Muscle activation of patients suffering from asymmetric ankle osteoarthritis during isometric contractions and level walking – A time–frequency analysis

Asymmetric osteoarthritis (OA) is a common type of OA in the ankle joint. OA also influences the muscles surrounding a joint, however, little is known about the muscle activation in asymmetric ankle OA. Therefore, the aim of this study was to characterize the patients’ muscle activation during isometric ankle torque measurements and level walking. Surface electromyography (EMG) was measured of gastrocnemius medialis (GM) and lateralis (GL), soleus (SO), tibialis anterior (TA), and peroneus longus (PL) in 12 healthy subjects and 12 ankle OA patients. To obtain time and frequency components of the EMG power a wavelet transformation was performed. Furthermore, entropy was introduced to characterize the homogeneity of the wavelet patterns.Patients produced lower plantar- and dorsiflexion torques and their TA wavelet spectrum was shifted towards lower frequencies. While walking, the patients’ muscles were active with a lower intensity and over a broader time–frequency region. In contrast to controls and varus OA patients, maximal GM activity of valgus OA patients lagged behind the activity of GL and SO. In both tasks, PL of the valgus patients contained more low frequency power. The results of this study will help to assess whether surgical interventions of ankle OA can reestablish the muscle activation patterns.     

The between-day reliability of peroneus longus EMG during walking

The peroneus longus (PL) is a rearfoot evertor, important in frontal plane foot motion. Studying PL function has been limited by previous electromyography (EMG) studies reporting poor between-day reliability. Due to its close proximity to adjacent muscles, EMG measures of PL may be susceptible to crosstalk, thus correct electrode placement is vital. The aim of this study was to use ultrasound to aid placement of small surface EMG electrodes and determine the between-day reliability of PL EMG in healthy participants’ walking. Ten participants walked barefoot and shod at a controlled, self-selected speed. Six trials per condition, per session, were recorded over two days (mean (SD): 5 (3) days apart). The muscle belly was located using ultrasound. EMG was recorded with surface electrodes (Trigno™ Mini, Delsys, Inc.) at 2000 Hz. Amplitude was normalized to the peak per gait cycle and time normalized to the gait cycle. Reliability of discrete variables were primarily assessed with the standard error of measurement (SEM), plus the coefficient of multiple correlation (CMC), the coefficient of variation (CV) and the intra-class correlation coefficient (ICC). The pattern of the EMG profile was consistent. The SEM of peak amplitude was 4% (3–8%) and 3% (2–5%) for barefoot and shod respectively. For timing of the peak the SEM was 2% (1–3%) and 1% (1–2%) for barefoot and shod respectively. Low SEM of discrete variables suggests good reliability of PL EMG during walking supporting the future use of this protocol. Therefore activation of PL can be confidently studied in repeated-measures study designs.     

Peak triceps surae muscle activity is not specific to knee flexion angles during MVIC

There is limited research on peak activity of the separate triceps surae muscles in select knee flexion (KF) positions during a maximum voluntary isometric contraction (MVIC) used to normalize EMG signals. The aim of this study was to determine how frequent peak activity occurred during an MVIC for soleus (SOL), gastrocnemius medialis (GM), and gastrocnemius lateralis (GL) in select KF positions, and if these peaks were recorded in similar KF positions. Forty-eight healthy individuals performed unilateral plantar-flexion MVIC in standing with 0°KF and 45°KF, and in sitting with 90°KF. Surface EMG of SOL, GM, and GL were collected and processed in 250 ms epochs to determine peak root-mean-square amplitude. Peak activity was most frequently captured in standing and rarely in sitting, with no position selective to SOL, GM or GL activity. Peak GM and GL activity was more frequent in 0°KF than 45°KF, and more often in similar KF positions than not. Peak SOL activity was just as likely in 45°KF as 0°KF, and more in positions similar to GM, but not GL. The EMG amplitudes were at least 20% greater in positions that captured peak activity over those that did not. The overall findings support performing an MVIC in more than one KF position to normalize triceps surae EMG. It is emphasized that no KF position is selective to SOL, GM, or GL alone.     

