak oxygen uptake (VO 2peak ). Maximal voluntary isometric contraction (MVC) strength as well as the electrically induced twitch produced during MVC [interpolated twitch (IT)] and at rest [resting twitch (RT)] were measured before and after running. The level of activation (LOA) during each MVC was calculated as LOA (%) 5 100(1 À IT/RT). Both MVC and LOA decreased (17 AE 16% and 19 AE 15%, respectively, Po0.05) after running, whereas RT did not change. The decrease in MVC was correlated with the decrease in LOA (r 5 0.87, Po0.05). The results demonstrate that after 2 h of treadmill running at an intensity of 75% of VO 2peak , there was a reduction in maximal voluntary plantar flexor muscle strength that was mainly related to central fatigue.

The goal of this study was to implement a button-free system for restoring load-bearing overground locomotion after spinal cord injury. For this purpose we investigated the use of two controllers; 1) an open-loop (OL) system that generated a predetermined rhythmic output, and 2) a closed-loop (CL) system that used information about the loading and position of the limbs to make appropriate transitions between the unloaded (swing) and loaded (stance) phases of the gait cycle. An if-then rule-based controller was designed that used separate rules to initiate swing and stance in the left and right legs. The OL and CL controllers were tested in anesthetized cats, implanted with intramuscular electrodes in 6 major extensor and flexor muscles of the hindlimbs. The controllers generated patterns of stimulation eliciting alternating hindlimb flexion and extension movements which acted to propel the partially supported animal along the length of a 2.5 m instrumented walkway. Our results indicate that although OL control is less sensitive to the selection of initial stimulation parameters, CL control has the advantage of being able to adjust to overcome increased walkway resistance and muscle fatigue.

The purpose of this study was to determine the extent to which scientific research influences college strength and conditioning coaching practices and to determine the training methods utilized. A total of 321 surveys were mailed to Division I strength and conditioning coaches, and the response rate was 42.7% (137 of 321 surveys). Results indicate that all subjects held a baccalaureate degree, the majority in a human performance-related field, and that 75% were Certified Strength and Conditioning Specialist (CSCS) certified. The respondents' most widely utilized professional resources were the Strength and Conditioning Journal (94%) and other collegiate coaches and programs (93%). Forty-seven percent of respondents indicated that other collegiate coaches and their programs were the most important sources of knowledge outside of formal education. The majority indicated that they used a periodization protocol (93%) utilizing multiple sets (97%), plyometrics (90%), explosive movements (88%), and Olympic lifts (85%). Respondents tend to rely on sources of information that may not be defined as scientific, as evidenced by the low priority given to peer-reviewed literature. Respondents also tend to employ the methods they utilized as athletes. Reliance on these sources may not take advantage of advances made through scientific research in exercise physiology, biomechanics, and more specifically the area of strength and conditioning.

Prosthetic manufacturers have marketed shockabsorbing pylons (SAPs) for attenuation of injurious loads from foot-ground contact. In this study, we compared a commonly prescribed SAP with a conventional rigid pylon, using a withinsubject design (n = 15 unilateral transtibial amputees), to assess effect on gait mechanics, measure transmitted accelerations in situ, and determine functional outcomes using step counts and questionnaires. No differences were found across pylons for self-selected walking speed, prosthetic-side step length, prosthetic-side loading rate and decelerative peak of the vertical ground reaction force, peak pylon acceleration, step count per week, or questionnaire results that examined pylon performance and subjects' pain and fatigue levels. The only statistically significant finding was for the prosthetic-side knee angle at initial contact, where subjects displayed an average of 2.6 degrees more flexion with the rigid pylon than the SAP while walking at a controlled speed (p = 0.004); this result indicates that transtibial amputees are able to modulate the effective stiffness of their residual limb in response to changes in prosthetic component stiffness. The results from the laboratory, field, and subjective outcome measurements suggest that the SAP in this study is as effective as a rigid pylon for unilateral transtibial amputees.

