Median Frequency Slope Research Articles

Shoulder muscle function in frozen shoulder syndrome patients following manipulation under anesthesia: A 6-month follow-up study

The present study evaluates changes in shoulder muscle function in patients with frozen shoulder syndrome (FSS) following manipulation under general anesthesia (MUA). Fifteen FSS patients with mean (±SD) age of 53.6±9.7 years were included in this study. Isometric endurance of the shoulder muscles was characterized by time and net impulse (NI), which were assessed with the patient holding a weight in the hand until exhaustion. Fatigability of the deltoid and trapezius muscles during isometric endurance test was assessed by electromyogram power spectrum median frequency (MF) slope per minute. Patients were also screened for daytime pain. Data were collected before MUA, and at 1 and 6 months postoperatively. Six months postoperatively, the MF slope for the trapezius and deltoid muscles of the involved and uninvolved shoulders did not differ (P>0.05), whereas NI remained lower and endurance time was longer (P<0.05). Shoulder pain was reduced as compared to preoperative levels (on visual analog scale) 1 and 6 months postoperatively (P<0.05). In patients with FSS, the fastest improvements in shoulder muscle NI, fatigability and pain take place in the first month after MUA; 6 months after MUA, however, NI and endurance time remained impaired for the involved shoulder. Physiotherapy should pay more attention to muscle function recovery. Level III, prospective follow-up study.

Disability and back muscle fatigability changes following two therapeutic exercise interventions in participants with recurrent low back pain

BackgroundThe level of disability and endurance of back muscles have been investigated, but there is conflicting evidence following specific exercise interventions for participants with recurrent low back pain (LBP). The purpose of this study was to compare the level of disability and slope of median frequency (MF) of thoracic and lumbar erector spinae (ES) muscles following core stabilization exercise (CSE) and spinal flexibility exercise (SFE).Material/MethodsIn total, 46 individuals participated in this study. There were 25 participants in the CSE intervention group (average age of 47.7±8.9 years) and 21 participants in the SFE group (average age of 53.1±9.0 years). Each group participated in the specific exercise intervention program for 4 weeks while maintaining their current activity and/or exercise levels. The Oswestry Disability Index (ODI) was used to measure the level of disability changes. The fatigability of the ES back muscles was measured by the slope of MF, using a modified Sorensen test.ResultsThe disability level decreased significantly following CSE intervention (t=2.23, p<0.05). However, there was no significant difference in muscle fatigability changes in the 4-week intervention period for either group.ConclusionsThe CSE intervention reduced disability level following the 4-week intervention period. Further studies are needed to investigate the effectiveness of specific back muscle exercises in longer intervention periods for back muscle fatigability.

Subjective and objective assessment of neuromuscular fatigue in female painters

The aim of this study was to evaluate subjectively and objectively neuromuscular fatigue in female painters before and after a workingday. The subjects (n=11) were female painters aged 22–60 years. The subjects completed a questionnaire and gave a subjective evaluation on muscle fatigue sensation in hands, trunk, back and lower limbs according to Borg's Category Ratio (CR-10) scale. Thereafter they performed 3-minute test of painting a wall, in the course of which the electromyographical (EMG) power spectral median frequency (MF) slope for biceps brachii, trapezius, deltoid and infraspinatus muscles was measured. The results indicated a significant change in the subjective muscle fatigue sensation in hands by 40%, lower limbs by 54% and trunk by 57% after the working day, compared to the beginning of the working day. EMG power spectral MF slope of the measured muscles did not differ significantly during the 3-minute wall coloring test before and after working day. It was concluded that subjective muscle fatigue sensation in hands, lower limbs and trunk was higher after the working day whereas it was less pronounced in the back. Muscle fatigue evaluated objectively by MF slope of EMG power spectrum from biceps brachii, trepezius, deltoid and infraspinatus muscles was not evident during the wall coloring test before and after the working day.

