Monitoring muscle fatigue following continuous load changes

Department of Human Factors EngineeringPrevious studies related to monitoring muscle fatigue during dynamic motion have focused on detecting the accumulation of muscle fatigue. However, it is necessary to detect both accumulation and recovery of muscle fatigue in dynamic muscle contraction while muscle load changes continuously. This study aims to investigate the development and recovery of muscle fatigue in dynamic muscle contraction conditions following continuous load changes. Twenty healthy males conducted repetitive elbow flexion and extension using 2kg and 1kg dumbbell, by turns. They performed the two tasks of different intensity (2kg intensity task, 1kg intensity task) alternately until they felt they could no longer achieve the required movement range or until they experienced unacceptable biceps muscle discomfort. Meanwhile, using EMG signal of biceps brachii muscle, fatigue detections were performed from both dynamic measurements during each dynamic muscle contraction task and isometric measurements during isometric muscle contraction right before and after each task. In each of 2kg and 1kg intensity tasks, pre, post and change value of EMG amplitude (AEMG) and center frequency were computed respectively. They were compared to check the validity of the muscle fatigue monitoring method using Wavelet transform with EMG signal from dynamic measurements. As a result, a decrease of center frequency in 2kg intensity tasks and an increase of center frequency in 1kg intensity tasks were detected. It shows that development and recovery of muscle fatigue were detected in 2kg and 1kg intensity tasks, respectively. Also, the tendency of change value of center frequency from dynamic measurements were corresponded with that from isometric measurements. It suggests that monitoring muscle fatigue in dynamic muscle contraction conditions using wavelet transform was valid to detect the development and recovery of muscle fatigue continuously. The result also shows the possibility of monitoring muscle fatigue in real-time in industry and it could propose a guideline in designing a human-robot interaction system based on monitoring user's muscle fatigue.clos

Estimation of Muscle Fatigue of Low Back upon the Muscle Stiffness

An estimation of muscle fatigue is very important study and many laboratory researchers had done actively in this field. The excellent measurement and analysis methods, however, have not established yet. The aim of this study was to investigate the muscle fatigue of low back, caused by sitting on the vehicle seat for a long time. The muscle viscoelasticity and the EMG (Electromyogram) were measured. The authors proposed the objective muscle fatigue index that was obtained from the result of PCA (Principal Component Analysis) by using the measured varlables. The objective muscle fatigue index suggests an adequate correlation with the subjective fatigue on the vehicle seat

Framework for Dynamic Evaluation of Muscle Fatigue in Manual Handling Work

Muscle fatigue is defined as the point at which the muscle is no longer able to sustain the required force or work output level. The overexertion of muscle force and muscle fatigue can induce acute pain and chronic pain in human body. When muscle fatigue is accumulated, the functional disability can be resulted as musculoskeletal disorders (MSD). There are several posture exposure analysis methods useful for rating the MSD risks, but they are mainly based on static postures. Even in some fatigue evaluation methods, muscle fatigue evaluation is only available for static postures, but not suitable for dynamic working process. Meanwhile, some existing muscle fatigue models based on physiological models cannot be easily used in industrial ergonomic evaluations. The external dynamic load is definitely the most important factor resulting muscle fatigue, thus we propose a new fatigue model under a framework for evaluating fatigue in dynamic working processes. Under this framework, virtual reality system is taken to generate virtual working environment, which can be interacted with the work with haptic interfaces and optical motion capture system. The motion information and load information are collected and further processed to evaluate the overall work load of the worker based on dynamic muscle fatigue models and other work evaluation criterions and to give new information to characterize the penibility of the task in design process.Comment: International Conference On Industrial Technology, Chengdu : Chine (2008

