Maximum Voluntary Contraction

This study was designed to test the hypothesis derived from information theory that increases in the variability of motor responses result from increases in perceptual-motor noise. Young adults maintained isometric force for extended periods at different levels of their maximum voluntary contraction. Force variability (SD) increased exponentially as a function of force level. However, the signal-to-noise ratio (M/SD), an index of information transmission, as well as measures of noise in both the time (approximate entropy) and frequency (power spectrum) domains, changed according to an inverted U-shaped function over the range of force levels. These findings indicate that force variability is not directly related to noise but that force output noisiness is positively correlated with the amount of information transmitted.

Objective: To demonstrate the errors in surface electromyogram (EMG) interpretation that can be made when the EMG signal is not normalized. Design: A case study as a proof of principle. Main Outcome Measures: The EMG amplitude between the upper and lower portions of the rectus abdominis in one subject during a trunk curl when the EMG signal was normalized (expressed as a percentage of a maximum voluntary contraction) and the amplitude when the signal was expressed in raw, unnormalized arbitrary units or raw millivolts directly read from the instrumentation. Results: Interpretation of the unnormalized EMG signal suggests that a large difference in neural activation of the upper and lower sections of the rectus abdominis is occurring. In this condition the average activity in the lower rectus is 60.9% of that in the upper portion. This interpretation is incorrect. When the EMG signal is normalized, the differences between the upper and lower segments are reduced. When normalized, the lower segment activity is equal to that of the upper segment. Conclusions: Because of the inherent EMG signal variability, clinical interpretation of surface EMG signals requires normalization of the signal for physiologic interpretation and for comparison between bilateral muscles and between the same muscle on different days and between different subjects. (J Manipulative Physiol Ther 1999;22:444–6)

The estimation of shoulder muscle force is important to understand the mechanism of rotator cuff injury. In general, mean parameter values are used as input for computational models. However, anatomic and biomechanical parameters vary widely among people. The purpose of this study was to evaluate shoulder muscle forces predicted by an electromyography-driven muscle model given neuromuscular parameters generated by Monte Carlo simulation. Normal distributions were used to model muscle moment arms; electromyographic and muscle physiological cross-section01 area data were modeled with log-normal distributions. Eight muscles were included in the model. Muscle force and joint moment were predicted on the basis of the simulated parameters. The results showed that the subscapularis and pectoralis major were substantial actuators for shoulder internal rokrtion. During maximum vokmtary contraction the median of the muscle Forces of the subscapularis and the pectoralis major were 1030 N and 462 N, respective/y. This study demonstrated that the Monte Carlo method could be used For muscle force prediction by integrating population variability of physiological parameter into a biomechanical muscle model. p Shoulder Elbow Surg 2000;9: 188-95.) The estimation of shoulder muscle force and the analysis of the relative contribution of each muscle to shoulder joint moment are necessary for understanding the mechanism of mobility and stability of the shoulder joint, the cause of rotator cuff injury, shoulder joint subluxation and dislocation, and other shoulder joint disorders. Because the internal shoulder muscle force cannot be measured

In a randomized clinical trial the efficacy of strength training was studied in patients with myotonic dystrophy (n ϭ 33) and in patients with Charcot-Marie-Tooth disease (n ϭ 29). Measurements were performed at the start and after 8, 16 and 24 weeks of progressive resistance training. Surface electromyography (SEMG) of proximal leg muscles was recorded during isometric knee extension at maximum voluntary contraction (MVC) and at 20, 40, 60 and 80% of MVC. Changes in MVC, maximum electrical activity and torque-EMG ratios (TER) were calculated. Fatigue was studied by determining the changes in endurance and in the decline of the median frequency (F med ) of the SEMG during a sustained contraction at 80% MVC. These parameters showed no significant changes after the training in either of the diagnostic groups. Only the Charcot-Marie-Tooth training group showed a gradual significant increase in mean MVC over the whole training period (21%). After 24 weeks, the increase in mean RMS was similar (25%), but this was mainly due to a sharp rise during the first 8 weeks of training (20%). The findings indicate that the initial strength increase was due to a neural factor, while the subsequent increase was mainly due to muscle hypertrophy.

The aims of this study were to analyse the effect of different body positions on pelvic floor muscle (PFM) assessment using digital muscle testing, manometry and transabdominal ultrasound. In addition, subject acceptance of each testing position was recorded. Subjects were 20 women's health physiotherapists. The testing protocol included the best of three maximum voluntary contractions tested in each of four positions (crook lying, supine, sitting and standing). Significant differences in muscle strength and subject acceptance between positions were found with each tool, most often between lying and upright positions. Digital muscle testing and vaginal squeeze-pressure scores were highest in the lying position, and vaginal resting pressure and transabdominal ultrasound scores were highest in the standing position. Subjects preferred the lying positions for internal examinations. The clinical significance of these differences and the reasons for these variations require further investigation.

This study compares dominant and non-dominant hand strength in both right-and left-handed participants. Maximum voluntary contraction (MVC) of the first dorsal interosseous (FDI) muscle, power grip strength and pulp-to-pulp pinch strength were assessed under carefully controlled conditions. No significant differences were observed between dominant and non-dominant hands in left-handed participants for all tests. Small but significant differences (0.1-3%) were observed between dominant and non-dominant hands in right-handed participants for all three tests. These differences were much smaller than those reported in other studies. Furthermore, considerable variability was observed in the relative strengths of the two hands for each participant. We conclude that clinicians must be cautious when using the '10% rule' to make comparisons between injured and uninjured hands.

