The contributions of program and afferent factors to the control of human walking

The relative contributions of program and afferent factors to the control of human locomotion were studied using physical modeling of abnormalities of the biomechanical structure of walking and simultaneous recording of the parameters of movement and muscle electrical activity. During walking, three zones of activity were observed in electromyograms: Mx (maximum-amplitude), Me (medium-amplitude), and L (low-amplitude) zones. The Mx and Me zones of activity were related to the period of programmed excitation of the neuronal sspinal cord structures, and the L zone, to the period of programmed inhibition. The afferent influences were effective only in zones Mx and Me, where they amplified, attenuated, or transferred the muscle activity by means of proprioceptive reflexes. Amplified activity was a result of afferent inflow from the muscle spindles and was observed in the cases of muscle strain and a considerable load on muscles. Attenuated activity was caused by a limited input from the Ia, Ib, and II afferents (during joint immobilization and “switching off” of the receptor field of the ankle joint and foot). The drastic decrease in the muscle activity upon the exclusion of the joint from locomotion was presumably caused by presynaptic inhibition of primary afferents, which was induced by supraspinal structures.     

A New Approach to the Analysis of Normal Muscle Electrical Activity during Walking in Humans

Introduction of short-term disturbances into the biomechanical structure of the human gait with simultaneous recording of the muscle electrical activity has been used to demonstrate that the human body has an intraspinal locomotor program consisting of an inhibition period, when afferent stimuli cause no response, and an excitation period, when the responses are expressed. The electromyographic profile of the leg muscles of subjects walking on a horizontal surface, up stairs, and down stairs may be divided into three zones. The H and M zones (the highest and moderate activities, respectively) correspond to the centrally programmed excitation period, and the L zone (low-amplitude activity), to the centrally programmed inhibition period. The difference between the former two zones is that the activity in the H zone is regular, whereas the M-zone activity is irregular and varies depending on biomechanical conditions. Apparently, the steady activity in the H zone is determined by the combined effect of the spinal generator of locomotion movements, cyclic supraspinal stimuli, and various (mainly proprioceptive) afferent impulses from the leg. An increase in the M-zone activity is mainly determined by afferent stimuli.     

Acute and delayed biochemical and physiological effects of exhaustive weightlifting exercise

The goal of the work was a study of the effect of exhaustive weightlifting exercise on prolonged changes in the physiological and biochemical variables characterizing the functional state of skeletal muscles. An exercise accentuated at muscles of the hip surface gave rise to a significant increase of the blood lactate concentration, which indicated that aerobic metabolism was a predominant mechanism of energy supply for muscle contraction. A reduction of the m. rectus femoris EMG amplitude and frequency, a decrease in the tone of tension, and an increase in the tone of relaxation were found immediately after exercise. One day later, the amplitude and the frequency of the EMG signal increased. On day 3, the activity of creatine kinase (CK, a marker of muscle injury) considerably increased, while the amplitude and frequency of EMG decreased. By the ninth day of recovery, all measured variables with the exception of CK were normalized. A significant negative correlation was found between the blood serum’s lactate concentration and m. rectus femoris EMG activity at the same time points. Blood serum CK activity and m. rectus femoris EMG and tone parameters were significantly correlated on the third postexercise day. The data demonstrate that exhaustive exercise-induced muscle injury resulted in phasic alterations in the electrical activity and the tone of the muscle apparently related to a decrease in pH because of lactate accumulation in the sarcoplasm and the cascade of reactions leading to muscle tissue damage.     

Heterogeneity of muscle activation in relation to force direction: A multi-channel surface electromyography study on the triceps surae muscle

Several skeletal muscles can be divided into sub-modules, called neuromuscular compartments (NMCs), which are thought to be controlled independently and to have distinct biomechanical functions. We looked for distinct muscle activation patterns in the triceps surae muscle (TS) using surface electromyography (EMG) during voluntary contraction. Nine subjects performed isometric and isotonic plantar flexions combined with forces along pre-defined directions. Besides the forces under the ball of the foot, multi-channel surface EMG was measured with electrodes homogeneously distributed over the entire TS. Using principal component analysis, common (global) components were omitted from the EMG signals, thereby estimating muscle activity sufficiently accurate to track fine fluctuations of force during an isotonic contraction (r = 0.80 ± 0.09). A subsequent cluster analysis showed a topographical organization of co-activated parts of the muscle that was different between subjects. Low and negative correlations between the EMG activity within clusters were found, indicating a substantial heterogeneity of TS activation. The correlations between cluster time series and forces at the foot in specific directions differed substantially between clusters, showing that the differentially activated parts of the TS had specific biomechanical functions.     

