Muscular Mechanisms Research Articles

Predictive simulations identify potential neuromuscular contributors to idiopathic toe walking

BackgroundMost cases of toe walking in children are idiopathic. We used pathology-specific neuromusculoskeletal predictive simulations to identify potential underlying neural and muscular mechanisms contributing to idiopathic toe walking. MethodsA musculotendon contracture was added to the ankle plantarflexors of a generic musculoskeletal model to represent a pathology-specific contracture model, matching the reduced ankle dorsiflexion range-of-motion in a cohort of children with idiopathic toe walking. This model was employed in a forward dynamic simulation controlled by reflexes and supraspinal drive, governed by a multi-objective cost function to predict gait patterns with the contracture model. We validated the predicted gait using experimental gait data from children with idiopathic toe walking with ankle contracture, by calculating the root mean square errors averaged over all biomechanical variables. FindingsA predictive simulation with the pathology-specific model with contracture approached experimental ITW data (root mean square error = 1.37SD). Gastrocnemius activation was doubled from typical gait simulations, but lacked a peak in early stance as present in electromyography. This synthesised idiopathic toe walking was more costly for all cost function criteria than typical gait simulation. Also, it employed a different neural control strategy, with increased length- and velocity-based reflex gains to the plantarflexors in early stance and swing than typical gait simulations. InterpretationThe simulations provide insights into how a musculotendon contracture combined with altered neural control could contribute to idiopathic toe walking. Insights into these neuromuscular mechanisms could guide future computational and experimental studies to gain improved insight into the cause of idiopathic toe walking.

Architecture, construction, retention, and repair of faecal shields in three tribes of tortoise beetles (Coleoptera, Chrysomelidae, Cassidinae: Cassidini, Mesomphaliini, Spilophorini).

Animal constructions are the outcomes of complex evolutionary, behavioural, and ecological forces. A brief review of diverse animal builders, the materials used, and the functions they provide their builders is provided to develop approaches to studying faecal-based constructions and faecal-carrying in leaf beetles (Coleoptera: Chrysomelidae). Field studies, rearing, dissections, photography, and films document shields constructed by larvae in two species in two tribes of the subfamily Cassidinae, Calyptocephalaattenuata (Spaeth, 1919) (Spilophorini), and Cassidasphaerula Boheman, 1853 (Cassidini). Natural history notes on an undetermined Cassidini species and Stolascucullata (Boheman, 1862) (Tribe Mesomphaliini) outline the life cycle of tortoise beetles and explain terms. Commonly, the cassidine shield comprises exuviae onto which faeces are daubed, producing a pyramidal-shaped shield that can cover most of the body (up to the pronotum). In Cal.attenuata the larval shield comprises only exuviae, while in Cass.sphaerula, instar 1 initiates the shield by extending its telescopic anus to apply its own faeces onto its paired caudal processes; at each moult the exuvia is pushed to the caudal process base but remains attached, then more faeces are applied over it. The larva's telescopic anus is the only tool used to build and repair the shield, not mouthparts or legs, and it also applies chemicals to the shield. Pupae in Cal.attenuata retain part of the exuviae-only shield of instar VI, while pupae in Cass.sphaerula retain either the entire 5th instar larval shield (faeces + all exuviae) or only the 5th larval exuvia. The caudal processes are crucial to shield construction, shield retention on the body, and as materials of the central scaffold of the structure. They also move the shield, though the muscular mechanism is not known. Altogether the faecal + exuviae shields may represent a unique morpho-behavioural synapomorphy for the crown-clade Cassidinae (10 tribes, ~ 2669 species) and may have been a key innovation in subsequent radiation. Defensive shields and domiciles may help explain the uneven radiation of chrysomelid subfamilial and tribal clades.

Muscle force-length dynamics during walking over obstacles indicates delayed recovery and a shift towards more 'strut-like' function in birds with proprioceptive deficit.