Effect of different ankle- and knee-joint positions on gastrocnemius medialis fascicle length and EMG activity during isometric plantar flexion

The purpose of this study was to provide evidence on the fact that the observed decrease in EMG activity of the gastrocnemius medialis (GM) at pronounced knee flexed positions is not only due to GM insufficiency, by examining muscle fascicle lengths during maximal voluntary contractions at different positions. Twenty-two male long distance runners (body mass: 78.5+/-6.7 kg, height: 183+/-6 cm) participated in the study. The subjects performed isometric maximal voluntary plantar flexion contractions (MVC) of their left leg at six ankle-knee angle combinations. To examine the resultant ankle joint moments the kinematics of the left leg were recorded using a Vicon 624 system with 8 cameras operating at 120 Hz. The EMG activity of GM, gastrocnemius lateralis (GL), soleus (SOL) and tibialis anterior (TA) were measured using surface electromyography. Synchronously, fascicle length and pennation angle values of the GM were obtained at rest and at the plateau of the maximal plantar flexion using ultrasonography. The main findings were: (a) identifiable differences in fascicle length of the GM at rest do not necessarily imply that these differences would also exist during a maximal isometric plantar flexion contraction and (b) the EMG activity of the biarticular GM during the MVC decreased at a pronounced flexed knee-joint position (up to 110 degrees ) despite of no differences in GM fascicle length. It is suggested that the decrease in EMG activity of the GM at pronounced knee flexed positions is due to a critical force-length potential of all three muscles of the triceps surae.     

Assessment of the activation modalities of gastrocnemius lateralis and tibialis anterior during gait: A statistical analysis

Aim of the study was to identify the different modalities of activation of gastrocnemius lateralis (GL) and tibialis anterior (TA) during gait at self-selected speed, by a statistical analysis of surface electromyographic signal from a large number (hundreds) of strides per subject. The analysis on fourteen healthy adults showed a large variability in the number of activation intervals, in their occurrence rate, and in the on-off instants, within different strides of the same walk. For each muscle, the assessment of the different modalities of activation (five for muscle) allowed to identify a single pattern, common for all the modalities and able to characterize the behavior of muscles during normal gait. The pattern of GL activity centered in two regions of the gait cycle: the transition between flat foot contact and push-off (observed in 100% of total strides) and the final swing (67.1 ± 15.9%). Two regions characterized also the pattern of TA activity: from pre-swing to following loading response (100%), and the mid-stance (30.5 ± 15.0%). This “normality” pattern represents the first attempt for the development in healthy young adults of a reference for dynamic EMG activity of GL and TA, in terms of variability of on-off muscular activity and occurrence rate during gait.     

Reliability of lower limb electromyography during overground walking: A comparison of maximal- and sub-maximal normalisation techniques

The purpose of this study was to determine the reliability of investigating electromyography (EMG) of selected leg muscles during walking. Tibialis posterior and peroneus longus EMG activity were recorded via intramuscular electrodes. Tibialis anterior and medial gastrocnemius EMG activity were recorded with surface electrodes. Twenty-eight young adults attended two test-sessions approximately 15 days apart. Relative and absolute measures of reliability were calculated for EMG timing and amplitude parameters during specific phases of the gait cycle. Maximum contractions and sub-maximal contractions were obtained via maximum isometric voluntary contractions and a very fast walking speed, respectively. Time of peak EMG amplitude for all muscles displayed relatively narrow limits of random error. However, reliability of peak and root mean square amplitude parameters for tibialis posterior and peroneus longus displayed unacceptably wide limits of random error, regardless of the normalisation reference technique. Whilst some amplitude parameters for tibialis anterior and medial gastrocnemius displayed good to excellent relative reliability, the corresponding values for absolute error were generally large.Timing and amplitude EMG parameters for all muscles displayed low to moderate coefficient of variation within each test session (range: 7–25%). Overall, between-participant variability was minimised with sub-maximal normalisation values. These results demonstrate that re-application of electrodes results in large random error between sessions, particularly with tibialis posterior and peroneus longus. Researchers planning studies of these muscles with a repeated-test design (e.g. to evaluate the effect of an intervention) must consider whether this level of error is acceptable.     

