Associations between cervical and scapular posture and the spatial distribution of trapezius muscle activity

The first aim of this investigation was to quantify the distribution of trapezius muscle activity with different scapular postures while seated. The second aim of this investigation was to examine the association between changes in cervical and scapular posture when attempting to recruit different subdivisions of the trapezius muscle. Cervical posture, scapular posture, and trapezius muscle activity were recorded from 20 healthy participants during three directed shoulder postures. Planar angles formed by reflective markers placed on the acromion process, C7, and tragus were used to quantify cervical and scapular posture. Distribution of trapezius muscle activity was recorded using two high-density surface electromyography (HDsEMG) electrodes positioned over the upper, middle, and lower trapezius. Results validated the assumption that directed scapular postures preferentially activate different subdivisions of the trapezius muscle. In particular, scapular depression was associated with a more inferior location of trapezius muscle activity (r = 0.53). Scapular elevation was coupled with scapular abduction (r = 0.52). Scapular adduction was coupled with cervical extension (r = 0.35); all other changes in cervical posture were independent of changes in scapular posture. This investigation provides empirical support for reductions in static loading of the upper trapezius and improvements in neck posture through verbal cueing of scapular posture.     

Good Postural Habits: A Pilot Investigation Using EMG Scanning of the Paraspinals

The assumption is tested that changes from poor to good postural habits can be identified by specific patterns in paraspinal activity. Paraspinal activity is measured by using an electromyographic (EMG) scanning procedure introduced by Cram. Two samples were addressed. The first sample consists of 32 pain-free medical students. Measurements were taken twice at intervals 3 min apart in a sitting position with arms hanging at the side. The first assessment refers to a normal and relaxed, and the second assessment to an upright physiological position of the spine recommended by Brügger. Data indicate that changes to good postural habits are represented by a significant decrease in the activity of the cervical paraspinal area (CPS), whereas in the trapezius and the thoracic area (T1, T6), the activity of the muscles is significantly increased. The hypothesis is put forward that these changes also occur as a consequence of a preventive low back school training. The second sample consists of 26 asymptomatic female employees of a medical hospital who had previously suffered from back pain attacks, but who were without pain during the assessments. Recordings taken before and after participation in the back school at 3 months apart show a similar pattern of significant changes in paraspinal activity (CPS, T6), although their magnitude is less pronounced. No pre-post changes could be observed in the trapezius. The findings partly support the hypothesis. Further research is needed to evaluate the relationship between EMG recordings and postural habits.     

EVOLUTION OF HINDLIMB POSTURE IN ARCHOSAURS: LIMB STRESSES IN EXTINCT VERTEBRATES

Abstract:  During the Triassic, some 250–200 million years ago, the basal archosaurs showed a transition from sprawling to erect posture. Past studies focused on changes in bone morphology, especially on the joints, as they reorientated from a sprawling to an erect posture. Here we introduce a biomechanical model to estimate the magnitude of femur stress in different postures, in order to determine the most reasonable postures for five basal archosaurs along the line to crocodiliforms (the rhynchosaur Stenaulorhynchus , the basal archosaur Erythrosuchus , the 'rauisuchian' Batrachotomus , the aetosaurs Desmatosuchus and Typothorax ). The results confirm a sprawling posture in basal taxa and an erect posture in derived taxa. Erect posture may have evolved as a strategy to reduce large bending stresses on the limb bone caused by heavy body weights in larger forms.     

Barrels VIII: Proceedings of a Satellite Symposium of the 1995 Society for Neuroscience Meeting

A meeting of somatosensory and developmental biologists was held on November 10 and 11, 1995, in San Diego, California, to consider recent findings pertaining to the somatosensory system. The focus of this, the eighth annual Barrels Symposium (Barrels VIII), was on somatosensory circuits and plasticity, and the development of somatosensory primary afferent projections and barrel-like aggregates in the brainstem, thalamus, and cortex     

Tetrapod postural shift estimated from Permian and Triassic trackways

Abstract:  The end-Permian mass extinction, 252 million years (myr) ago, marks a major shift in the posture of tetrapods. Before the mass extinction, terrestrial tetrapods were sprawlers, walking with their limbs extended to the sides; after the event, most large tetrapods had adopted an erect posture with their limbs tucked under the body. This shift had been suspected from the study of skeletal fossils, but had been documented as a long process that occupied some 15–20 myr of the Triassic. This study reads posture directly from fossil tracks, using a clear criterion for sprawling vs erect posture. The track record is richer than the skeletal record, especially for the Early and Middle Triassic intervals, the critical 20 myr during which period the postural shift occurred. The shift to erect posture was completed within the 6 myr of the Early Triassic and affected both lineages of medium to large tetrapods of the time, the diapsids and synapsids.     