Protein-energy malnutrition in anorexia nervosa is an under-recognised cause of muscle dysfunction. To characterise the skeletal myopathy that occurs in patients with severe anorexia nervosa, muscle function and structure were comprehensively examined in eight young adult female patients with severe (40%) self-induced weight loss. All of the patients showed impaired muscle function on strength and exercise measurement. The maximum voluntary

Few studies have been carried out on the changes in biomechanical loading on low-back tissues during prolonged lifting. The purpose of this paper was to develop a model for continuously estimating erector spinae muscle loads during repetitive lifting and lowering tasks. The model was based on spine kinematics and bilateral lumbar and thoracic erector spinae electromyogram (EMG) signals and was developed with the data from eight male subjects. Each subject performed a series of isometric contractions to develop extensor moments about the low back. Maximum voluntary contractions (MVCs) were used to normalize all recorded EMG and moment time-histories. Ramp contractions were used to determine the non-linear relationship between extensor moments and EMG amplitudes. In addition, the most appropriate low-pass filter cut-off frequencies were calculated for matching the rectified EMG signals with the moment patterns. The mean low-pass cut-off frequency was 2.7 (0.4) Hz. The accuracy of the non-linear EMG-based estimates of isometric extensor moment were tested with data from a series of six rapid contractions by each subject. The mean error over the duration of these contractions was 9.2 (2.6)% MVC. During prolonged lifting sessions of 20 min and of 2 h, a model was used to calculate changes in muscle length based on monitored spine kinematics. EMG signals were first processed according to the parameters determined from the isometric contractions and then further processed to account for the effects of instantaneous muscle length and velocity. Simple EMG estimates were found to underestimate peak loading by 9.1 (4.0) and 25.7 (11.6)% MVC for J.R. Potvin (12N) eccentric and concentric phases of lifting respectively, when compared to load estimates based on the mechanically corrected EMG. To date, the model has been used to analyze over 5300 lifts.

Upper extremity muscle injuries from rock climbing are common. Knowledge of the activity of specific muscles during climbing may allow the development of training programs to reduce these injuries. This study evaluated the electrical activity of the first interosseous (IN), brachioradialis (BR), flexor digitorum superficialis (FD), and biceps brachii (BB) muscles in seven climbers by integrated electromyography (IEMG) during finger-tip pull-ups. The climbers, with forearms pronated, performed three consccutive pull-ups. Each pull-up consisted of: (1) hanging using four fingers of each hand, (2) pullup to maximum elbow flexion, (3) slow return to starting position. The IEMG during maximum voluntary contraction (MVC) was obtained for each muscle separately, and the IEMG was normalized to MVC. During hanging, FD showed the highest normalized IEMG (0.64±0.20). During pull-up, the highest IEMG was produced by FD (0.69 ±0.25) and BR (0.67±0.19), while BB showed only 0.33 ±0.12 and IN 0.09±0.06. During lowering, FD again had the highest IEMG (0.74±0.24), while the EMG from BR was decreased to 0.42±0.14 and BB to 0.15±0.15. BR and BB showed an abrupt peak in EMG during pull-up and lowering, as opposed to FD which remained constantly highly activated, which suggests that FD does not contribute to elbow flexion even though it crosses the elbow joint. The high activation of FD and BR may explain their elevated incidence of injury during climbing. Thus, a reduction in climbing-related muscle injuries may be achieved by a training program that emphasizes conditioning of the BR and FD muscles.

Individuals with hemiparetic stroke often exhibit an abnormal coupling between the frontal plane of the hip and saggital plane of the knee during gait. The purpose of this study was to determine if stretch sensitive reflexes, which are known to be altered following stroke, exhibit similar coupling between the muscles of the hip and knee in the post-stroke population. Eighteen subjects were recruited for this study including ten with hemiparesis resulting from stroke and eight unimpaired, age-matched controls. A servomotor was used to apply ramp and hold perturbations to both the hip and knee joints in separate sessions and electromyographic activity was recorded in eight muscles of the lower limb. Hip abduction perturbations elicited abnormal activation in rectus femoris (RF) in seven of ten stroke subjects with amplitudes ranging from 3.2 to 12.5% of the maximum voluntary contraction (MVC). Only two of eight control subjects exhibited any activity in RF and these responses were only 2.1 and 2.7% of MVC. To determine if the responses in the stroke group were a result of muscle stretch, a musculoskeletal model was used to simulate the experimental abduction perturbations and estimate muscle length changes. The simulation revealed that RF should be shortened by the perturbations and this suggests that the response was not likely due to direct stretch. Moreover, knee flexion perturbations elicited responses in the hip adductors (AL) with a mean amplitude of 5.1 ± 3.8% of MVC across all stroke subjects while no significant responses were recorded in controls. The presence of a reciprocal, reflex-mediated coupling between RF and AL following stroke suggests that changes in the excitability of spinal networks may contribute to the development of abnormal inter-joint coordination patterns observed during hemiparetic gait.

