Neuromuscular characteristics of eccentric, concentric and isometric contractions of the knee extensors.

PURPOSE: We compared voluntary drive and corticospinal responses during eccentric (ECC), isometric (ISOM) and concentric (CON) muscle contractions to shed light on neurophysiological mechanisms underpinning the lower voluntary drive in a greater force production in ECC than other contractions. METHODS: Sixteen participants (20-33 years) performed ISOM and isokinetic (30°/s) CON and ECC knee extensor contractions (110°-40° knee flexion) in which electromyographic activity (EMG) was recorded from vastus lateralis. Voluntary activation (VA) was measured during ISOM, CON and ECC maximal voluntary contractions (MVCs). Transcranial magnetic stimulation elicited motor-evoked potentials (MEPs) and corticospinal silent periods (CSP) during MVCs and submaximal (30%) contractions, and short-interval intracortical inhibition (SICI) in submaximal contractions. RESULTS: MVC torque was greater (P < 0.01) during ECC (302.6 ± 90.0 Nm) than ISOM (269.8 ± 81.5 Nm) and CON (235.4 ± 78.6 Nm), but VA was lower (P < 0.01) for ECC (68.4 ± 14.9%) than ISOM (78.3 ± 13.1%) and CON (80.7 ± 15.4%). In addition, EMG/torque was lower (P < 0.02) for ECC (1.9 ± 1.1 µV.Nm-1) than ISOM (2.2 ± 1.2 µV.Nm-1) and CON (2.7 ± 1.6 µV.Nm-1), CSP was shorter (p < 0.04) for ECC (0.097 ± 0.03 s) than ISOM (0.109 ± 0.02 s) and CON (0.109 ± 0.03 s), and MEP amplitude was lower (P < 0.01) for ECC (3.46 ± 1.67 mV) than ISOM (4.21 ± 2.33 mV) and CON (4.01 ± 2.06 mV). Similar results were found for EMG/torque and CSP during 30% contractions, but MEP and SICI showed no differences among contractions (p > 0.05). CONCLUSIONS: The lower voluntary drive indicated by reduced VA during ECC may be partly explained by lower corticospinal excitability, while the shorter CSP may reflect extra muscle spindle excitation of the motoneurons from vastus lateralis muscle lengthening.

The Spontaneous Incidence of Neurological Clinical Signs in Preclinical Species Using Cage-side Observations or High-definition Video Monitoring: A Retrospective Analysis.

When conducting toxicology studies, the interpretation of drug-related neurological clinical signs such as convulsions, myoclonus/myoclonic jerks, tremors, ataxia, and salivation requires an understanding of the spontaneous incidence of those observations in commonly used laboratory animal species. The spontaneous incidence of central nervous system clinical signs in control animals from a single facility using cage-side observations or high definition video monitoring was retrospectively analyzed. Spontaneous convulsions were observed at low incidence in Beagle dogs and Sprague-Dawley rats but were not identified in cynomolgus monkeys and Göttingen minipigs. Spontaneous myoclonic jerks and muscle twitches were observed at low incidence in Beagle dogs, cynomolgus monkeys, and Sprague-Dawley rats but were not seen in Göttingen minipigs. Spontaneous ataxia/incoordination was identified in all species and generally with a higher incidence when using video monitoring. Salivation and tremors were the two most frequent spontaneous clinical signs and both were observed in all species. Data from the current study unveil potential limitations when using control data obtained from a single study for toxicology interpretation related to low incidence neurological clinical signs while providing historical control data from Beagle dogs, cynomolgus monkeys, Sprague-Dawley rats, and Göttingen minipigs.

Neuromuscular and gene signaling responses to passive whole-body heat stress in young adults.

