Mean Electromyographic Amplitude Research Articles

Influence of post-rotary transient vestibular tone imbalance on muscular synergies during walking and running

It is known from animal experiments that the vestibulospinal pathway is an effector control of the vestibular nucleus, whose stimulation generates an increase in the muscular tone during the stance phase of walk without affecting the muscular coordination. Increasing movement speed (walk to run) inhibits peripheral vestibular afferents in favour of central automatic motor programs. The aim of this study was to quantify the impact of a transient vestibular tone imbalance (TVTI) on the level of muscular activity and muscular synergies during walking and running, in human. Eleven asymptomatic participants aged between 20 and 28 years took part in the study. Participants were instructed to walk or run for a distance of 10 m with the eyes closed (control conditions). They also were instructed to perform the same tasks after 10 rotations on an armchair at 360°/s, before being abruptly stopped (experimental conditions). For each condition, muscular synergies were extracted by using the non-negative matrix factorization on the surface electromyographic (EMG) signal of 8 lower limb muscles. Additionally, the change in muscle activation (ΔEMG) due to the TVTI in each mode of locomotion (walk or run) was determined by the mean EMG amplitude during the TVTI condition with the one during the control condition. The lateral deviation of locomotion was quantified by a Vicon 3D analysis system. Muscle synergies were similar across conditions (in number, composition and activation), while ΔEMG of the stance phase during walking was significantly ( P = 0.038) higher than during running. The TVTI increased the lateral deviation in both modes of locomotion ( P < 0.001) but this effect was higher in walking than running ( P = 0.001). This study corroborated previous findings that vestibular inputs were differentially regulated depending on the locomotion speed but had no effect on the underlying muscle coordination of locomotion. This result could open a new paradigm of rehabilitation of vestibulopathic subjects, by training them to flexibly regulated the weightings among sensory inputs to produce the motor response.

Monitoring of the posterior cricoarytenoid muscle represents another option for neural monitoring during thyroid surgery: Normative vagal and recurrent laryngeal nerve posterior cricoarytenoid muscle electromyographic data.

Intraoperative neural monitoring (IONM) of laryngeal nerves using electromyography (EMG) is routinely performed using endotracheal tube surface electrodes adjacent to the vocalis muscles. Other laryngeal muscles such as the posterior cricoarytenoid muscle (PCA) are indirectly monitored. The PCA may be directly and reliably monitored through an electrode placed in the postcricoid region. Herein, we describe the method and normative data for IONM using PCA EMG. Retrospective review. Data were reviewed retrospectively for thyroid and parathyroid surgery patients with IONM of laryngeal nerves from January to August 2016. Recordings of vocalis and PCA EMG amplitudes and latencies with stimulation of laryngeal nerves were obtained using endotracheal (ET) tube-based and postcricoid surface electrodes. Data comprised EMG responses in vocalis and PCA recording channels with stimulation of the vagus, recurrent laryngeal nerve (RLN), and external branch of the superior laryngeal nerve from 20 subjects (11 left, 9 right), as well as PCA EMG threshold data with RLN stimulation from 17 subjects. Mean EMG amplitude was 725.69 ± 108.58 microvolts (µV) for the ipsilateral vocalis and 329.44 ± 34.12 µV for the PCA with vagal stimulation, and 1,059.75 ± 140.40 µV for the ipsilateral vocalis and 563.88 ± 116.08 µV for the PCA with RLN stimulation. There were no statistically significant differences in mean latency. For threshold cutoffs of the PCA with RLN stimulation, mean minimum and maximum threshold intensities were 0.37 milliamperes (mA) and 0.84 mA, respectively. This study shows robust and reliable PCA EMG waveforms with direct nerve stimulation. Further studies will evaluate feasibility and application of the PCA electrode as a complementary quantitative tool in IONM. 4. Laryngoscope, 128:283-289, 2018.

Reinnervated Split-Muscle Technique for Creating Additional Myoelectric Sites in an Animal Model.