Análise espectral do sinal EMG de exercício incremental em ciclistas e não ciclistas usando as transformadas de Fourier e Wavelet

The aim of this study was to compare the electromyographic indices of fatigue (slope of median frequency) calculated with the fast Fourier transform (FFT) and wavelet transform (WT) in trained and untrained individuals during cycle exercise. A second objective was to compare the variance of the spectral parameters (median frequency - MF) obtained by the FFT and WT during exercise. Twelve cyclists and non-cyclists performed a maximal incremental test to determine the peak power (Wp) and electromyographic activity of the vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), semitendinous (ST) and tibialis anterior (TA). Mean values of median frequency, determined by the FFT and WT, were used for the spectral analysis of the electromyographic signals of the studied muscles. The analyzed parameters were obtained for each time period corresponding to 0, 25, 50, 75, and 100% of total duration of the maximal incremental test. No statistically significant differences were found in the values of MF and electromyographic indices of fatigue between the two techniques (FT and WT) both in the cyclists and non-cyclists group (P&gt;0.05). Regarding the MF variance, statistically significant differences were found in all analyzed muscles, as well as in different time periods, both in the cyclists and non-cyclists groups when comparing the FFT and WT techniques (P&lt;0.05). The WT seems to be more adequate to dynamic tasks, since it does not require the signal to be quasi-stationary, unlike the limitation imposed upon the use of the FFT.

The effect of continuous ultrasound on chronic non-specific low back pain: a single blind placebo-controlled randomized trial

BackgroundNon-specific chronic low back pain (NSCLBP) is one of the most common musculoskeletal disorders around the world including Iran. One of the most widely used modalities in the field of physiotherapy is therapeutic ultrasound (US). Despite its common use, there is still inconclusive evidence to support its effectiveness in patients with NSCLBP. The objective of this study was to evaluate the effect of continuous US compared with placebo US additional to exercise therapy for patients with NSCLBP.MethodsIn this single blind placebo controlled study, 50 patients with NSCLBP were randomized into two treatment groups: 1) continuous US (1 MHz &1.5 W/cm2) plus exercise 2) placebo US plus exercise. Patients received treatments for 4 weeks, 10 treatment sessions, 3 times per week, every other day. Treatment effects were assessed in terms of primary outcome measures: 1) functional disability, measured by Functional Rating Index, and 2) global pain, measured by a visual analog scale. Secondary outcome measures were lumbar flexion and extension range of motion (ROM), endurance time and rate of decline in median frequency of electromyography spectrum during a Biering Sorensen test. All outcome variables were measured before, after treatment, and after one-month follow-up. An intention to treat analysis was performed. Main effects of Time and Group as well as their interaction effect on outcome measures were investigated using repeated measure ANOVA.ResultsAnalysis showed that both groups had improved regarding function (FRI) and global pain (VAS) (P < .001). Lumbar ROM as well as holding time during the Sorensen test and median frequency slope of all measured paravertebral muscles did not change significantly in either group (P > .05). Improvement in function and lumbar ROM as well as endurance time were significantly greater in the group receiving continuous US (P < .05).ConclusionsThe study showed that adding continuous US to a semi supervised exercise program significantly improved function, lumbar ROM and endurance time. Further studies including a third group of only exercise and no US can establish the possible effects of placebo US.Trial registrationNTR2251

Differential patterns of muscle modification in women with episodic and chronic tension-type headache revealed using surface electromyographic analysis