Linear relationship between electromyography and shear wave elastography measurements persists in deep muscles of the upper extremity

Recent works have demonstrated a linear relationship between muscle activation and shear modulus in various superficial muscles. As such, it may be possible to overcome limitations of traditional electromyography (EMG) methods by assessing activation using shear wave elastography. However, the relationship has not been wholly validated in deep muscles. This study measured the association between squared shear wave velocity, which is related to shear modulus, and activation within superficial and deep muscles. This relationship was also compared between surface and intramuscular EMG electrodes. We simultaneously recorded EMG and shear wave velocity in one deep (brachialis) and one superficial (brachioradialis) muscle in ten healthy individuals during isometric elbow flexion across a wide range of contraction intensities. Muscle activation and squared shear wave velocity demonstrated good reliability (ICC > 0.75) and showed a linear relationship (P < 0.05) for all muscle/EMG electrode type combinations (study conditions) after down-sampling. Study condition was not a significant within-subject factor to the slope or intercept of the relationship (P > 0.05). This work demonstrates that activation of both superficial and deep muscles can be assessed noninvasively using ultrasound shear wave elastography and is a critical step toward demonstrating elastography’s utility as an alternative to EMG.     

The history of surface electromyography

The history of muscle pain and dysfunction is viewed through the lens of a four factor theory of histologic (tissue related) issues, psychologic (emotional) issues, sensory motor (movement) issues, and biomechanical (postural) issues. The historical antecedents of surface electromyography are reviewed.     

Limb and digit orientation during vertical clinging in Bibron's gecko,Chondrodactylus bibronii (A. Smith, 1846) and its bearing on the adhesive capabilities of geckos

Geckos with subdigital adhesive pads can scale smooth vertical surfaces in defiance of gravity. The deployment of the adhesive system is activated by the musculoskeletal system during active traverses of such surfaces, but adhesion on such substrata can also be achieved by passive means, with the body weight of the gecko applying tensile loading to the adhesive setae, maintaining prolonged, static contact with the surface. To investigate whether passively induced adhesion is employed by geckos holding station on smooth vertical surfaces, we investigated the magnitude of shear force generation for the manus and pes, and the positioning of the limb segments and digits in Chondrodactylus bibronii in freely selected resting postures (head‐up, head‐down and facing laterally to the left and right). Our results indicate that different subsets of digits occupy positions consistent with them being passively loaded in different body orientations. Limb segment and digit orientation are consistent within, and differ between, the resting postures, and relatively few of the 20 digits are positioned to take advantage of gravitationally induced loading in any posture. The pedal digits have greater adhesive potential than the manual ones and, more frequently, capitalize on passive loading than do manual digits. This is especially evident in the commonly adopted head‐down resting posture.     

Higher ventilatory responses during and after passive walking-like leg movement in older individuals

Background

Minute ventilation (V·E) during walking has been shown to be higher in older individuals than in young individuals, but the mechanisms underlying the higher ventilatory response is unclear. Central command and peripheral neural reflex are important neural control mechanisms underlying ventilatory response during exercise. Passive leg movement has been used to exclude the influence of central command due to the lack of voluntary activation of muscles. The aim of the present study was to compare the ventilatory response during and after passive walking-like leg movement (PWM) in young and older individuals.

Methods

Eight young subjects (20 ± 2 years) and seven older subjects (70 ± 1 years) participated in this study. Subjects spent 7 minutes in a quiet standing (QS) position. Thereafter, they performed 14-minute rhythmic PWM at 1 Hz and this was followed by 7 minutes of QS.

Results

V·E values during pre-PWM QS were calculated as 1-minute averages using data obtained between 5 and 6 minutes. V·E values at pre-PWM QS in the young and older groups were 8.4 ± 2.1 and 7.5 ± 1.2 l/minute, respectively. V·E values increased significantly at the first minute of PWM to 11.4 ± 2.2 and 10.4 ± 2.5 l/minute in the young and older groups, respectively (P <0.001). In the young group, V·E at the last minute of PWM (9.2 ± 2.0 l/minute) was not significantly different from that at pre-PWM QS due to a decline in V·E, whereas V·E at the last minute of PWM in the older group (9.4 ± 2.2 l/minute) was still significantly higher (P <0.01). On the other hand, V·E at the first minute of post-PWM QS (7.2 ± 1.8 l/minute) was significantly lower than that during pre-PWM QS in the young group (P <0.05) but not in the older group.