Relationships between muscle lactate accumulation and surface EMG activities during isokinetic contractions in man

In order to investigate the relationship between metabolic state and myoelectrical activity in working muscle during short term intense exercise, eleven healthy males performed isokinetic knee extensions at an angular velocity of 180 deg X sec-1 for 30 and 60 s. The median frequency (MF) of the surface electromyogram (EMG) recorded from vastus lateralis was decreased while the time lag of torque production after the onset of electrical activity (EMD) was increased during exercise. These changes (MF and EMD) corresponded well to muscle lactate accumulation in the same muscle. Over the exercise period, the integrated EMG/knee extension peak torque ratio (E/T ratio) was increased, which indicated a decrease in the efficiency of electrical activity. It was concluded that the changes in the frequency components of the EMG and in the contractile property of the muscle during short term intense exercise correlated with lactate accumulation in the identical muscle, and that the decrease in efficiency of the electrical activity in the muscle suggested peripheral fatigue.     

Technique for interpretation of electromyography for concentric and eccentric contractions in gait

We present a technique to combine muscle shortening and lengthening velocity information with electromyographic (EMG) profiles during gait. A biomechanical model was developed so that each muscle's length could be readily calculated over time as a function of angles of the joints it crossed. The velocity of shortening and lengthening of the muscle fiber was then calculated, and with computer graphics this information was overlaid on the EMG profiles. Thus, researchers and clinicians were not only able to interpret the processed EMG signal as level of activity (tension) but also to gain insight as to the muscles' role as generators (muscle shortening) or absorbers (muscle lengthening) of energy. Six common muscles are documented, using database profiles; soleus (SOL), medial gastrocnemius (MG), tibialis anterior (TA), vastus lateralis (VL), rectus femoris (RF), and semitendinosus (ST). The protocol thus demonstrates a relatively simple technique for calculating muscle fiber velocity and for combining that velocity information with EMG activity profiles.     

Neuromuscular organization and regional EMG activity of the pectoralis in the pigeon

In order to improve our understanding of the neuromuscular control of the most massive avian flight muscle, we studied the innervation pattern of the pigeon pectoralis. Nine primary branches from the rostral trunk and nine to ten branches from the caudal trunk of the pectoral nerve were identified by microdissection in ten pigeons. The region of muscle that each branch innervates was delineated by nerve stimulation studies (ten pigeons) and six regions were confirmed by glycogen depletion (ten pigeons). In pigeons, branches from the rostral nerve innervate the anterior 3/5 of the sternobrachialis (SB) head of the pectoralis and branches from the caudal trunk innervate the posterior 1/2 of the SB and all of the throacobrachials (TB). In the SB, individual branches of the rostral pectoral nerve innervate wedge-shaped muscle regions (each approximately 1.3 cm wide), collectively forming a fan shaped arrangement along the sternal carina. Adjacent muscle regions partially overlap at their boundaries. Within the thoracobrachialis (TB) head of the pectrolis, muscle regions are wider. There is a region in mid-SB-where the innervation territories of the rostral and caudal nerves oferlap. Electromyographic (EMG) activity patterns were recorded within ten of the identified muscle regions during take-off, level flapping flight, and landing. Onset of EMG activity and EMG intensity within various muscle regions exhibits significant differences both within a wingbeat cycle and among different modes of flight. The innervation pattern of the pectoralis presents the anatomical substrate for neuromuscular compartmentalization and differential EMG activity within the pectoralis may reflect sensory-motor partitioning. The extent to which the neuromuscular compartmentalization of the pectoralis corresponds to its ability to produce an array of force vectors to the wing awaits further more detailed biomechanical studies. © 1993 Wiley-Liss, Inc.     