Recent studies of in vivo muscle function in guinea fowl revealed that distal leg muscles rapidly modulate force and work to stabilize running in uneven terrain. Previous studies focused on running only, and it remains unclear how muscular mechanisms for stability differ between walking and running. Here, we investigated in vivo function of the lateral gastrocnemius (LG) during walking over obstacles. We compared muscle function in birds with intact (iLG) versus self-reinnervated LG (rLG). Self-reinnervation results in proprioceptive feedback deficit due to loss of monosynaptic stretch reflex. We tested the hypothesis that proprioceptive deficit results in decreased modulation of EMG activity in response to obstacle contact, and a delayed obstacle recovery compared with that for iLG. We found that total myoelectric intensity (Etot) of iLG increased by 68% in obstacle strides (S0) compared with level terrain, suggesting a substantial reflex-mediated response. In contrast, Etot of rLG increased by 31% in S0 strides compared with level walking, but also increased by 43% in the first post-obstacle (S+1) stride. In iLG, muscle force and work differed significantly from level walking only in the S0 stride, indicating a single-stride recovery. In rLG, force increased in S0, S+1 and S+2 compared with level walking, indicating three-stride obstacle recovery. Interestingly, rLG showed little variation in work output and shortening velocity in obstacle terrain, indicating a shift towards near-isometric strut-like function. Reinnervated birds also adopted a more crouched posture across level and obstacle terrains compared with intact birds. These findings suggest gait-specific control mechanisms in walking and running.

How is neuromuscular fatigability affected by perceived fatigue and disability in people with multiple sclerosis?

Whereas fatigue is recognized to be the main complaint of patients with multiple sclerosis (PwMS), its etiology, and particularly the role of resistance to fatigability and its interplay with disability level, remains unclear. The purposes of this review were to (i) clarify the relationship between fatigue/disability and neuromuscular performance in PwMS and (ii) review the corticospinal and muscular mechanisms of voluntary muscle contraction that are altered by multiple sclerosis, and how they may be influenced by disability level or fatigue. Neuromuscular function at rest and during exercise are more susceptible to impairement, due to deficits in voluntary activation, when the disability is greater. Fatigue level is related to resistance to fatigability but not to neuromuscular function at rest. Neurophysiological parameters related to signal transmission such as central motor conduction time, motor evoked potentials amplitude and latency are affected by disability and fatigue levels but their relative role in the impaired production of torque remain unclear. Nonetheless, cortical reorganization represents the most likely explanation for the heightened fatigability during exercise for highly fatigued and/or disabled PwMS. Further research is needed to decipher how the fatigue and disability could influence fatigability for an ecological task, especially at the corticospinal level.

Is fatigue a muscular phenomenon in Parkinson's disease? Implications for rehabilitation.

Fatigue in Parkinson's disease (PD) compromises patients' physical activity and poses questions on how to plan correct rehabilitation training. In addition, the relationship between subjective perceived fatigue and fatigue in motor performance is not yet entirely understood. Therefore, a conclusive interpretation of muscular mechanisms of fatigue in PD has not yet been achieved. Among the various instrumental evaluations for fatigue, multichannel surface electromyography (sEMG) is a recognized tool that permits the study of myoelectric manifestations of fatigue. The aim of this study was to assess if muscles in PD show a different myoelectric fatigue pattern compared to the muscles of healthy age-matched subjects. The design was observational controlled study. Idiopathic Parkinson's Disease, Hohen &Yahr II and III stage, Parkinsonian Fatigue Scale average score ≥2.95, no therapy modification in the 4 weeks preceding the study; exclusion criteria: mini mental state examination ≤24, upper limb disease/symptoms that might interfere with sEMG analysis, presence of other fatigue-related conditions. Twenty patients were selected according to these criteria. Twenty untrained healthy subjects were matched. All subjects underwent a muscle fatigue protocol and a sEMG analysis of the right biceps brachii muscle during electrically stimulated and voluntary contractions in order to obtain a myoelectric fatigue muscular pattern. The myoelectric pattern is characterized by the modifications of the following sEMG variables: reduction of mean frequency and muscle fiber conduction velocity, increase of average rectified value. No statistical differences were observed between groups for sEMG variables and muscular electric behavior in all contraction conditions (all P>0.05). Our results show that parkinsonian muscles do not differ from the muscles of healthy age-matched subjects in developing peripheral myoelectric fatigue. Nevertheless, the role of fatigue perception at rest and particularly during physical activity must be clearly understood in order to further target the rehabilitative approach for fatigued parkinsonian patients and to reduce hypomobility. In rehabilitative terms, these findings allow us to highlight the possibility of performing sustained training with isometric contractions in PD subjects; therefore, fatigue "per se" does not constitute a barrier for the execution of muscular exercises, likewise intensive.

