Optimal bipolar system positioning to provide information about the trapezius activity associated with scapular retraction during shoulder exercises for resistance training.

Objective. Recently, the use of EMG biofeedback to make subjects aware of the stabilizer activation associated with scapular retraction during exercise has been of interest, and challenges related to EMG detection have been addressed. Whether there is an optimal bipolar positioning that discriminates the stabilizer activation with retraction from a neutral scapular position during resistance exercises is an open issue that we address here by simultaneously mapping different positions using high-density surface electromyography (HD-sEMG).Approach. Sixteen resistance-trained males performed five pulling exercises with and without scapular retraction, namely barbell rows, dumbbell rows, pull-downs at a lat machine, seated rows, and TRX (total resistance exercises) system rows. HD-sEMG was acquired in a monopolar mode from the medial and lower trapezius (8 × 4 electrodes and inter-electrode distance (ied): 10 mm) and different bipolar systems were simulated in terms of positioning, interelectrode distance, and orientation with respect to the spine: longitudinal with three ieds (20 mm, 30 mm, and 40 mm), one transversal, and two diagonals (ied: 20 mm), totalling six EMG sets. To identify the optimal electrode pair that was able to distinguish between the presence or absence of scapular retraction, we computed: (i) the root mean square (RMS) map for each condition and the difference between them, obtaining a differential RMS map per subject; and (ii) the intersection of cumulative maps, by summing the differential (binary) maps from all subjects.Main results. For the lower trapezius, the results revealed that the diagonal direction (45 degrees; ied: 20 mm) obtained the greater occurrence of intersecting segments within and between exercises than the other electrode configurations, showing low variability for the optimal positioning across exercises. Electrode configuration varied within and between the pulling exercises for the medial trapezius.Significance. This study allows us to identify an optimal bipolar positioning (consistent across subjects and exercises) for lower trapezius activity assessment, representing a guideline for electrode positioning when EMG biofeedback is adopted for selective activation of the lower trapezius during pulling exercises.

Screening, diagnosis and monitoring of sarcopenia: When to use which tool?

BACKGROUND & AIMS: Sarcopenia is a muscle disorder associated with loss of muscle mass, strength and function. Early screening, diagnosis and treatment may improve outcome in different disease conditions. A wide variety of tools for estimation of muscle mass is available and each tool has specific technical requirements. However, different investigational settings and lack of homogeneity of populations influence the definition of gold standards, proving it difficult to systematically adopt these tools. Recently, the European Working Group on Sarcopenia in Older People (EWGSOP) published a revised recommendation (EWGSOP-2) and algorithm for using tools for screening and diagnosing sarcopenia. However, agreement of the EWGSOP2 criteria with other classifications is poor and although an overview of available tools is valuable, for the purpose of clinical decision-making the reverse is useful; a given scenario asks for the most suitable tools. RESULTS: Tools were identified for screening, diagnostics and longitudinal monitoring of muscle mass. For each of these clinical scenarios the most appropriate tools were listed and for each technique their usability is specified based on sensitivity and specificity. Based on this information a specific recommendation is made for each clinical scenario. CONCLUSION: This narrative review provides an overview of currently available tools and future developments for different clinical scenarios such as screening, diagnosis and longitudinal monitoring of alterations in muscle status. It supports clinical decision-making in choosing the right tools for muscle mass quantification depending on the need within a given clinical scenario as well as the local availability and expertise.

Central and peripheral fatigue in knee and elbow extensor muscles after a long-distance cross-country ski race.

Although elbow extensors (EE) have a great role in cross-country skiing (XC) propulsion, previous studies on neuromuscular fatigue in long-distance XC have investigated only knee extensor (KE) muscles. In order to investigate the origin and effects of fatigue induced by long-distance XC race, 16 well-trained XC skiers were tested before and after a 56-km classical technique race. Maximal voluntary isometric contraction (MVC) and rate of force development (RFD) were measured for both KE and EE. Furthermore, electrically evoked double twitch during MVC and at rest were measured. MVC decreased more in KE (-13%) than in EE (-6%, P = 0.016), whereas the peak RFD decreased only in EE (-26%, P = 0.02) but not in KE. The two muscles showed similar decrease in voluntary activation (KE -5.0%, EE -4.8%, P = 0.61) and of double twitch amplitude (KE -5%, EE -6%, P = 0.44). A long-distance XC race differently affected the neuromuscular function of lower and upper limbs muscles. Specifically, although the strength loss was greater for lower limbs, the capacity to produce force in short time was more affected in the upper limbs. Nevertheless, both KE and EE showed central and peripheral fatigue, suggesting that the origins of the strength impairments were multifactorial for the two muscles.