EMG monitoring in functional electrostimulation]

When using functional electrical stimulation (FES), correct adjustment of stimulation parameters, and monitoring of the stimulated muscle is mandatory if tissue damage is to be avoided. Although several FES systems are already in regular use, a method for direct muscle monitoring is still lacking. This paper investigates the suitability of the electromyogram (EMG) for such a purpose. In six sheep, the right latissimus dorsi muscle (LDM) and the associated thoracodorsal nerve were exposed. Stimulation was effected via electrodes placed on the nerve. Three electrodes were placed in the LDM for EMG recording, and the tendon was connected to a force transducer for isometric force measurement. Stimulation was applied for one second (burst), followed by a three-second pause. The stimulation current was increased in 0.2 mA steps, starting at 0 mA and ending at 4 mA. Throughout the investigation, the EMG signal was monitored with an oscilloscope. In addition, the EMG signal and the force transducer signal were recorded for subsequent analysis. An analysis of the data of all six sheep revealed an almost linear relationship between muscle force and m-wave amplitude (magnitude of r = 0.95, p < 0.001). M-wave monitoring during EMG recording with three intramuscular electrodes is a reliable method of monitoring FES-induced muscle activity, but the absolute force cannot be measured.     

Vagal contributions to respiratory muscle activity during eupnea in the awake dog.

We examined the effects of reversible vagal cooling on respiratory muscle activities in awake chronically instrumented tracheotomized dogs. We specifically analyzed electromyographic (EMG) activity and its ventilatory correlates, end-expiratory lung volume (EELV) and diaphragmatic resting length via sonomicrometry. Elimination of phasic and tonic mechanoreceptor activity by vagal cooling doubled the EMG activity of the costal, crural, and parasternal muscles, with activation occurring sooner relative to the onset of inspiratory flow. Diaphragmatic postinspiration inspiratory activity in the intact dog coincided with a brief mechanical shortening of the diaphragm during early expiration; vagal blockade removed both the electrical activity and the mechanical shortening. Vagal blockade also doubled the EMG activity of a rib cage expiratory muscle, the triangularis sterni, but reduced that of an abdominal expiratory muscle, the transversus abdominis. Within-breath electrical activity of both muscles occurred sooner relative to the onset of expiratory flow during vagal blockade. Vagal cooling was also associated with a 12% increase in EELV and a 5% decrease in end-expiratory resting length of the diaphragm. We conclude that vagal input significantly modulates inspiratory and expiratory muscle activities, which help regulate EELV efficiently and optimize diaphragmatic length during eupneic breathing in the awake dog.     

Electromyographic data do not support a progressive recruitment of muscle fibers during exercise exhibiting a VO2 slow component

The origin of the slow component (SC) of oxygen uptake kinetics, presenting during exercise above the ventilatory threshold (VT), remains unclear. Possible physiologic mechanisms include a progressive recruitment of type II muscle fibers. The purpose of this study was to examine alterations in muscle activity through electromyography (EMG) and mean power frequency (MPF) analysis during heavy cycling exercise. Eight trained cyclists (mean +/- S.E.; age = 30 +/- 3 years, height = 1771 +/- 4 cm, weight = 73.8 +/- 6.5 kg, VO2max = 4.33 +/- 0.28 l min(-1)) completed transitions from 20W to a workload equaling 50% of the difference between V(T) and VO2max. VO2 was monitored using a breath-by-breath measurement system, and EMG data were gathered from surface electrodes placed on the gastrocnemius lateralis and vastus lateralis oblique. Breath-by-breath data were time aligned, averaged, interpolated to 1-s intervals, and modeled with non-linear regression. Mean power frequency (MPF) and RMS EMG values were calculated for each minute during the exercise bout. Additionally, MPF was determined using both isolated EMG bursts and complete pedal revolutions. All subjects exhibited a VO2 SC (mean amplitude = 0.98 +/- 0.16 l min(-1)), yet no significant differences were observed during the exercise bout in MPF or RMS EMG data (p > 0.05) using either analysis technique. While it is possible that the sensitivity of EMG may be insufficient to identify changes in muscle activity theorized to affect the VO2 SC, the data indicated no relationship between MPF/EMG and the SC during heavy cycling.     