Backround. The present study assessed the relationship between various strength-power tests and maximal running velocity parameters.
Methods. Nine trained males were tested on four separate occasions. On the first occasion the maximum running velocity (MRV), stride rate (SR) and stride length (SL) were measured over 35 m. On the second occasion maximal vertical jumps [squat jump (SJ), standing broad jump (SJ), counter movement jump (CMJ) and drop jumps (DJ) from heights of 30, 50 and 80 cm] were performed on a force platform: On the third occasion the maximal bilateral isometric force (MBIF) of leg extensors and the force time characteristics (f-t 10-30%, f-t 10-60% and f-t 10-90%) were determined using a leg extension machine connected to a force plate. On the final fouth occasion peak anaerobic power was measured via repeated 6 s maximum cycle sprints. Pearson product-moment correlation coefficients were calculated for all the aformentioned parameters.
Results. The correlation coefficients showed that MRV correlated significantly with f-t 10-60%  and DJ30 (r = -0.73 and r =0.73, p<0.05 respectively).  In addition, SR and SL  showed significant, and critical for SR, relationship with f-t 10-60% (r = -0.82, p<0.01 and r = 0.75, p<0.05 respectively).
Conclusions. The present findings suggest that the ability to produce force quickly, as measured by the time to achieve 60% of maximum voluntary contraction is related to sprinting performance, with the coefficient of determination accounting for 53% of the variance in the data. These data also showed that sprinting ability is linked with drop jumping performance, especially the drop jump from a height of 30 cm. It is suggested that the above tests may prove useful in preparing and testing the sprinting ability and sprint specific strength levels.

This study compares dominant and non-dominant hand strength in both right-and left-handed participants. Maximum voluntary contraction (MVC) of the first dorsal interosseous (FDI) muscle, power grip strength and pulp-to-pulp pinch strength were assessed under carefully controlled conditions. No significant differences were observed between dominant and non-dominant hands in left-handed participants for all tests. Small but significant differences (0.1-3%) were observed between dominant and non-dominant hands in right-handed participants for all three tests. These differences were much smaller than those reported in other studies. Furthermore, considerable variability was observed in the relative strengths of the two hands for each participant. We conclude that clinicians must be cautious when using the '10% rule' to make comparisons between injured and uninjured hands.

PURPOSE: This study was designed to evaluate the anatomic and functional consequences of lateral internal sphincterotomy in patients who developed anal incontinence and in matched controls. METHODS: The study includes 13 patients with anal incontinence after lateral internal sphincterotomy and 13 controls who underwent the same operation and were continent and satisfied with the results of the procedure. Patients underwent clinical evaluation, anorectal manometry, pudendal nerve terminal motor latency testing, and endoanal ultrasonography. RESULTS: Sphincterotomies were longer in incontinent patients (75 vs. 57 percent), but the resting pressure and length of the highpressure zone were not different between groups. Surprisingly, maximum voluntary contraction was higher in incontinent patients than in continent controls (136 vs. 100 mmHg). Rectal sensation and pudendal nerve terminal motor latency were similar in both groups. The defect in the internal sphincter was wider in incontinent patients than in continent controls (17.3 vs. 14.4 mm), but these differences were not statisticaUy significant. The thickness of the internal sphincter measured by endoanal ultrasound was identical in both groups, but the external sphincter was thinner in incontinent patients both at the site of the sphincterotomy (6.8 vs. 8.1 ram) and in the posterior midline (7.1 vs. 8.6 ram). CONCLUSIONS: Anal incontinence after lateral internat sphincterotomy is directly related to the length of the sphincterotomy. Whether secondary to preoperative sphincter abnormality or the result of lateral internal sphincterotomy, the external sphincter is thinner in incontinent patients than in continent controls. [

Procedures for the quantitative analysis of clinical electromyographic (EMG) signals detected simultaneously using selective or micro and non-selective or macro electrodes are presented. The procedures first involve the decomposition of the micro signals and then the quantitative analysis of the resulting motor unit action potential trains (MUAPTs) in conjunction with the associated macro signal. The decomposition procedures consist of a series of algorithms that are successively and iteratively applied to resolve a composite micro EMG signal into its constituent MUAPTs. The algorithms involve the detection of motor unit action potentials (MUAPs), MUAP clustering and supervised classification and they use shape and firing pattern information along with data dependent assignment criteria to obtain robust performance across a variety of EMG signals. The accuracy, extent and speed with which a set of 10 representative 20-30 s, concentric needle detected, micro signals could be decomposed are reported and discussed. The decomposition algorithms had a maximum and average error rate of 2.5% and 0.7%, respectively, on average assigned 88.7% of the detected MUAPs and took between 4 to 8 s. Quantitative analysis techniques involving average micro and macro MUAP shapes, the variability of micro MUAPs shapes and motor unit firing patterns are described and results obtained from analysis of the data set used to evaluate the decomposition algorithms are summarized and discussed.

The purpose of this study was to examine the effects of interelectrode distance (IED) on the absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) versus isokinetic and isometric torque relationships for the biceps brachii muscle. Ten adults [mean ± SD age = 22.0 ± 3.4 years] performed submaximal to maximal, isokinetic and isometric muscle actions of the dominant forearm flexors. Following determination of isokinetic peak torque (PT) and the isometric maximum voluntary contraction (MVC), the subjects performed randomly ordered, submaximal step muscle actions in 10% increments from 10% to 90% PT and MVC. Surface EMG signals were recorded simultaneously from bipolar electrode arrangements placed over the biceps brachii muscle with IEDs of 20, 40, and 60 mm. Absolute and normalized EMG amplitude (lVrms and %max) increased linearly with torque during the isokinetic and isometric muscle actions (r 2 range = 0.988-0.998), but there were no significant changes for absolute or normalized EMG MPF (Hz or %max) from 10% to 100% PT and MVC. In some cases, there were significant (p < 0.05) differences among the three IED arrangements for absolute EMG amplitude and MPF values, but not for the normalized values. These findings suggested that for the biceps brachii muscle, IEDs between 20 and 60 mm resulted in similar patterns for the EMG amplitude or MPF versus dynamic and isometric torque relationships. Furthermore, unlike the absolute EMG amplitude and MPF values, the normalized EMG data were not influenced by changes in IED between 20 and 60 mm. Thus, normalized EMG data can be compared among previous studies that have utilized different IED arrangements.