In this paper two diVerent models of brain regulation of exercise performance are critically compared: the central governor model proposed by Noakes and colleagues, and an alternative psycholobiological model based on motivational intensity theory.

Empirical evidence suggests that our nervous system considers many objectives when performing various tasks. With the progression of fatigue, researchers have noted increase in both joint moment variability and muscular cocontraction during isometric force production tasks. Muscular cocontraction increases joint stability, but is metabolically costly. Thus, our nervous system must select a compromise between joint stability and energy efficiency. Interestingly, the continuous increase in cocontraction with fatigue suggests there may be a shift in the relative weighting of these objectives. Here we test the notion of dynamic objective weightings. Using multi-objective optimization, we found a shift in objective weighting that favoured joint stability at the expense of energy efficiency during fatigue. This shift was highly correlated with muscular cocontraction (R(2)=0.78, p&lt;0.001) and elbow moment variability in the time (R(2)=0.56, p&lt;0.01) and frequency (R(2)=0.57, p&lt;0.01)...

Objectives: To compare muscle recruitment, maximal force, and rate of force development changes following different resistance exercise protocols with a constant volume-load. Design: Within-subjects randomized crossover trial. Methods: Fourteen (n = 14) resistance trained male participants completed three different resistance exercise protocols involving 20 squat repetitions, prescribed at 80% of 1-repetition-maximum. Protocol A consisted of 5 sets of 4 repetitions with 3 min inter-set rest intervals, protocol B was 5 sets of 4 repetitions with 20 s inter-set rest intervals, and the rest-pause method was an initial set to failure with subsequent sets performed with a 20 s inter-set rest interval. Maximal squat isometric force output and rate of force development (RFD) were measured before, immediately upon completion (IP), and 5 min (5P) following each protocol. Muscle activity from 6 different thigh and hip muscles was measured with surface electromyography (EMG) at each time point, and during every squat repetition. Results: Participants completed the rest-pause method in 2.1 ± 0.4 sets, with a total protocol duration of 103 s compared to 140 s and 780 s for protocols B and A, respectively. All protocols elicited similar decreases (p < 0.05) in maximal force and RFD at IP, with full recovery at 5P. Increased motor unit recruitment was observed during the rest-pause method compared to both protocols A and B for all muscles measured (p < 0.05). Conclusions: As a result of the increased EMG during exercise and no greater post-exercise fatigue, it was concluded that the rest-pause method may be an efficacious training method for resistance-trained individuals.

Muscle fatigue has been known to differentially affect the activation level of the primary motor cortices (MIs) of the brain's two hemispheres. Whether this fatigue-related decoupling influence on the motor cortical signals extends beyond the motor action to the after-fatigue-task resting state is unknown. This question can be addressed by analyzing functional connectivity (FC) of low-frequency oscillations of resting-state functional MRI (fMRI) signals of the MIs. Low-frequency oscillations (<0.08 Hz) have been detected in many fMRI studies and appear to be synchronized between functionally related areas. These patterns of FC have been shown to differ between normal and various pathological states. The purpose of this study was to examine muscle fatigue-induced resting-state interhemispheric motor cortex FC changes in healthy subjects. We hypothesized that muscle fatigue would create a temporary “disrupted state” in the brain, and would decrease resting state interhemispheric motor cortical FC. Ten healthy subjects performed repetitive unilateral handgrip contractions that induced significant muscle fatigue, with resting state fMRI data collected before and after the task. After excluding two subjects due to gross head motion, interhemispheric motor cortex FC was assessed by cross-correlating the MI fMRI signal time courses. We found that the number of significant interhemispheric correlations in the MI fMRI signals decreased significantly after the performance of the fatigue task. These results suggest that resting state interhemispheric motor cortex FC may be used as an index of recovery from fatigue.

