Flexor Responses Research Articles

The Effects of the StartReact on Reaction Time, Rate of Force Development, and Muscle Activity in Biceps Brachii

ABSTRACTThe StartReact test, increasingly popular for assessing cortico‐reticular functioning, is a valid method to influence the firing of reticulospinal tract neurons noninvasively. However, there remains limited evidence on how different stimuli employed in the StartReact test impact motor output in humans. The present study tested elbow flexor responses of 33 adults (aged 26–48 years) to visual stimuli only (LED light), audio‐visual (80 dB) stimuli, and startle‐inducing audio‐visual (120 dB) stimuli sitting with the arm supinated in an electromechanical dynamometer. Surface electromyogram (EMG) recorded muscle activity from the right biceps brachii muscle. Participants were presented with 20 stimuli for each of the three conditions in pseudorandom order with interstimulus intervals of ~8 s. Reaction times were calculated from the stimulus trigger to the initial rise in the EMG signal above 7 × SD from baseline. Rate of torque development (RTD) and EMG signals were recorded throughout and analyzed over their initial 50 ms and 100 ms time‐windows. Reaction times were reduced from visual (169 ± 23) to audio‐visual (140 ± 23) and further reduced to startle‐inducing audio‐visual stimuli (108 ± 19, p < 0.001). While RTD and EMG were consistently greatest following startle‐inducing stimuli (p < 0.001), they were also enhanced following all audio‐visual stimuli over 100 ms (p < 0.05). It appears that startle‐inducing audio‐visual stimuli result in shorter reaction times, increased RTD, and enhanced muscle activity within the initial 50 ms, likely from subcortical upregulation. However, the 100 ms time‐window suggests cortical upregulation following all audio‐visual stimuli considering the longer transmission times.

The efficacy of myofascial release at the cervicothoracic region in patients with rotator cuff repairs: A randomized controlled pilot study

BackgroundCoactivation between tonic and phasic muscles is essential for correct posture and movement. Impaired movement patterns and postural changes facilitate the flexor response to protect painful tissue in the injured area. Tone changes between tonic and phasic muscles lead to an imbalance in the rotator cuff (RC) muscles. DesignA randomized controlled pilot study. PurposeThe purpose of this study is to determine the effects of applying myofascial release (MFR) to the muscles in the cervicothoracic region for the treatment of fascia limitations in patients with postoperative RC tear. Materials and methodsA total of 20 patients were randomly divided into 2 groups. The patients in the control group performed exercises, whereas those in the MFR group performed exercises in addition to MFR. Pain intensity, grip strength, pectoralis minor flexibility, Constant Murley Score (CMS), and Short Form-36 (SF-36) score were evaluated. Pain intensity was recorded before and after the MFR sessions. ResultsThere were no significant differences between the groups regarding pain, grip strength, pectoralis minor flexibility, CMS values, or SF-36 score (p > 0.05). There were significant differences in pain levels measured before and after all MFR sessions. Moreover, a significant decrease is shown between the first and last sessions in the MFR group (p < 0.05). ConclusionMFR can be useful, especially in postoperative RC patients who have pain in the early period. Significant reductions in pain intensity after MFR can help prepare patients for exercise and reduce pain-related medication use.

Does footedness affect bilateral plantar flexor responses to sudden stance perturbations under unilateral lower leg muscular fatigue?

BACKGROUND: Analysis of performance asymmetries has indicated that the right and left cerebral hemispheres are specialized for specific functions of motor control. AIM: In the current investigation, we aimed to evaluate the effect of leg dominance on electrical activation of the plantar flexor muscles in responses to unanticipated stance perturbations in a state muscular fatigue of the dominant leg. METHOD: Fatigue was induced through ankle isometric contraction targeting 40% of maximum voluntary contraction. Muscle activation of the triceps surae of the dominant and non-dominant legs were compared in reactive responses to unanticipated load released from the trunk, leading to forward body sway. Muscular responses were analyzed in two states: pre-fatigue and fatigue of the triceps surae muscles of the dominant leg only. RESULTS: Analysis of magnitude of muscular activation for balance recovery following perturbations revealed fatigue-related compensatory activation in the lateral gastrocnemius muscle, as indicated by over-activation of the non-fatigued/non-dominant leg to compensate for the low muscular activation of the dominant/fatigued leg in the unilateral fatigue state. CONCLUSION: Compensatory behavior between the legs was not evident in the medial gastrocnemius and soleus muscles. Lack of effects related to leg dominance indicates that footedness did not affect automatic muscular responses either in the pre-fatigue or fatigue states.