This study investigated endurance times as percentages of maximum voluntary contractions (MVCs) in 12 healthy females (mean 25.874.3 years) in 5 postures and at 7% MVCs. The shoulder postures utilized were 30/90 (shoulder forward flexion=301 and included elbow angle=901), 60/90, 90/120, 120/150, and 150/180. The %MVCs were 5%, 15%, 30%, 45%, 60%, 75%, and 90% of MVC at each of these postures. Outcome measures included: endurance times, ratings of perceived exertion, fatigue ratings, pain ratings, and surface electromyography (trapezius and middeltoid). As expected the endurance time decreased non-linearly with an increase in %MVC. However, the relationship between endurance time and %MVC differed significantly from Rohmert's curve and suggests it considerably overestimates endurance times for %MVCs o45% and it underestimates endurance times for %MVCs >45%. This study's curve did not become asymptotic even at 5% MVC. Shoulder posture (shoulder forward flexion angle) had a significant effect on endurance time. In general, endurance time decreased with an increase in shoulder flexion angle up to 1201 and then it increased. Thus, overhead work (hands above the head) would appear to be better designed with a greater degree of forward flexion, rather than in front of the worker at lower degrees of forward flexion.

This study's main objective was to determine if upper-limb (UL) muscular demand was reduced when individuals with a spinal cord injury (SCI) performed a sitting pivot transfer (SPT) in the preferred direction compared with that in a nonpreferred direction. Fourteen individuals (mean +/standard deviation age 47.0 +/-8.3 yr, height 1.80 +/-0.08 m, and weight 75.3 +/-11.3 kg) with SCI levels ranging from the sixth cervical to first sacral vertebra levels volunteered to participate in this study during the 2008 National Disabled Veterans Winter Sports Clinic. Surface electromyography (EMG) was used to record activity of the biceps, triceps, deltoid, pectoralis major, trapezius, and latissimus dorsi bilaterally during SPTs. These transfers were performed in each of the preferred and nonpreferred directions from the individuals' wheelchairs to a padded tub bench of even height. To quantify electromyographic muscular utilization ratio (MUR EMG ), we normalized EMG data recorded during the transfer tasks to values obtained during static maximum voluntary contraction and then multiplied this ratio by 100 to obtain a percentage MUR EMG (%MUR EMG ). The overall peak %MUR EMG and the area under the %MUR EMG curve were selected as primary outcome measures. Similar peak %MUR EMGs were found between the preferred and nonpreferred transfer directions for all muscles from which data were recorded (p = 0.053 to 0.961). The peak %MUR EMGs were also found to be similar between the leading and trailing ULs during the transfers in all muscles from which data were recorded (p = 0.125 to 0.838), except for the anterior deltoid, which was found to be solicited the most in the trailing UL (p = 0.008). Comparable areas under the %MUR EMG curves were calculated between the preferred and nonpreferred transfer directions for all muscles (p = 0.289 to 0.678) and between the leading and trailing ULs (p = 0.104 to 0.946). These results indicate that direction preference expressed by individuals with SCI when transferring between seats of even height is not explained by relative muscular demand differences.

The purpose of this study was to quantify the effects of concurrent physical and mental demands on the upper extremity muscle activity during static exertions. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensity (5%, 25%, 45%, 65%, and 85% maximum voluntary contraction (MVC)) in the presence and absence of a mental task (Stroop color word test). Muscular responses were quantified using surface electromyography (EMG) and motor performance was measured through force fluctuations. Subjective assessments were obtained through the NASA-TLX tool and the Borg CR-10 Scale. In general, a decrease in mean anterior and posterior deltoid muscle activity and co-contraction index (CCI) of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher physical exertion levels compared to the lower levels. Furthermore, the additional mental task resulted in decreased upper and lower arm muscle activity, specifically at the 45% MVC level. Motor performance improved at the middle exertion levels, but was adversely affected by the mental task at higher exertion levels. Decreased motor performance at higher loads may have been a result of decreased muscular effort to maintain the loads in a steady posture. Both mental and physical demand adversely affected the NASA-TLX ratings, however, ratings using the Borg CR-10 Scale were only sensitive to changes in physical demand. Relevance to industry: Workplace tasks, such as jobs performed by healthcare workers, assembly line workers, and computer operators, have become more multidimensional in the recent years; with workers experiencing combined physical and mental demands in their daily jobs, yet their effect on muscular responses is not clearly understood. Results from this study suggest that certain physical exertion levels are more susceptible to interference by mental demands than others.

Purpose: This study was conducted to test whether a low-frequency vibration-like stimulus (rapid variable resistance) applied during a single session of knee extension exercise would alter muscle performance. Methods: Torque, knee joint angle, EMG activity of rectus femoris (RF) and vastus lateralis (VL) muscles, and VL muscle oxygenation status (near-infrared spectroscopy) were recorded during metronome-guided knee extension exercise. Nine healthy adults completed four trials exercising at contraction intensities of 35% (L) or 70% (H) of one-repetition maximum (1RM) in control (no vibration, Vbj) or vibrated condition (superimposed 10-Hz vibration-like stimulus, Vb+). Maximum voluntary contraction and 1RM were tested pre-and postexercise. Results: During 1RM tests, muscle dynamic strength (P = 0.02) and power (P = 0.05) were significantly higher during vibrated rather than nonvibrated trials, and strength was significantly higher post-than preexercise (P = 0.002), except during LVbj trial. Median spectral frequency of VL and RF EMG activity was significantly higher during postexercise than preexercise 1RM test in the vibration trials but unchanged in the control trials (P G 0.02). The rate of muscle deoxygenation was 58% faster during H than L exercise (P = 0.001), and vibration superimposition tended to speed muscle deoxygenation rate (P = 0.065, 36% effect size) particularly during L trials. Conclusion: Vibration superimposition during knee extension exercise at low contraction intensity enhanced muscle performance. This effect appears to result from adaptation of neural factors such as motor unit excitability (recruitment and firing frequency, conduction velocity of excitation) in response to sensory receptor stimulation. Muscle vibration may increase the training effects derived from light-to-moderate exercise.

