Elasmosaur (Reptilia: Sauropterygia) neck flexibility: implications for feeding strategies.

Elasmosaurs were extremely long-necked, aquatic reptiles that used four flippers for locomotion. Their distinctive long neck distinguishes them from all other Mesozoic forms, yet the potential uses and constraints of this structure are poorly understood, particularly with regard to feeding. Several associated series of elasmosaurian cervical vertebrae were used to measure ranges of potential flexion. Two-dimensional models, based on a complete specimen of the Late Cretaceous elasmosaur Aphrosaurus furlongi, were created to measure mobility in both vertical and horizontal planes. Accuracy of the models was assessed through comparative analyses with currently extant vertebrate analogues (e.g. snake, turtle, seal). Results suggest that the elasmosaurian neck was capable of a 75-177 degrees ventral, 87-155 degrees dorsal, and 94-176 degrees lateral range of movement depending upon the thickness of cartilage reconstructed between each vertebra. Neck postures such as a 'swan-like' S-shape are shown to be implausible because they require >360 degrees vertical flexion. However, maintenance of a straight neck while swimming, together with considerable lateral and/or ventral movement during prey capture and feeding are feasible.     

Changes in saccadic reaction time while maintaining neck flexion in the elderly

We investigated changes in saccadic reaction time during maintenance of neck flexion in elderly individuals. Subjects comprised 49 volunteers, including 19 young adults and 30 elderly adults. Elderly subjects were separated into 2 groups (trained group: n=18; untrained group: n=12) based on responses to a questionnaire concerning activities of daily living. Saccadic reaction time was measured at angles of neck flexion of 0 degrees (resting position), 10 degrees and 20 degrees , with the chin either resting on a stand (chin-on) or not (chin-off). Reaction time was determined as the latency to the beginning of eye movement toward the lateral target, which was moved at random intervals in jumps of 20 degrees amplitude. In the chin-on posture, the angle of neck flexion had no significant effect on reaction time in any group. In the chin-off posture, the flexion angle significantly affected reaction time in both young and elderly trained groups. Significant shortenings of the reaction time were obtained at 10 degrees and 20 degrees neck flexion in the young group, and at 20 degrees neck flexion in the elderly trained group. No significant shortening of reaction time was noted in the elderly untrained group. These findings suggest that neural function associated with shortening of saccadic reaction time due to neck extensor activity decreases with age, and the decrements become more marked with inactivity in daily life.     

Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using 'interventional' MRI

The aim of this study was to image tibio-femoral movement during flexion in the living knee. Ten loaded male Caucasian knees were initially studied using MRI, and the relative tibio-femoral motions, through the full flexion arc in neutral tibial rotation, were measured. On knee flexion from hyperextension to 120 degrees , the lateral femoral condyle moved posteriorly 22 mm. From 120 degrees to full squatting there was another 10 mm of posterior translation, with the lateral femoral condyle appearing almost to sublux posteriorly. The medial femoral condyle demonstrated minimal posterior translation until 120 degrees . Thereafter, it moved 9 mm posteriorly to lie on the superior surface of the medial meniscal posterior horn. Thus, during flexion of the knee to 120 degrees , the femur rotated externally through an angle of 20 degrees . However, on flexion beyond 120 degrees , both femoral condyles moved posteriorly to a similar degree. The second part of this study investigated the effect of gender, side, load and longitudinal rotation. The pattern of relative tibio-femoral movement during knee flexion appears to be independent of gender and side. Femoral external rotation (or tibial internal rotation) occurs with knee flexion under loaded and unloaded conditions, but the magnitude of rotation is greater and occurs earlier on weight bearing. With flexion plus tibial internal rotation, the pattern of movement follows that in neutral. With flexion in tibial external rotation, the lateral femoral condyle adopts a more anterior position relative to the tibia and, particularly in the non-weight bearing knee, much of the femoral external rotation that occurs with flexion is reversed.     