This study proposes a novel reinnervated split-muscle operation to create additional myoelectric sites as sources of command signals of myoelectric prostheses for enhanced dexterous hand-to-wrist motions. The aim of this study was to investigate the postprocedure electromyographic properties of the muscles as distinct myoelectric sites in a rat model. The reinnervated split-muscle group (n = 6) had the gastrocnemius muscle separated along its longitudinal axis and nerves transferred to each new muscle (peroneal nerve to lateral muscle head and tibial to medial one); the non-split-muscle group (n = 6) only had nerve transfers with its muscle intact. Functional testing was conducted after 10 weeks. The main parameter is the difference in mean electromyographic amplitude between the new muscles, with greater values indicating better separability. After the reinnervated split-muscle procedure, there is a significant increase of the average ratio between two muscles compared with the control group, from 0.44 (range, 0.02 to 0.86) to 0.77 (range, 0.35 to 0.98) (p = 0.011). In addition, compared with the non-split muscle group, nerve transfer in the split-muscle group is more successful in reaching its intended target muscle. A reinnervated split-muscle procedure could be beneficial for acquiring a more precise and discrete command signal in upper limb amputees, thus enabling the creation of more dexterous prosthetic arm.

Intra-Individual Variability of Surface Electromyography in Front Crawl Swimming

The variability of electromyographic (EMG) recordings between and within participants is a complex problem, rarely studied in swimming. The importance of signal normalization has long been recognized, but the method used might influence variability. The aims of this study were to: (i) assess the intra-individual variability of the EMG signal in highly skilled front crawl swimmers, (ii) determine the influence of two methods of both amplitude and time normalization of the EMG signal on intra-individual variability and of time normalization on muscle activity level and (iii) describe the muscle activity, normalized using MVIC, in relation to upper limb crawl stroke movements. Muscle activity of rectus abdominis and deltoideus medialis was recorded using wireless surface EMG in 15 adult male competitive swimmers during three trials of 12.5 m front crawl at maximal speed without breathing. Two full upper limb cycles were analyzed from each of the swimming trials, resulting in six full cycles used for the intra-individual variability assessment, quantified with the coefficient of variation (CV), coefficient of quartile variation (CQV) and the variance ratio (VR). The results of this study support previous findings on EMG patterns of deltoideus medialis and rectus abdominis as prime mover during the recovery (45% activity relative to MVIC), and stabilizer of the trunk during the pull (14.5% activity) respectively. The intra-individual variability was lower (VR of 0.34–0.47) when compared to other cyclic movements. No meaningful differences were found between variability measures CV or VR when applying either of the amplitude or the time normalization methods. In addition to reporting the mean amplitude and standard deviation, future EMG studies in swimming should also report the intra-individual variability, preferably using VR as it is independent of peak amplitude, provides a good measure of repeatability and is insensitive to mean EMG amplitude and the degree of smoothing applied.

Individual Responses for Muscle Activation, Repetitions, and Volume during Three Sets to Failure of High- (80% 1RM) versus Low-Load (30% 1RM) Forearm Flexion Resistance Exercise

This study compared electromyographic (EMG) amplitude, the number of repetitions completed, and exercise volume during three sets to failure of high- (80% 1RM) versus low-load (30% 1RM) forearm flexion resistance exercise on a subject-by-subject basis. Fifteen men were familiarized, completed forearm flexion 1RM testing. Forty-eight to 72 h later, the subjects completed three sets to failure of dumbbell forearm flexion resistance exercise with 80% (n = 8) or 30% (n = 7) 1RM. EMG amplitude was calculated for every repetition, and the number of repetitions performed and exercise volume were recorded. During sets 1, 2, and 3, one of eight subjects in the 80% 1RM group demonstrated a significant linear relationship for EMG amplitude versus repetition. For the 30% 1RM group, seven, five, and four of seven subjects demonstrated significant linear relationships during sets 1, 2, and 3, respectively. The mean EMG amplitude responses show that the fatigue-induced increases in EMG amplitude for the 30% 1RM group and no change in EMG amplitude for the 80% 1RM group resulted in similar levels of muscle activation in both groups. The numbers of repetitions completed were comparatively greater, while exercise volumes were similar in the 30% versus 80% 1RM group. Our results, in conjunction with those of previous studies in the leg extensors, suggest that there may be muscle specific differences in the responses to high- versus low-load exercise.