Increased EMG-EMG coherence in the theta and alpha bands during bimanual force modulation

During the execution of movements, error correction processes have been inferred by EEG activation at oscillation frequencies in the theta (4–8 Hz) and alpha (8–12 Hz) bands. The current study examined whether evidence for error detection and correction could be found at the muscular level through the use of EMG-EMG coherence, which quantifies the amount of synchronous EMG activity between limbs in the frequency domain. Participants (n = 13) performed a bimanual force production task involving either wrist flexors or extensors under conditions in which the force was to be held constant or continuously modulated. As predicted, the modulation of changing force output resulted in significantly greater force variability and increased EMG-EMG coherence throughout the theta and alpha band for both flexor and extensor responses. These results are consistent with EEG activation frequencies associated with error correction, motor reprogramming and sustained attention and indicate that evidence for these cortical processes can also be observed at the muscular level in the form of correlated EMG frequency content between limbs.

Brain Infarction in the Artery of Percheron Supply Area due to Reversible Cerebral Vasoconstriction Syndrome

An ischemic stroke caused by the occlusion of the artery of Percheron encompasses both posterior thalami, and the resulting clinical presentation can mask the clinical presentation of a stroke. We present the case report of a 62-year-old female patient who was admitted to our emergency department in a soporous state after initial headache and dizziness. A neurological exam found left-sided spasticity and a flexor response to pain. Systemic thrombolysis was administered after an urgent computerized tomography (CT) of the brain with angiography. The interventional radiologist proposed a digital subtraction angiography which found a vasospasm in the right medial cerebral artery from the M2 seg- ment reaching distally, and a balloon dilation was done. Following the endovascular procedure, a CT scan showed ischemia in both posterior thalami. Additionally, the patient’s neurological impairment improved at that moment showing Parinaud syndrome, drowsiness, and left-sided palsy. The patient experienced a possible reversible cerebral vasoconstriction syndrome, the cause of which is still unknown, which resulted in an ischemic stroke. The typical clinical presentation of that syndrome was lacking, probably due to the presence of the artery of Percheron ipsilateral to the vasospasm. Our goal in presenting this case study is to draw attention to the artery of Percheron syndrome as a potential clinical sign of an acute ischemic stroke that can easily lead us to be misled.

Characterization of the influence of the dominant tract on hand closing post stroke based on the Fugl-Meyer score

While stroke survivors with moderate or mild impairment are typically able to open their hand at will, those with severe impairment cannot. Abnormal synergies govern the arm and hand in stoke survivors with severe impairment, so hand opening, which is required to overcome the working synergy, is an extremely difficult task for them to achieve. It is universally accepted that alternative tracts including the cortico-reticulospinal tract (CRST), employed in the case that the corticospinal tract (CST) is damaged by stroke, brings about such abnormal synergies. Here we note that hand closing is enabled by alternative tracts as well as the CST, and a research question arises: Does motor characteristics while closing the hand depend on the integrity of the CST? In this study, we evaluate the abilities of 17 stroke survivors to flex and relax the metacarpophalangeal (MCP) joints and investigate whether motor characteristics can be distinguished based on CST integrity which is estimated using upper-extremity Fugl-Meyer (UEFM) scores. UEFM scores have been perceived as an indirect indicator of CST integrity. We found that participants with the UEFM score above a certain value, who are assumed to use the CST, moves the MCP joints more smoothly (P < 0.05) and activates the flexors to flex the joints faster (P < 0.05), in comparison to participants with low UEFM scores, who are assumed to preferentially use alternative tracts. The results imply that use of alternative tracts (i.e. the CRST) results in a degradation in movement smoothness and slow activation of MCP flexors. We present evidence that responses of flexors of the MCP joints following stroke depend on the degree of impairment which is hypothesized to originate from preferentially use of different neural motor pathways.

Clinical Predictors of Vibrator-Assisted Ejaculation following Spinal Cord Injury: A Prospective Observational Study.