Measurements of human strength can be important during analyses of physical activities. Such measurements have often taken the form of the maximum voluntary torque at a single joint angle and angular velocity. However, the available strength varies substantially with joint position and velocity. When examining dynamic activities, strength measurements should account for these variations. A model is presented of maximum voluntary joint torque as a function of joint angle and angular velocity. The model is based on wellknown physiological relationships between muscle force and length and between muscle force and velocity and was tested by fitting it to maximum voluntary joint torque data from six different exertions in the lower limb. Isometric, concentric and eccentric maximum voluntary contractions were collected during hip extension, hip flexion, knee extension, knee flexion, ankle plantar flexion and dorsiflexion. Model parameters are reported for each of these exertion directions by gender and age group. This model provides an efficient method by which strength variations with joint angle and angular velocity may be incorporated into comparisons between joint torques calculated by inverse dynamics and the maximum available joint torques. r

Handle diameter was manipulated to evaluate the affect on muscle oxygenation and blood volume in the extensor carpi radialis and the flexor digitorum superficialis during rhythmic isometric gripping tasks. Power grip contractions were performed at 15% of maximum voluntary contraction (MVC) at a work:rest cycle of 10:5-s, with three different handles (30, 40, and 50 mm) for a period of 15-min by 19 participants. MVC was significantly greater for the 30 and 40 mm handle than for the 50 mm handle. TOI, the average hemoglobin saturation, and cHb, total hemoglobin (blood volume) were significantly different when working with the 30 and 40 mm handles than with the 50 mm handle, with a decreasing TOI and increasing cHb observed with the larger handle. This finding suggests that the two smaller handles had similar tissue oxygenation and blood volume requirements during repetitive gripping, and less oxygenated hemoglobin was available when gripping the larger handle. Significant interactions between handle diameter and muscle groups in TOI and cHb, were also observed, implying differential contributions of the flexor and extensor muscles. The results suggest that for the hand-handle interface it is not only important to consider handle diameter, but also perfusion of both flexor and extensor muscles. Relevance to industry: Job requirements often dictate tool configuration. Based on an evaluation using a low-level cyclic power grip, for the general population cylindrical handles of 30-40 mm diameter may be superior to a 50 mm handle, not only in grip force capacity, but also because of the improved tissue perfusion characteristics.

PURPOSE: This study was designed to evaluate the anatomic and functional consequences of lateral internal sphincterotomy in patients who developed anal incontinence and in matched controls. METHODS: The study includes 13 patients with anal incontinence after lateral internal sphincterotomy and 13 controls who underwent the same operation and were continent and satisfied with the results of the procedure. Patients underwent clinical evaluation, anorectal manometry, pudendal nerve terminal motor latency testing, and endoanal ultrasonography. RESULTS: Sphincterotomies were longer in incontinent patients (75 vs. 57 percent), but the resting pressure and length of the highpressure zone were not different between groups. Surprisingly, maximum voluntary contraction was higher in incontinent patients than in continent controls (136 vs. 100 mmHg). Rectal sensation and pudendal nerve terminal motor latency were similar in both groups. The defect in the internal sphincter was wider in incontinent patients than in continent controls (17.3 vs. 14.4 mm), but these differences were not statisticaUy significant. The thickness of the internal sphincter measured by endoanal ultrasound was identical in both groups, but the external sphincter was thinner in incontinent patients both at the site of the sphincterotomy (6.8 vs. 8.1 ram) and in the posterior midline (7.1 vs. 8.6 ram). CONCLUSIONS: Anal incontinence after lateral internat sphincterotomy is directly related to the length of the sphincterotomy. Whether secondary to preoperative sphincter abnormality or the result of lateral internal sphincterotomy, the external sphincter is thinner in incontinent patients than in continent controls. [

Force control ability was investigated in 10 males and 10 females, between 5 and 15 years old with spastic hemiplegia (mild and moderate hand dysfunction), and an aged-matched control group (eight males, 12 females). An isometric force production task at five different levels of maximum voluntary contraction (MVC) was performed. Results showed that MVC generated with the affected hand (AH)