Evaluation of Forearm Muscle Fatigue from Operating a Motorcycle Clutch

A laboratory experiment evaluated the effect of motorcycle clutch design on the electromyography (EMG) activity of the primary agonist finger flexor muscle in the forearm. The goal was to compare muscle fatigue resulting from operation of two different motorcycle clutches in simulated traffic. EMG activity from the flexor digitorum superficialis (FDS) muscle of 12 female and 11 males were recorded while each participant operated an existing motorcycle clutch (requiring 98 N peak force) as well as an alternate design (requiring 36 N peak force) during 60-minute simulations. Muscle fatigue was quantified by measuring the decrease in median frequency of the EMG signals. Compared to operating the existing clutch, male participants experienced a significant decrease in muscle fatigue between 14 to 31% when operating the alternate clutch. Females experienced a decrease of 27 to 49%. In addition to reduced muscle fatigue, the alternate clutch was overwhelmingly preferred by participants and was rated superior for ease of use and comfort. Results provide a better understanding of the effect of clutch design on riders’ muscular loading and implications for design improvements

Sex Differences in Fatigability of Dynamic Contractions

Women are usually less fatigable than men during single-limb isometric contractions, primarily because of sex-related differences in contractile mechanisms. It is less clear whether these sex differences in muscle fatigue occur for dynamic fatiguing tasks. This review highlights new findings that the sex difference in fatigability for dynamic shortening contractions with a single limb is dependent on the contraction velocity and the muscle group involved. Recent studies demonstrate that women are less fatigable than men for a dynamic task as follows: (i) the elbow-flexor muscles at slow- but not high-velocity contractions; and (ii) the knee-extensor muscles when muscle fatigue was quantified as a reduction in the maximal voluntary isometric contraction force after the dynamic fatiguing task. Contractile mechanisms are responsible for the sex difference in muscle fatigue of the dynamic contractions, with no evidence for a sex difference in the reduction in voluntary activation (i.e. central fatigue). Thus, these findings indicate that the sex difference in muscle fatigue of dynamic contractions is task specific. These data also challenge the assumption that men and women respond in a similar manner to training and rehabilitation that involve fatiguing contractions to overload the neuromuscular system. There is, however, a tremendous opportunity for conducting high-impact studies to gain insight into those factors that define the sex-based differences in muscle fatigue during dynamic tasks. Such studies can define the boundaries to human performance in both men and women during athletic endeavours, ergonomic tasks and rehabilitation

Muscle Fatigue During Cardiopulmonary Resuscitation Chest Compressions

The performance of Cardio Pulmonary Resuscitation (CPR) chest compressions on a patient provide critical blood flow and oxygen delivery to the heart and brain. The objective of this study was to establish the relationship between the rate of muscle fatigue and chest compression performance. It was hypothesized that if performance of chest compressions cause fatigue after five minutes, then the rate of muscle fatigue will be indicated through surface electromyography (sEMG) measurements. Four participants (M=2, F=2) volunteered to perform chest compressions on a CPR mannequin. sEMG electrodes were placed on the participants’ dominant limb anterior deltoid muscle to capture muscle activity while performing chest compressions. Each participant completed four sets of CPR chest compressions with a two minute rest period between sets. Data was analyzed through the iWrox LabScribe™ software. The absolute interval, root mean square, and minimum and maximum amplitudes for each signal were collected for data analysis. The mean amplitude percent decline was calculated for each set of chest compressions in three-minute intervals for each participant. Examination of the rate of decline between subjects, indicating muscle fatigue was evident. The hypothesis was therefore accepted; there was convincing muscle fatigue shown through sEMG measurements while CPR chest compressions were performed. If the study was to be replicated, the author recommends that the study involve more participants to confirm the established data

Exercise-induced respiratory muscle fatigue: implications for performance

It is commonly held that the respiratory system has ample capacity relative to the demand for maximal O-2 and CO2 transport in healthy humans exercising near sea level. However, this situation may not apply during heavy-intensity, sustained exercise where exercise may encroach on the capacity of the respiratory system. Nerve stimulation techniques have provided objective evidence that the diaphragm and abdominal muscles are susceptible to fatigue with heavy, sustained exercise. The fatigue appears to be due to elevated levels of respiratory muscle work combined with an increased competition for blood flow with limb locomotor muscles. When respiratory muscles are prefatigued using voluntary respiratory maneuvers, time to exhaustion during subsequent exercise is decreased. Partially unloading the respiratory muscles during heavy exercise using low-density gas mixtures or mechanical ventilation can prevent exercise-induced diaphragm fatigue and increase exercise time to exhaustion. Collectively, these findings suggest that respiratory muscle fatigue may be involved in limiting exercise tolerance or that other factors, including alterations in the sensation of dyspnea or mechanical load, may be important. The major consequence of respiratory muscle fatigue is an increased sympathetic vasoconstrictor outflow to working skeletal muscle through a respiratory muscle metaboreflex, thereby reducing limb blood flow and increasing the severity of exercise-induced locomotor muscle fatigue. An increase in limb locomotor muscle fatigue may play a pivotal role in determining exercise tolerance through a direct effect on muscle force output and a feedback effect on effort perception, causing reduced motor output to the working limb muscles