The purpose of this study was to examine the effects of fatigue on biomechanical indices of soccer kick performance. Ten male amateur soccer players performed maximal instep kicks prior to, in the middle and after the implementation of a 90 min intermittent exercise protocol. Three-dimensional data, ground reaction forces (GRFs) and segmental moments were measured during the kick while blood lactate and ammonia concentrations were monitored throughout the protocol. Analysis of variance designs with repeated measures indicated a significant increase in ammonia (P<0.01) and lactate levels (P<0.01) following fatigue. The GRFs and joint displacement curves during the kick remained unaltered after fatigue (P>0.01). However, post-fatigue maximum angular velocity of the shank, the net moments acting on the shank and the resultant joint moments were significantly lower compared with the corresponding pre-exercise values (P<0.01). The velocity of the ball was 24.69 m/s prior to the protocol and significantly decreased to 21.78 m/s after (P<0.01). Similarly, the ball/foot speed ratio significantly (P<0.01) declined from 1.40±0.12 (pre-fatigue) to 1.33±0.18 (post-fatigue). The present results suggest that an exercise protocol that simulates soccer game conditions results in significant impairment of soccer kick performance. This could be attributed to alterations of the function of the neuromuscular system and force generation capacity, which may have altered the mechanics of soccer kick performance.

The amounts of water, carbohydrate and salt that athletes are advised to ingest during exercise are based upon their effectiveness in attenuating both fatigue as well as illness due to hyperthermia, dehydration or hyperhydration. When possible, fluid should be ingested at rates that most closely match sweating rate. When that is not possible or practical or sufficiently ergogenic, some athletes might tolerate body water losses amounting to 2% of body weight without significant risk to physical well-being or performance when the environment is cold (e.g. 5-108C) or temperate (e.g. 21-228C). However, when exercising in a hot environment (4308C), dehydration by 2% of body weight impairs absolute power production and predisposes individuals to heat injury. Fluid should not be ingested at rates in excess of sweating rate and thus body water and weight should not increase during exercise. Fatigue can be reduced by adding carbohydrate to the fluids consumed so that 30-60 g of rapidly absorbed carbohydrate are ingested throughout each hour of an athletic event. Furthermore, sodium should be included in fluids consumed during exercise lasting longer than 2 h or by individuals during any event that stimulates heavy sodium loss (more than 3-4 g of sodium). Athletes do not benefit by ingesting glycerol, amino acids or alleged precursors of neurotransmitter. Ingestion of other substances during exercise, with the possible exception of caffeine, is discouraged. Athletes will benefit the most by tailoring their individual needs for water, carbohydrate and salt to the specific challenges of their sport, especially considering the environment's impact on sweating and heat stress.

The purpose of this study was to determine the eVects of beta-alanine supplementation and high-intensity interval training (HIIT) on electromyographic fatigue threshold (EMG FT ) and eYciency of electrical activity (EEA). A total of 46 men completed four, 2-min work bouts on a cycle ergometer. Using bipolar surface electrodes, the EMG amplitude was averaged and plotted over the 2-min. The resulting slopes were used to calculate EMG FT and EEA. Following initial testing, all participants were randomly assigned to either placebo (PL; n = 18), beta-alanine (BA; n = 18) or control groups (CON; n = 10). Following randomization, participants engaged in 6 weeks of HIIT training. SigniWcant improvements in EMG FT and EEA resulted for both training groups. In conclusion, HIIT appeared to be the primary stimulus eVecting EMG FT or EEA, suggesting adaptations from HIIT may be more inXuential than increasing skeletal muscle carnosine levels on delaying fatigue in recreationally active men.

Children differ from adults in many muscular performance attributes such as size-normalized strength and power, endurance, fatigability and the recovery from exhaustive exercise, to name just a few. Metabolic attributes, such as glycolytic capacity, substrate utilization, and VO2 kinetics also differ markedly between children and adults. Various factors, such as dimensionality, intramuscular synchronization, agonist-antagonist coactivation, level of volitional activation, or muscle composition, can explain some, but not all of the observed differences. It is hypothesized that, compared with adults, children are substantially less capable of recruiting or fully employing their higher-threshold, type-II motor units. The review presents and evaluates the wealth of information and possible alternative factors in explaining the observations. Although conclusive evidence is still lacking, only this hypothesis of differential motor-unit activation in children and adults, appears capable of...