Neural Signatures of Handgrip Fatigue in Type 1 Diabetic Men and Women.

Type 1 diabetes (T1D) is associated with reduced muscular strength and greater muscle fatigability. Along with changes in muscular mechanisms, T1D is also linked to structural changes in the brain. How the neurophysiological mechanisms underlying muscle fatigue is altered with T1D and sex related differences of these mechanisms are still not well investigated. The aim of this study was to determine the impact of T1D on the neural correlates of handgrip fatigue and examine sex and T1D related differences in neuromuscular performance parameters, neural activation and functional connectivity patterns between the motor regions of the brain. Forty-two adults, balanced by condition (healthy vs T1D) and sex (male vs female), and performed submaximal isometric handgrip contractions until voluntary exhaustion. Initial strength, endurance time, strength loss, force variability, and complexity measures were collected. Additionally, hemodynamic responses from motor-function related cortical regions, using functional near-infrared spectroscopy (fNIRS), were obtained. Overall, females exhibited lower initial strength (p < 0.0001), and greater strength loss (p = 0.023) than males. While initial strength was significantly lower in the T1D group (p = 0.012) compared to the healthy group, endurance times and strength loss were comparable between the two groups. Force complexity, measured as approximate entropy, was found to be lower throughout the experiment for the T1D group (p = 0.0378), indicating lower online motor adaptability. Although, T1D and healthy groups fatigued similarly, only the T1D group exhibited increased neural activation in the left (p = 0.095) and right (p = 0.072) supplementary motor areas (SMA) over time. A sex × condition × fatigue interaction effect (p = 0.044) showed that while increased activation was observed in both T1D females and healthy males from the Early to Middle phase, this was not observed in healthy females or T1D males. These findings demonstrate that T1D adults had lower adaptability to fatigue which they compensated for by increasing neural effort. This study highlights the importance of examining both neural and motor performance signatures when investigating the impact of chronic conditions on neuromuscular fatigue. Additionally, the findings have implications for developing intervention strategies for training, rehabilitation, and ergonomics considerations for individuals with chronic conditions.

Neuromuscular determinants of explosive torque: Differences among strength-trained and untrained young and older men.

This study compared the differences in neural and muscular mechanisms related to explosive torque in chronically strength-trained young and older men (>5years). Fifty-four participants were allocated into four groups according to age and strength training level: older untrained (n=14; 65.6±2.9years), older trained (n=12; 63.6±3.8years), young untrained (n=14; 26.2±3.7years), and young trained (n=14; 26.7±3.4years). Knee extension isometric voluntary explosive torque (absolute and normalized as a percentage of maximal voluntary torque) was assessed at the beginning of the contraction (ie, 50, 100, and 150ms-T50, T100, and T150, respectively), and surface electromyogram (sEMG) amplitude (normalized as a percentage of sEMG recorded during maximal voluntary isometric contraction) at 0-50, 50-100, and 100-150 time windows. Supramaximal electrically evoked T50 was assessed with octet trains delivered to the femoral nerve (8 pulses at 300Hz). Voluntary T50, T100, and T150 were higher for trained than untrained in absolute (P<0.001) and normalized (P<0.030) terms, accompanied by higher sEMG at 0-50, 50-100, and 100-150ms (P<0.001), and voluntary T50/octet T50 ratio for trained. Greater octet T50 was observed for the young trained (P<0.001) but not for the older trained (P=0.273) compared to their untrained counterparts. Age effect was observed for voluntary T50, T100, and T150 (P<0.050), but normalization removed these differences (P>0.417). Chronically strength-trained young and older men presented a greater explosive torque than their untrained pairs. In young trained, the greater explosive performance was attributed to enhanced muscular and neural mechanisms, while in older trained to neural mechanisms only.