Repetitive use of hand-held power tools, due to their potential to generate forces greater than an operator capacity, is associated with work-related upper extremity musculoskeletal disorders. This laboratory study investigated the effects of power tool-induced torque reaction and work:rest pattern on peripheral circulatory responses during repetitive nutrunner operations. Twenty men completed eight fastener-driving sessions that consisted of two different work:rest patterns of 360 repetitive tasks both at slow-and fast-pace using a pneumatic nutrunner, which was equipped with an instrumented tool handle with a custom-designed force gauge that measures grip force in real time, on a torque reaction assembly joint and a control joint. Near-infrared spectroscopy (NIRS) was simultaneously used to monitor changes in tissue oxygenation and blood volume from flexor digitorum superficialis and extensor digitorum communis. The mean grip force exerted by participants during sessions with no torque buildup was 33% of their maximum voluntary contraction whereas during sessions with torque buildup it was of 57% maximum voluntary contraction. Additionally, throughout a session the rate of changes in grip force decreased more with the latter (À0.007 and À0.022 N/drive, respectively) suggesting considerable effort during torque buildup by the participants. Correspondingly, in the flexor muscles greater deoxygenation was observed than that of extensor muscles for all sessions, suggesting greatest metabolic demand from the flexors during torque buildup. Tissue oxygenation index, representing the dynamic balance between oxygen delivery and oxygen consumption in the tissue was similar during both combinations of pace and work:rest ratios in the flexors. On the contrary, tissue oxygenation index in the extensor region was higher during sessions of slow-pace and work with rest breaks compared to sessions of fast-pace and work with no rest, suggesting that the tool operations with faster work pace and continuous work with no rest breaks results in greatest decrease in oxygen saturation. These findings imply that spectroscopy-derived measures are able to reflect upper extremity physical demands experienced by the tool operators, and therefore NIRS is a useful alternative technique to broaden the understanding of tissue physiological changes resulted from upper extremity activities. Relevance to the industry: With advances in technology, more hand-held power tools are repetitively being used on assembly lines in various industries. Although powered tools enhance performance and efficiency, these tools have the potential to result in forces that are often associated with development of musculoskeletal disorders in the upper extremities. This study provided an alternative, non-invasive physiological approach to enhance the understanding of man (hand) and machine (tool) interaction in work productivity factors (e.g., work pace and work:rest patterns).

Functional magnetic resonance imaging (fMRI) studies of the human motor system have commonly used movement paradigms which contain a dynamic component; however, the relationship between the fMRI signal for motor tasks with and without a dynamic component is not known. We have investigated the relationship between the fMRI signal during a static finger flexion task and during dynamic finger flexion at 1-3 Hz, each at two levels of force (5% and 10% of maximum voluntary contraction). A small fMRI response could be recorded from only a few subjects during the static tasks. In contrast, a substantial fMRI response occurred during dynamic tasks in all subjects at both levels of force. The fMRI response was not significantly correlated with force or movement rate during the dynamic tasks. It is concluded that the factors responsible for generating an fMRI response are fundamentally different during steady contractions compared to those involving a dynamic component, and that the fMRI signal may be more sensitive to changes in the pattern of neural activation rather than the ongoing firing rate or extent of activation.

This study investigated possible motor unit (MU) firing patterns underlying changes in biceps brachii (BB) surface electromyographic (SEMG) activity in 96 participants who performed isometric actions of the elbow flexors at 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVC). We also conducted a modeling investigation to determine the extent to which a model would fit the experimental results. Experimentally, there was a linear increase (277%; p < 0.01) in root-mean-square (RMS) amplitude with increasing force. The mean power frequency (MNF) remained stable from 40% to 80% of MVC, but there was a decrease (8.2%; p < 0.01) between 80% and 100% of MVC. A modeling approach was taken wherein well-known recruitment and rate-coding schemes activated MUs whose basic building block was the muscle fibre action potential. Two conditions were investigated: (1) an increase in firing rate (rate-coding) and (2) synchronization. The levels of rate-coding and synchronization were selected to produce a linear RMS-force relationship as observed in the experimental data. Then, the impact of these two strategies on changes in MNF was assessed. The MNF remained stable from 40% to 80% of maximum excitation for both the rate-coding and synchronization conditions. There was a decrease in MNF between 80% and 100% of maximum excitation for both modeling conditions, similar to that observed for the experimental data. Thus, at these high forces at which experimental data are technically difficult to obtain, the model supports the idea that both rate-coding and synchronization are responsible for the changes observed in surface EMG amplitude and frequency characteristics.

Background: Quadriceps weakness and loss of muscle mass predict mortality in chronic obstructive pulmonary disease (COPD). It was hypothesised that a reduced quadriceps cross-sectional area could be detected by ultrasound in patients with COPD compared with healthy subjects, and that measurements relate to strength and fat-free mass (FFM). Methods: Rectus femoris muscle cross-sectional area (RF CSA ) was measured by ultrasound and whole-body FFM estimated using electrical bioimpedance. Quadriceps strength was measured by maximum voluntary contraction and twitch tension (TwQ) following magnetic femoral nerve stimulation. Results: 26 healthy volunteers of mean (SD) age 63 (9) years and 30 patients with COPD of mean (SD) age 67 (9) years and percentage predicted forced expiratory volume in 1 s (FEV 1 ) 48.0 (20.8)% with a similar FFM (46.9 (9.3) kg vs 46.1 (7.3) kg, p = 0.193) participated in the study. Mean RF CSA was reduced in patients with COPD by 25% of the mean value in healthy subjects(2115 mm 2 ; 95% CI 2177 to 254, p = 0.001) and was related to MRC dyspnoea scale score, independent of FFM or sex. Maximum voluntary contraction strength was linearly related to RF CSA in patients with COPD (r = 0.78, p,0.001). TwQ force per unit of RF CSA was similar in both healthy individuals and those with COPD (mean (SD) 17 (4) g/mm 2 vs 18 (3) g/mm 2 , p = 0.657). Voluntary contraction strength per unit of RF CSA was dependent on central quadriceps activation and peripheral oxygen saturation in COPD. Conclusion: Ultrasound measurement of RF CSA is an effort-independent and radiation-free method of measuring quadriceps muscle cross-sectional area in patients with COPD that relates to strength.