The aim of this study was to investigate the effect of a multi-directional soccer-specific fatigue protocol on sprinting kinematics in relation to hamstring injury risk. Nine semi-professional soccer players (Mean +/- SD: Age: 21.3 +/- 2.9 year; Height 185.0 +/- 8.7 cm; Body Mass 81.6 +/- 6.7 kg) completed the SAFT(90); a multi-directional, intermittent 90 min exercise protocol representative of soccer match-play. The 10m sprint times and three-dimensional kinematic data were recorded using a high-speed motion capture system (Qualisys Track Manager) every 15 min during the SAFT(90). A significant time dependent increase was observed in sprint time during the SAFT(90) (P&amp;lt;0.01) with a corresponding significant decrease in stride length (P&amp;lt;0.01). Analysis of the kinematic sprint data revealed significantly reduced combined maximal hip flexion and knee extension angle, indicating reduced hamstring length, between pre-exercise and half-time (P&amp;lt;0.01) and pre-exercise and full-time (P&amp;lt;0.05). These findings revealed that the SAFT(90) produced time dependent impairments in sprinting performance and kinematics of technique which may result from shorter hamstring muscle length. Alterations in sprinting technique may have implications for the increased predisposition to hamstring strain injury during the latter stages of soccer match-play.

Most mathematical models of athletic training require the quantification of training intensity and quantity or 'dose'. We aim to summarize both the methods available for such quantification, particularly in relation to cycle sport, and the mathematical techniques that may be used to model the relationship between training and performance. Endurance athletes have used training volume (kilometres per week and/or hours per week) as an index of training dose with some success. However, such methods usually fail to accommodate the potentially important influence of training intensity. The scientific literature has provided some support for alternative methods such as the session rating of perceived exertion (sRPE ((Author: this abbreviation is not used again in the abstract-ok to delete?))), which provides a subjective quantification of the intensity of exercise; and the heart rate-derived training impulse (TRIMP) method, which quantifies the Approval for publication Signed Date Number of amended pages returned AQ3

The electromyography (EMG) signals give information about different features of muscle function. Realtime measurements of EMG have been used to observe the dissociation between the electrical and mechanical measures that occurs with fatigue. The purpose of this study was to detect fatigue of biceps brachia muscle using timefrequency methods and independent component analysis (ICA). In order to realize this aim, EMG activity obtained from activated muscle during a phasic voluntary movement was recorded for 14 healthy young persons and EMG signals were observed in time-frequency domain for determination of fatigue. Time-frequency methods are used for the processing of signals that are non-stationary and time varying. The EMG contains transient signals related to muscle activity. The proposed method for the detection of muscle fatigue is automated by using artificial neural networks (ANN). The results show that ANN with ICA separates EMG signals from fresh and fatigued muscles, hence providing a visualization of the onset of fatigue over time. The system is adaptable to different subjects and conditions since the techniques used are not subject or workload regime specific.