The contribution of postural balance analysis in older adult fallers: A narrative review.

OBJECTIVE: Falls are a serious health problem for older adults. Several studies have identified the decline of postural balance as one of the main risk factors for falls. Contrary to what may be believed, the capability of force platform measurements to predict falls remains uncertain. The focus of this narrative review is the identification of postural characteristics of older adults at risk of falling using both static and dynamic postural balance assessments. METHODS: The literature analysis was conducted on Medline/PubMed. The search ended in May 2015. RESULTS: Centre of pressure (CoP) path length, CoP velocity and sway in medial lateral and anterior-posterior are the variables that distinguish older adult fallers from non-fallers. DISCUSSION: Recommendations to medical personnel on how to provide efficient balance training for older adults are offered, discussing the relevance and limitations of postural stability on static and dynamic board in falling risk prevention.

Do sweep rowers symmetrically activate their low back muscles during indoor rowing?

This study investigates whether sweep rowers activate their low back muscles asymmetrically when exercising on a rowing ergometer. Given that indoor rowing imposes equal loading demands to left and right back muscles, any side differences in activation are expected to reflect asymmetric adaptations resulting from sweep rowing. In addition to trunk kinematics, surface electromyograms (EMGs) were sampled from multiple skin locations along the lumbar spine of six elite, sweep rowers. The distribution of EMG amplitude along the spine was averaged across strokes and compared between sides. Key results indicate a significant effect of trunk side on EMG amplitude and on the low back region where EMG amplitude was greatest. Such side differences were unlikely because of trunk lateral inclination and rotation, which were smaller than 5° for all rowers tested. Moreover, asymmetries manifested differently between participants; there was not a clear predominance of greater EMG amplitude toward the right/left side in portside/starboard rowers. These results suggest that (a) even during indoor rowing, sweep rowers activate asymmetrically their low back muscles; (b) factors other than rowing side might be associated with low back asymmetries; (c) spatial distribution of surface EMG amplitude is sensitive to bilateral changes in back muscles' activation.

Muscle fatigue induced by two different resistances: Elastic tubing versus weight machines.

Elastic tubes are devices relatively inexpensive, easy to use, portable and safe, which are claimed to provide advantages with respect to training with free weights or weight machine. The aim of this work was to assess neuromuscular modification induced by the use of two different muscle contraction modalities (elastic versus weight resistances) until exhaustion. Fourteen healthy physically active male students (age: 28±6 years; body mass 72.1±11.0kg; height: 173.5±6.9cm) were recruited. They were requested to reach exhaustion with dynamic contraction at 70% of their own One Repetition Maximal (1RM) using, in two different days and in random order, Thera Band® tubes or traditional weight plates on an arm machine designed and built for those tasks. Before and after such contractions a standardized fatiguing isometric test (3 Maximal Voluntary Contractions, MVC plus 60s at 60% MVC) was requested to assess differences induced by the exhaustion sessions. During fatiguing tests surface EMG signals were recorded from biceps brachii muscle with linear arrays of eight electrodes (silver bars 10mm apart, 5mm long, and 1mm diameter) in single differential configuration. Initial values and rates of change of Average Rectified Value (ARV), MeaN power Frequency (MNF) and muscle fiber Conduction Velocity (CV) were calculated to compare the effects of the two contraction modalities. No differences were found between "elastic session" and "weight session" PRE MVCs (31.9±8.8 and 29.9±8.3nm, respectively) and endurance times (28±6 and 26±7s, respectively). The same was observed for POST values. During the post-contraction isometric fatigue test, the only parameters influenced by the contraction modality were the initial CV and the rate of change in CV which were 12% and 37% greater (p<0.05) respectively after contractions performed with elastic resistance compared to free weights. These findings confirm others for which contractions done with the use of elastic band seem to require greater muscle activation; moreover, they highlight a sort of "muscle conditioning" after that specific contraction modality which requires the use of faster motor units. It is thus possible to consider the practical use of such elastic devices to increase the neuromuscular activation, for instance in specific rehabilitation settings where slow movements with minimal risk of injury are requested (post surgery rehabilitation, physical activity with elderly people or children).

Surface EMG: the issue of electrode location.