Introduction Infertility in men with spinal cord injury (SCI) occurs due to combination of factors like erectile dysfunction, ejaculatory failure, and semen abnormalities. Penile vibratory stimulation (PVS) is a known method of treatment for anejaculation. Predicting successful outcome of PVS depends on several clinical factors, which assess the intactness of the neural arc pertaining to the spinal ejaculation pattern generator. This study reports the clinical predictors for successful candidacy for a PVS trial in males with SCI. Methods Twenty-three males with SCI, satisfying the inclusion criteria, were recruited in this prospective observational study. Participants underwent two trials of PVS with single high-amplitude vibrator. The clinical predictors recorded were neurological level, superficial abdominal reflex, cremasteric reflex, bulbocavernosus reflex, plantar reflex, ankle jerk, knee jerk, lower abdominal sensation, and hip flexor response. In addition, somatic responses during PVS were recorded and corelated. Participants who had successful ejaculation were “responders” and the others were termed as “nonresponders.” Binary logistic regression analysis of the clinical parameters was done to compare responders against nonresponders. Results Of the twenty-three males (mean age 33.2 ± 6.8 years) with paraplegia, all four persons with neurological level above T9 had successful ejaculation with PVS. Among all the clinical parameters in the study, presence of somatic responses showed statistical significance in predicting successful ejaculation ( p -value = 0.02). Conclusion This study reports that in men with SCI, along with the level of injury, somatic responses and other clinical reflexes, should be considered concurrently to predict the outcome of vibrator assisted ejaculation.

Effect of photobiomodulation therapy on trunk flexor performance after incisional hernia repair: a randomized controlled trial.

To investigate the effect of two photobiomodulation approaches on trunk flexor performance after incisional hernia repairand to compare the effects of both wavelengths. Forty-five patients were randomly distributed after isokinetic trunk flexor assessments into infrared laser, red laser, and placebo groups. Each patient received laser treatment followed by a traditional physical therapy program. In laser treatment, 24 points in both recti were irradiated by infrared or red laser light with the following parameters; 0.6J per point, 214.28J/cm2 as energy density, and 17.85W/cm2 as intensity, while the control group received a placebo approach. All groups received clinical treatments at a rate of 3 sessions per week for 4weeks; in addition, the physical therapy program was continued on other days for all groups. Isokinetic trunk flexor strength was measured before treatment and 4weeks after treatment as in each measurement, fatigue protocol was designed, and the trunk flexor strength was measured before fatigue test while the trunk flexor resistance to fatigue was measured after fatigue test. After 4weeks, pre-and post-fatigue trunk flexor strengths in both laser groups were significantly increased compared to pre-and post-fatigue trunk flexor strength in the placebo group, respectively, and there was no significant difference between the two laser groups.Photobiomodulation approaches enhance trunk flexor response to exercise after incisional hernia repair. This enhancement leads to greater strength and more fatigue resistance for the trunk flexors in photobiomodulation groups compared to the placebo groupand no difference between the two photobiomodulation effects.

Evaluation of pain and flexor reflex responses and their association with clinical parameters in patients with fibromyalgia.

In the present study, we aimed to evaluate electrophysiological outcomes of flexor reflexes (FR) emerging in response to painful stimuli in fibromyalgia (FM) patients. This study included a total of 21 female FM patients (mean age 36.8±8.0 years; range, 20 to 50 years) and 28 healthy female controls (mean age 37.3±8.8 years; range, 22 to 53 years). Clinical features of the patients, Fibromyalgia Impact Questionnaire (FIQ), Beck Depression Inventory (BDI), and Beck Anxiety Inventory (BAI) scores were recorded. Electrophysiological stimulation threshold, visual analog scale (VAS) scores of generated pain after each stimulation, current intensity, flexor responses obtained from muscles, and electrophysiological measurement of these responses were noted. The threshold for perception of electrical current was higher and resistance level to maximum electrical current was lower in FM patients (p<0.05). The VAS scores of FM patients under maximum electrical current were higher than the control group (p<0.05), while the lowest current value in which FR response obtained in FM patients was lower (p<0.05). The latency was lower, amplitude was higher, and response area was wider in FM patients (p<0.05). No significant relationship between the FIQ, BDI, BAI scores and stimulant perception threshold levels was found in FM patients (p>0.05). Based on these findings, FR responses may be useful as an electrophysiological parameter in FM diagnosis.