Relationship Between Dental Occlusion Class, Head Position and Body Posture of The Upper Part of the Body

The close anatomical and neuronal (sensory and motor) linkage between the upper cervical spine and the craniofacial section documented in literature accounts for relationships between the jaw position and the inclination of the cervical spine. The issue of relationships between dental occlusion, body posture and temporomandibular disorders is a controversial topic in dentistry, and it is often a source of speculations. A description of the available knowledge about the physiology of the body posture – dental occlusion relationship is fundamental to discuss the possible diagnostic and therapeutic implications of the assessment of body posture in subjects with occlusal abnormalities or patients with temporomandibular disorders. The orthostatic position of the skull is kept by a complex muscular mechanism involving head, neck and shoulder girdle muscles. Since TMJ, cervical spine and occlusion are intimately related, a functional abnormality or the position of one of them may affect the function or the position of the others (Baião da Neiva et al., 2011). Object of the study: relationship between dental occlusion class, head position and body posture of the upper part of the body. Aim of the study: to determine relationship between dental occlusion class, head position and body posture of upper part of the body. Methods and organization of the study: The study involved 52 subjects. Participants were divided into two age groups: first group (n = 42, 20–28 years) and second group (n = 10, 45–49). 1987 W. W. K. Hoeger subjective volunteer’s posture evaluation model, where the deviation from the norm was defined by score, was chosen for the evaluation. Also the posture was rated digitally. Subjects’ photographs of posture were rated by software AutoCAD 2013 programme. Dental occlusion was assessed according to Angle classification. Conclusion: No strong, statistically significant linkage between the evaluated parameters were found. Additional research is needed to ground scientifically based relationship between masticatory system, musculoskeletal system and body posture.Keywords: dental occlusion class, head position, body posture.

Six Sessions of Sprint-Interval Training Did Not Improve Endurance and Neuromuscular Performance in Untrained Men.

Previous research demonstrated that six sessions of cycling sprint-interval training (SIT) within a duration of only 2 weeks can increase endurance performance considerably. Primarily muscular mechanisms have been under investigation explaining such performance improvements. However, it has been shown in other exercise tasks that training-induced changes also occur at the level of the central nervous system. Therefore, we hypothesized to observe an enhanced neuromuscular performance in conjunction with an increase in endurance performance after 2 weeks of SIT. Therefore, we randomly assigned 19 healthy men (26 ± 5 years) to a control (n = 10) or a training group (n = 9), the latter performing a replication of the SIT protocol from Burgomaster et al. Before and after the training intervention, both groups performed a cycling endurance test until exhaustion. Neuromuscular function of the right vastus lateralis muscle was assessed before and after each endurance task by the means of maximal voluntary isometric contractions (MVCs). The variables of interest being MVC, voluntary activation was measured by peripheral nerve stimulations (VAPNS), by transcranial magnetic stimulation (VATMS), as well as potentiated resting twitches (Qtw,pot). We did not find any significant differences between the groups in the control variable time to exhaustion in the endurance task. In addition, we did not observe any time × group interaction effect in any of the neuromuscular parameters. However, we found a significant large-sized time effect in all neuromuscular variables (MVC, = 0.181; VATMS, = 0.250; VAPNS, = 0.250; Qtw,pot, = 0.304) as well as time to exhaustion = 0.601). In contrast to other studies, we could not show that a short-term SIT is able to increase endurance performance. An unchanged endurance performance after training most likely explains the lack of differences in neuromuscular variables between groups. These findings demonstrate that replication studies are needed to verify results no matter how strong they seem to be. Differences over time for the variables of neuromuscular fatigue irrespective of group (MVC, + 9.3%; VATMS, + 0.2%; VAPNS, + 6.3%; Qtw,pot, + 6.3%) demonstrate test-retest effects that should be taken into consideration in future training studies and emphasize the inevitable necessity for controlled experiments.