Patterns of leg muscle recruitment vary between novice and highly trained cyclists

This study compared patterns of leg muscle recruitment and coactivation, and the relationship between muscle recruitment, coactivation and cadence, in novice and highly trained cyclists. Electromyographic (EMG) activity of tibialis anterior (TA), tibialis posterior (TP), peroneus longus (PL), gastrocnemius lateralis (GL) and soleus (SOL) was recorded using intramuscular fine-wire electrodes. Four experimental conditions of varying cadence were investigated. Differences were evident between novice and highly trained cyclists in the recruitment of all muscles. Novice cyclists were characterized by greater individual variance, greater population variance, more extensive and more variable muscle coactivation, and greater EMG amplitude in periods between primary EMG bursts. Peak EMG amplitude increased linearly with cadence and was not different at individual preferred cadence in either novice or highly trained cyclists. However, EMG amplitude in periods between primary EMG bursts, as well as the duration of primary EMG bursts, increased with increasing cadence in novice cyclists but were not influenced by cadence in highly trained cyclists. Our findings suggest that muscle recruitment is highly skilled in highly trained cyclists and less refined in novice cyclists. More skilled muscle recruitment in highly trained cyclists is likely a result of neuromuscular adaptations due to repeated performance of the cycling movement in training and competition.     

Reduced plantar-flexors extensibility but improved selective motor control associated with age in young children with unilateral cerebral palsy and equinovalgus gait

BackgroundChildren with spastic cerebral palsy gradually lose muscle extensibility but the interplay between the muscular and neurological components of the condition is unclear especially in the pathophysiology of equinovalgus gait.AimThis study aimed to quantify the muscular and neurological disorders in young children with unilateral cerebral palsy, and to investigate the role of the peroneus longus (PL) in equinovalgus gait.Design, setting and population: This was an observational study with prospective assessments of 31 children (median age: 2.9 years, range: 2–6) from outpatient clinic in a tertiary teaching hospital.MethodsClinical measures of plantar flexor extensibility (X_V1), stretch response (X_V3), and active ankle dorsiflexion angle (X_A) were obtained as well as walking velocity and electromyography of tibialis anterior (TA), gastrocnemius medialis (GM) and PL during walking.ResultsWe found reduced extensibility of the triceps surae on the paretic side (effect size r = 0.73, p < 0.001 for soleus and r = 0.68, p < 0.001 for gastrocnemius) and a correlation between reduced triceps surae extensibility and earlier stretch response (ρ = 0.5, p = 0.004). During the swing phase, there was major co-contraction between TA and GM/PL, and significantly larger activation of PL compared to GM (r = 0.46, p = 0.011). Both GM and PL activation decreased with age.ConclusionsOur results suggest gradual deterioration of the muscular disorder and a link between the muscular and neurological disorders, although plantar flexor co-contraction improved with age. The PL was more activated than the GM and may be considered an intervention target to treat equinovalgus gait.     

Backpack load affects lower limb muscle activity patterns of female hikers during prolonged load carriage

This study investigated the effect of prolonged load carriage on lower limb muscle activity displayed by female recreational hikers. Electromyography (EMG) signals from vastus lateralis (VL), biceps femoris (BF), semitendinosus (ST), tibialis anterior (TA) and gastrocnemius (GM) were recorded for fifteen female hikers carrying four loads (0%, 20%, 30% and 40% body weight (BW)) over 8 km. Muscle burst duration, muscle burst onset relative to initial contact and integrated EMG signals (iEMG) were calculated to evaluate muscle activity, whereas the shift in mean power frequency (MPF) was used to evaluate muscle fatigue. Increased walking distance significantly decreased the MPF of TA; decreased the iEMG for VL, ST and GM; and shortened VL muscle burst duration. Furthermore, carrying 20–40% BW loads significantly increased VL and GM iEMG and increased BF muscle burst duration, whereas a 40% BW load caused a later VL muscle burst onset. The differences observed in muscle activity with increased load mass seem to be adjustments aimed at maintaining balance and attenuating the increased loads placed on the lower limbs during gait. Based on the changes in muscle activity, a backpack load limit of 30% BW may reduce the risk of lower limb injury for female hikers during prolonged walking.     

Role of triangularis sterni during coughing and sneezing in dogs

Studies in mammals have found that during breathing the triangularis sterni (TS) muscle regulates expiratory airflow and the end-expiratory position of the rib cage and furthermore that the respiratory activity of this muscle is influenced by a variety of chemical and mechanical stimuli. To assess the role of the TS during coughing and sneezing, electromyograms (EMGs) recorded from the TS were compared with EMGs of the transversus abdominis (TA) in eight pentobarbital-anesthetized dogs. During coughing induced by mechanically stimulating the trachea or larynx (n = 7 dogs), peak EMGs increased from 23 +/- 2 to 74 +/- 5 U (P less than 0.00002) for the TS and from 21 +/- 6 to 66 +/- 4 U (P less than 0.0002) for the TA. During sneezing induced by mechanically stimulating the nasal mucosa (n = 3 dogs), peak EMG of the TS increased from 10 +/- 3 to 66 +/- 7 U (P less than 0.005) and peak EMG of the TA increased from 10 +/- 2 to 73 +/- 7 U (P less than 0.02). For both muscles the shape of the EMG changed to an early peaking form during coughs and sneezes. Peak expiratory airflow during coughs of different intensity correlated more closely with peak TS EMG in three dogs and with peak TA EMG in four dogs; peak expiratory airflow during sneezes of different intensity correlated more closely with peak TS than TA EMG in all three animals. These results suggest that the TS is actively recruited during coughing and sneezing and that different neuromuscular strategies may be utilized to augment expiratory airflow.     