Modulation of forelimb and hindlimb muscle activity during quadrupedal tied-belt and split-belt locomotion in intact cats

The modulation of the neural output to forelimb and hindlimb muscles when the left and right sides step at different speeds from one another in quadrupeds was assessed by obtaining electromyography (EMG) in seven intact adult cats during split-belt locomotion. To determine if changes in EMG during split-belt locomotion were modulated according to the speed of the belt the limb was stepping on, values were compared to those obtained during tied-belt locomotion (equal left–right speeds) at matched speeds. Cats were chronically implanted for EMG, which was obtained from six muscles: biceps brachii, triceps brachii, flexor carpi ulnaris, sartorius, vastus lateralis and medial gastrocnemius. During tied-belt locomotion, cats stepped from 0.4 to 1.0m/s in 0.1m/s increments whereas during split-belt locomotion, cats stepped with left–right speed differences of 0.1 to 0.4m/s in 0.1m/s increments. During tied-belt locomotion, EMG burst durations and mean EMG amplitudes of all muscles respectively decreased and increased with increasing speed. During split-belt locomotion, there was a clear differential modulation of the EMG patterns between flexors and extensors and between the slow and fast sides. Changes in the EMG pattern of some muscles could be explained by the speed of the belt the limb was stepping on, while in other muscles there were clear dissociations from tied-belt values at matched speeds. Therefore, results show that EMG patterns during split-belt locomotion are modulated to meet task requirements partly via signals related to the stepping speed of the homonymous limb and from the other limbs.

Effects of Vibration on Dynamic and Stabiliser Muscle Activities during the Press Up

A pilot study investigating the influence of vibration during press ups on myoelectrical activity of both dynamic and stabiliser muscles. Nine male participants (21.1 ± 3.4 years, 1.68 ± 0.03 m, 72.3 ± 9.5 kg), performed press ups under 3 conditions: without vibration, low amplitude and frequency vibration (30L; 1.2 mm, 30 Hz) high amplitude and frequency vibration (40H; 1.9 mm, 40 Hz). Press ups were completed in a randomised order for a period of 15 s with 3 min rest. 3D motion capture with synchronous surface electromyography (EMG) of dynamic muscles (triceps, pectoralis major) and stabiliser muscles (serratus anterior, lower trapezius muscles). The introduction of vibration to press ups did not result in kinematic changes to exercises. No muscles analysed displayed significant increases in mean EMG amplitude in response to 30L VIB in the eccentric or the concentric phase of the exercise. 40H Vibration significantly increased EMG amplitudes of all muscles (p < 0.05) except the lower trapezius. Greater increases were observed during the concentric phase of movement. These results indicate that vibration influences muscle activity during press up exercises. However, further studies are required including additional information such as the transmission of vibration to the neck and head, should be completed.

Effects of Cooling on Ankle Muscle Strength, Electromyography, and Gait Ground Reaction Forces.

The effects of cooling on neuromuscular function and performance during gait are not fully examined. The purpose of this study was to investigate the effects of local cooling for 20 min in cold water at 10°C in a climate chamber also at 10°C on maximal isometric force and electromyographic (EMG) activity of the lower leg muscles. Gait ground reaction forces (GRFs) were also assessed. Sixteen healthy university students participated in the within subject design experimental study. Isometric forces of the tibialis anterior (TA) and the gastrocnemius medialis (GM) were measured using a handheld dynamometer and the EMG was recorded using surface electrodes. Ground reaction forces during gait and the required coefficient of friction (RCOF) were recorded using a force plate. There was a significantly reduced isometric maximum force in the TA muscle (P < 0.001) after cooling. The mean EMG amplitude of GM muscle was increased after cooling (P < 0.003), indicating that fatigue was induced. We found no significant changes in the gait GRFs and RCOF on dry and level surface. These findings may indicate that local moderate cooling 20 min of 10°C cold water, may influence maximal muscle performance without affecting activities at sub-maximal effort.