Functional magnetic resonance imaging (fMRI) was used to investigate the changes in blood oxygenation level dependent (BOLD) signal, cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMR(O(2))) accompanying neuronal inhibition. Eight healthy volunteers performed a periodic right-hand pinch grip every second using 5% of their maximum voluntary contraction (MVC), a paradigm previously shown to produce robust ipsilateral neuronal inhibition. To simultaneously quantify CBF and BOLD signals, an interleaved multislice pulsed arterial spin labeling (PASL) and T(2)*-weighted gradient echo sequence was employed. The CMR(O(2)) was calculated using the deoxyhemoglobin dilution model, calibrated by data measured during graded hypercapnia. In all subjects, BOLD, CBF and CMR(O(2)) signals increased in the contralateral and decreased in the ipsilateral primary motor (M1) cortex. The relative changes in CMR(O(2)) and CBF were linearly related, with a slope of approximatel...

The relationship between relative force, electromyogram (EMG) and time to fatigue was examined in seven male and seven female subjects [mean (SD) age, 21.7 (3.2) years] during isometric handgrip exercise. Subjects performed sustained submaximal contractions of the right handgrip at three different intensities: 30%, 50%, and 75% of the pretrial maximum voluntary contraction (MVC). EMG was sampled in 1-s epochs every 15 s during the contractions, and the integrated EMG (IEMG) values were then normalized to that of the pretrial MVC. As expected, time to fatigue was longest at 30% MVC and shortest at 75% MVC, but women performed consistently longer than men at each of the three intensities [-woman vs men; 400.7 (35.8) vs 364.3 (34.4) s, 205.1 (15.6) vs 139.4 (13) s, and 89.9 (11.4) vs 66.4 (6.4) s, for 30%, 50%, and 75% MVC, respectively; P < 0.05)]. IEMG increased in a non-linear fashion over time during each trial, with the magnitude of IEMG being proportional to the intensity of the contraction. At the endurance limit, IEMG was greatest in the 75% MVC trial, however, no IEMG Values reached those obtained in the related MVC [30%, 57.2 (6.9)%; 50%, 84.6 (5.7)%; 75%, 92.8 (7.4)%]. In conclusion, endurance time during sustained submaximal isometric handgrip exercise is dependent up on the intensity of the effort, with women having significantly larger endurance times than men. The related increase in IEMG is also proportional to the intensity of effort, however, the factors causing force to fail prior to the final IEMG reaching its predicted maximum remain to be elucidated.

The paper studies a surface e/ectromyogram (SEMG) decomposition technique suitable for identification of complete motor unit (MU) firing patterns and their motor unit action potentials (MUAPs) during low-level isometric voluntary muscle contractions. The algorithm was based on a correlation matrix of measurements, assumed unsynchronised (uncorrelated) MU firings, exhibited a very low computational complexity and resolved the superimposition of MUAPs. A separation index was defined that identified the time instants of an MU's activation and was eventually used for reconstruction of a complete MU innervation pulse train. In contrast with other decomposition techniques, the proposed approach worked well also when the number of active MUs was slightly underestimated, if the MU firing patterns partly overlapped and if the measurements were noisy. The results on synthetic SEMG show 100% accuracy in the detection of innervation pulses down to a signal-to-noise ratio (SNR) of lOdB, and 934-4.6% (mean4-standard deviation) accuracy with 0 dB additive noise. In the case of real SEMG, recorded with an array of 61 electrodes from biceps brachii of five subjects at 10% maximum voluntary contraction, seven active MUs with a mean firing rate of 14.1 Hz were identified on average.

In surface electromyography (sEMG), the distribution of motor unit potential (MUP) velocities has been shown to reflect the proportion of faster and slower propagating MUPs. This study investigated whether the distribution of MUP velocities could distinguish between sprinters (n = 11) and endurance athletes (n = 12) in not-specifically trained muscle (biceps brachii) during prolonged dynamic exercises at low forces. sEMG was acquired during 4 min' exercises: unloaded, 5%, 10% and 20% of maximal voluntary contraction (MVC). The features extracted from the sEMG were: the mean muscle conduction velocity -estimated using the inter-peak latency and cross-correlation methods, the within-subject skewness (expressing the proportions of faster and slower propagating MUPs) and the within-subject standard deviation of MUP velocities (SD-mup). Sprinters showed a greater proportion of faster propagating MUPs than endurance athletes. During fatigue, the SD-mup of sprinters broadened progressively, whereas that of endurance athletes did not. The findings suggest that sprinters conveyed a greater proportion of faster motor units than endurance athletes and that motor unit behavior during fatigue differed between groups. Thus, the distribution of MUP velocities enables distinction between a muscle of sprinters and endurance athletes during prolonged dynamic exercises at low forces. , CV calculated by the IPL method; CV-cc, CV calculated by the cross-correlation method; MUP-V = MUP, velocity = propagation velocity of a MUP; Sk, skewness of the within-subject MUP velocities; SD-mup, standard deviation of the within-subject MUP velocities = spread; FF type, fast-twitch/ fatigable muscle fiber type = fast/glycogenic FG = type IIb; FR type, fast-twitch/ fatigue-resistant fiber type = fast oxidative/glycogenic FOG = type IIa; S type, slowtwitch/fatigue-resistant fiber type = slow/oxidative SO = type I.