Tension-type headache (TTH) is a prototypical disorder in which muscular factors play a key role in the pathogenesis. This study was designed to understand muscular dysfunction in patients with episodic (ETTH) and chronic TTH (CTTH) using surface electromyography analysis (SEMG). Women with frequent ETTH (n=14), CTTH (n=14) and age-matched controls (n=13) were recruited. SEMG data were recorded from the masseter, sternocleidomastoid, and upper trapezius muscles during maximum voluntary contraction and sustained voluntary isometric clenching, the neck flexion endurance test and shoulder elevation for 30s. The root mean square (RMS) and median frequency (MDF) of the SEMG signal were measured throughout the test. The fatigue index, which is the MDF slope during sustained muscle contraction, decreased significantly faster in the ETTH and CTTH groups compared with that in the control (p<0.05). The mean absolute RMS and relative percentage values at the initial and final period during sustained isometric contraction decreased significantly in the CTTH group (p<0.05). Furthermore, headache clinical parameters (frequency and duration) were negatively correlated with the amplitude values (p<0.05). A different muscle firing pattern or some muscle modifications in patients with CTTH may reflect reorganization of the motor-control strategy.

Spectral analysis of EMG using intramuscular electrodes reveals non-linear fatigability characteristics in persons with chronic low back pain

Greater fatigability across lumbar extensors has been reported in persons with chronic low back pain (LBP), however, extensor atrophy tends to be local to the site of pain. Therefore, specific ultrasound guided local and remote intramuscular electromyographic recordings were undertaken during an isometric horizontal trunk hold in two carefully matched cohorts; persons with and without LBP. The test was performed to self-determined maximal hold time, and the control group held the horizontal position longer (P<0.001). A power spectral analysis was performed to calculate the normalized median frequency (NMF) slope for both the first and last 30s of the fatigue test due to the group difference in hold times. There were no significant group differences in NMF slope at the first 30s of testing (P=0.650). The NMF slope for the first and last 30s was not different in healthy subjects (P=0.688), but was different in persons with LBP, illustrated by shallowing of the slope at the last 30s of the test (P=0.008). A between muscle comparison in the LBP group showed greater non-linear behavior in the deep multifidus (painful region) in contrast to T10 longissimus thoracis (nonpainful region) (P=0.013). Possible explanations for these findings are discussed.

The effects of triceps surae fatigue on the torque and electromyographic parameters in athletes compared with non-athletes

The common description of muscular fatigue is the failure of muscle in maintaining a target force. Even in sustained contraction, when muscle force is held at a stable level, physiological, biomechanical and electromyographic changes can occur. The purpose of this study is to compare the effects of triceps surae (TS) fatigue on the torque, falling slope and electromyographic (EMG) parameters between athletes and non-athletes. Nineteen healthy women (10 non-athletes and 9 basketball players) participated in this study. After warm-up, subjects performed one maximum voluntary contraction (MVC) followed by fatigue test including sustained maximum isometric contraction of TS until the peak torque (PT) decreased to 50% of maximum value. Immediately after the test, subjects were asked to perform one MVC; then, root mean square (RMS), median frequency (MDF), median frequency slope (MDF slope), PT, falling slope (FSL) and the amount of pain were measured. In both groups shift of MDF slope to negative values, significant decrease of MDF and RMS occurred at the end of the fatigue test (P < 0.05). Immediately after the test, PT decreased significantly in both groups (P < 0.05), however, decrease of FSL was significant in non-athletes (P < 0.05) but not in athletes. After fatigue test, increase in Pain was significant in both groups (P < 0.05). Before fatigue test, at the end, and immediately after the test, MDF of non-athletes was more than athletes. There was no significant difference in RMS between the two groups. Our findings suggest that TS fatigue affects EMG parameters, PT and pain in athletes and non-athletes similarly.