Conclusions

Ventilatory response during and after PWM is higher in older individuals than in young individuals. This may be associated with a mechanism(s) other than central command. Our findings may explain part of the higher V·E response while walking in older individuals.     

Treatment of phantom limb pain with combined EMG and thermal biofeedback: a case report

Phantom pain is a frequent consequence of the amputation of an extremity and causes considerable discomfort and disruption of daily activities. This study describes a patient with extreme phantom limb pain following amputation of the right upper limb. The treatment consisted of 6 sessions of EMG biofeedback followed by 6 sessions of temperature biofeedback. The patient did not use a prosthesis and had not received previous treatment for chronic pain. Results demonstrated complete elimination of phantom limb pain after treatment, which was maintained at a 3- and 12-month follow-up. Pain relief covaried with increase in skin temperature at stump and perceptual telescoping (retraction of phantom limb into stump).     

Gender differences in neck/shoulder muscular patterns in response to repetitive motion induced fatigue

Previous studies have associated amplitude and frequency characteristics of the electromyogram (EMG) to the risk of developing musculoskeletal disorders (MSDs) with repetitive tasks. However, few studies have investigated whether EMG variability and between-muscle activity characteristics may be associated with MSD risk. Twenty-six healthy volunteers (13 men, 13 women) performed a repetitive pointing task at shoulder height until scoring 8 on a Borg CR-10 scale. Electromyographic (EMG) signals were recorded from six neck/shoulder muscle sites. EMG amplitude (RMS), variability and mutual information (MI) among muscle pairs were computed. Muscle fatigue was evidenced by increased EMG RMS of four muscles (Upper Trapezius (UT): +17%; supraspinatus (SUPRA): +28%; middle deltoid: +13%; biceps brachii: +38%) and increased SUPRA variability. Correlations between minute 1 patterns and endurance time indicated that in women, initially high variability in UTR (r = 0.79) and SUPRA (r = 0.71) predicted higher endurance, whereas in men, initially low MI in LT–UT (?0.69) and in LT–SUPRA (?0.77) pairs predicted high endurance. Significant correlations suggest that variability and between-muscle patterns may be associated with fatigue and injury mechanisms, in a gender-specific way. Differing fatigue mechanisms between genders could help explain gender differences in injury mechanisms.     

Postural reactions of humans in upright stance: Dependence on different visual conditions and the level of stiffness in the ankle joints

We checked on the supposition that the magnitude of postural reactions to an unexpected postural disturbance in upright stance in humans can be determined to a considerable extent by the level of background stiffness in the ankle joints. For this purpose, we estimated changes in the joint stiffness under different conditions of visual control; these values were estimated within the period of background body oscillations (i.e., before the beginning of a compensatory motor reaction) and compared with those in the course of postural reactions evoked by vibrational stimulation of the ankle (shin) muscles. Experiments were carried where the subjects stood with open and closed eyes (OE and CE, respectively) and while standing wearing spectacles with frosted glass passing only diffuse light (DL). In the course of the tests, the subjects stood in the usual comfortable vertical position (hereafter, standard stance) or in the same position but with the possibility to lightly touch an immobile object by a finger (stance with additional support). Such technique was used to weaken the effects of CE and DL on background sways of the body and to lead these sways close to the level typical of OE conditions. The joint stiffness was estimated using an approach based on frequency filtration of oscillations of the center of pressure of the feet (CPF) that allowed us to select signals proportional to displacements of the total center of gravity (CG) of the body and to calculate the difference between oscillations of the CPF and CG (a CPF-CG variable). The CPF-CG variable is proportional to the horizontal acceleration of the CG and, therefore, can be used for estimation of the changes in stiffness in the ankle joints. Under conditions of standard stance, the usual conditions rather similarly influenced both variables (CG and CPF-CG) in the course of both background body oscillations and a postural response. The examined variables were the greatest under CE conditions, decreased under conditions of perception of DL, and became smallest with OE. At standing with additional support, the dependence of the examined variables on visual conditions disappeared within the period of background body oscillations (before the beginning of postural reactions). In this case, the magnitude of oscillations of the CPF-CG variable under CE and DL conditions decreased to the level observed at standing under OE conditions. The magnitude of CG displacements induced by vibrational stimulations of the muscles remained, nevertheless, clearly dependent on visual conditions (the same regularities were observed as in the case of standing with no additional support). Thus, our findings demonstrate that the correlation between the characteristics of postural reactions in the upright stance and the level of ankle joint stiffness is not single-valued. Neirofiziologiya/Neurophysiology, Vol. 39, No. 2, pp. 146–153, March–April, 2007.     