Effects of Stability by Using Different Types of Taping on Knee Joint during a Jump-stop Task

The purpose of this study was to investigate the effects of stability by using different types of taping on knee joint during a jump-stop task. Eight healthy males (aged=19.5±1.2 year, height=174.3±5.9 cm, weight=65.9±4.2 kg) were participated in this study. All the participants performed a jump-stop task under three knee taping conditions (traditional taping, Kinesio taping and non-taping). A high speed camera (Mega Speed 30 Ks), two AMTI force plates and four Biovision electromyography (EMG) systems were used synchronously to collect kinematic, kinetic and EMG data during the landing phase. The Kwon3D and DASYLab 6.0 software were used for further analyses of the data. The results indicated that smaller maximal anteroposterior force and fewer displacement of anteroposterior center of pressure were observed under the traditional and Kinesio taping conditions than the non-taping condition. A smaller average loading rate was reported with the Kinesio taping compared to the non-taping. Regarding kinematic parameters, an increased knee flexion angle at peak impact was observed under the traditional and Kinesio taping conditions than the non-taping condition. A larger maximum knee flexion angle was reported under the Kinesio taping compared to the non-taping. Furthermore, smaller mean EMG amplitudes were found in the rectus femoris and gastrocnemius muscles under the traditional and Kinesio taping conditions. The study concluded that the traditional and Kinesio taping techniques effectively increases the stability by giving a strong support and limiting the forward displacement of the anterior cruciate ligament at a jump-stop task. The Kinesio taping is also beneficial to increase the range of motion of knee joint.

Effects of Three Bridging Exercises on Local and Global Muscles of Middle Aged Women

[Purpose] This study investigated the muscle activity differences of three different lumbar stabilization exercises in a comparison of middle-aged and young women. [Subjects] Seventeen middle-aged women and fifteen young women were enrolled in this study. Patients with a history of any neurologic disorders, orthopedic disorders, or cardiopulmonary problems that would have affected their lumbar stabilization exercise performance were excluded. [Methods] All subjects performed 3 exercises while the surface electromographic activity was recorded of the rectus abdominis, internal oblique, multifidus, and iliocostalis lumbolum. The mean electromyographic amplitudes obtained during the exercise were normalized to the amplitude of maximal voluntary isometric contraction (%MVIC) to produce an inter-individually comparable muscle activity index. [Results] The highest muscle activity of middle-aged women was observed in the ring bridging exercise. The middle-aged women had higher levels of all muscle activaties than the young women, particularly in the multifidus muscle and iliocostalis lumborum. No significant difference in muscle activity ratio was observed between the local muscles and global muscles in the three different exercises, though the muscle activity ratio was the highest in the ring bridging exercise. The young women group showed a higher ratio of the internal oblique/rectus abdominus than the middle aged women in the bridging exercise. [Conclusion] The ring bridging exercise should be used for stabilizing the lumbar area because the young women showed a higher ratio than the middle aged women.

Cocontraction of Ankle Dorsiflexors and Transversus Abdominis Function in Patients With Low Back Pain