This study aimed to investigate whether acute passive heat stress 1) decreases muscle Maximal Voluntary Contraction (MVC); 2) increases peripheral muscle fatigue; 3) increases spinal cord excitability, and 4) increases key skeletal muscle gene signaling pathways in skeletal muscle. Examining the biological and physiological markers underlying passive heat stress will assist us in understanding the potential therapeutic benefits. MVCs, muscle fatigue, spinal cord excitability, and gene signaling were examined after control or whole body heat stress in an environmental chamber (heat; 82 °C, 10% humidity for 30 min). Heart Rate (HR), an indicator of stress response, was correlated to muscle fatigue in the heat group (R = 0.59; p < 0.05) but was not correlated to MVC, twitch potentiation, and H reflex suppression. Sixty-one genes were differentially expressed after heat (41 genes >1.5-fold induced; 20 < 0.667 fold repressed). A strong correlation emerged between the session type (control or heat) and principal components (PC1) (R = 0.82; p < 0.005). Cell Signal Transduction, Metabolism, Gene Expression and Transcription, Immune System, DNA Repair, and Metabolism of Proteins were pathway domains with the largest number of genes regulated after acute whole body heat stress. Acute whole-body heat stress may offer a physiological stimulus for people with a limited capacity to exercise.

Comparison of Physiological Effects Induced by Two Compression Stockings and Regular Socks During Prolonged Standing Work.

OBJECTIVE: The goal of this study was to evaluate and compare lower-leg muscle fatigue, edema, and discomfort induced by the prolonged standing of security guards wearing regular socks and those wearing 15-20 or 20-30 mmHg compression stockings as intervention. BACKGROUND: Compression stockings are sometimes used by individuals standing all day at work. However, quantitative evidence showing their potential benefits for lower-leg health issues in healthy individuals during real working conditions is lacking. METHOD: Forty male security employees participated in the study. All were randomly assigned to the control or one of the two intervention groups (I15-20 or I20-30). Lower-leg muscle twitch force, volume, and discomfort ratings were measured before and after their regular 12-hr standing work shift. RESULTS: Significant evidence of lower-leg long-lasting muscle fatigue, edema, and discomfort was observed after standing work for guards wearing regular socks. However, no significant changes were found for guards wearing either compression stockings. CONCLUSION: In healthy individuals, compression stockings seem to attenuate efficiently the tested outcomes in the lower leg resulting from prolonged standing. APPLICATION: Occupational activities requiring prolonged standing may benefit from 15-20 or 20-30 mmHg compression stockings. As similar benefits were observed for both levels of compression, the lower level may be sufficient.

The muscle twitch profile assessed with motor unit magnetic resonance imaging.

Localised signal voids in diffusion-weighted (DW) images of skeletal muscle have been postulated to occur as a result of muscle fibre contraction and relaxation. We investigated the contrast mechanism of these signal voids using a combination of modelling and experimental measurements by employing DW and phase contrast (PC) imaging sequences. The DW signal and PC signal were simulated for each time point of a theoretical muscle twitch. The model incorporated compaction (simulating actively contracting muscle fibres) and translation (simulating passively moving surrounding fibres). The model suggested that the DW signal depended on contraction time and compaction whereas the PC signal depended on contraction time, compaction and translation. In a retrospective study, we tested this model with subgroup analyses on 10 healthy participants. Electrical nerve stimulation was used to generate muscle twitches in lower leg muscles; the resulting force was measured using an MR-compatible force transducer. At current levels causing a visible muscle twitch (~13 mA), the width of the first signal drop in the DW signal (mean ± SD: 103 ± 20 ms) was comparable with the force contraction time (93 ± 34 ms; intraclass correlation coefficient [ICC] = 0.717, P = .010). At current levels activating single motor units (~9 mA), the contraction time determined from the DW signal was 75 ± 13 ms and comparable with the PC contraction time (81 ± 15 ms; ICC = 0.925, P = .001). The maximum positive velocity was 0.55 ± 0.26 cm/s and the displacement was 0.20 ± 0.10 mm. Voxel-wise analysis revealed localised DW changes occurring together with more widespread phase changes. In conclusion, local signal attenuations in DW images following muscle fibre activation are primarily caused by compaction. The PC sequence also detects translating muscle tissue being passively pulled. The magnitude of the changes in DW and PC images depends on the twitch's contractile properties and percentage contraction. DW imaging and PC imaging can therefore measure twitch profiles of skeletal muscle fibres.

Physiological and neuromotor changes induced by two different stand-walk-sit work rotations.