This paper contributes to clarifying the conditions under which electrode position for surface EMG detection is critical and leads to estimates of EMG variables that are different from those obtained in other nearby locations. Whereas a number of previous works outline the need to avoid the innervation zone (or the muscle belly), many authors place electrodes in the central part or bulge of the muscle of interest where the innervation zone is likely to be. Computer simulations are presented to explain the effect of the innervation zone on amplitude, frequency and conduction velocity estimates from the signal and the need to avoid placing electrodes near it. Experimental signals recorded from some superficial muscles of the limbs and trunk (abductor pollicis brevis, flexor pollicis brevis, biceps, upper trapezius, vastus medialis, vastus lateralis) were processed providing support for the findings obtained from simulations. The use of multichannel techniques is recommended to estimate the location of the innervation zone and to properly choose the optimal position of the detection point(s) allowing meaningful estimates of EMG variables during movement analysis.

Differences in myoelectric manifestations of fatigue in sprinters and long distance runners.

The aim of this study was to determine whether the rate of change of surface EMG variables during a constant force isometric fatiguing contraction (80% MVC, 30 s of duration) of vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles is able to distinguish between nine sprinters and nine long distance runners. Signals were recorded with linear arrays of eight electrodes. Muscle fiber conduction velocity (CV), mean frequency (MNF) of EMG signal power spectrum and average rectified value (ARV) of the EMG signal were calculated both from the whole signal (global approach) and from motor unit action potentials (MUAP distribution approach) extracted from the signal. Results showed significant differences only in the MUAP distribution approach. For this approach, the rates of change of conduction velocity (CV) (both absolute and normalized with respect to the initial value) were found to be always greater in the sprinter (VMO: -0.012 +/- 0.011 m s(-2) and -0.25 +/- 0.21%/s; VL: -0.014 +/- 0.009 m s(-2) and -0.27 +/- 0.17%/s) than in the long distance runner group (VMO: -0.004 +/- 0.006 m s(-2) and -0.08 +/- 0.14%/s; VL: 0.003 +/- 0.012 m s(-2) and 0.08 +/- 0.26%/s) (VL: p = 0.016, VMO: p = 0.034). No differences were observed in the CV initial values and in rates of change of MNF, while MNF initial values recorded from the VMO were found to be greater (119.6 +/- 25.1 Hz) in the sprinter group than in the long distance runner group (99.2 +/- 12.1 Hz, p = 0.016). A correlation was found between initial values and rates of change of CV in the VMO (r = 0.61, p < 0.01, N = 18, Spearman correlation coefficient). The consistency of these findings with the expected fiber type composition between sprinters and long distance runners and the identification of a set of candidated variables for the assessment of muscle adaptation during training and/or rehabilitation programs represent the main results of the study.

Surface EMG signal alterations in Carpal Tunnel syndrome: a pilot study.

Carpal Tunnel syndrome (CTS) is one of the most common compartmental syndromes and nerve conduction studies are widely considered as the standard to diagnose the pathology. The purpose of this pilot study was to investigate whether multichannel surface electromyography can detect muscle alterations in patients diagnosed with severe CTS. Surface EMG signals were recorded at 10, 20, 30, and 80% MVC from the flexor and abductor pollicis brevis muscles of five patients with CTS and five control subjects. Subjects with severe CTS showed different interference patterns, lower signal amplitude, lower neuromuscular efficiency, and lower myoelectric manifestations of fatigue with respect to the control group. At submaximal levels, action potentials recorded from the flexor and abductor pollicis brevis muscles of the CTS group were characterized by lower conduction velocity and lower mean spectral frequency than the healthy group. These findings support, among others, the hypothesis of a selective loss of fast motor units (type II fiber) associated with CTS.

Myoelectric manifestations of fatigue in vastus lateralis, medialis obliquus and medialis longus muscles.

The purpose of this study was to determine whether surface electromyography (EMG) assessment of myoelectric manifestations of muscle fatigue is capable of detecting differences between the vastus lateralis and medialis muscles which are consistent with the results of previous biopsy studies. Surface EMG signals were recorded from the vastus medialis longus (VML), vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles during isometric knee extension contractions at 60% and 80% of the maximum voluntary contraction (MVC) for 10s and 60s, respectively. Initial values and rate of change of mean frequency (MNF), average rectified value (ARV) and conduction velocity (CV) of the EMG signal were calculated. Comparisons between the two force levels revealed that the initial values of MNF for the VL muscle were greater at 80% MVC compared to 60% MVC (P<0.01). Comparisons between the vasti muscles demonstrated lower initial values of CV for VMO compared to VL at 60% MVC (P<0.01) and lower than VML and VL at 80% MVC (P<0.01). In addition, initial values of MNF were higher for VL with respect to both VML and VMO at 80% MVC (P<0.01) and initial estimates of ARV were higher for VMO compared to VML at both force levels (P<0.01 at 60% MVC and P<0.05 at 80% MVC). For the sustained contraction at 80% MVC, VL demonstrated a greater decrease in CV over time compared to VMO (P<0.05). These findings suggest that surface EMG signals and their time course during sustained isometric contractions may be useful to non-invasively describe functional differences between the vasti muscles.