Efeito do treinamento de caminhada no declive em variáveis neuromusculares

Walking involves small adjustments to maintain body balance. However, the demand for these adjustments may be different during downhill walking. The aim of this study was to analyze the effect of periodized downhill walking training on neuromuscular responses of knee flexors (KF). Seventeen active males (Age = 22.9 ± 3.9 years) were randomly assigned into two groups: control, level walking (CG, N = 8) and downhill walking (DWG, N = 9). Individuals performed the following procedures, in different days: 1) Maximal voluntary contractions to determine peak torque (PT) and rate of torque development (RTD) at different time intervals from the onset of muscle contraction. The test was performed before (Pre) and after (Post) a 4-week downhill walking training period. PT and peak RTD did not change after the training period (p > 0.05). However, there was significant increase in RTD at 150 ms and 200 ms after the onset of muscle contraction (p < 0.05). Additionally, the electromyographic activity (root mean square) of the biceps femoris and semitendineous muscles presented an increase after the training period (p < 0.05). Thus, downhill walking training can promote improvement RTD and muscle activity in the late phase of muscle contraction, which can have important implications during downhill walking, in which a rapid action of KF can help body balance against the disturbance generated by the slope.

Efeito do treinamento de caminhada no declive em variáveis neuromusculares

Walking involves small adjustments to maintain body balance. However, the demand for these adjustments may be different during downhill walking. The aim of this study was to analyze the effect of periodized downhill walking training on neuromuscular responses of knee flexors (KF). Seventeen active males (Age = 22.9 ± 3.9 years) were randomly assigned into two groups: control, level walking (CG, N = 8) and downhill walking (DWG, N = 9). Individuals performed the following procedures, in different days: 1) Maximal voluntary contractions to determine peak torque (PT) and rate of torque development (RTD) at different time intervals from the onset of muscle contraction. The test was performed before (Pre) and after (Post) a 4-week downhill walking training period. PT and peak RTD did not change after the training period (p &gt; 0.05). However, there was significant increase in RTD at 150 ms and 200 ms after the onset of muscle contraction (p &lt; 0.05). Additionally, the electromyographic activity (root mean square) of the biceps femoris and semitendineous muscles presented an increase after the training period (p &lt; 0.05). Thus, downhill walking training can promote improvement RTD and muscle activity in the late phase of muscle contraction, which can have important implications during downhill walking, in which a rapid action of KF can help body balance against the disturbance generated by the slope.

F56. Description of neurophysiological findings in mononeuritis multiple as a neurologic manifestation of borrelia burgdorferi infection - Case report

Introduction The infection for Borrelia burgdorferi is a zoonosis, in which the spirochaetes can be transmitted to human beings only by the bite of infected ixodid ticks, the spirochaete is maintained at high levels in populations of field mice or birds, the likelihood of having it is dependent on geography, recreational habits of the patient, and season. It is a multisistemic disease it can affect central nervous system. Neurological manifestations often referred to as Lyme neuroborreliosis are reported in up to 12% of patients with Lyme disease. In Europe and the United States seroprevalencia is 1–27%. This has not been determined in Mexico yet. In Mexico are few reports and series of cases published about Lyme neuroborreliosis, being a subdiagnosed disease in patients with neurological clinical manifestations. Methods Male 23 yo, carpenter. He started eight months earlier with symmetric paresthesias of both hands with ascending distribution from distal to proximal, presented inability to hold work tools with both hands, paresthesias in the plantar region and paresis of the lower limbs, ascending from distal to proximal, preventing him from walking and requiring help, finally prostration. PE: Generalized atrophy of distal predominance, interosseous atrophy of thenar and hypothenar, proximal upper limb 4/5, distal 3/5, proximal and distal lower limbs 4/5, absent bilateral patellar reflex. Bilateral plantar flexor response. Hypopallesthesia, altered arthrokinesia in both lower limbs and right hand. Unsteady gait with a broad base, short and slow steps with help. Romberg positive. Results Neurophysiological studies. Somatosensory evoked potentials (SSEP) of upper limbs with peripheral response integration at the level of the brachial plexus (N9) asymmetric by left prolongation and absence of responses from posterior cords (N13). SSEP of lower limbs with complete and bilateral absence of responses from popliteal fossa. N. median left, N. ulnar right, delay in nerve conduction velocity. Bilateral tibial with prolonged latency. N. median left with prolongation of peak latency. N. ulnar voltage asymmetry by right depression. F response of bilateral ulnar nerve did not elicit response. Bilateral tibial nerve with prolonged latencies and frequency of reduced evocation. The neurophysiological study showed evidence of multiple mononeuropathy that involves all four limbs asymmetrically. Ig G by Western blot versus Borrelia burgdorferi was positive in blood. It was prescribed ceftriaxone 1 g IV BID for 14 days, after this treatment showed neurological improvement, he continued with doxycycline 100 mg orally BID for a month. Conclusion Neuropathies in patients with chronic Lyme disease commonly present as non-vasculitic multiple mononeuritis, the motor deficit follows the multiple pattern. This case is based on an unusual neurological manifestation together with the exclusive predilection for affection of the central nervous system, having as main geographical and occupational risk factors.