To investigate the coupling between the hemodynamic and metabolic changes following functional brain activation as well as interictal epileptiform discharges (IEDs), blood oxygenation level dependent (BOLD), perfusion and oxygen consumption responses to a unilateral distal motor task and interictal epileptiform discharges (IEDs) were examined via continuous EEG-fMRI. Seven epilepsy patients performed a periodic (1 Hz) right-hand pinch grip using¨8% of their maximum voluntary contraction, a paradigm previously shown to produce contralateral M1 neuronal excitation and ipsilateral M1 neuronal inhibition. A multi-slice interleaved pulsed arterial spin labeling and T 2 *-weighted gradient echo sequence was employed to quantify cerebral blood flow (CBF) and BOLD changes. EEG was recorded throughout the imaging session and reviewed to identify the IEDs. During the motor task, BOLD, CBF and cerebral metabolic rate of oxygen consumption (CMR O 2 ) signals increased in the contra-and decreased in the ipsilateral primary motor cortex. The relative changes in CMR O 2 and CBF were linearly related, with a slope of 0.46 T 0.05. The ratio of contra-to ipsilateral CBF changes was smaller in the present group of epilepsy patients than in the healthy subjects examined previously. IEDs produced both increases and decreases in BOLD and CBF signals. In the two case studies for which the estimation criteria were met, the coupling ratio between IED-induced CMR O 2 and CBF changes was estimated at 0.48 T 0.17. These findings provide evidence for a preserved coupling between hemodynamic and metabolic changes in response to both functional activation and, for the two case studies available, in response to interictal epileptiform activity. D

During eccentric exercise contracting muscles are forcibly lengthened, to act as a brake to control motion of the body. A consequence of eccentric exercise is damage to muscle fibres. It has been reported that following the damage there is disturbance to proprioception, in particular, the senses of force and limb position. Force sense was tested in an isometric force-matching task using the elbow flexor muscles of both arms before and after the muscles in one arm had performed 50 eccentric contractions at a strength of 30% of a maximum voluntary contraction (MVC). The exercise led to an immediate reduction of about 40%, in the force generated during an MVC followed by a slow recovery over the next four days, and to the development of delayed onset muscle soreness (DOMS) lasting about the same time. After the exercise, even though participants believed they were making an accurate match, they made large matching errors, in a direction where the exercised arm developed less force than the unexercised arm. This was true whichever arm was used to generate the reference forces, which were in a range of 5-30% of the reference armÕs MVC, with visual feedback of the reference armÕs force levels provided to the participant. The errors were correlated with the fall in MVC following the exercise, suggesting that participants were not matching force, but the subjective effort needed to generate the force: the same effort producing less force in a muscle 0167-9457/$ -see front matter Ó weakened by eccentric exercise. The errors were, however, larger than predicted from the measured reduction in MVC, suggesting that factors other than effort might also be contributing. One factor may be DOMS. To test this idea, force matches were done in the presence of pain, induced in unexercised muscles by injection of hypertonic (5%) saline or by the application of noxious heat to the skin over the muscle. Both procedures led to errors in the same direction as those seen after eccentric exercise.

It is not known how the mode of exercise, dynamic and static exercises, aVects the limb volume. Therefore, the purpose of this study was to investigate hand and wrist volume (HWV) after dynamic and static handgrip exercise. Nine healthy subjects (age 31.8 § 7.3 years; height 172.0 § 5.7 cm; body mass 66.9 § 8.1 kg, mean § SD) volunteered for this study. HWV was measured with a hand and wrist volumeter before and immediately after dynamic and static exercises. Initially during rest, HWV was measured after the hand was passively hung for 5 min. Handgrip exercises with an ergonomic hand exerciser were performed at 20% of maximum voluntary contraction in right and left hands by static and dynamic exercises, respectively. Both dynamic and static handgrip exercises consisted of six sets of 30-s contractions with 10s rest intervals between exercise bouts. The dynamic handgrip exercise was performed by repetitive contraction and relaxation of the hand at a maximum frequency. In order to determine intensity of handgrip exercises, maximum isometric handgrip strength of the right and left hand was measured with a handgrip dynamometer. Data are presented as mean § SD. After dynamic and static handgrip exercises, HWV increased signiWcantly, and these increases represent 2.2 § 0.7% (P < 0.001) and 1.4 § 0.8% (P < 0.001) of resting HWV, respectively. The elevation of HWV after dynamic exercise was signiWcantly higher than that after static exercise (P < 0.05). These results suggest that the higher HWV after dynamic exercise may be caused by higher increased interstitial Xuid volume, capillary volume and venous volume in hand and wrist tissues.

Respiratory muscle fatigue has been reported following short bouts of high-intensity exercise, and prolonged, moderate-intensity exercise, as evidenced by decrements in inspiratory and expiratory mouth pressures. However, links to functionally relevant outcomes such as breathing effort have been lacking. The present study examined dyspnoea and leg fatigue during a treadmill marathon in nine experienced runners. Maximal inspiratory and expiratory pressure, peak inspiratory and expiratory flow, forced vital capacity, and forced expiratory volume in one second were assessed before, immediately after, and four and 24 hours after a marathon. During the run, leg effort was rated higher than respiratory effort from 18 through 42 km (P < 0.05). Immediately after the marathon, there were significant decreases in maximal inspiratory pressure and peak inspiratory flow (from 118 ± 20 cm H2O and 6.3 ± 1.4 litres · s−1 to 100 ± 22 cm H2O and 4.9 ± 1.5 litres · s−1 respectively; P < 0.01), while expiratory function remained unchanged. Leg maximum voluntary contraction force was significantly lower post-marathon. Breathing effort correlated significantly with leg fatigue (r = 0.69), but not inspiratory muscle fatigue. Our results confirm that prolonged moderate-intensity exercise induces inspiratory muscle fatigue. Furthermore, they suggest that the relative intensity of inspiratory muscle work during exercise makes some contribution to leg fatigue.