Influence of the sample collection method on salivary interleukin-6 levels in resting and post-exercise conditions.

Previous studies demonstrated that no significant relationships exist between salivary and serum IL-6 in resting conditions and following exercise and that appropriate saliva collection procedures allow to avoid analytical drawbacks. This investigation aimed to: (a) compare the effects of two methods of saliva collection on IL-6 assay; (b) search for correlation between salivary and serum IL-6 in resting and post-exercise conditions; (c) evaluate the IL-6 response to isometric contractions. Seventeen sedentary subjects and fifteen athletes underwent one blood and two salivary draws: saliva was collected chewing on cotton salivettes and using a plastic straw (SA method and ST method, respectively). Afterwards, the athletes only completed a fatiguing isometric exercise of the knee extensors and blood and saliva were sampled after the exercise. In the entire group (n=32), ST method produced higher IL-6 levels than SA method and serum sampling. The exercise elicited significant responses of lactate, serum IL-6, salivary IL-6 (by ST method): salivary IL-6 values using the ST collection method were higher at each sampling point than with the SA method. The correlation analyses applied to both resting levels in the entire group and absolute changes above baseline in the athlete group showed that: (1) no significant relationships exist between serum and salivary IL-6 levels; (2) the greater the salivary IL-6 measurement, the higher the resultant inaccuracy of the SA method; (3) significant correlations exist between isometric force and mechanical fatigue during exercise and peaks of lactate and serum IL-6. These data provided demonstration of a cotton-interference effect for the results of salivary IL-6 assay and confirmed the lack of significant correlation between salivary and serum IL-6 in resting and post-exercise conditions.

Corticotroph axis sensitivity after exercise: comparison between elite athletes and sedentary subjects.

Strenuous exercise activates the hypothalamic-pituitary-adrenal (HPA) axis. Several reports showed that physical training is associated with a decreased efficiency of the feedback control of HPA axis. The aims of the present study were: 1) to evaluate the differences in the mechanical, hormonal, and lactate responses to a high-intensity isokinetic exercise among different groups of competitive athletes (CA, no.=20) of power and endurance disciplines and sedentary controls (SED, no.=10); 2) to determine the effects of the training status on the HPA axis responsiveness following exercise, as indirectly evaluated by the rates of ACTH, cortisol, and DHEA recovery after exercise. CA and SED fulfilled eight sets of twenty concentric contractions of the knee extensors at 180 degrees/sec angular velocity throughout a constant range of motion (100 degrees). There was a rest period of 30 sec between each set and a 3-min rest period between the two legs. Before, immediately after the isokinetic exercise and at different times in the subsequent 120 min of recovery, blood and saliva were sampled to determine plasma ACTH, salivary cortisol, serum DHEA, and serum lactate concentrations. CA showed a higher cortisol response to exercise than SED, whereas no differences were found in the responses of ACTH, DHEA and lactate. In the athlete group the exercise-induced increases of ACTH, cortisol, and lactate were higher in power athletes with respect to endurance athletes. No differences were observed between athletes and SED in the rates of hormonal recovery after exercise: this finding does not support the concept that a reduced feedback control of HPA axis can represent a feature of trained individuals.

Interleukin-6 response to isokinetic exercise in elite athletes: relationships to adrenocortical function and to mechanical and myoelectric fatigue.