Voluntary muscle activation and evoked volitional-wave responses as a function of torque

Introduction: This study employed a unique stimulation paradigm which allowed for the simultaneous assessment of voluntary activation levels (VA) via twitch-interpolation, and the evoked V-wave responses of the plantar flexors during submaximal and maximal contractions. Test-retest reliability was also examined. Methods: Fourteen participants repeated a stimulation protocol over four visits to assess VA and evoked V-wave amplitude across torque levels ranging from 20% to 100% MVC. MVC torque and EMG amplitude were also measured. Results: VA increased nonlinearly with torque production and plateaued by 80% MVC. V-wave amplitude increased linearly from 20% to 100% MVC. There were no differences in any dependent variable across visits (p > 0.05). VA demonstrated moderate to substantial reliability across all torque levels (ICC = 0.76–0.91) while V-wave amplitude exhibited fair to moderate reliability from 40% to 100% (ICC = 0.48–0.74). Discussion: We were able to reliably collect VA and the V-wave simultaneously in the plantar flexors. Collection of VA and V-wave during the same contraction provides distinct information regarding the contribution of motor-unit recruitment and descending cortico-spinal drive/excitability to force production.

A systematic and quantitative evaluation of plantar stimulation: The effect of type, pattern, force of stimulation in eliciting an accurate plantar response

ObjectivesSystematic and quantitative evaluation of the plantar reflex has been infrequently studied in the past and can help assess the vexing variables encountered in its elicitation. The objective of this study was to determine the effect of type, pattern and force of stimulation in eliciting an accurate plantar response in patients with pyramidal dysfunction and healthy individuals. Patients and methodsA special instrument was designed to give a predesigned force of stimulus. The plantar surface of foot was divided into nine parts and point and stroke stimulations were studied systematically in pyramidal weakness feet (cases) and healthy control feet (controls) with predefined forces. Results were tabulated and statistically analysed. ResultsStroke stimulation was superior to point stimulation in eliciting plantar response. There was no significant difference in the responses to the three predefined forces used for stroke stimulations. Sensitivity of Babinski sign was 72.9% and specificity was 100%. In pyramidal weakness feet, extensor responses were significantly elicited from lateral starting stroke patterns (67%) and on moving medially they were replaced by flexor responses (44%). Withdrawal responses increased with the stimulations reaching the distal foot and with the curvilinear component of stimulations. Sensitivity responses (related to the sensitivity of an individual) contaminate the plantar response and occasionally make its interpretation difficult. In subjects with bilateral sensitivity with unilateral disease, knowing the sensitivity pattern on the normal side improved the interpretation of plantar response on the abnormal side. ConclusionsBased on this study, the optimal method for eliciting Babinski sign accurately is to stroke the lateral aspect of the sole of the foot in a straight line up to mid foot. This should be performed in both feet three times, and if the weakness is unilateral, it should be performed in the normal leg first to aid interpretation of the affected leg.

Neuromuscular responses of the plantar flexors to whole-body vibration.