The abdominal draw-in maneuver (ADIM) with cocontraction has been shown to be a more effective method of activating the transversus abdominis (TrA) in healthy adults than the ADIM alone. Whether such an augmented core stabilization exercise is effective in managing low back pain (LBP) remains uncertain. To determine the effect of 2 weeks of ADIM and cocontraction training on abdominal muscle thickness and activation timing and to monitor pain and function in patients with LBP. Case-control study. Local orthopaedic clinic and research laboratory. Twenty patients with mechanical LBP (age = 27.20 ± 6.46 years, height = 166.25 ± 8.70 cm, mass = 58.10 ± 11.81 kg) and 20 healthy, age-matched people (age = 24.25 ± 1.59 years, height = 168.00 ± 8.89 cm, mass = 60.65 ± 11.99 kg) volunteered for the study. Both the LBP and control groups received ten 30-minute sessions of ADIM and cocontraction training of the tibialis anterior (TA) and rectus femoris (RF) muscles over a 2-week period. A separate, mixed-model analysis of variance was computed for the thicknesses of the TrA, internal oblique (IO), and external oblique muscles. The differences in mean and peak electromyographic (EMG) amplitudes, onset time, and latency were compared between the groups. The visual analog pain scale, Pain Disability Index, and LBP rating scale were used to assess pain in the LBP group before and after the intervention. We found an interaction between the LBP and control groups and a main effect from pretest to posttest for only TrA muscle thickness change (F₁,₃₈ = 6.57, P = .01). Reductions in all pain measures were observed after training (P < .05). Group differences in peak and mean EMG amplitudes and onset time values for TrA/IO and TA were achieved (P < .05). The RF peak (t₃₈ = 3.12, P = .003) and mean (t₃₈ = 4.12, P = .001) EMG amplitudes were different, but no group difference was observed in RF onset time (t₃₈ = 1.63, P = .11) or the cocontracted TrA/IO peak (t₃₈ = 1.90, P = .07) and mean (t₃₈ = 1.81, P = .08). The test-retest reliability for the muscle thickness measure revealed excellent correlations (intraclass correlation coefficient range, 0.95-0.99). We are the first to demonstrate that a cocontraction of the ankle dorsiflexors with ADIM training might result in a thickness change in the TrA muscle and associated pain management in patients with chronic LBP.

Novel augmented ADIM training using ultrasound imaging and electromyography in adults with core instability

To determine the effect of novel augmented abdominal drawing-in maneuver (ADIM) training using rehabilitative ultrasound imaging (RUSI) and electromyography (EMG) in adults with core instability. A convenience sample of 20 young adults with core instability (female =4; mean age ± standard deviation=24.4 ± 2.9 years) was recruited. Core instability was determined by the formal test. All subjects underwent an intensive ADIM that was augmented by comprehensive visual feedback via a pressure biofeedback unit, RUSI, and EMG. The intervention was provided for 20 minutes a day, 7 days a week, over a two-week period. The paired t-test showed that both transverse abdominal (TrA) and internal oblique (IO) muscle thickness during ADIM were significantly greater than at rest (p= 0.000). However, external oblique (EO) muscle thickness remained relatively unchanged. The mean EMG amplitudes of the EO and erector spinae (ES) muscles were significantly decreased after the intervention (p=0.001, p=0.008). The intra-class correlation coefficient (ICC(1,2)) showed the excellent test-retest reliability for muscle thickness (ranging from 0.90 to 0.98 in the prone position). This is the first evidence to demonstrate that the novel augmented ADIM training can effectively improve the lumbo-pelvic stabilization in adults with core instability.

Recruitment of the plantar intrinsic foot muscles with increasing postural demand

BackgroundThe aim of this study was to determine the difference in activation patterns of the plantar intrinsic foot muscles during two quiet standing tasks with increasing postural difficulty. We hypothesised that activation of these muscles would increase with increasing postural demand and be correlated with postural sway. MethodsIntra-muscular electromyographic (EMG) activity was recorded from abductor hallucis, flexor digitorum brevis and quadratus plantae in 10 healthy participants while performing two balance tasks of graded difficulty (double leg stance and single leg stance). These two standing postures were used to appraise any relationship between postural sway and intrinsic foot muscle activity. FindingsSingle leg stance compared to double leg stance resulted in greater mean centre of pressure speed (0.24ms−1 versus 0.06ms−1, respectively, P≤0.05) and greater mean EMG amplitude for abductor hallucis (P≥0.001, ES=0.83), flexor digitorum brevis (P≤0.001, ES=0.79) and quadratus plantae (P≤0.05, ES=0.4). EMG amplitude waveforms for all muscles were moderate to strongly correlated to centre of pressure (CoP) medio-lateral waveforms (all r≥0.4), with muscle activity amplitude increasing with medial deviations of the CoP. Intra-muscular EMG waveforms were all strongly correlated with each other (all r≥0.85). InterpretationsActivation of the plantar intrinsic foot muscles increases with increasing postural demand. These muscles are clearly important in postural control and are recruited in a highly co-ordinated manner to stabilise the foot and maintain balance in the medio-lateral direction, particularly during single leg stance.