The potential of rotating postures to alleviate the effects of prolonged standing and sitting postures has been advocated to attenuate the accumulation of muscle fatigue, considered a precursor to musculoskeletal disorders. We aimed to evaluate the effects of two posture rotations, both including standing, walking, sitting, on physiological and neuromotor measures. Twenty-two participants followed two posture rotations, with different rest-break distributions, for 5.25 h. Lower-leg muscle twitch force, volume, force control and discomfort perception were evaluated during and after work exposure on two non-consecutive days. Significant changes in all measures indicate a detrimental effect in lower-leg long-lasting muscle fatigue, oedema, performance and discomfort after 5 h for both exposures. However, for both exposures recovery was significant 1 h and 15 h post-workday. Differences between the two rotation schedules were not significant. Hence, stand-walk-sit posture rotation promotes recovery of the tested measures and is likely to better prevent muscle fatigue accumulation. Practitioner summary: Lower-leg muscle twitch force, volume, force control, and discomfort were quantified during and after 5 h of stand-walk-sit work rotations with two different rest-break distributions. Measures revealed similar significant effects of work exposures regardless of rotation; which did not persist post-work. This beneficial recovery contrasts with the standing only situations. Abbreviations: MSDs: musculoskeletal disorders; MTF: muscle twitch force; RMSE: root mean square error; MVC: maximum voluntary contraction; M: mean; SE: standard error.

Physiological changes during prolonged standing and walking considering age, gender and standing work experience.

Occupational standing is associated with musculoskeletal and venous disorders. The aim was to investigate whether lower leg oedema and muscle fatigue development differ between standing and walking and whether age, gender and standing work habituation are factors to consider. Sixty participants (15 young females, 15 young males, 15 older males, and 15 young males habituated to standing work) were included and required to stand/walk for 4.5 hours in three periods with two seated breaks. Waterplethysmography/bioelectrical impedance, muscle twitch force and surface electromyography were used to assess lower leg swelling (LLS) and muscle fatigue as well as gastrocnemius muscle activity, respectively. While standing led to LLS and muscle fatigue, walking did not. Low-level medial gastrocnemius activity was not continuous during standing. No significant influence of age, gender and standing habituation was observed. Walking can be an effective prevention measure to counteract the detrimental effects of quasi-static standing.Practitioner summary: Prolonged standing leads to lower leg oedema and muscle fatigue while walking does not. The primary cause of fatigue may be in other muscles than the medial gastrocnemius. Walking may be an effective prevention measure for health risks of occupational standing when included intermittently.Abbreviation: BI: bioelectrical impedance; LLS: lower leg swelling; SEMG: surface electromyography; MTF: muscle twitch force; WP: waterplethysmography; Bsl: Baseline; L: Lunch; E: Evening; MTM: method times measurement; EA: electrical activity; IQR: interquartile range; p: percentile; M: mean; SE: standard error; Adj: adjusted.

Anodal and cathodal transcranial direct current stimulation can decrease force output of knee extensors during an intermittent MVC fatiguing task in young healthy male participants.

Transcranial direct current stimulation (tDCS) has the capacity to enhance force output during a short-lasting maximal voluntary contraction (MVC) as well as during a long-lasting submaximal voluntary contraction until task failure. However, its effect on an intermittent maximal effort is not known. We hypothesized that anodal tDCS applied during or before a maximal fatigue task increases the amplitude of maximal voluntary contraction (aMVC) and voluntary activation (VA) in young healthy male participants. We measured VA, potentiated twitch at rest (Ptw), root mean square electromyogram (EMG), and aMVC during a fatiguing task that consisted of 35 × 5 s MVC of knee extensors and was performed during tDCS or 10 min after the end of tDCS (sham, anodal, or cathodal treatments). No effect of tDCS was detected on the first MVC but, when compared to sham tDCS, both anodal tDCS and cathodal tDCS reduced aMVC when tDCS was applied during the task (p < .001) and only anodal tDCS reduced aMVC when applied 10 min before the task (p = .03). The reductions in aMVC were accompanied by reductions in EMG of M. vastus lateralis for both tDCS treatments as well as in Ptw only during anodal tDCS and in VA only during cathodal tDCS. Both cathodal tDCS and anodal tDCS impaired force production during an intermittent fatiguing MVC task. The detrimental effects were stronger when tDCS was applied during the task. Here, cathodal and anodal tDCS specifically affected Ptw and VA indicating different underlying mechanisms.