The present study aimed to analyze neuromuscular, physiological and perceptual responses to a single bout of five different dynamic squat exercise protocols. In a randomized and counterbalanced order, fifteen male resistance-trained athletes (mean±SD; age: 23.1±1.9 years, body mass: 77.4±8.0 kg) completed a traditional multiple sets (MS: 4 x 6, 85% 1RM), drop sets (DS: 1 x 6, 85% 1RM + 3 drop sets), eccentric overload (EO: 4 x 6, 70% 1RM concentric, 100% 1RM eccentric), flywheel YoYo TM Squat (FW: 4 x 6, all-out), and a plyometric jump protocol (PJ: 4 x 15, all-out). Blood lactate (La), ratings of perceived exertion (RPE), counter movement jump height (CMJ), multiple rebound jump performance (MRJ), maximal voluntary isometric contraction force (MVIC), serum creatine kinase (CK) and delayed onset muscle soreness (DOMS) were measured. Immediately post-exercise, La was significantly (p<0.001) higher in FW (mean±95% CL; 12.2±0.9 mmol•L-1) and lower in PJ (3.0±0.8 mmol•L-1) compared to MS (7.7±1.5 mmol•L-1), DS (8.5±0.6 mmol•L-1) and EO (8.2±1.6 mmol • L-1), accompanied by similar RPE responses. Neuromuscular performance (CMJ, MRJ) significantly remained decreased (p<0.001) from 0.5 to 48 h post-exercise in all protocols. There was a significant time x protocol interaction (p<0.05) in MRJ with a significant lower performance in DS, EO and FW compared to PJ (0.5 h post-exercise), and in EO compared to all other protocols (24 h post-exercise). A significant main time effect with peak values 24 h post-exercise was observed in CK serum concentrations (p<0.001), but there was no time x protocol interaction. In conclusion, (1.) metabolic and perceptual demands were higher in FW and EO compared to MS, DS and PJ, (2.) neuromuscular fatigue was consistent up to 48 h postexercise in all protocols, and (3.) EO induced the greatest neuromuscular fatigue.

The purpose of this study was to determine the extent to which scientific research influences college strength and conditioning coaching practices and to determine the training methods utilized. A total of 321 surveys were mailed to Division I strength and conditioning coaches, and the response rate was 42.7% (137 of 321 surveys). Results indicate that all subjects held a baccalaureate degree, the majority in a human performance-related field, and that 75% were Certified Strength and Conditioning Specialist (CSCS) certified. The respondents' most widely utilized professional resources were the Strength and Conditioning Journal (94%) and other collegiate coaches and programs (93%). Forty-seven percent of respondents indicated that other collegiate coaches and their programs were the most important sources of knowledge outside of formal education. The majority indicated that they used a periodization protocol (93%) utilizing multiple sets (97%), plyometrics (90%), explosive movements (88%), and Olympic lifts (85%). Respondents tend to rely on sources of information that may not be defined as scientific, as evidenced by the low priority given to peer-reviewed literature. Respondents also tend to employ the methods they utilized as athletes. Reliance on these sources may not take advantage of advances made through scientific research in exercise physiology, biomechanics, and more specifically the area of strength and conditioning.

We investigated the role of fatigue in muscle strain injuries using the extensor digitorum longus muscles of 48 rabbits. The muscles of the rabbits were fatigued by 25% or 50% then stretched to failure and compared with the contralateral controls. Three rates of stretch were used. The force to muscle failure was reduced in the fatigued leg in all groups (range, 93% to 97.4%