Enhanced physical performance following whole-body vibration (WBV) has been attributed to increased muscle activity; however, few studies have measured the mechanisms underlying these changes. The objective of this study was to measure the responsiveness of the Ia pathway as well as contractile properties in 16 young adults (24±2years, eight men, eight women) following repeated bouts of acute WBV (45Hz, 2mm). Hoffman reflexes (H-reflex), compound muscle action potentials (M-wave), and twitch contractile properties were measured prior to and immediately following five 1-minute WBV exposures, and at 3, 5, 10, and 20minute post-WBV. M-wave and H-reflex amplitudes decreased by 8% (P<.001) and by 46% (P<.05), respectively, whereas peak twitch torque decreased by 9% (P<.01) and rate of twitch torque development slowed 8% (P<.05). Percent voluntary activation and maximal plantar flexor torque were unchanged as a consequence of WBV (P>.05). In response to acute WBV, the root mean square of the soleus electromyography signal (EMGRMS ) increased by 8%, while the EMGRMS of the lateral gastrocnemius increased by 3% (P<.05). These data indicate that the responsiveness of the Ia pathway is diminished and contractile function is impaired immediately following WBV, and that the neural mechanisms underlying improved performance following WBV lie in alternative hypotheses possibly involving spindle disfacilitation or Golgi afferent modulation.

Involvement of spinal α2 -adrenoceptors in prolonged modulation of hind limb withdrawal reflexes following acute noxious stimulation in the anaesthetized rabbit.

The role of spinal α 2‐adrenoceptors in mediating long‐lasting modulation of hind limb withdrawal reflexes following acute noxious chemical stimulation of distant heterotopic and local homotopic locations has been investigated in pentobarbitone‐anaesthetized rabbits. Reflexes evoked in the ankle extensor muscle medial gastrocnemius (MG) by electrical stimulation of the ipsilateral heel, and reflexes elicited in the ankle flexor tibialis anterior and the knee flexor semitendinosus by stimulation at the base of the ipsilateral toes, could be inhibited for over 1 h after mustard oil (20%) was applied to either the snout or into the contralateral MG. The heel–MG response was also inhibited after applying mustard oil across the plantar metatarsophalangeal joints of the ipsilateral foot, whereas this homotopic stimulus facilitated both flexor responses. Mustard oil also caused a significant pressor effect when applied to any of the three test sites. The selective α2‐adrenoceptor antagonist, RX 821002 (100–300 μg, intrathecally), had no effect on reflexes per se, but did cause a decrease in mean arterial blood pressure. In the presence of the α2‐blocker, inhibitory and facilitatory effects of mustard oil on reflexes were completely abolished. These data imply that long‐lasting inhibition of spinal reflexes following acute noxious stimulation of distant locations involves activation of supraspinal noradrenergic pathways, the effects of which are dependent on an intact α2‐adrenoceptor system at the spinal level. These pathways and receptors also appear to be involved in facilitation (sensitization) as well as inhibition of reflexes following a noxious stimulus applied to the same limb.

Correlation of Resting Elbow Angle with Spasticity in Chronic Stroke Survivors

To evaluate whether resting joint angle is indicative of severity of spasticity of the elbow flexors in chronic stroke survivors. Seventeen hemiparetic stroke subjects (male: n = 13; female: n = 4; age: 37-89 years; 11 right and 6 left hemiplegia; averaged 54.8 months after stroke, ranging 12-107 months) participated in the study. The number of subjects with modified Ashworth scale score (MAS) = 0, 1, 1+, 2, and 3 was 3, 3, 5, 3, and 3, respectively. In a single experimental session, resting elbow joint angle, MAS, and Tardieu scale score (Tardieu R1) were measured. A customized motorized stretching device was used to stretch elbow flexors at 5, 50, and 100°/s, respectively. Biomechanical responses (peak reflex torque and reflex stiffness) of elbow flexors were quantified. Correlation analyses between clinical and biomechanical assessments were performed. Resting elbow joint angle showed a strong positive correlation with Tardieu R1 (r = 0.77, p < 0.01) and a very strong negative correlation with MAS (r = -0.89, p < 0.01). The resting angle also had strong correlations with biomechanical measures (r = -0.63 to -0.76, p < 0.01). Our study provides experimental evidence for anecdotal observation that the resting elbow joint angle correlates with severity of spasticity in chronic stroke. Resting angle observation for spasticity assessment can and will be an easy, yet a valid way of spasticity estimation in clinical settings, particularly for small muscles or muscles which are not easily measurable by common clinical methods.

Are Females More Resistant to Extreme Neuromuscular Fatigue?