Muscular and Vascular Issues Induced by Prolonged Standing With Different Work-Rest Cycles With Active or Passive Breaks.

OBJECTIVE: The aim of this study was to evaluate the long-lasting motor, behavioral, physiological, and perceptual effects of prolonged standing work in three work-rest cycle conditions including passive or active rest breaks. BACKGROUND: Muscle fatigue has been evidenced after prolonged standing work through physiological and neuromotor measures. It has been postulated that muscle fatigue induced by prolonged work could be attenuated by appropriate scheduling of work and rest periods. However, investigations in this domain remain limited. METHOD: Thirty participants simulated standing work for 5 hr with work-rest cycles of short, medium, or long standing periods including passive or active breaks. Lower-leg muscle twitch force (MTF), muscle oxygenation, lower-leg volume, postural stability, force control, and discomfort perception were quantified on 2 days. RESULTS: Prolonged standing induced significant changes in all measures immediately after 5 hr of work, indicating a detrimental effect in long-lasting muscle fatigue, performance, discomfort, and vascular aspects. Differences in the measures were not significant between work cycles and/or break type. CONCLUSION: Similar physiological and motor alterations were induced by prolonged standing. The absence of difference in the effects induced by the tested work-rest cycles suggests that simply altering the work-rest cycle may not be sufficient to counteract the effects of mainly static standing work. Finally, standing for 3 hr or more shows clear detrimental effects. APPLICATION: Prolonged standing is likely to contribute to musculoskeletal and vascular symptoms. A limitation to less than 3 hr of mostly static standing in occupational activities could avoid alterations leading to these symptoms.

Cyclic muscle twitch contraction inhibits immobilization-induced muscle contracture and fibrosis in rats.

We investigated the effects of cyclic muscle twitch contraction caused by neuromuscular electrical stimulation (NMES) on immobilization-induced muscle contracture and fibrosis in rats. Twenty-nine rats were divided into control, immobilization, and immobilization with muscle contraction groups. The ankle joints of the immobilization and muscle contraction rats were fixed in full plantar flexion with a plaster cast for 4 weeks. In the muscle contraction group, cyclic muscle twitch contraction of the soleus muscle was induced using a commercial device (1 Hz, 4 ± 2 mA, 60 min/day, 5 times/week) with the ankle joint immobilized. The dorsiflexion range of ankle joint motion in the muscle contraction group was significantly greater than that in the immobilization group. The expressions of fibrosis-related genes (i.e., hypoxia inducible factor-1α, transforming growth factor-ß1, α-smooth muscle actin, and types I and III collagen) were significantly decreased in the muscle contraction group compared to the immobilization group. The fluorescence intensities of type I and type III collagen in the perimysium and endomysium in the muscle contraction group were significantly decreased compared to the immobilization group. These results suggest that cyclic muscle twitch contraction induced by NMES might alleviate skeletal muscle fibrosis, reducing immobilization-induced muscle contracture.

An acute session of roller massage prolongs voluntary torque development and diminishes evoked pain.

INTRODUCTION: Roller massage (RM) has been reported to reduce pain associated with exercise-induced muscle soreness and increase range of motion without force or activation impairments. The objective was to examine RM effects on evoked pain and contractile properties. METHODS: Twelve men received three sets of 30-s RM at a perceived discomfort level of 7/10 on a visual analogue scale on the ipsilateral (IPSI-R) stimulated plantar flexors (PF), contralateral PF (CONTRA-R), Sham (light rolling on stimulated PF), or Control. At pre-test, post-test, and 5-min post-test, they received evoked maximal twitch, tetanus, and 70% maximal tetanic stimulation, and performed a maximal voluntary isometric contraction (MVIC). Data analysis included perceived pain and contractile properties. RESULTS: The 70% tetanus illustrated significant 9-10% increases in pain perception with Sham and Control at post- and 5-min post-test, respectively (p < 0.01). There was no pain augmentation with IPSI-R and CONTRA-R. There were no main effects or interactions for most contractile properties. However, MVIC force developed in the first 200 ms showed 9.5% (p = 0.1) and 19.1% (p = 0.03) decreases with IPSI-R at post-test and 5-min post-test. CONCLUSION: Data suggest that RM-induced neural inhibition decreased MVIC F200 and nullified the testing-induced increase in evoked pain associated with 70% tetanic stimulation.