Exercise stimulates the release of interleukin-6 (IL-6). Aims of the study were to: (a) analyse the IL-6 response to exercise in power (n = 7) and endurance athletes (n = 13); (b) determine the effects of the IL-6 production on mechanical and myoelectric fatigue; (c) evaluate the relationship between IL-6 and adrenocortical responses. EMG variables (conduction velocity, mean power frequency, average rectified value), ACTH, cortisol, DHEA, IL-6, myoglobin, and lactate were analysed before and after an isokinetic exercise. The exercise elicited significant mechanical and myoelectric fatigue as well as significant biochemical responses. Power athletes showed IL-6 and lactate responses higher than endurance athletes. The correlation analyses showed that the greater the mechanical fatigue, the greater the increases in lactate and IL-6. No correlations were found between IL-6 and EMG variables. No relationships were found between IL-6 and cortisol, after correction for ACTH levels. In conclusion, the muscular IL-6 production, as inferred by its circulating levels, had no detectable effects on the myoelectric manifestations of fatigue and the cortisol response to exercise was not related to the amount of circulating IL-6, but only to the activation of ACTH secretion.

Confounding factors in water EMG recordings: an approach to a definitive standard.

This work presents a study on the influence of the aqueous environment on the surface EMG (sEMG) signal recorded in bipolar montage from the abductor pollicis brevis muscle, when only the forearm is immersed in water. Ten men, 30.1+/-4.0 (mean +/- SD) years old, performed ten 2-s 40% MVC isometric contractions of the abductor pollicis brevis muscle in two controlled environments (air and water, at a temperature of 32 degrees C). They were always equipped with electrodes protected with a waterproof adhesive tape. No significant variations (paired Wilcoxon test) due to the environments were observed in the median frequency of the power spectrum (MDF) and in the root mean square (RMS) value of the sEMG signal. These results allow us to assess the methodological criteria to properly record sEMG signals in water and provide the basis to explain different findings obtained by other authors.

Differential responses of serum and salivary interleukin-6 to acute strenuous exercise.

Physical exercise is associated with elevation of serum levels of interleukin-6 (IL-6) because of its production in the muscles. The use of IL-6 measurements in saliva has been proposed in the field of immunopathology, mainly involving salivary gland disease. We evaluated the responses of serum and salivary IL-6 in two different groups of athletes submitted to different types of controlled strenuous exercise (spinning activity and maximal isokinetic test). Serum and salivary samples for IL-6 measurements, and serum samples for lactate and myoglobin determination before and after exercise, were obtained. Salivary IL-6 was measured by ELISA after dilution experiments and compared with results obtained by immunoradiometric assay. Spinning activity elicited significant increases in all the variables, and no correlation was found among the respective variations. A significant response to the isokinetic exercise was observed for serum IL-6, lactate and myoglobin only; no correlation was found between serum and salivary IL-6. Our study demonstrated that serum and salivary IL-6 responses to exercise are dissociated, possibly in relation to the lack of relationships between the systemic/muscular and the salivary routes of IL-6 production. Analytical issues that concern IL-6 measurement in saliva deserve attention, notably regarding the collection method used to absorb saliva. Concomitant monitoring of serum markers of inflammation, muscle metabolism and damage can provide information about muscle function properties and adaptations to physical effort in different types of athletes.

Lack of correlation between sternocleidomastoid and scalene muscle fatigability and duration of symptoms in chronic neck pain patients.

AIMS OF THE STUDY: Despite the evidence of greater fatigability of the superficial cervical flexor muscles in neck pain patients, the relationship between duration of neck pain and muscle fatigue has not been investigated. This study examined the relationship between myoelectric manifestations of sternocleidomastoid (SCM) and anterior scalene (AS) muscle fatigue and duration of neck pain in a group of patients with chronic neck pain. MATERIALS AND METHODS: Twenty chronic neck pain patients with a history of pain ranging between 1 and 25 years (mean 6.15, S.D. 5.48 years) participated in this study. Myoelectric signals were recorded from the SCM and AS muscles from the side of greatest pain as patients performed sustained sub-maximal isometric cervical flexion contractions at 25% and 50% of the maximum voluntary contraction (MVC). The initial value and slope of the mean frequency (MNF), average rectified value (ARV) and conduction velocity (CV) of the EMG signals were calculated. Correlation analysis was applied to determine whether a relationship existed between the duration of neck pain and estimates of EMG variables. RESULTS AND CONCLUSIONS: No significant correlation was found between duration of pain and estimates of the MNF, ARV and CV for either SCM or AS contracting at 25% and 50% MVC. The length of history of neck pain does not appear to correlate with the extent of SCM and AS muscle fatigability in patients with chronic neck pain. This finding may be due to an increase of muscle fatigability occurring within the first few years of neck pain, which is not followed by signs of increased fatigue after this time. This was supported by the finding of significant correlations between duration of pain and AS fatigability on a subgroup of patients with pain duration less than 5 years. Future studies are warranted to examine how early signs of cervical muscle fatigability are evident after the onset of neck pain as this will have implications for rehabilitation.