Electromyographic analysis of rotator cuff muscles in patients with rotator cuff tendinopathy: A systematic review

The shoulder is inherently an unstable joint which heavily relies on the neuromuscular activation of the rotator cuff (RC) complex for stability during movement. Currently, there is no consensus regarding how the activity of RC muscles is affected among individuals with a RC tendinopathy (RCTe). This study reviewed the evidence of studies comparing the electromyographic (EMG) activity of any RC muscle of shoulders with a symptomatic RCTe to asymptomatic shoulders. Eight databases were searched. Data from 343 participants (201 symptomatic and 209 asymptomatic shoulders) were analyzed from 10 out of 402 included studies. Strong evidence for the infraspinatus and supraspinatus during isometric contractions and limited evidence for the supraspinatus and infraspinatus during isokinetic contractions suggest that the muscular activity is not altered among individuals with a RCTe during these types of contraction. Very limited evidence indicates reduced muscle activity for the infraspinatus and subscapularis in the presence of a RCTe during isotonic contractions, and no alterations for the supraspinatus or teres minor were identified. Lastly, conflicting to moderate evidence suggests alterations in RC muscle activity during unrestrained movements and swimming. These findings indicate that EMG deficits associated with a RCTe can best be appreciated during unrestrained movements.     

Acute and remote biochemical and physiological effects of exhaustive weightlifting exercise

The goal of the work was a study of exhaustive weightlifting exercise effect on prolonged changes in physiological and biochemical variables characterized functional status of skeletal muscles. An exercise gave rise to significant blood lactate concentration increase that was indicative of an anaerobic metabolism to be a predominant mechanism of muscle contraction energy supply. A reduction of m. rectus femoris EMG activity (amplitude and frequency), tonus of tension and an increase in tonus of relaxation were found immediately after exercise. Both EMG amplitude and frequency were increased 1 day post-exercise. However, after 3 days of recovery, EMG amplitude and frequency were decreased again and, in parallel, blood serum creatine kinase (CK) activity was significantly increased. After 9 recovery days, all measured variables with the exception of CK were normalized. A significant reverse correlation was found between blood serum lactate concentration and m. rectus femoris EMG activity at the same time points. Blood serum CK activity and m. rectus femoris EMG and tonus variables were observed to be significantly reversely correlated on the 3rd post-exercise day. Presented data demonstrate that exhaustive exercise-induced muscle injury resulted in phase alterations in electrical activity and tonus which correlated with lactate concentration and CK activity in blood serum.     

A maximal isokinetic pedalling exercise for EMG normalization in cycling

An isometric maximal voluntary contraction (iMVC) is mostly used for the purpose of EMG normalization, a procedure described in the scientific literature in order to compare muscle activity among different muscles and subjects. However, the use of iMVC has certain limitations. The aims of the present study were therefore to propose a new method for the purpose of EMG amplitude normalization in cycling and assess its reliability. Twenty-three cyclists performed 10 trials of a maximal isokinetic protocol (MIP) on a cycle ergometer, then another four sub-maximal trials, whilst the EMG activity of four lower limbs muscles was registered. During the 10 trials power output (CV = 2.19) and EMG activity (CV between 4.46 and 8.70) were quite steady. Furthermore, their maximal values were reached within the 4th trial. In sub-maximal protocol EMG activity exhibited an increase as a function of exercise intensity.MIP entails a maximal dynamic contraction of the muscles involved in the pedalling action and the normalization session is performed under the same biomechanical conditions as the following test session. Thus, it is highly cycling-specific.MIP has good logical validity and within-subject reproducibility. Three trials are enough for the purpose of EMG normalization in cycling.     