The broad range of contractile behaviour of the avian pectoralis: functional and evolutionary implications

Wing-assisted incline running (WAIR) in birds combines the use of the wings and hindlimbs to ascend otherwise insurmountable obstacles. It is a means of escape in precocial birds before they are able to fly, and it is used by a variety of juvenile and adult birds as an alternative to flight for exploiting complex three-dimensional environments at the interface of the ground and air. WAIR and controlled flapping descent (CFD) are the bases of the ontogenetic-transitional wing hypothesis, wherein WAIR and CFD are proposed to be extant biomechanical analogs for incremental adaptive stages in the evolutionary origin of flight. A primary assumption of the hypothesis is that work and power requirements from the primary downstroke muscle, the pectoralis, incrementally increase from shallow- to steep-angled terrestrial locomotion, and between terrestrial and aerial locomotion. To test this assumption, we measured in vivo force, electromyographic (EMG) activity and length change in the pectoralis of pigeons (Columba livia) as the birds engaged in shallow and steep WAIR (65 and 85 deg, respectively) and in three modes of slow flight immediately following take-off: ascending at 80 deg, level and descending at -60 deg. Mean EMG amplitude, muscle stress, strain, work and power were minimal during shallow WAIR and increased stepwise from steep WAIR to descending flight and level flight to reach the highest levels during ascending flight. Relative to resting length of the pectoralis, fractional lengthening (maximum muscle strain) was similar among behaviors, but fractional shortening (minimum muscle strain) was absent during WAIR such that the pectoralis did not shorten to less than the resting length. These data dramatically extend the known range of in vivo contractile behavior for the pectoralis in birds. We conclude that WAIR remains a useful extant model for the evolutionary transition from terrestrial to aerial locomotion in birds because work and power requirements from the pectoralis increase incrementally during WAIR and from WAIR to flight.

Effect of Heel Lifts on Plantarflexor and Dorsiflexor Activity During Gait

Previous investigators have shown that high heels decrease the muscle activity of the gastrocnemius muscle during gait. However, it is not known whether commonly used in-shoe heel lifts of lower heights will demonstrate similar effects on muscle activity. The aim of this study was to determine whether heel lifts alter the muscle activity of the ankle plantarflexors and dorsiflexors during the stance phase of gait among individuals with limited gastrocnemius extensibility. This study used a repeated measures design. Twenty-four healthy volunteers (12 males and 12 females) with less than 5 degrees of passive ankle dorsiflexion with the knee extended participated in the study. Electromyography (EMG), computerized motion analysis, and a force plate were used to measure mean muscle activity of the lateral gastrocnemius, medial gastrocnemius, soleus and tibialis anterior muscles during the stance phase of gait across three walking conditions. Muscle activity was measured as participants ambulated at a self-selected speed in athletic shoes alone and with heel lifts of 6 mm and 9 mm inserted in athletic shoes. Between heel-strike and heel-off, the mean EMG amplitude of the medial gastrocnemius increased with both 6 and 9 mm heel lifts and the amplitude of the tibialis anterior increased with 9 mm heel lifts compared to shoes alone. Between heel-strike and heel-off, there were no significant differences in mean EMG amplitude of the lateral gastrocnemius or soleus muscles walking in heel lifts compared to shoes alone. Between heel-off and toe-off, there were no significant differences in mean EMG amplitude of the lateral gastrocnemius, medial gastrocnemius, soleus, or tibialis anterior muscles when walking in heel lifts compared to shoes alone. Heel lifts increase muscle activity of the medial gastrocnemius and tibialis anterior muscles between heel-strike and heel-off among individuals with limited gastrocnemius extensibility. We were unable to confirm a decrease in muscle activity when using heel lifts.