Long-Lasting Changes in Muscle Twitch Force During Simulated Work While Standing or Walking.

OBJECTIVE: The aim of this study was to evaluate the long-lasting effects of prolonged standing work on a hard floor or floor mat and slow-pace walking on muscle twitch force (MTF) elicited by electrical stimulation. BACKGROUND: Prolonged standing work may alter lower-leg muscle function, which can be quantified by changes in the MTF amplitude and duration related to muscle fatigue. Ergonomic interventions have been proposed to mitigate fatigue and discomfort; however, their influences remain controversial. METHOD: Ten men and eight women simulated standing work in 320-min experiments with three conditions: standing on a hard floor or an antifatigue mat and walking on a treadmill, each including three seated rest breaks. MTF in the gastrocnemius-soleus muscles was evaluated through changes in signal amplitude and duration. RESULTS: The significant decrease of MTF amplitude and an increase of duration after standing work on a hard floor and on a mat persisted beyond 1 hr postwork. During walking, significant MTF metrics changes appeared 30 min postwork. MTF amplitude decrease was not significant after the first 110 min in any of the conditions; however, MTF duration was significantly higher than baseline in the standing conditions. CONCLUSION: Similar long-lasting weakening of MTF was induced by standing on a hard floor and on an antifatigue mat. However, walking partially attenuated this phenomenon. APPLICATION: Mostly static standing is likely to contribute to alterations of MTF in lower-leg muscles and potentially to musculoskeletal disorders regardless of the flooring characteristics. Occupational activities including slow-pace walking may reduce such deterioration in muscle function.

Long-Term Muscle Fatigue After Standing Work.

OBJECTIVE: The aims of this study were to determine long-term fatigue effects in the lower limbs associated with standing work and to estimate possible age and gender influences. BACKGROUND: The progressive accumulation of muscle fatigue effects is assumed to lead to musculoskeletal disorders, as fatigue generated by sustained low-level exertions exhibits long-lasting effects. However, these effects have received little attention in the lower limbs. METHOD: Fourteen men and 12 women from two different age groups simulated standing work for 5 hr including 5-min seated rest breaks and a 30-min lunch. The younger group was also tested in a control day. Muscle fatigue was quantified by electrically induced muscle twitches (muscle twitch force [MTF]), postural stability, and subjective evaluation of discomfort. RESULTS: MTF showed a significant fatigue effect after standing work that persisted beyond 30 min after the end of the workday. MTF was not affected on the control day. The center of pressure displacement speed increased significantly over time after standing work but was also affected on the control day. Subjective evaluations of discomfort indicated a significant increase in perception of fatigue immediately after the end of standing work; however, this perception did not persist 30 min after. Age and gender did not influence fatigue. CONCLUSION: Objective measures show the long-term effects of muscle fatigue after 5 hr of standing work; however, this fatigue is no longer perceived after 30 min of rest postwork. APPLICATION: The present results suggest that occupational activities requiring prolonged standing are likely to contribute to lower-extremity and/or back disorders.

Muscle oxygenation and time to task failure of submaximal holding and pulling isometric muscle actions and influence of intermittent voluntary muscle twitches.