EMG sensor location: Does it influence the ability to detect differences in muscle contraction conditions?

Even though it is well known that electromyography (EMG) characteristics are influenced by electrode placement it is common to use a single pair of sensors per muscle for EMG. This study was designed to determine if the ability to distinguish between contraction conditions was influenced by sensor location. Subjects (n = 10; 27+/-5.3 years; 82+/-13.4 kg; 178+/-7.1 cm) completed six elbow flexor conditions: three isometric contraction intensities (100% maximum effort, 80%, 50%) and three isotonic contraction intensities (heavy weight, 80% and 50% of the weight). Three pairs of electrodes were placed centrally, medially and laterally on the biceps brachii belly in line with the muscle fibers. Isometric contractions were held for 5s, with the middle 3 s analyzed. Isotonic exercises included five repetitions of elbow flexion-extension, with the middle three repetitions analyzed. Average EMG (EMG(AVG)), root mean square EMG (EMG(RMS)) and mean power frequency (MPF) were calculated for each extracted data set. Dependent variables were analyzed using 2 (contraction type) x 3 (intensity) repeated measures ANOVAs per sensor. EMG(AVG) was influenced by the interaction between contraction type and intensity for all sensors (p < 0.05). EMG(RMS) as well as MPF were influenced by the interaction between contraction type and intensity for the lateral and central leads (p < 0.05) but not the medial leads (p > 0.05). Different conclusions could have been reached from the same experiment due to different sensor locations. These differences were primarily related to comparing contraction types (i.e., isotonic vs. isometric).     

Femoral anteversion influences vastus medialis and gluteus medius EMG amplitude: composite hip abductor EMG amplitude ratios during isometric combined hip abduction-external rotation.

This prospective study evaluated differences in vastus medialis (VM) and gluteus medius (GM) EMG amplitude:composite hip abductor (gluteus maximus, gluteus medius, tensor fascia lata) EMG amplitude ratios among subjects with low or high relative femoral anteversion. Data were collected during the performance of a non-weight bearing, non-sagittal plane maximal volitional effort isometric combined hip abduction-external rotation maneuver. Eighteen nonimpaired athletically active females participated in this surface EMG study. Medial hip rotation (relative femoral anteversion estimate) was measured with a handheld goniometer. Subjects were grouped by medial hip rotation displacement (group 1 < or = 42 degrees =36.1+/-7 degrees and group 2 > 42 degrees =52.7+/-7 degrees ) for statistical analysis (Mann Whitney U-tests, p < 0.05). Group 2 had decreased VM (42+/-23% vs. 69+/-30%, U=19, p=0.034) and GM (62+/-25% vs. 96+/-39%, U=19, p=0.034) normalized mean peak EMG amplitude:composite mean peak hip abductor EMG amplitude ratios compared to group 1. Decreased normalized VM (-27%) and GM (-34%) EMG amplitudes among subjects with increased relative femoral anteversion suggest reduced dynamic frontal and transverse plane femoral control from these muscles, possibly contributing to the increased incidence of non-contact knee injury observed among athletic females.     

Reaction time and electromyographic activity during a sprint start

Eight male sprinters were filmed running three maximal starts over 3 m on a long force platform. The subjects were divided into two groups (n = 4) according to the leg on which the electromyograph (EMG) electrodes were fixed. When in the set position one group had electrodes on the front leg (FLG) and the other group on the rear leg (RLG). The EMG activities of the gastrocnemius caput laterale muscle (GA), vastus lateralis muscle (VL), biceps femoris caput longum muscle (BF), rectus femoris muscle (RF) and gluteus maximus muscle (GM) were recorded telemetrically using surface electrodes. Total reaction time (TRT) was defined as the time from the gun signal until a horizontal force was produced with a value 10% above the base line. Pre-motor time was defined as the time from the gun signal until the onset of EMG activity and motor time (MT) as the time between the onset of EMG activity and that of force production. Reproducibility of the reaction time variables was satisfactory (r = 0.79-0.89; coefficient of variation = 8.8%-11.6%). The TRT was 0.121 s, SD 0.014 in FLG and 0.119 s, SD 0.011 in RLG. The MT ranged from 0.008 s, SD 0.009 (GM) to 0.057 s, SD 0.050 (GA) in FLG and from 0.018 s, SD 0.029 (GA) to 0.045 s, SD 0.009 (GM) in RLG. In some individual cases there were no MT values before horizontal force production.(ABSTRACT TRUNCATED AT 250 WORDS)     