Neuromuscular efficiency of the sternocleidomastoid and anterior scalene muscles in patients with chronic neck pain.

PURPOSE: This study compared the neuromuscular efficiency (NME) of the sternocleidomastoid (SCM) and anterior scalene (AS) muscles between 20 chronic neck pain patients and 20 asymptomatic controls. METHOD: Myoelectric signals were recorded from the sternal head of SCM and the AS muscles as subjects performed sub-maximal isometric cervical flexion contractions at 25 and 50% of the maximum voluntary contraction (MVC). The NME was calculated as the ratio between MVC and the corresponding average rectified value of the EMG signal. Ultrasonography was used to measure subcutaneous tissue thickness over the SCM and AS to ensure that differences did not exist between groups. RESULTS: For both the SCM and AS muscles, NME was shown to be significantly reduced in patients with neck pain at 25% MVC (p<0.05). Subcutaneous tissue thickness over the SCM and AS muscles was not different between groups. CONCLUSIONS: Reduced NME in the superficial cervical flexor muscles in patients with neck pain may be a measurable altered muscle strategy for dysfunction in other muscles. This aberrant pattern of muscle activation appears to be most evident under conditions of low load. NME, when measured at 25% MVC, may be a useful objective measure for future investigation of muscle dysfunction in patients with neck pain.

Spatio-temporal evaluation of neck muscle activation during postural perturbations in healthy subjects.

The purpose of this study was to examine the spatio-temporal activation of the sternocleidomastoid (SCM) and cervical extensor (CE) muscles with respect to the deltoid muscle onset during rapid voluntary upper limb movement in healthy volunteers. The repeatability and reliability of the spatio-temporal aspects of the myoelectric signals were also examined. Ten subjects performed bilateral and unilateral rapid upper limb flexion, abduction and extension in response to a visual stimulus. EMG onsets and normalised root mean square (nRMS) values were calculated for the SCM and CE muscles. Subjects attended three testing sessions over non-consecutive days allowing the repeatability and reliability of these measures to be assessed. The SCM and CE muscles demonstrated feed-forward activation (activation within 50 ms of deltoid onset) during rapid arm movements in all directions. The sequence and magnitude of neck muscle activation displayed directional specificity, however, the neck flexor and extensor muscles displayed co-activation during all perturbations. EMG onsets demonstrated high repeatability in terms of repeated measure precision (nSEM in the range 1.9-5.7%). This was less evident for the repeatability of nRMS values. The results of this study provide a greater understanding of cervical neuromotor control strategies. During bilateral and unilateral upper limb perturbations, the SCM and CE muscles demonstrate feed-forward co-activation. It seems apparent that feed-forward activation of neck muscles is a mechanism necessary to achieve stability for the visual and vestibular systems, whilst ensuring stabilisation and protection of the cervical spine.

A method for positioning electrodes during surface EMG recordings in lower limb muscles.

PURPOSE: The aim of this work is to provide information about the degree of inter-subject uniformity of location of innervation zone (IZ) in 13 superficial muscles of the lower limb. The availability of such information will allow researchers to standardize and optimize their electrode positioning procedure and to obtain accurate and repeatable estimates of surface electromyography (sEMG) signal amplitude, spectral variables and muscle fiber conduction velocity. METHODS: Surface EMG signals from gluteus maximus, gluteus medius, tensor faciae latae, biceps femoris, semitendinosus, vastus medialis obliquus, vastus lateralis, rectus femoris, tibialis anterior, peroneus longus, soleus, gastrocnemius medialis and lateralis muscles of ten healthy male subjects aged between 25 and 34 years (average = 29.2 years, S.D. = 2.5 years) were recorded to assess individual IZ location and signal quality. RESULTS: Tensor faciae latae, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius medialis and lateralis showed a high level of both signal quality and IZ location uniformity. In contrast, rectus femoris, gluteus medius and peroneus longus were found to show poor results for both indexes. Gluteus maximus, vastus medialis obliquus and tibialis anterior were found to show high signal quality but low IZ location uniformity. Finally, soleus muscle was found to show low signal quality but high IZ location uniformity. CONCLUSIONS: This study identifies optimal electrode sites for muscles in the lower extremity by providing a standard landmarking technique for the localization of the IZ of each muscle so that surface EMG electrodes can be properly positioned between the IZ and a tendon.