Tubal muscles determine embryo implantation site; prognosis of ectopic pregnancy at chronic functional disorders

Mammalian oviducts contain smooth muscles and inward-facing ciliated epithelium. Muscular contractions, not ciliary beating, propel oocytes through the oviduct towards the uterus. In crawling gastropods (unique models for studying the functioning of phasic smooth muscles), muscular contractions, propagating along the foot sole, play a principal role in determining the crawling rate. We have described the muscular mechanisms controlling the crawling rate and hypothesize here that the same mechanisms provide embryo transportation through the human fallopian tube. The data collected for gastropods were transferred to the human fallopian tube, using embryo speed and tube length (tonus) instead of crawling speed and sole length. Smooth muscle active states: tonic contraction/relaxation and rhythmic contractions (peristalsis) are involved in ovum transport. The ovum/embryo speed is linearly correlated with the tonus of the longitudinal and/or the circular muscles of the tube. Some known bioactive substances control muscular tonus and we suppose embryo speed through the contraction force of muscle cells involved in peristaltic waves. Other known substances facilitate peristalsis and we suppose that they have no effect on muscular tonus and increase dose-dependently embryo speed through the number of muscle cells recruited in peristaltic waves (at a constant wave frequency). This number depends on the physiological state of the woman. The combination of all possible effects and the ability of muscles to contract rhythmically determine the embryo speed and its implantation site. This hypothesis is the first description of the tubal muscular mechanisms that determine normal and any type of ectopic pregnancy at chronic disorders of tubal contractility. How to predict ectopic pregnancy? We have reason to assume that the intensity of rhythmic uterine contractions reflects that in the fallopian tube. It is known that uterine contractility significantly increases during the preovulatory phase and decreases during the mid-luteal phase. The hypothesis supposes that in women with increased risk of ectopic pregnancy, decreased uterine contractility during the preovulatory phase in comparison with the norm indicates a future tubal/abdominal gestation; increased uterine contractility during this phase and/or the mid-luteal phase as compared to the norm points to a future cervical pregnancy. The optimal methods for recording uterine activity are up to clinicians.

Blood flow-restricted training enhances thigh glucose uptake during exercise and muscle antioxidant function in humans

This study examined the effects of blood-flow-restricted (BFR)-training on thigh glucose uptake at rest and during exercise in humans and the muscular mechanisms involved. Ten active men (~25 y; VO2max ~50 mL/kg/min) completed six weeks of training, where one leg trained with BFR (cuff pressure: ~180 mmHg) and the other leg without BFR. Before and after training, thigh glucose uptake was determined at rest and during exercise at 25% and 90% of leg incremental peak power output by sampling of femoral arterial and venous blood and measurement of femoral arterial blood flow. Furthermore, resting muscle samples were collected. After training, thigh glucose uptake during exercise was higher than before training only in the BFR-trained leg (p < 0.05) due to increased glucose extraction (p < 0.05). Further, BFR-training substantially improved time to exhaustion during exhaustive exercise (11 ± 5% vs. CON-leg; p = 0.001). After but not before training, NAC infusion attenuated (~50–100%) leg net glucose uptake and extraction during exercise only in the BFR-trained leg, which coincided with an increased muscle abundance of Cu/Zn-SOD (39%), GPX-1 (29%), GLUT4 (28%), and nNOS (18%) (p < 0.05). Training did not affect Mn-SOD, catalase, and VEGF abundance in either leg (p > 0.05), although Mn-SOD was higher in BFR-leg vs. CON-leg after training (p < 0.05). The ratios of p-AMPK-Thr172/AMPK and p-ACC-Ser79/ACC, and p-ACC-Ser79, remained unchanged in both legs (p > 0.05), despite a higher p-AMPK-Thr172 in BFR-leg after training (38%; p < 0.05). In conclusion, BFR-training enhances glucose uptake by exercising muscles in humans probably due to an increase in antioxidant function, GLUT4 abundance, and/or NO availability.

Monitoring Muscle Fatigue Progression during Dynamic Exercise.