Muscle Fatigue Analysis Using OpenSim

In this research, attempts are made to conduct concrete muscle fatigue analysis of arbitrary motions on OpenSim, a digital human modeling platform. A plug-in is written on the base of a muscle fatigue model, which makes it possible to calculate the decline of force-output capability of each muscle along time. The plug-in is tested on a three-dimensional, 29 degree-of-freedom human model. Motion data is obtained by motion capturing during an arbitrary running at a speed of 3.96 m/s. Ten muscles are selected for concrete analysis. As a result, the force-output capability of these muscles reduced to 60%-70% after 10 minutes' running, on a general basis. Erector spinae, which loses 39.2% of its maximal capability, is found to be more fatigue-exposed than the others. The influence of subject attributes (fatigability) is evaluated and discussed

Muscle fatigue degrades force sense at the ankle joint

To investigate the effects of muscle fatigue on force sense at the ankle joint, 10 young healthy adults were asked to perform an isometric contra-lateral force ankle-matching task in two experimental conditions of: (1) no-fatigue and (2) fatigue of the plantar-flexor muscles. Measures of the overall accuracy and the variability of the force matching performances were determined using the absolute error and the variable error, respectively. Results showed less accurate and less consistent force matching performances in the fatigue than no fatigue condition, as indicated by decreased absolute and variable errors, respectively. The present findings evidence that muscle fatigue degrades force sense at the ankle joint

Effect of expiratory muscle fatigue on exercise tolerance and locomotor muscle fatigue in healthy humans

High-intensity exercise (> or =90% of maximal O(2) uptake) sustained to the limit of tolerance elicits expiratory muscle fatigue (EMF). We asked whether prior EMF affects subsequent exercise tolerance. Eight male subjects (means +/- SD; maximal O(2) uptake = 53.5 +/- 5.2 ml.kg(-1).min(-1)) cycled at 90% of peak power output to the limit of tolerance with (EMF-EX) and without (CON-EX) prior induction of EMF and for a time equal to that achieved in EMF-EX but without prior induction of EMF (ISO-EX). To induce EMF, subjects breathed against an expiratory flow resistor until task failure (15 breaths/min, 0.7 expiratory duty cycle, 40% of maximal expiratory gastric pressure). Fatigue of abdominal and quadriceps muscles was assessed by measuring the reduction relative to prior baseline values in magnetically evoked gastric twitch pressure (Pga(tw)) and quadriceps twitch force (Q(tw)), respectively. The reduction in Pga(tw) was not different after resistive breathing vs. after CON-EX (-27 +/- 5 vs. -26 +/- 6%; P = 0.127). Exercise time was reduced by 33 +/- 10% in EMF-EX vs. CON-EX (6.85 +/- 2.88 vs. 9.90 +/- 2.94 min; P < 0.001). Exercise-induced abdominal and quadriceps muscle fatigue was greater after EMF-EX than after ISO-EX (-28 +/- 9 vs. -12 +/- 5% for Pga(tw), P = 0.001; -28 +/- 7 vs. -14 +/- 6% for Q(tw), P = 0.015). Perceptual ratings of dyspnea and leg discomfort (Borg CR10) were higher at 1 and 3 min and at end exercise during EMF-EX vs. during ISO-EX (P < 0.05). Percent changes in limb fatigue and leg discomfort (EMF-EX vs. ISO-EX) correlated significantly with the change in exercise time. We propose that EMF impaired subsequent exercise tolerance primarily through an increased severity of limb locomotor muscle fatigue and a heightened perception of leg discomfort