Soccer is the most commonly played sport in the world, with an estimated 265 million active soccer players by 2006. Inherent to this sport is the higher risk of injury to the anterior cruciate ligament (ACL) relative to other sports. ACL injury causes the most time lost from competition in soccer which has influenced a strong research focus to determine the risk factors for injury. This research emphasis has afforded a rapid influx of literature defining potential modifiable and non-modifiable risk factors that increase the risk of injury. The purpose of the current review is to sequence the most recent literature that reports potential mechanisms and risk factors for non-contact ACL injury in soccer players. Most ACL tears in soccer players are non-contact in nature. Common playing situations precluding a non-contact ACL injury include: change of direction or cutting maneuvers combined with deceleration, landing from a jump in or near full extension, and pivoting with knee near full extension and a planted foot. The most common non-contact ACL injury mechanism include a deceleration task with high knee internal extension torque (with or without perturbation) combined with dynamic valgus rotation with the body weight shifted over the injured leg and the plantar surface of the foot fixed flat on the playing surface. Potential extrinsic non-contact ACL injury risk factors include: dry weather and surface, and artificial surface instead of natural grass. Commonly purported intrinsic risk factors include: generalized and specific knee joint laxity, small and narrow intercondylar notch width (ratio of notch width to the diameter and cross sectional area of the ACL), pre-ovulatory phase of menstrual cycle in females not using oral contraceptives, decreased relative (to quadriceps) hamstring strength and recruitment, muscular fatigue by altering neuromuscular control, decreased “core” strength and proprioception, low trunk, hip, and knee flexion angles, and high dorsiflexion of the ankle when performing sport tasks, lateral trunk displacement and hip adduction combined with increased knee abduction moments (dynamic knee valgus), and increased hip internal rotation and tibial external rotation with or without foot pronation. The identified mechanisms and risk factors for non-contact ACL injuries have been mainly studied in female soccer players; thus, further research in male players is warranted. Non-contact ACL injuries in soccer players likely has a multi-factorial etiology. The identification of those athletes at increased risk may be a salient first step before designing and implementing specific pre-season and in-season training programs aimed to modify the identified risk factors and to decrease ACL injury rates. Current evidence indicates that this crucial step to prevent ACL injury is the only option to effectively prevent the sequelae of osteoarthritis associated with this traumatic injury.

Background "Use it or lose it" is a well known saying which is applicable to boys with Duchenne Muscular Dystrophy (DMD). Besides the direct effects of the muscular dystrophy, the increasing effort to perform activities, the fear of falling and the use of personal aids indirectly impair leg and arm functions as a result of disuse. Physical training could oppose this secondary physical deterioration. The No Use is Disuse (NUD) study is the first study in human subjects with DMD that will examine whether a low-intensity physical training is beneficial in terms of preservation of muscle endurance and functional abilities. The study consists of two training intervention studies: study 1 "Dynamic leg and arm training for ambulant and recently wheelchair-dependent boys with DMD and, study 2 "Functional training with arm support for boys with DMD who have been confined to a wheelchair for several years". This paper describes the hypotheses and methods of the NUD study. Methods Study 1 is an explorative randomized controlled trial with multiple baseline measurements. Thirty boys with a DNA-established diagnosis of DMD will be included. The intervention consists of a six-months physical training during which boys train their legs and arms with active and/or assisted cycling training equipment. The primary study outcomes are muscle endurance and functional abilities, assessed with a Six-Minute Bicycle Test and the Motor Function Measure. Study 2 has a within-group repeated measurements design and will include ten boys with DMD who have already been confined to a wheelchair for several years. The six-months physical training program consists of 1) a computer-assisted training and 2) a functional training with an arm support. The primary study outcome is functional abilities of the upper extremity, assessed with the Action Research Arm Test. Discussion The NUD study will fill part of the gap in the current knowledge about the possible effects of training in boys with DMD and will increase insight into what type of exercise should be recommended to boys with DMD. The study will finish at the end of 2010 and results are expected in 2011. Trial registration The Netherlands National Trial Register1631

Hyperkalemic periodic paralysis (HyperKPP) is a disease characterized by periods of myotonic discharges and paralytic attacks causing weakness, the latter associated with increases in plasma [K(+)]. The myotonic discharge is due to increased Na(+) influx through defective Na(+) channels that triggers generation of several action potentials. The subsequent increase in extracellular K(+) concentration causes excessive membrane depolarization that inactivates Na(+) channels triggering the paralysis. None of the available treatments is fully effective. This paper reviews the capacity of Na(+) K(+)ATPase pumps, KATP and ClC-1 Cl(-) channels in improving membrane excitability during muscle activity and how using these three membrane components we can study future and more effective treatments for HyperKPP patients. The review of current patents related to HyperKPP reinforces the need of novel approaches for the treatment of this channelopathy.