Fatigue‐related changes in fascicle–tendon geometry over repeated contractions: Difference between synergist muscles

Fatigue-induced changes in force production of synergist muscles were evaluated through observation of fascicle-tendon geometry and electromyography (EMG). Seven subjects performed 60 maximal isometric plantar flexions intermittently. No statistically significant intermuscle difference was observed in the decrease of mean EMG amplitudes or mean power frequency for the medial gastrocnemius (MG) and soleus (SOL) muscles. The tendon elongation of MG significantly decreased after the 19th contraction, and MG fascicle length increased after the 29th contraction, while SOL fascicle and tendon length did not change except for the last contraction. The declines in torques were highly correlated with the increase of MG fascicle length and decrease in tendon elongation in each subject, while no consistent relationship was found for SOL. These results suggest that changes in force-production of MG and SOL over repeated contractions differ, which is reflected in fascicle-tendon geometry.

Prolonged Alterations In Hindlimb Emg Following Acl Transection In An Experimental Model Of Osteoarthritis

Alterations in knee joint loading and hind limb kinematics following anterior cruciate ligament transection (ACLT) have been associated with the onset of osteoarthritis (OA) through a reduction in joint loads. Knee joint loads have been directly measured nine days following ACLT, and subsequent changes in joint kinematics have been documented over the span of one year. However, the magnitude and duration of muscle activation adaptations in the hindlimb remain unknown following ACLT. PURPOSE: To quantify long-term changes in cat hindlimb muscle activation patterns following ACLT. METHODS: In this pilot study, indwelling bipolar electromyographic (EMG) electrodes were surgically implanted in four synergist muscle pairs on the cat hindlimb: rectus femoris (RF) and vastus lateralis (VL); semitendonosis (ST) and semimembranosus (SM); extensor digitorum longus (EDL) and tibialis anterior (TA); and medial gastrocnemius (MG) and soleus (SOL). EMG and high speed video data were recorded during level treadmill walking before ACLT and at 1, 2, 3, 4, and 6 weeks, and at 2, 6, 8, and 9 months following ACLT. RESULTS: Following ACLT, there was a reduction in mean EMG activation of the VL during stance, with an immediate increase in mean EMG amplitude in the RF during swing phase only. Both the SM and ST increased activity during stance phase for nine months after ACLT. Following ACLT, the EDL exhibited an extra burst of activity just prior to, or at paw strike in addition to the increased activity at paw off. Activity in the MG also increased during stance up to nine months, and the onset of muscle activation occurred earlier following ACLT for the SOL and MG. CONCLUSION: Following ACLT the knee flexor and extensor muscles demonstrate compensatory activation patterns that may stiffen the hindlimb, and predispose the knee joint to increased loads. The two-joint EDL muscle is recruited at paw strike following ACLT, suggesting that this muscle may function to assist in stabilizing the ACL deficient joint as a knee extensor in co-contraction with the hamstring muscles. Furthermore, long term increases in activation of the dorsiflexor and plantarflexor muscles during stance may further contribute to increasing joint loads leading to OA.

Medial And Lateral Gastrocnemius Activation Differences During Heel Raise Exercise With Three Different Foot Positions