Effects of handicraft sitting postures on lower trunk muscle fatigue

The purpose of this study was to assess trunk muscle fatigue in seated handicraft tasks using surface electromyography (sEMG) and visual analogue scale (VAS) ratings for trunk discomfort, and to assess the relationship of these responses. Twenty-three participants were randomly assigned to assumed crossed-leg and heel sitting postures for 30 min. Normalised median frequency (NMF) slopes for lumbar multifidus (LM) and internal oblique (IO) muscles and VAS ratings were recorded. Results revealed that the crossed-leg posture produced significantly steeper NMF slopes for both sides of the LM and IO muscles than heel sitting. Greater VAS ratings were found in crossed-leg sitting posture than the heel sitting posture. The NMF slopes and the VAS ratings had significant negative correlations for both postures. Findings support heel sitting in handicraft tasks over crossed-leg sitting due to greater trunk muscle fatigue and discomfort during the latter posture. Results support VAS ratings as a complementary method to sEMG for identifying trunk muscle fatigue. Practitioner Summary: Trunk muscle fatigue in handicraft work is a potential risk for low back pain. Based on EMG and discomfort analyses, heel sitting is preferred to crossed-leg posture. Discomfort ratings are consistent with EMG measures in identifying trunk muscle fatigue in such postures.

Evaluation of muscle fatigue of wheelchair basketball players with spinal cord injury using recurrence quantification analysis of surface EMG

Wheelchair basketball is the most popular exercise activity among individuals with spinal cord injury (SCI). The purpose of this study was to investigate muscular endurance and fatigue in wheelchair basketball athletes with SCI using surface electromyography (SEMG) and maximal torque values. SEMG characteristics of 10 wheelchair basketball players (WBP) were compared to 13 able-bodied basketball players and 12 sedentary able-bodied subjects. Participants performed sustained isometric elbow flexion at 50% maximal voluntary contraction until exhaustion. Elbow flexion torque and SEMG signals were recorded from three elbow flexor muscles: biceps brachii longus, biceps brachii brevis and brachioradialis. SEMG signals were clustered into 0.5-s epochs with 50% overlap. Root mean square (RMS) and median frequency (MDF) of SEMG signals were calculated for each muscle and epoch as traditional fatigue monitoring. Recurrence quantification analysis was used to extract the percentage of determinism (%DET) of SEMG signals. The slope of the %DET for basketball players and WBP showed slower increase with time than the sedentary able-bodied control group for three different elbow flexor muscles, while no difference was observed for the slope of the %DET between basketball and WBP. This result indicated that the athletes are less fatigable during the task effort than the nonathletes. Normalized MDF slope decay exhibited similar results between the groups as %DET, while the slope of the normalized RMS failed to show any significant differences among the groups (p>0.05). MDF and %DET could be useful for the evaluation of muscle fatigue in wheelchair basketball training. No conclusions about special training for WBP could be determined.

Quadriceps short-term resistance exercise in subjects with resistant hypertension

INTRODUCTION: Resistant arterial hypertension may lead to muscle disuse and reduced functional capacity due to arterial and target-organs lesions. The main objective of this work is to evaluate the quadriceps strength and fatigue tolerance after a program of resistance exercise in subjects with resistant primary hypertension. METHODS: Six patients under pharmacological treatment were submitted to a four-week resistance exercise training program for the quadriceps (8-14 repetitions, 3 sets, 3 days per week). Strength was evaluated by isometric dynamometry, as the percentage change in maximum voluntary contraction over the four week program. Fatigue was analyzed by surface electromyography, as the change in both root mean square value and intercept of median frequency slope of vastus medialis and vastus lateralis. RESULTS: Significant increase in the maximum voluntary contraction was observed (p = 0.04). Fatigue tolerance was not improved as seen by root mean square as well as in the intercept of median frequency (p &gt; 0.05). Additionally, no significant changes were observed in resting arterial blood pressure and heart rate throughout the training period. CONCLUSION: The prescribed protocol seemed to successfully increase localized muscle strength without negatively affecting the monitored cardiovascular variables in patients with resistant hypertension under pharmacological treatment.