Unchanged H-reflex during a sustained isometric submaximal plantar flexion performed with an EMG biofeedback

The aim of this study was to assess H-reflex plasticity and activation pattern of the plantar flexors during a sustained contraction where voluntary EMG activity was controlled via an EMG biofeedback. Twelve healthy males (28.0 ± 4.8 yr) performed a sustained isometric plantar flexion while instructed to maintain summed EMG root mean square (RMS) of gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) muscles fixed at a target corresponding to 80% maximal voluntary contraction torque via an EMG biofeedback. Transcutaneous electrical stimulation of the posterior tibial nerve was evoked during the contraction to obtain the maximal H-reflex amplitude to maximal M-wave amplitude ratio (H_sup/M_sup ratio) from GL, GM and soleus (SOL) muscles. Neuromuscular function was also assessed before and immediately after exercise. Results showed a decrease in SOL activation during sustained flexion (from 65.5 ± 6.4% to 42.3 ± 3.8% maximal EMG, p < 0.001), whereas summed EMG RMS of GL and GM remained constant (59.7 ± 4.8% of maximal EMG on average). No significant change in the H_sup/M_sup ratio was found for SOL, GL and GM muscles. Furthermore, it appears that the decrease in maximal voluntary contraction torque (?20.4 ± 2.9%, p < 0.001) was related to both neural and contractile impairment. Overall, these findings indicate that the balance between excitation and inhibition affecting the motoneuron pool remains constant during a sustained contraction where myoelectrical activity is controlled via an EMG biofeedback or let free to vary.     

Changes in muscle geometry during forearm pronation and supination and their relationships to EMG cross-correlation measures

Geometric artifact may alter the amplitude and frequency of the electromyography (EMG) signal. Artifacts include the changing geometry of muscles with respect to electrodes and potential crosstalk from adjacent muscles. This study addresses: (1) the geometrical relationships between common electrode placement sites for six forearm muscles, (2) the geometrical change of forearm muscles in pronation and supination, and (3) the relationships between EMG cross-correlation and muscle geometry. EMG and ultrasonography images were recorded during pronation, supination, and neutral forearm postures while exerting 20% maximum grip strength. Proportions of anatomical structures were then calculated for 15 mm, 20 mm, and 25 mm radial pick-up zone distances, representing greater than 90% of observed myoelectrical signal energy. We found that guidelines for electrode placements were supported and no single posture maximized the proportion of the target muscle detected. Secondly, other muscles were present in the most conservative 15 mm radius pick up zone; it is unlikely that surface EMG can completely differentiate between forearm muscle activities. Thirdly, forearm orientation did not appear to be an important factor in changing the geometrical relationships between surface electrodes and the muscles studied, and fourthly, certain muscles (e.g., FDS) may be more vulnerable to EMG crosstalk.     

Influence of gait velocity on gastrocnemius muscle fascicle behaviour during stair negotiation

The gastrocnemius medialis (GM) muscle plays an important role in stair negotiation. The aim of the study was to investigate the influence of cadence on GM muscle fascicle behaviour during stair ascent and descent. Ten male subjects (young adults) walked up and down a four-step staircase (with forceplates embedded in the steps) at three velocities (63, 88 and 116 steps/min). GM muscle fascicle length was measured using ultrasonography. In addition, kinematic and kinetic data of the lower legs, and GM electromyography (EMG) were measured. For both ascent and descent, the amount of fascicular shortening, shortening velocity, knee moment, ground reaction force and EMG activity increased monotonically with gait velocity. The ankle moment increased up to 88 steps/min where it reached a plateau. The lack of increase in ankle moment coinciding with further shortening of the fascicles can be explained by an increased shortening of the GM musculotendon complex (MTC), as calculated from the knee and ankle angle changes, between 88 and 116 steps/min only. For descent, the relative instant of maximum shortening, which occurred during touch down, was delayed at higher gait velocities, even to the extent that this event shifted from the double support to the single support phase.     