BACKGROUND: Isometric muscle actions can be performed either by initiating the action, e.g., pulling on an immovable resistance (PIMA), or by reacting to an external load, e.g., holding a weight (HIMA). In the present study, it was mainly examined if these modalities could be differentiated by oxygenation variables as well as by time to task failure (TTF). Furthermore, it was analyzed if variables are changed by intermittent voluntary muscle twitches during weight holding (Twitch). It was assumed that twitches during a weight holding task change the character of the isometric muscle action from reacting (≙ HIMA) to acting (≙ PIMA). METHODS: Twelve subjects (two drop outs) randomly performed two tasks (HIMA vs. PIMA or HIMA vs. Twitch, n = 5 each) with the elbow flexors at 60% of maximal torque maintained until muscle failure with each arm. Local capillary venous oxygen saturation (SvO2) and relative hemoglobin amount (rHb) were measured by light spectrometry. RESULTS: Within subjects, no significant differences were found between tasks regarding the behavior of SvO2 and rHb, the slope and extent of deoxygenation (max. SvO2 decrease), SvO2 level at global rHb minimum, and time to SvO2 steady states. The TTF was significantly longer during Twitch and PIMA (incl. Twitch) compared to HIMA (p = 0.043 and 0.047, respectively). There was no substantial correlation between TTF and maximal deoxygenation independently of the task (r = - 0.13). CONCLUSIONS: HIMA and PIMA seem to have a similar microvascular oxygen and blood supply. The supply might be sufficient, which is expressed by homeostatic steady states of SvO2 in all trials and increases in rHb in most of the trials. Intermittent voluntary muscle twitches might not serve as a further support but extend the TTF. A changed neuromuscular control is discussed as possible explanation.

Superior Laryngeal Nerve Signal Attenuation Influences Voice Outcomes in Thyroid Surgery.

OBJECTIVES/HYPOTHESIS: The objective was to identify whether injury of the external branch of the superior laryngeal nerve (EBSLN) or changes in EBSLN parameters after dissection during thyroidectomies correlate with changes in voice quality postoperatively. STUDY DESIGN: Prospective multicenter case series. METHODS: A prospective multicenter study was conducted on patients undergoing thyroidectomies with intraoperative nerve monitoring. Electromyography waveforms of EBSLN stimulation before (S1) and after superior pole dissection (S2) were evaluated using endotracheal tube (ETT) and cricothyroid intramuscular (CTM) electrodes. Voice outcomes were assessed using Voice-Related Quality of Life Surveys and Voice Handicap Index. RESULTS: A total of 131 at-risk EBSLNs were evaluated in 80 patients. Two nerves showed loss of CTM twitch coupled with an absent S2 signal response. Complete EBSLN loss of signal was more likely with: 1) Cernea EBSLN anatomic classification Type 2B; 2) with a longer distance from the sternothyroid muscle insertion site; and 3) with larger lobar volumes (P < .05). Patients who experienced a more than 50% decrement in CTM amplitudes of S2 (n = 7) by CTM electrodes had a statistically significant decline in their voice outcomes compared to those who did not (n = 69) (P < .05). CONCLUSIONS: Patients experienced worse voice outcomes when at least one EBSLN response amplitude decreased by more than 50% after dissection when measured by CTM needle electrodes. CTM needle electrodes have an ability to measure finer amplitude changes compared to ETT electrodes, may represent a safe method to deduce subtle EBSLN injuries, and may serve to optimize voice outcomes during thyroidectomy. CTM needle electrodes are safe and tolerated well. LEVEL OF EVIDENCE: 4 Laryngoscope, 131:1436-1442, 2021.

Skeletal muscle function during the progression of cancer cachexia in the male ApcMin/+ mouse.

While cancer-induced skeletal muscle wasting has been widely investigated, the drivers of cancer-induced muscle functional decrements are only beginning to be understood. Decreased muscle function impacts cancer patient quality of life and health status, and several potential therapeutics have failed in clinical trials due to a lack of functional improvement. Furthermore, systemic inflammation and intrinsic inflammatory signaling's role in the cachectic disruption of muscle function requires further investigation. We examined skeletal muscle functional properties during cancer cachexia and determined their relationship to systemic and intrinsic cachexia indices. Male ApcMin/+ (MIN) mice were stratified by percent body weight loss into weight stable (WS; <5% loss) or cachectic (CX; >5% loss). Age-matched C57BL/6 littermates served as controls. Tibialis anterior (TA) twitch properties, tetanic force, and fatigability were examined in situ. TA protein and mRNA expression were examined in the nonstimulated leg. CX decreased muscle mass, tetanic force (Po), and specific tetanic force (sPo). Whole body and muscle fatigability were increased in WS and CX. CX had slower contraction rates, +dP/d t and -dP/d t, which were inversely associated with muscle signal transducer and activator of transcription 3 ( STAT3) and p65 activation. STAT3 and p65 activation were also inversely associated with Po. However, STAT3 was not related to sPo or fatigue. Muscle suppressor of cytokine signaling 3 mRNA expression was negatively associated with TA weight, Po, and sPo but not fatigue. Our study demonstrates that multiple functional deficits that occur with cancer cachexia are associated with increased muscle inflammatory signaling. Notably, muscle fatigability is increased in the MIN mouse before cachexia development. NEW & NOTEWORTHY Recent studies have identified decrements in skeletal muscle function during cachexia. We have extended these studies by directly relating decrements in muscle function to established cachexia indices. Our results demonstrate that a slow-fatigable contractile phenotype is developed during the progression of cachexia that coincides with increased muscle inflammatory signaling. Furthermore, regression analysis identified predictors of cancer-induced muscle dysfunction. Last, we report the novel finding that whole body and muscle fatigability were increased before cachexia development.