To develop and validate a novel model for assessment of peripheral fatigue progression during dynamic exercise. Seven males and four females (24 ± 3 yr) completed one-legged knee-extensor exercise at 40% of peak power output (PPO) for 12 min (40% PPO). Additionally, an exhaustive bout lasting approximately 6 min (84% ± 2% PPO; 59 ± 10 W) was contrasted to two bouts completed at ±5% of the target workload. Trials were completed in randomized order. Percutaneous electrical stimulation of m. vastus lateralis during the passive knee-flexion phase allowed quantification of maximal twitch force every 30 s in parallel with RPE. Elicited twitch force remained unchanged during the 40% PPO trial. During the three exhaustive bouts, exercise differed in duration (561 ± 154 s, 366 ± 64 s, 245 ± 61 s; P < 0.001) and amplitude of elicited twitch force showed a curvilinear decline across time. Elicited twitch force at exhaustion was approximately 60% reduced and similar between the exhaustive trials (intraclass correlation coefficient, 0.76; 95% confidence interval, 0.48-0.92). The increase in RPE during exercise was strongly correlated to the gradually reduced evoked twitch force (repeated-measures correlation, 0.89; 95% confidence interval, 0.62-0.97). The developed model permits quantification of muscle fatigue progression during continuous dynamic one-legged knee-extension and a biphasic fatigue pattern is demonstrated during intense exercise. The model is sensitive to small changes in intensity, and it provides a novel approach for studying muscular mechanisms and their temporal relation to fatigue progression in vivo.

Urethral regions with differential tissular composition may underlie urinary continence and voiding function in female rats.

To analyze, in female rats, the anatomical and histological features of the urethra and its relationship with the vagina and clitoris, and its innervation. Seventeen adult female Wistar rats were used. Gross anatomy and acetylcholinesterase (AchE) histochemistry were performed to describe the urethral features, adjacent structures, and innervation. The histomorphometric characteristics of the urethra were determined in transversal, longitudinal, or coronal sections stained with Masson's Trichrome. The female rat urethra is not a homogeneous tubular organ. The pre-pelvic and pelvic regions are firmly attached to the vagina with belt-like striated fibers forming a urethra-vaginal complex. The bulbar regions have curved segments and a narrow lumen. The clitoral region is characterized by a urethra-clitoral complex surrounded by a vascular plexus. The lumen area and thickness of the urethral layers significantly varied between regions (P < 0.05). Innervation of the urethra arrives from the major pelvic ganglion, the dorsal nerve of the clitoris (DNC), and the motor branch of the sacral plexus (MBSP). Differential tissular composition of the urethra may underlie urinary continence and voiding dysfunction through different physiological mechanisms. The urethra-vagina complex seems to be the main site controlling urinary continence through active muscular mechanisms, while the bulbar urethra provides passive mechanisms and the urethra-clitoris complex seems to be crucial for distal urethral closure by means of a periurethral vascular network.

Mechanisms for the increased fatigability of the lower limb in people with type 2 diabetes.

Fatiguing exercise is the basis of exercise training and a cornerstone of management of type 2 diabetes mellitus (T2D); however, little is known about the fatigability of limb muscles and the involved mechanisms in people with T2D. The purpose of this study was to compare fatigability of knee extensor muscles between people with T2D and controls without diabetes and determine the neural and muscular mechanisms for a dynamic fatiguing task. Seventeen people with T2D [ten men and seven women: 59.6 (9.0) yr] and twenty-one age-, body mass index-, and physical activity-matched controls [eleven men and ten women: 59.5 (9.6) yr] performed one hundred twenty high-velocity concentric contractions (one contraction/3 s) with a load equivalent to 20% maximal voluntary isometric contraction (MVIC) torque with the knee extensors. Transcranial magnetic stimulation (TMS) and electrical stimulation of the quadriceps were used to assess voluntary activation and contractile properties. People with T2D had larger reductions than controls in power during the fatiguing task [42.8 (24.2) vs. 26.4 (15.0)%; P < 0.001] and MVIC torque after the fatiguing task [37.6 (18.2) vs. 26.4 (12.1)%; P = 0.04]. People with T2D had greater reductions than controls in the electrically evoked twitch amplitude after the fatiguing task [44.0 (20.4) vs. 35.4 (12.1)%, respectively; P = 0.01]. However, the decrease in voluntary activation was similar between groups when assessed with electrical stimulation [12.1 (2.6) vs. 12.4 (4.4)% decrease; P = 0.84] and TMS ( P = 0.995). A greater decline in MVIC torque was associated with larger reductions of twitch amplitude ( r2 = 0.364, P = 0.002). Although neural mechanisms contributed to fatigability, contractile mechanisms were responsible for the greater knee extensor fatigability in men and women with T2D compared with healthy controls. NEW & NOTEWORTHY Transcranial magnetic stimulation and percutaneous muscle stimulation were used to determine the contributions of neural and contractile mechanisms of fatigability of the knee extensor muscles after a dynamic fatiguing task in men and women with type 2 diabetes (T2D) and healthy age-, body mass index-, and physical activity-matched controls. Although neural and contractile mechanisms contributed to greater fatigability of people with T2D, fatigability was primarily associated with impaired contractile mechanisms and glycemic control.