To examine the skeletal muscle characteristics of power lifters, 5 competitive power lifters (PL; X Ϯ SE; age ϭ 31.0 Ϯ 1.5 years, squat ϭ 287.7 Ϯ 15.7 kg, bench press ϭ 170.5 Ϯ 17.7 kg, and deadlift ϭ 284.2 Ϯ 7.5 kg) and 5 untrained control subjects (CON; age ϭ 27.3 Ϯ 3.3 years) served as subjects. Isokinetic squat force and power was greater (p Ͻ 0.05) for the PL at all bar velocities (0.20, 0.82, and 1.43 m · s Ϫ1 ), as was vertical jump height and estimated power. Muscle biopsies from the vastus lateralis m. revealed significant differences for percent fiber type (PL, IIA ϭ 45.5 Ϯ 1.6%, IIB ϭ 1.3 Ϯ 0.8%; CON, IIA ϭ 33.4 Ϯ 3.1%, IIB ϭ 12.0 Ϯ 2.4%); percent fiber type area (PL, IIA ϭ 51.8 Ϯ 1.6%, IIB ϭ 1.3 Ϯ 0.8%; CON, IIA ϭ 43.5 Ϯ 3.4%, IIB ϭ 12.4 Ϯ 2.6%); and percent myosin heavy chain isoform (PL, IIa ϭ 59.5 Ϯ 6.1%; CON, 46.5 Ϯ 2.5%). Muscle fiber characteristics were significantly correlated (r ϭ Ϯ 0.61) with numerous strength and power measures for the PL. These data illustrate the muscle fiber characteristics necessary for the maximal force production requirements of power lifting.

The purpose of this study was to examine the changes in peak power output, blood lactate concentrations and surface electromyographic activity (sEMG) of the agonist [vastus lateralis (VL) and vastus medialis (VM)] and the antagonist [biceps femoris (BF)] muscles at two angular positions intervals (90-67°and 23-0°of knee flexion), during a set of 10 repetitions leading to failure of bilateral leg press exercise. Fatiguing exercise resulted in increased blood lactate concentrations, the agonist mean rectified voltage (MRV) at 90-67°of flexion, the antagonist average MRV at 23-0°of flexion and the spectral parameter proposed by Dimitrov (FI nsm5 ) (P \ 0.01-0.05). Significant decreases (P \ 0.01-0.05) were observed in power output, median frequency (F med ) of the agonist muscles at both angular position intervals and of the antagonist muscle at 90-67°of flexion. No changes were observed in the antagonist/agonist MRV activation ratio. The present data suggest that the shift of frequency spectrum to lower frequencies and the accumulation of lactate and/or H ? , but not the antagonist/agonist MRV activation ratio, may be relevant independent factors associated with fatigue.

The rating of perceived exertion (RPE) could be a practical measure of global exercise intensity in team sports. The purpose of this study was to examine the relationship between heart rate (%HR peak ) and blood lactate ([BLa − ]) measures of exercise intensity with each player's RPE during soccer-specific aerobic exercises. Mean individual %HR peak , [BLa − ] and RPE (Borg's CR 10-scale) were recorded from 20 amateur soccer players from 67 soccer-specific small-sided games training sessions over an entire competitive season. The small-sided games were performed in three 4 min bouts separated with 3 min recovery on various sized pitches and involved 3-, 4-, 5-, or 6-players on each side. A stepwise linear multiple regression was used to determine a predictive equation to estimate global RPE for small-sided games from [BLa − ] and %HR peak . Partial correlation coefficients were also calculated to assess the relationship between RPE, [BLa − ] and %HR peak . Stepwise multiple regression analysis revealed that 43.1% of the adjusted variance in RPE could be explained by HR alone. The addition of [BLa − ] data to the prediction equation allowed for 57.8% of the adjusted variance in RPE to be predicted (Y = −9.49 − 0.152 %HR peak + 1.82 [BLa − ], p < 0.001). These results show that the combination of [BLa − ] and %HR peak measures during small-sided games is better related to RPE than either %HR peak or [BLa − ] measures alone. These results provide further support the use of RPE as a measure of global exercise intensity in soccer.