Postcranial anatomy of Haldanodon exspectatus (Mammalia, Docodonta) from the Late Jurassic (Kimmeridgian) of Portugal and its bearing for mammalian evolution

The postcranium of the Late Jurassic docodont Haldanodon exspectatus Kühne & Krusat, 1972 is represented by a partial skeleton and isolated bones of other individuals from the Late Jurassic (Kimmeridgian) of the Guimarota coal mine in Portugal. Haldanodon exhibits adaptations for a fossorial lifestyle such as stout and short limb bones and humeri with greatly expanded distal joints and strong deltopectoral crests. Short first and second phalanges and moderately curved and laterally compressed terminal phalanges with lateral grooves suggest that Haldanodon was a scratch-digger. The dorso-ventrally elongated, triangular scapula has a convex transverse profile with strongly laterally reflected anterior and posterior scapula margins, enclosing a deep trough-like 'infraspinous fossa'. A supraspinous fossa is not developed. The saddle-shaped glenoid facet is mainly formed by the coracoid and orientated antero-ventrally indicating a sprawling gait. No epiphyses were detected and the wide size range of humerus and femur possibly indicate a lifelong growth. Haldanodon is more derived than Morganucodon by complete reduction of the procoracoid, absence of the procoracoid foramen, and a peg-like coracoid. It shares with monotremes a postscapular fossa that is absent in Morganucodon . A PAUP analysis based on 280 cranio-dental and postcranial characters corroborated the position of Haldanodon above morganucodontids and below Hadrocodium .  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 145 , 219–248.     

Surface EMG: The issue of electrode location

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

Specific and Nonspecific Visual Influences on the Stability of the Vertical Posture in Humans

We studied physiological mechanisms of vision-related stabilization of the vertical posture in humans using a stabilographic technique; spontaneous deviations of the projection of the center of gravity during quiet stance and magnitudes of the postural response to vibratory stimulation of proprioceptors of the lower leg muscles under varied conditions of visual control were measured. The stability of quiet stance, as estimated according to the root mean square value of the sagittal component of the stabilogram, was the best with eyes open. Vibration-induced postural responses were the smallest also under these conditions. Spontaneous postural sway and the amplitude of response to vibratory stimulation increased when only a central sector of visual field (20 ang. deg) was preserved and, especially, under conditions of closed eyes and horizontal inversion of visual perception using prismatic spectacles. Parallel changes in the quantitative stabilographic indices and amplitude of vibration-induced postural responses show that the intensity of the latter is probably determined by the background stiffness of the musculoskeletal system. We tried to estimate separately the contributions of the stiffness factor, on the one hand, and specific visual influences, on the other hand, by testing the parameters of quiet stance and postural responses under conditions of standing while lightly touching a support with the index finger. We found that the influence of the conditions of visual control on the stability of quiet stance while touching the support was eliminated. At the same time, the magnitude of postural responses to vibratory stimulation decreased but, nonetheless, changed with visual conditions in the same manner as when standing without additional support. We conclude that vision performs a dual function in the control of the vertical posture; it forms the basis for the spatial reference system and serves the source of information on the movements of one's body.     

The influence of task and angle on torque production and muscle activity at the elbow

This study investigated the effect of changing internal mechanical variables and task demands on muscle activity and torque production during high effort isometric contractions of the elbow flexors. The effect of adding a 50% maximal voluntary contraction (MVC) of supination to an MVC of elbow flexion was studied over a range of angles from 30° to 110° of elbow flexion. Surface EMGs were recorded from the biceps brachii (BIC), brachioradialis (BRAD) and triceps brachii (TRI) of 10 healthy subjects. BIC was the only muscle to show a consistent trend of increasing root mean square (rms) EMG with increasing elbow flexion angle. BIC activity also remained constant or increased with the addition of the supination task at all angles. In contrast, BRAD showed decreased activity when supination was added at several angular positions. Maximal flexion torque was reduced when the second task of submaximal supination was added. This torque reduction was statistically significant at all angles except 70° and appeared related to the decreased contribution from BRAD. In a small subset of subjects, however, BRAD activity did not decrease when the second degrees of freedom (df) task was added. These subjects exhibited higher flexion torques averaged over task than the majority, at all angles except 30°. These data support the view that internal mechanical considerations influence the manner in which the central nervous system (CNS) distributes activity to muscular synergists in response to altered task demands. Further, subject-specific patterns exist which must be recognized if these findings are to be incorporated in training or rehabilitation programmes.