Shoulder muscle activation and fatigue during a controlled forceful hand grip task

PurposeReliable electromyographic evaluation of the shoulder in common painful conditions is a major challenge due to a reduced range of movement and pain-related muscle inhibition. This study investigates the use of a hand grip task for the assessment of shoulder muscle activation. MethodsMuscle activity and fatigue for supraspinatus and infraspinatus muscles were measured in 16 healthy controls using fine-wire electrodes during a controlled gripping task at 50% of maximum voluntary contraction, in a standardized sitting and arm position. Changes in muscle activity and fatigue were measured by the time-slope of root mean square amplitude and median frequency, respectively. ResultsA significant positive amplitude slope (p<0.01) was found for both supraspinatus and infraspinatus, indicating that the task resulted in increasing muscle activity. Judging by the median frequency slope, there was no sign of fatigue progression. ConclusionA standardized hand grip task in a neutral position activates key rotator cuff muscles. This might provide a method for electromyographic assessment of shoulder girdle muscles which avoids problems due to pain-related limitation of movement, and might be useful in the development and monitoring of shoulder rehabilitation strategies.

Reliability of measurements of endurance time, electromyographic fatigue and recovery, and associations to activity limitations, in patients with lumbar disc herniation

Electromyographic (EMG) spectral parameters and endurance tests for back muscles have long been used to estimate low-back muscle fatigue. The present purpose was to evaluate the test-retest reliability of a fatigue-testing protocol and to investigate associations between activity limitations and fatigue in patients with lumbar disc herniation. To evaluate the reliability, endurance time, EMG spectral parameters and ratings of lumbar muscle fatigue and back pain were measured three times in 15 patients with lumbar disc herniation. The patients performed a modified Sørensen test with concurrent recordings of electromyography from the lumbar muscles at four recording sites. Ratings of their perceived fatigue and pain on a Borg scale were collected simultaneously. Recovery over five minutes was recorded. Questionnaires about activity, participation, self-efficacy and health were also used. Endurance time had an ICC of 0.85 indicating good reliability. Initial, end and median frequency recovery had intraclass correlation coefficients (ICCs) over 0.6 that is acceptable but with large standard errors of measurement. The median frequency slopes for the four recording sites had ICCs of 0.19-0.48. Agreement coefficients for the Borg ratings ranged between 0.78 and 0.97. Moderate correlation was found between activity limitations and endurance time. Endurance time measurement and Borg ratings may be recommended for evaluating intervention both with groups of patients, i.e. for research purposes, and for individuals. The median frequency parameters may be recommended for groups only. The study shows the importance of establishing the reliability of the patient category if the results are to be used to evaluate intervention.

EMG analysis of lumbar paraspinal muscles as a predictor of the risk of low-back pain

Studies of EMG power spectra have established associations between low-back pain (LBP) and median frequency (MF). This 2-year prospective study investigates the association of LBP with EMG variables over time. 120 health care workers underwent paraspinal EMG measurements and assessment of back pain disability. The EMG recordings were performed under isometric trunk extension at 2/3 maximum voluntary contraction and acquired from erector spinae muscles at the level of L4/L5. 108 (90%) subjects were reviewed at a minimum 2-year follow up. 16 out of 93 subjects with no history of chronic low-back pain became worse as measured by time off work, disability, reported pain and self-assessment rating. The value of the EMG variable half-width at inception demonstrated significant association with changes in subject's outcome measure and their own assessment of their LBP at follow up (p < 0.05). Based on self-assessment data, subjects with no history of chronic LBP with half-width of greater than 56 Hz were at threefold greater risk of developing back pain compared with the remainder of the population (p = 0.045). The value of the initial median frequency (IMF) and MF slope at inception were also associated with the subjects' own assessment of LBP at follow up. Subjects with an IMF greater than 49 Hz were at 5.8-fold greater risk of developing back pain compared with the remainder of the population (p = 0.014). EMG variables recorded from lumbar paraspinal muscles can identify a sub group of subjects at increased risk of developing low-back pain in the future.