The purpose of this study was to examine the differences in electromyographic activity of agonist and antagonist knee musculature between a maximal and a submaximal isokinetic fatigue protocol. Fourteen healthy males (age: 24.3 ± 2.5 years) performed 25 maximal (MIFP) and 60 submaximal (SIFP) isokinetic concentric efforts of the knee extensors at 60°s À1 , across a 90°range of motion. The two protocols were performed a week apart. The EMG activity of vastus medialis (VM), vastus lateralis (VL) and biceps femoris (BF) were recorded using surface electrodes. The peak torque (PT) and average EMG (aEMG) were expressed as percentages of pre-fatigue maximal value. One-way analysis of variance indicated a significant (p < 0.05) decline of PT during the maximal (45.7%) and submaximal (46.8%) protocols. During the maximal test, the VM and VL aEMG initially increased and then decreased. In contrast, VM and VL aEMG continuously increased during submaximal testing (p < 0.05). The antagonist (BF) aEMG remained constant during maximal test but it increased significantly and then declined during the submaximal testing. The above results indicate that agonist and antagonist activity depends on the intensity of the selected isokinetic fatigue test.

To determine the effects of prolonged simulated tennis on performance and the ergogenic potential of caffeine, carbohydrates, and cooling. Methods: Twelve highly trained male tennis players (age 18.3 ± 3.0 y, height 178.8 ± 8.5 cm, body mass 73.95 ± 12.30 kg, mean ± SD) performed 4 simulated matches (2 h 40 min) against a ball machine on an indoor hard court. The counterbalanced experimental trials involved caffeine supplementation (3 mg/kg), carbohydrate supplementation (6% solution), precooling and intermittent cooling, and placebo control. Physiological markers (core temperature, heart rate, blood lactate, and blood glucose), subjective responses (ratings of perceived exertion and thermal sensation), stroke velocity and accuracy, serve kinematics, and tennis-specific perceptual skill quantified the efficacy of interventions. Results: Significant effects of time (P < .01) reflected increased physiological demand, reduced serve velocity and ground-stroke velocity and accuracy, and a slowing of the serve racket-arm acceleration phase. Caffeine increased serve velocity (165 ± 15 km/h) in the final set of the match (P = .014) compared with placebo (159 ± 15 km/h, P = .008) and carbohydrate (158 ± 13 km/h, P = .001) conditions. Carbohydrate and cooling conditions afforded physiological advantage (increased blood glucose, P < .01, and reduced preexercise thermal sensation, P < .01) but did not affect performance relative to the placebo condition. Conclusions: Prolonged simulated tennis induced significant decrements in tennis skills. Caffeine supplementation partly attenuated the effects of fatigue and increased serve velocity. In contrast, carbohydrate and cooling strategies had little ergogenic effect on tennis performance.

Fatigue in the legs is a problem experienced by skiers. It has been suggested that optimal orthotics may reduce muscle fatigue for a given movement task by minimising muscle activity (Med. Sci. Sports Exerc. 31 (1999) S421). The aims were to determine whether EMG would provide an independent method of analysing myoelectric fatigue in the vastus lateralis (VL) during a skier's squat and whether orthotics could affect this fatigue response. Six skiers performed skier's squats for as long as possible with no orthotic, low volume orthotics and high volume orthotics in their ski boots. Bipolar, active surface electrodes recorded EMG activity in the VL throughout each squat. Results for the EMG median frequency showed a significant shift in the power density spectrum towards the lower frequencies (P < 0:05) at the end of the contraction, suggesting that myoelectric fatigue was occurring and was measurable using EMG. All conditions displayed a significant decrease in median frequency at the end of the contraction (P ¼ 0:001). The high volume orthotic showed a significant reduction in myoelectric fatigue, however, there was no difference in the duration of squats across the three conditions (P > 0:05). Subjective and objective findings support the use of the high volume foot orthotic for skiers. #