Relating neuromuscular control to functional anatomy of limb muscles in extant archosaurs

Electromyography (EMG) is used to understand muscle activity patterns in animals. Understanding how much variation exists in muscle activity patterns in homologous muscles across animal clades during similar behaviours is important for evaluating the evolution of muscle functions and neuromuscular control. We compared muscle activity across a range of archosaurian species and appendicular muscles, including how these EMG patterns varied across ontogeny and phylogeny, to reconstruct the evolutionary history of archosaurian muscle activation during locomotion. EMG electrodes were implanted into the muscles of turkeys, pheasants, quail, guineafowl, emus (three age classes), tinamous and juvenile Nile crocodiles across 13 different appendicular muscles. Subjects walked and ran at a range of speeds both overground and on treadmills during EMG recordings. Anatomically similar muscles such as the lateral gastrocnemius exhibited similar EMG patterns at similar relative speeds across all birds. In the crocodiles, the EMG signals closely matched previously published data for alligators. The timing of lateral gastrocnemius activation was relatively later within a stride cycle for crocodiles compared to birds. This difference may relate to the coordinated knee extension and ankle plantarflexion timing across the swing-stance transition in Crocodylia, unlike in birds where there is knee flexion and ankle dorsiflexion across swing-stance. No significant effects were found across the species for ontogeny, or between treadmill and overground locomotion. Our findings strengthen the inference that some muscle EMG patterns remained conservative throughout Archosauria: for example, digital flexors retained similar stance phase activity and M. pectoralis remained an ‘anti-gravity’ muscle. However, some avian hindlimb muscles evolved divergent activations in tandem with functional changes such as bipedalism and more crouched postures, especially M. iliotrochantericus caudalis switching from swing to stance phase activity and M. iliofibularis adding a novel stance phase burst of activity.     

Tibialis posterior EMG activity during barefoot walking in people with neutral foot posture

The aim of this study was to characterize the electromyographic (EMG) profile of tibialis posterior during barefoot walking in order to establish a reference database for neutral foot posture. Fifteen participants had their foot posture screened using the six-item Foot Posture Index. Bipolar intramuscular electrodes were inserted into tibialis posterior and peroneus longus utilizing ultrasound guidance. Surface electrodes were placed over medial gastrocnemius, peroneus brevis and tibialis anterior. EMG and footswitch gait characteristics were recorded whilst participants completed 10 barefoot walking trials. Individual and grand ensemble averages were used to characterize the intensity profiles for each muscle. Results indicated that for most of the participants, tibialis posterior displayed two bursts of EMG activity, with the first burst during the initial contact phase and the second burst during midstance. However, there was significant variability between participants. The grand ensemble average for tibialis posterior was comparable to peroneus longus which displayed similar temporal and intensity characteristics. It is suggested that this may reflect a synergistic relationship between these muscles during stance phase, although this was not consistent for all participants. Further research is required to determine if this relationship is altered in abnormal foot posture and whether it is clinically important. In conclusion, the EMG profile of tibialis posterior during the gait cycle appeared to be highly variable among participants. However, the authors believe that EMG findings from the participants with neutral foot posture in this study may be used for comparison to EMG patterns in people with abnormal foot posture and individuals affected by musculoskeletal disease.     

Evolution of surface electromyography: From muscle electrophysiology towards neural recording and interfacing

Surface electromyography (EMG) comprises a recording of electrical activity from the body surface generated by muscle fibres during muscle contractions. Its characteristics depend on the fibre membrane potentials and the neural activation signal sent from the motor neurons to the muscles. EMG has been classically used as the primary investigation tool in kinesiology studies in a variety of applications. More recently, surface EMG techniques have evolved from single-channel methods to high-density systems with hundreds of electrodes. High-density EMG recordings can be deconvolved to estimate the discharge times of spinal motor neurons innervating the recorded muscles, with algorithms that have been developed and validated in the last two decades. Within limits and with some variability across muscles, these techniques provide a non-invasive method to study relatively large populations of motor neurons in humans. Surface EMG is thus evolving from a peripheral measure of muscle electrical activity towards a neural recording and neural interfacing signal. These advances in technology have had a major impact on our fundamental understanding of the neural control of movement and have exposed new perspectives in neurotechnologies. Here we provide an overview and perspective of modern EMG technology, as derived from past achievements, and its impact in neurophysiology and neural engineering.     