Is cricothyroid muscle twitch predictive of the integrity of the EBSLN in Thyroid Surgery?

OBJECTIVE: Cricothyroid (CT) muscle twitch inspection with neurostimulation is a widely accepted method to identify the external branch of the superior laryngeal nerve (EBSLN) and its integrity in thyroid surgery. However, there has been no large-scale research to evaluate the diagnostic values of CT muscle twitch inspection based on postoperative electromyography (EMG) results, which are considered the gold standard. In this study, we aimed to demonstrate the diagnostic value of CT muscle twitch inspection based on postoperative EMG. STUDY DESIGN: Prospective cohort study. METHODS: A total of 454 patients underwent primary thyroid surgery. Among them, 55 patients were excluded because of preoperative vocal fold palsy, problems with the stimulator, or refusal to participate in the EMG study. Finally, 399 patients were prospectively enrolled in this study. Intraoperatively, CT muscle twitch was inspected with neurostimulation. Bilateral EMG examination of the CT muscle was performed 2 to 3 months postoperatively in all patients. RESULTS: A total of 712 EBSLNs at risk were analyzed in this study. Of these, 21 (2.9%) nerves were visually identified, and positive CT muscle twitch by neurostimulation was observed in 694 (97.5%). Normal results on postoperative EMG of the CT muscle were reported in 657 (92.3%). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 97.7%, 5.5%, 92.5%, and 16.7%, respectively. CONCLUSION: CT muscle twitch inspection could be a useful intraoperative tool to determine EBSLN integrity considering its high sensitivity and PPV. However, the test may not completely replace EMG for evaluating EBSLN integrity due to its low specificity and NPV. LEVEL OF EVIDENCE: 2b. Laryngoscope, 2654-2661, 2018.

Plantar flexor muscle weakness and fatigue in spastic cerebral palsy patients.

BACKGROUND: Patients with cerebral palsy develop an important muscle weakness which might affect the aetiology and extent of exercise-induced neuromuscular fatigue. AIM: This study evaluated the aetiology and extent of plantar flexor neuromuscular fatigue in patients with cerebral palsy. METHODS: Ten patients with cerebral palsy and 10 age- and sex-matched healthy individuals (∼20 years old, 6 females) performed four 30-s maximal isometric plantar flexions interspaced by a resting period of 2-3s to elicit a resting twitch. Maximal voluntary contraction force, voluntary activation level and peak twitch were quantified before and immediately after the fatiguing task. RESULTS: Before fatigue, patients with cerebral palsy were weaker than healthy individuals (341±134N vs. 858±151N, p<0.05) and presented lower voluntary activation (73±19% vs. 90±9%, p<0.05) and peak twitch (100±28N vs. 199±33N, p<0.05). Maximal voluntary contraction force was not significantly reduced in patients with cerebral palsy following the fatiguing task (-10±23%, p>0.05), whereas it decreased by 30±12% (p<0.05) in healthy individuals. CONCLUSIONS: Plantar flexor muscles of patients with cerebral palsy were weaker than their healthy peers but showed greater fatigue resistance. WHAT THIS PAPER ADDS: Cerebral palsy is a widely defined pathology that is known to result in muscle weakness. The extent and origin of muscle weakness were the topic of several previous investigations; however some discrepant results were reported in the literature regarding how it might affect the development of exercise-induced neuromuscular fatigue. Importantly, most of the studies interested in the assessment of fatigue in patients with cerebral palsy did so with general questionnaires and reported increased levels of fatigue. Yet, exercise-induced neuromuscular fatigue was quantified in just a few studies and it was found that young patients with cerebral palsy might be more fatigue resistant that their peers. Thus, it appears that (i) conflicting results exist regarding objectively-evaluated fatigue in patients with cerebral palsy and (ii) the mechanisms underlying this muscle fatigue - in comparison to those of healthy peers - remain poorly understood. The present study adds important knowledge to the field as it shows that when young adults with cerebral palsy perform sustained maximal isometric plantar flexions, they appear less fatigable than healthy peers. This difference can be ascribed to a better preservation of the neural drive to the muscle. We suggest that the inability to drive their muscles maximally accounts for the lower extent of exercise-induced neuromuscular fatigue in patients with cerebral palsy.