Validation of a simplified method for muscle volume assessment

The present study investigated the validity of a simplified muscle volume assessment that uses only the maximum anatomical cross-sectional area (ACSA_max), the muscle length (L_M) and a muscle-specific shape factor for muscle volume calculation ( Albracht et al., 2008, J Biomech 41, 2211–2218). The validation on the example of the triceps surae (TS) muscles was conducted in two steps. First L_M, ACSA_max, muscle volume and shape factor were calculated from magnet resonance image muscle reconstructions of the soleus (SO), gastrocnemius medialis (GM) and lateralis (GL) of a group of untrained individuals (n=13), endurance (n=9) and strength trained (n=10) athletes. Though there were significant differences in the muscle dimensions, the shape factors were similar across groups and were in average 0.497±0.026, 0.596±0.030, and 0.556±0.041 for the SO, GM and GL respectively. In a second step, the shape factors were applied to an independent recreationally active group (n=21) to compare the muscle volume assessed by the simplified method to the results from whole muscle reconstructions. There were no significant differences between the volumes assessed by the two methods. In conclusion, assessing TS muscle volume on the basis of the reported shape factors is valid across populations and the root mean square differences to whole muscle reconstruction of 7.9%, 4.8% and 8.3% for SO, GM and GL show that the simplified method is sensitive enough to detect changes in muscle volume in the context of degeneration, atrophy or hypertrophy.     

Rib cage and abdominal expiratory muscle responses to CO2 and esophageal distension

The present study compared the responses of rib cage and abdominal expiratory muscles to chemical and mechanical stimuli. In pentobarbital-anesthetized spontaneously breathing dogs, electromyograms (EMG) were recorded from the triangularis sterni (TS) and transverse abdominis (TA) muscles using bipolar intramuscular wire electrodes. During resting oxygen breathing, both muscles were electrically active during expiration. Progressive hyperoxic hypercapnia significantly augmented the expiratory activity of both the TA and the TS. However, the mean percent increases in electrical activity in response to CO2 were substantially greater for the TA than for the TS at all PCO2 levels greater than 50 Torr (P less than 0.01). Occlusion of the airway at end inspiration significantly delayed the onset of TS EMG (from 0.35 +/- 0.07 to 3.35 +/- 0.67 sec; P less than 0.002) and decreased TS EMG rate of rise (P less than 0.002), but did not significantly alter these parameters for the TA. Esophageal distension increased TS EMG in all dogs (by mean of 220 +/- 64%; P less than 0.01), but in contrast decreased TA EMG in all dogs (by a mean of 63 +/- 12%; P less than 0.001). The response to esophageal distention occurred in a graded manner and appeared to be mediated predominantly via vagal afferents. We concluded that expiratory muscles of the rib cage and abdomen manifest substantial differences in their electrical responses to chemoreceptor, pulmonary stretch receptor, and esophageal mechanoreceptor stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)     

Crosstalk in surface electromyography of the proximal forearm during gripping tasks.

Electromyographic (EMG) crosstalk was systematically analyzed to evaluate the magnitude of common signal present between electrode pairs around the forearm. Surface EMG was recorded and analyzed from seven electrode pairs placed circumferentially around the proximal forearm in six healthy individuals. The cross-correlation function was used to determine the amount of common signal, which was found to decrease as the distance between electrode pairs increased, but was not significantly altered by forearm posture (pronation, neutral, supination). Overall, approximately 40% common signal was detected between adjacent electrode pairs (3 cm apart), dropping to about 10% at 6 cm spacing and 2.5% at 9 cm. The magnitude of common signal approached 50% between adjacent electrode pairs over the extensor muscles, while over 60% was observed between neighbouring sites on the flexor aspect of the forearm. Although flexor and extensor EMG amplitude was similar, less than 2% common signal was present between flexor and extensor electrode pairs during both pinch and grasp tasks. Maximum grip force production was not affected by forearm rotation for pinch, but reduced 18% from neutral (mid-prone) to pronation during grasp (p=0.01). In spite of differences in grip force, mean muscle activity did not vary between the three forearm postures during maximum pinch or grasp trials. While this study improved our knowledge of crosstalk and electrode spacing issues, further examination of forearm EMG is required to improve understanding of muscle loading, EMG properties and motor control during gripping tasks.