Erectile function and bulbospongiosus EMG activity in estrogen-maintained castrated rats vary with behavioral context.

Electromyographic (EMG) activity in the bulbospongiosus muscles (BS) was recorded to monitor potential castration-induced alterations in muscle activity during copulation and reflexive erections. EMG recordings were made from intact male rats and from castrated rats maintained from 7 to 50 days on estradiol benzoate (300 micrograms/day) or testosterone (200 micrograms/day). Despite a 40-50% postcastration reduction in the weight of the BS and accessory sexual glands in estrogen-treated rats, the pattern of EMG activity during copulation was similar across groups. In estradiol-treated males, the EMG burst frequency during mounts and burst duration during intromissions exceeded the parameters of intact males and of castrated males maintained on testosterone. Between intromissions, and following ejaculatory patterns, estrogen-treated males displayed spontaneous muscle bursts accompanied by visually confirmed erection of the glans penis, but these males quickly lost the capacity for reflexive erections. These data demonstrate that despite castration-induced atrophy of the penile muscles and, presumably, their spinal motor nuclei, the motor output to these muscles is maintained following androgen removal. The capacity for substantial penile erection is retained during copulation long after reflexive erections have diminished.     

Comparing electro- and mechano-myographic muscle activation patterns in self-paced pediatric gait

Electromyography (EMG) is the standard modality for measuring muscle activity. However, the convenience and availability of low-cost accelerometer-based wearables makes mechanomyography (MMG) an increasingly attractive alternative modality for clinical applications. Literature to date has demonstrated a strong association between EMG and MMG temporal alignment in isometric and isokinetic contractions. However, the EMG-MMG relationship has not been studied in gait. In this study, the concurrence of EMG- and MMG-detected contractions in the tibialis anterior, lateral gastrocnemius, vastus lateralis, and biceps femoris muscles were investigated in children during self-paced gait. Furthermore, the distribution of signal power over the gait cycle was statistically compared between EMG-MMG modalities. With EMG as the reference, muscular contractions were detected based on MMG with balanced accuracies between 88 and 94% for all muscles except the gastrocnemius. MMG signal power differed from that of EMG during certain phases of the gait cycle in all muscles except the biceps femoris. These timing and power distribution differences between the two modalities may in part be related to muscle fascicle length changes that are unique to muscle motion during gait. Our findings suggest that the relationship between EMG and MMG appears to be more complex during gait than in isometric and isokinetic contractions.     

Upper trapezius muscle activity patterns during repetitive manual material handling and work with with a computer mouse.

Firstly, upper trapezius EMG activity patterns were recorded on the dominant side of 6 industrial production workers and on the side operating a computer mouse of 14 computer-aided design (CAD) operators to study differences in acute muscular response related to the repetitiveness of the exposure. The work tasks were performed with median arm movement frequencies ranging from 5 min(-1) to 13 min(-1) and were characterized by work cycle times ranging from less than 30 sec to several days. However, the static and median EMG levels and EMG gap frequencies were similar for all work tasks indicating that shoulder muscle loads may be unaffected by large variations in arm movement frequencies and work cycle times. An exposure variation analyses (EVA) showed that the EMG activity patterns recorded during production work were more repetitive than during CAD work, whereas CAD work was associated with more static muscle activity patterns, both may be associated with a risk of developing musculoskeletal symptoms. Secondly, upper trapezius EMG activity patterns recorded on the mouse side of the CAD operators were compared with those recorded on the non-mouse side to study differences in muscular responses potentially related to the risk of developing shoulder symptoms which were more prevalent on the mouse side. The number of EMG gaps on the mouse side were significantly lower than the values for the upper trapezius on the non-mouse side indicating that more continuous activity was present in the upper trapezius muscle on the mouse side and EVA analyses showed a more repetitive muscle activity pattern on the mouse side. These findings may be of importance to explain differences in the prevalence of shoulder symptoms.