Spectral and entropy changes for back muscle fatigability following spinal stabilization exercises

The entropy of electromyography (EMG) signals suggests a possible tool for the clinical assessment of low back pain (LBP). However, a general physiological mechanism for entropy and pain and/or dysfunction following exercise intervention is still unknown. This comparative study investigated the differences between entropy levels of the EMG signals and the slope of median frequency (MF) based on power spectrum analysis in chronic LBP subjects after 4 weeks of spinal stabilization exercises (SSEs). In total, 46 subjects (24 female and 22 male) participated in the exercise program; the EMG signals of their thoracic and lumbar erector spinae muscles were measured. Following the SSEs, the level of pain as measured by the Million Visual Analog Scale decreased significantly from 3.80 to 2.81 (T = 3.42, p = 0.001). The Shannon entropy levels of the EMG signals were not different based on the back muscles (F = 2.86, p = 0.09) but demonstrated a significant interaction with pain level (F = 7.17, p = 0.01). The slope of MF differed among the muscles (F = 12.06, p = 0.01); however, no interaction with the level of pain was found (F = 0.19, p = 0.66). Therefore, the Shannon entropy of the EMG signals might be a useful and valuable clinical tool to measure pain following intervention.

Fatigability of back extensor muscles and low back pain during pregnancy

Background Back pain is the most frequently reported musculo-skeletal problem during pregnancy. High muscle fatigability has been associated with back pain in the general population. During pregnancy, the gradual increase in loads may have a training effect, increasing strength and endurance of back muscles. This adaptation however may be too slow, or insufficient to be significant in light of other changes during pregnancy. Methods Thirty-two pregnant women performed a fatigue test which consisted of maintaining a fixed load of 70 Nm for 60 s while the surface EMG of the longissimus lumborum and multifidus muscles were recorded bilaterally at 14, 24 and 34 weeks of pregnancy. The measure of fatigability was the highest absolute slope of the median frequency of the power spectrum of the EMG of the four muscles. Occurrence and severity of back pain were reported on questionnaires at 14, 19, 24, 29 and 34 weeks. Binomial logistic regressions between back pain occurrence and the median frequency slopes were calculated. Findings None of the five logistic analyses demonstrated an improvement of the one-predictor model over the constant-only model, which indicates that the degree of fatigability of back extensor muscles did not predict the occurrence of back pain in our sample. Interpretation Fatigability of back extensor muscles was not found to be a predictor of back pain during pregnancy. This result should be taken with caution due to the small number of participants and broad definition of back pain used, and should be confirmed by studies with a larger number of participants.

Long term reliability of EMG measurements in adults with cystic fibrosis

The aim of this study was to investigate the long term reliability of surface electromyography (sEMG) measurements in adults with cystic fibrosis (CF). Eighteen healthy subjects (CO) and sixteen adults with CF were tested on two occasions, six weeks apart. sEMG was recorded from the rectus femoris, vastus lateralis and vastus medialis obliquus muscles during maximal voluntary contraction (MVC) and 50% MVC until exhaustion. Quadriceps muscle activity during 50% MVC was described using four measures (initial, final, normalized and slope values) for both frequency and time domain. Relative (ICC) and absolute (SEM) reliabilities were applied to asses test-retest reliability. In CF group, median frequency (MDF) values for 100% MVC and initial, final and normalized final MDF for 50% MVC demonstrated moderate to very high relative reliability (ICC = 0.60–0.91) and low variability (SEM = 5.5–13%). MDF slope showed large variability in both groups. Root mean square (RMS) values were not reproducible in both groups whatever the intensity of exercise and can not be recommended as outcomes parameters. In conclusion, sEMG measurements during maximal and submaximal isometric contractions could be valid and reliable tools for clinical applications in cystic fibrosis patients but mainly in the frequency domain and from rectus femoris.