Neural and Muscular Contributions to the Age-Related Reductions in Rapid Strength.

The purposes of this study were to investigate the age-related differences in absolute and normalized plantarflexion rate of torque development (RTD) at early (0-50 ms) and late (100-200 ms) time intervals and to examine specific neural and muscular mechanisms contributing to these differences. Thirty-two young (20.0 ± 2.1 yr) and 20 older (69.5 ± 3.3 yr) recreationally active men performed rapid plantarflexion isometric muscle actions to examine absolute and normalized RTD and muscle activation using EMG at early and late time intervals. Ultrasonography was used to examine medial gastrocnemius muscle size, echo intensity (EI), and muscle architecture (fascicle length [FL] and pennation angle [PA]). The older men were weaker (23.9%, P < 0.001) and had lower later absolute and normalized RTD (P = 0.001-0.034) variables when compared with the young men. The older men also had higher EI (P < 0.001), smaller PA (P = 0.004), and lower later EMG amplitude values (P = 0.009-0.046). However, there were no differences in early RTD and EMG amplitude values, muscle size, or FL between groups (P = 0.097-0.914). Lower late RTD values were related to higher EI, smaller PA, and lower EMG amplitude values (r = -0.28-0.59, P = 0.001-0.044); however, late RTD values were no longer related to PA after normalizing to peak torque. Age-related alterations in muscle quality (EI), architecture, and muscle activation may influence rapid torque production at late time intervals (≥100 ms) from contraction onset. These findings highlight specific neuromuscular factors that influence the age-related reductions in RTD, which has been shown to significantly influence function and performance in older adults.

Monosynaptic Stretch Reflex Fails to Explain the Initial Postural Response to Sudden Lateral Perturbations.

Postural reflexes are essential for locomotion and postural stability, and may play an important role in the etiology of chronic back pain. It has recently been theoretically predicted, and with the help of unilateral perturbations of the trunk experimentally confirmed that the sensorimotor control must lower the reflex amplitude for increasing reflex delays to maintain spinal stability. The underlying neuromuscular mechanism for the compensation of postural perturbations, however, is not yet fully understood. In this study, we applied unilateral and bilateral sudden external perturbations to the trunk of healthy subjects and measured the muscular activity and the movement onset of the trunk. We found that the onset of the trunk muscle activity is prior to, or coincident with, the onset of the trunk movement. Additionally, the results of our experiments imply that the muscular response mechanism integrates distant sensory information from both sides of the body. These findings rule out a simple monosynaptic stretch reflex in favor of a more complex polysynaptic postural reflex mechanism to compensate postural perturbations. Moreover, the previously predicted negative correlation between reflex delay and reflex gain was also confirmed for bilateral perturbations.

Tension-Type Headache: Epidemiology, Diagnosis, and Pathophysiology

Tension-type headache (TTH) is a significant but underappreciated condition that is much more frequent than migraine, 42% versus 11%, and produces significant socioeconomic burden. Why then do research advances in this condition seem to lag? One reason is that precise epidemiologic data are lacking, with lifetime prevalence estimates varying from about 13 to 78%. Also, classification is confounded by whether or not to include the occasional but universal headache as TTH. Furthermore, TTH pathophysiology is debated, with some feeling that the pathophysiology of TTH is similar to and on a spectrum with migraine, and some feeling that it is entirely separate and related to peripheral and muscular mechanisms. More recently, central pain mechanisms have also been implicated in the pathophysiology. In addition, a large body of information connects stress and TTH. Although TTH varies widely in frequency and severity among and within patients, TTH pain, compared with pain in other headache types, could be characterized generally as more mild in severity and more generalized in location. This review discusses the current epidemiologic data and diagnostic challenges in TTH and the current pathophysiologic mechanisms.