Force estimation in fatigue condition using a muscle-twitch model during isometric finger contraction.

We propose a force estimation method in fatigue condition using a muscle-twitch model and surface electromyography (sEMG). The twitch model, which is an estimate of force by a single spike, was obtained from sEMG features and measured forces. Nine healthy subjects performed isometric index finger abduction until exhaustion for a series of dynamic contractions (0-20% MVC) to characterize the twitch model and static contractions (50% MVC) to induce muscle fatigue. Muscle fatigue was identified based on the changes of twitch model; the twitch peak decreased and the contraction time increased as muscle fatigue developed. Force estimation performance in non-fatigue and fatigue conditions was evaluated and its results were compared with that of a conventional method using the mean absolute value (MAV). In non-fatigue conditions, the performance of the proposed method (0.90 ±â€¯0.05) and the MAV method (0.88 ±â€¯0.06) were comparable. In fatigue conditions, the performance was significantly improved for the proposed method (0.87 ±â€¯0.05) compared with the MAV (0.78 ±â€¯0.09).

Contribution of intraoperative neuromonitoring to the identification of the external branch of superior laryngeal nerve.

OBJECTIVE: We evaluated the contribution of intraoperative neuromonitoring to the visual and functional identification of the external branch of the superior laryngeal nerve. MATERIAL AND METHODS: The prospectively collected data of patients who underwent thyroid surgery with intraoperative neuromonitoring for external branch of the superior laryngeal nerve exploration were assessed retrospectively. The surface endotracheal tube-based Medtronic NIM3 intraoperative neuromonitoring device was used. The external branch of the superior laryngeal nerve function was evaluated by the cricothyroid muscle twitch. In addition, contribution of external branch of the superior laryngeal nerve to the vocal cord adduction was evaluated using electromyographic records. RESULTS: The study included data of 126 (female, 103; male, 23) patients undergoing thyroid surgery, with a mean age of 46.2±12.2 years (range, 18-75 years), and 215 neck sides were assessed. Two hundred and one (93.5%) of 215 external branch of the superior laryngeal nerves were identified, of which 60 (27.9%) were identified visually before being stimulated with a monopolar stimulator probe. Eighty-nine (41.4%) external branch of the superior laryngeal nerves were identified visually after being identified with a probe. Although 52 (24.1%) external branch of the superior laryngeal nerves were identified with a probe, they were not visualized. Intraoperative neuromonitoring provided a significant contribution to visual (p<0.001) and functional (p<0.001) identification of external branch of the superior laryngeal nerves. Additionally, positive electromyographic responses were recorded from 160 external branch of the superior laryngeal nerves (74.4%). CONCLUSION: Intraoperative neuromonitoring provides an important contribution to visual and functional identification of external branch of the superior laryngeal nerves. We believe that it can not be predicted whether the external branch of the superior laryngeal nerve is at risk or not and the nerve is often invisible; thus, intraoperative neuromonitoring may routinely be used in superior pole dissection. Glottic electromyography response obtained via external branch of the superior laryngeal nerve stimulation provides quantifiable information in addition to the simple visualization of the cricothyroid muscle twitch.