Reliability difference between spectral and entropic measures of erector spinae muscle fatigability

This study investigated back muscle fatigability of the erector spinae (ES) muscles during submaximal contractions with the use of surface electromyography (sEMG). It was important to confirm the reliability of measurements for characterizing neuromuscular alterations by establishing the difference between the Shannon (information) entropy and the power spectrum analysis in subjects with low back pain (LBP). The data was collected on two different days, one week apart, and the between-days reliability of these measures was examined. Thirty-two gender-matched subjects completed the modified Sorenson test; 16 of the subjects were female while 16 were male. The entropy of the sEMG signal was more reliable than either the median frequency (MF) or the slope of the MF. The intraclass correlation coefficient (ICC) was higher for the entropy than for the MF slope. The ICC values of entropy for between-day measurements were higher (0.82–0.85) than MF (0.54–0.64) and MF slope (0.26–0.30). The standard errors of measurement (SEM) values for entropy were lower (0.04–0.05) than MF (3.10–3.60) and MF slope (0.03–0.04). The Pearson correlation coefficients of the entropy were significantly higher (0.75–0.77) than those of the MF (0.38–0.47) and the MF slope (0.15–0.18). Therefore, the results of this study indicated that the entropy analysis could provide a reliable measure of muscle fatigability.

Assessment of the validity of the Biering-Sørensen test for measuring back muscle fatigue based on EMG median frequency characteristics of back and hip muscles

The aims of the present study were (1) to investigate the differences in median frequency characteristics between back and hip muscles of healthy subjects during a Biering-Sørensen test, (2) to determine if the Biering-Sørensen test is a valid test for measuring back muscle fatigue, and (3) to standardise the Biering-Sørensen test by using objective movement analysis when defining endurance time, and compare this to the original method based on tactile feedback. Twenty healthy subjects participated in this experiment. The electromyographic activity of eight back and hip muscles was bilaterally measured. In addition three-dimensional data of the lumbar region were collected with an ultrasound movement analysis system. Median frequencies were computed from the EMG power spectra. Two methods of determining the endurance time of the Biering-Sørensen test yielded highly correlated but significantly different normalized median frequency slope values (NMF slope). Significant differences in NMF slope values between several back and hip muscles could be demonstrated. Low to moderate correlation coefficients were shown between NMF slope values and endurance time. Multiple stepwise linear regression analyses revealed that only NMF slope of the thoracic part of the iliocostalis lumborum muscle could significantly predict the test endurance time. The findings of the present study support the validity of the Biering-Sørensen test for measuring back muscle fatigue.

Within-day and between-days reliability of quadriceps isometric muscle fatigue using mechanomyography on healthy subjects

This study aimed to examine within-day and between-days intratester reliability of mechanomyography (MMG) in assessing muscle fatigue. An accelerometer was used to detect the MMG signal from rectus femoris. Thirty one healthy subjects (15 males) with no prior knee problems initially performed three maximum voluntary contractions (MVCs) using an ISOCOM dynamometer. After 10 min rest, subjects performed a fatiguing protocol in which they performed three isometric knee extensions at 75% MVC for 40 s. The fatiguing protocol was repeated on two other days, two to four days apart for between-days reliability. MMG activity was determined by overall root mean squared amplitude (RMS), mean power frequency (MPF) and median frequency (MF) during a 40 s contraction. RMS, MPF and MF linear regression slopes were also analysed. Intraclass Correlation Coefficients (ICC); ICC1,1 and ICC1,2 were used to assess within-day reliability and between-days reliability respectively. Standard error of measurement (SEM) and smallest detectable difference (SDD) described the within-subjects variability. MMG fatigue measures using linear regression slopes showed low reliability and large between-days error (ICC1,2 = 0.43–0.46; SDD = 306.0–324.8% for MPF and MF slopes respectively). Overall MPF and MF, on the other hand, were reliable with high ICCs and lower SDDs compared to linear slopes (ICC1,2 = 0.79–0.83; SDD = 21.9–22.8% for MPF and MF respectively). ICC1,2 for overall MMG RMS and linear RMS slopes were 0.81 and 0.66 respectively; however, the SDDs were high (56.4% and 268.8% respectively). The poor between-days reliability found in this study suggests caution in using MMG RMS, MPF and MF and their corresponding slopes in assessing muscle fatigue.