Instructional guidelines from some national exercise certification organizations recommend performing heel raise exercise with varying initial foot positions to alter the involvement of the gastrocnemius' medial (MG) or lateral (LG) head. PURPOSE: To compare MG and LG activation during the concentric (CP) and eccentric (EP) phases of heel raise exercise using neutral (N), internally-rotated (IR) and externally-rotated (ER) foot positions. The term "foot position" was maintained for consistency with instructional texts, though the initial foot position reflects hip rotation. METHODS: Twelve healthy subjects (9 male, 3 female; 24.0 ± 3.8yrs) with resistance training experience performed free-weight (bar loaded to 30% body mass) heel raise exercise on a 3.8 cm block. Surface electromyographic (EMG) activity was recorded during five repetitions under each of the N, IR and ER foot positions, divided into CP and EP phases, and ensemble averaged within phase. Mean EMG amplitude, normalized to maximum voluntary contraction, was calculated. Separate two-factor (position by head) repeated measures analysis of variance were used for each phase. Simple main effects post hoc analyses of the significant (P <.05) interactions were conducted. RESULTS: During EP, significantly greater MG activity compared to LG activity was revealed for both N and ER. During CP, significantly greater LG activity compared to the MG occurred for IR. Further, post hoc analyses on the EP revealed that MG activity using ER was significantly greater than MG activity using IR or N. Likewise, analysis of CP revealed that LG activity using IR was significantly greater than LG activity using ER or N. CONCLUSION: Altering foot positions during the heel raise exercise does alter relative muscle activation as measured by surface EMG. The MG is activated to a significantly greater extent than the LG during EP using N and ER, while the LG displays significantly greater muscle activity than the MG during CP using IR. Further research is recommended to elucidate the role of the contraction phases in these differences.

Acute fatigue‐induced changes in muscle mechanical properties and neuromuscular activity in elite handball players following a handball match

The purpose of the present study was to determine the acute fatigue development in muscle mechanical properties and neuromuscular activity in response to handball match play. Male elite handball players (n = 10) were tested before and after a simulated handball match for maximal isometric strength [maximal voluntary contraction (MVC)] and rate of force development (RFD) with synchronous electromyography (EMG) recording, while maximal vertical jump parameters were assessed using force plate analysis. Quadriceps and hamstrings MVC and RFD decreased significantly post-match (approximately 10%, P < 0.05 and approximately 16-21%, P < 0.05, respectively). During quadriceps, MVC mean EMG amplitude [mean average voltage (MAV)] decreased for the vastus lateralis (VL) and rectus femoris (RF) (21-42%, P < or = 0.05), while MAV also decreased in the antagonist biceps femoris (BF) muscle (48-55%, P < 0.01). During hamstring MVC, MAV was reduced in BF (31%, P < 0.01). Maximum EMG amplitude during quadriceps MVC was reduced for the VL (28%, P < 0.01) and the RF (5%, P < 0.05). During hamstring MVC, maximum EMG was reduced for BF (21%, P < 0.01). Post-match maximal jump height was reduced (5.2%, P < 0.01), as was also work (6.8%, P < 0.01), velocity of center of mass (2.4-4.0%, P < 0.01) and RFD (approximately 30%, P < 0.05). In conclusion, maximal (MVC) and rapid muscle force characteristics (RFD, impulse) were acutely affected concurrently with marked reductions in muscle EMG following handball match play, which may potentially lead to impaired functional performance.

Abnormal surface EMG during clinically normal wrist movement in cervical dystonia

We investigated whether patients with cervical dystonia (CD) have abnormal muscle activation in non-dystonic body parts. Eight healthy controls and eight CD patients performed a flexion-extension movement of the right wrist. Movement execution was recorded by surface electromyography (EMG) from forearm muscles. Although patients had no complaints concerning wrist movement and had no apparent difficulty in executing the task, they demonstrated lower mean EMG amplitude (flexor: 0.32 mV and extensor: 0.61 mV) than controls (flexor: 0.67 mV; P = 0.021 and extensor: 1.18 mV; P = 0.068; borderline significant). Mean extensor muscle contraction was prolonged in patients (1860 ms) compared with controls (1334 ms; P = 0.026). Variation in mean EMG amplitude over movements tended to be higher in patients (flexor: 43% and extensor: 35%) than controls (flexor: 34%; P = 0.072 and extensor: 26%; P = 0.073). These results suggest that CD patients also have abnormal muscle activation in non-dystonic body parts at a subclinical level. This would support the concept that in dystonia, non-dystonic limbs are in a 'pre-dystonic state'.