Despite interest in the possibility of females outperforming males in ultraendurance sporting events, little is known about the sex differences in fatigue during prolonged locomotor exercise. This study investigated possible sex differences in central and peripheral fatigue in the knee extensors and plantar flexors resulting from a 110-km ultra-trail-running race. Neuromuscular function of the knee extensors and plantar flexors was evaluated via transcranial magnetic stimulation (TMS) and electrical nerve stimulation before and after an ultra-trail-running race in 20 experienced ultraendurance trail runners (10 females and 10 males matched by percent of the winning time by sex) during maximal and submaximal voluntary contractions and in relaxed muscle. Maximal voluntary knee extensor torque decreased more in males than in females (-38% vs -29%, P = 0.006) although the reduction in plantar flexor torque was similar between sexes (-26% vs -31%). Evoked mechanical plantar flexor responses decreased more in males than in females (-23% vs -8% for potentiated twitch amplitude, P = 0.010), indicating greater plantar flexor peripheral fatigue in males. Maximal voluntary activation assessed by TMS and electrical nerve stimulation decreased similarly in both sexes for both muscle groups. Indices of knee extensor peripheral fatigue and corticospinal excitability and inhibition changes were also similar for both sexes. Females exhibited less peripheral fatigue in the plantar flexors than males did after a 110-km ultra-trail-running race and males demonstrated a greater decrease in maximal force loss in the knee extensors. There were no differences in the magnitude of central fatigue for either muscle group or TMS-induced outcomes. The lower level of fatigue in the knee extensors and peripheral fatigue in the plantar flexors could partly explain the reports of better performance in females in extreme duration running races as race distance increases.

Acute Effects of Concentric vs. Eccentric Exercise on Force Steadiness and Electromyographic Responses of the Forearm Flexors

The purpose of this study was to examine the acute effects of concentric (CON) vs. eccentric (ECC) exercise on isometric strength, force steadiness, and surface electromyographic (EMG) responses of the forearm flexors. Fifteen resistance-trained men (mean ± SD: age = 23.7 ± 3.5 years; height = 178.9 ± 4.7 cm; body weight = 86.2 ± 9.8 kg) performed 6 sets of 10 maximal CON isokinetic or ECC isokinetic muscle actions using the dominant forearm flexors on 2 separate experimental visits. Before and immediately after the exercise interventions, isometric strength testing and submaximal trapezoid isometric contractions were performed, with bipolar EMG signals detected from the biceps brachii. The coefficient of variation of the force output from the mid 8-second portion of each submaximal trapezoid isometric contraction was calculated to assess force steadiness. In addition, the EMG signal was selected from the same portion as the force signal. The results showed that both CON and ECC caused similar isometric strength losses, but ECC caused a greater loss of force steadiness than CON. In addition, EMG amplitude increased similarly after both exercise interventions, but the magnitude of the increase in EMG mean frequency after ECC tended to be smaller, when compared with that after CON. These findings suggested that, even for resistance-trained individuals that are more resistant to ECC exercise-induced muscle damage than untrained individuals, their ability to maintain a steady submaximal force can be impaired after a bout of ECC exercise.

Effects of acute dehydration on neuromuscular responses of exercised and nonexercised muscles after exercise in the heat.

Dehydration can impair aerobic performance, but its effects on muscular strength are still unclear. This study evaluated the effect of dehydration induced by cycling in the heat on exercised (knee extensors) and nonexercised (elbow flexors) muscles' strength and activation. Ten healthy recreationally active and nonacclimatized men (age, 22.71 ± 2.21 years old; body mass (BM), 77.94 ± 7.35 kg; height, 1.76 ± 6.46 m; body fat, 18.93 ± 3.01%) cycled in the heat in 2 separate sessions: dehydrated (DHY) and euhydrated (EUH). Dehydrated session led to a 2% BM loss, and water ingestion prevented the water loss in the euhydrated session. Knee extensor and elbow flexor maximal isometric torques and muscle activation were assessed before and after exercising in both sessions. Knee extensor torque decreased 15.8% (p < 0.001; 294.27 ± 44.82-247.16 ± 40.54) in dehydrated session, whereas no significant reduction (2.98%; p = 0.348; 291.99 ± 48.37-281.74 ± 38.65) was observed in the euhydrated session. No significant session-time interaction (p = 0.098) was observed for elbow flexor responses (DHY, 67.51 ± 14.53-62.95 ± 13.60; EUH, 68.26 ± 13.06-67.87 ± 13.89). Muscle activation capacity was unaffected by the hydration status. Maintenance of euhydration state during cycling in the heat may attenuate strength impairments caused by water loss in exercised muscle groups.