Crawling without wiggling: muscular mechanisms and kinematics of rectilinear locomotion in boa constrictors.

A central issue for understanding locomotion of vertebrates is how muscle activity and movements of their segmented axial structures are coordinated, and snakes have a longitudinal uniformity of body segments and diverse locomotor behaviors that are well suited for studying the neural control of rhythmic axial movements. Unlike all other major modes of snake locomotion, rectilinear locomotion does not involve axial bending, and the mechanisms of propulsion and modulating speed are not well understood. We integrated electromyograms and kinematics of boa constrictors to test Lissmann's decades-old hypotheses of activity of the costocutaneous superior (CCS) and inferior (CCI) muscles and the intrinsic cutaneous interscutalis (IS) muscle during rectilinear locomotion. The CCI was active during static contact with the ground as it shortened and pulled the axial skeleton forward relative to both the ventral skin and the ground during the propulsive phase. The CCS was active during sliding contact with the ground as it shortened and pulled the skin forward relative to both the skeleton and the ground during the recovery phase. The IS shortened the ventral skin, and subsequent isometric activity kept the skin stiff and shortened during most of static contact while overlapping extensively with CCI activity. The concentric activity of the CCI and CCS supported Lissmann's predictions. Contrary to Lissmann, the IS had prolonged isometric activity, and the time when it shortened was not consistent with providing propulsive force. Decoupling propulsion from axial bending in rectilinear locomotion may have facilitated economical locomotion of early snakes in subterranean tunnels.

Dysfunctional Voiding in Pediatrics: A Review of Pathophysiology and Current Treatment Modalities.

In Dysfunctional Voiding (DV), the external urethral sphincter or pelvic diaphragm (consisting of striated muscle) contracts during voiding, contrary to normal physiological mechanism. In Flowmetry plus pelvic Electromyography (EMG), the perineal surface electrodes will show a persistent activity during voiding. The cause is believed to be the persistence of an immature bladder control. The overall prevalence of DV is estimated between 7 and 11% of girls of school age. Symptoms of DV comprise a range of symptoms, deriving from outlet obstruction, incomplete voiding and elevated Post Micturition Residual (PMR): from daytime urine leaks, nocturnal enuresis, Urinary Tract Infections (UTI), or Vesicoureteral reflux (VUR), to the final decompensation of upper urinary tract in extreme cases. The literature reflects a high prevalence of constipation among these patients: between 33 and 56% of dysfunctional voiders are constipated. Initially, therapy of functional voiding disorders such as DV, comprises a series of fundamental principles called Urotherapy or voiding re-education. Currently, Urinary animated Biofeedback (Bfb) is the treatment modality of choice. This therapy discloses patients their own physiological and muscular mechanisms. Majority of the studies on Bfb efficacy reflect an improvement/ cure rate of around 70-80%. Initial flowmetric improvement followed by symptom relief or clinical improvement as the Bfb sessions continue, is likely to occur. It has been observed that there are two variables associated with clinical success of Bfb in DV syndrome: the absence of PMR at the end of treatment and an adequate or even aggressive constipation management.

Tension-Type Headache: Epidemiology, Diagnosis, and Pathophysiology

Tension-type headache (TTH) is a significant but underappreciated condition that is much more frequent than migraine, 42% versus 11%, and produces significant socioeconomic burden. Why then do research advances in this condition seem to lag? One reason is that precise epidemiologic data are lacking, with lifetime prevalence estimates varying from about 13 to 78%. Also, classification is confounded by whether or not to include the occasional but universal headache as TTH. Furthermore, TTH pathophysiology is debated, with some feeling that the pathophysiology of TTH is similar to and on a spectrum with migraine, and some feeling that it is entirely separate and related to peripheral and muscular mechanisms. More recently, central pain mechanisms have also been implicated in the pathophysiology. In addition, a large body of information connects stress and TTH. Although TTH varies widely in frequency and severity among and within patients, TTH pain, compared with pain in other headache types, could be characterized generally as more mild in severity and more generalized in location. This review discusses the current epidemiologic data and diagnostic challenges in TTH and the current pathophysiologic mechanisms.