Effects of gender and foot-landing techniques on lower extremity kinematics during drop-jump landings

The purpose of this study was to assess kinematic lower extremity motion patterns (hip flexion, knee flexion, knee valgus, and ankle dorsiflexion) during various foot-landing techniques (self-preferred, forefoot, and rear foot) between genders. 3-D kinematics were collected on 50 (25 male and 25 female) college-age recreational athletes selected from a sample of convenience. Separate repeated-measures ANOVAs were used to analyze each variable at three time instants (initial contact, peak vertical ground reaction force, and maximum knee flexion angle). There were no significant differences found between genders at the three instants for each variable. At initial contact, the forefoot technique (35.79 degrees +/- 11.78 degrees ) resulted in significantly (p = .001) less hip flexion than did the self-preferred (41.25 degrees +/- 12.89 degrees ) and rear foot (43.15 degrees +/- 11.77 degrees ) techniques. At peak vertical ground reaction force, the rear foot technique (26.77 degrees +/- 9.49 degrees ) presented significantly lower (p = .001) knee flexion angles as compared with forefoot (58.77 degrees +/- 20.00 degrees ) and self-preferred (54.21 degrees +/- 23.78 degrees ) techniques. A significant difference for knee valgus angles (p = .001) was also found between landing techniques at peak vertical ground reaction force. The self-preferred (4.12 degrees +/- 7.51 degrees ) and forefoot (4.97 degrees +/- 7.90 degrees ) techniques presented greater knee varus angles as compared with the rear foot technique (0.08 degrees +/- 6.52 degrees ). The rear foot technique created more ankle dorsiflexion and less knee flexion than did the other techniques. The lack of gender differences can mean that lower extremity injuries (e.g., ACL tears) may not be related solely to gender but may instead be associated with the landing technique used and, consequently, the way each individual absorbs jump-landing energy.     

Upper airway extraluminal tissue pressure fluctuations during breathing in rabbits.

Transmural pressure at any level in the upper airway is dependent on the difference between intraluminal airway and extraluminal tissue pressure (ETP). We hypothesized that ETP would be influenced by topography, head and neck position, resistive loading, and stimulated breathing. Twenty-eight male, New Zealand White, anesthetized, spontaneously breathing rabbits breathed via a face mask with attached pneumotachograph to measure airflow and pressure transducer to monitor mask pressure. Tidal volume was measured via integration of the airflow signal. ETP was measured with a pressure transducer-tipped catheter inserted in the tissues of the lateral (ETPlat, n = 28) and anterior (ETPant, n = 21) pharyngeal wall. Head position was controlled at 30, 50, or 70 degrees, and the effect of addition of an external resistor, brief occlusion, or stimulated breathing was examined. Mean ETPlat was approximately 0.7 cmH2O greater than mean ETPant when adjusted for degree of head and neck flexion (P < 0.05). Mean, maximum, and minimum ETP values increased significantly by 0.7-0.8 cmH2O/20 degrees of head and neck flexion when adjusted for site of measurement (P < 0.0001). The main effect of resistive loading and occlusion was an increase in the change in ETPlat (maximum - minimum ETPlat) and change in ETPant at all head and neck positions (P < 0.05). Mean ETPlat and ETPant increased with increasing tidal volume at head and neck position of 30 degrees (all P < 0.05). In conclusion, ETP was nonhomogeneously distributed around the upper airway and increased with both increasing head and neck flexion and increasing tidal volume. Brief airway occlusion increased the size of respiratory-related ETP fluctuations in upper airway ETP.     

Biomechanics of the vertebrae and associated osteoderms of the Early Permian amphibian Cacops aspidephorus

Two series of osteoderms associated with the anterior three-quarters of the presacral vertebral column of the Early Permian temnospondylous amphibian Cacops aspidephorus have important implications for biomechanics of the axial skeleton. An internal series consists of an osteoderm fused to the distal tip of each neural spine. Lying dorsal to the internal series and overlapping each internal osteoderm is a second external series. The orientation of the zygapophyseal facets implies modest lateral flexion with limited coupled axial rotation of the column. However, the osteoderms restricted any possible lateral flexion through their inverted V-shape, strongly angled overlap between each external osteoderm and its neighbouring internal osteoderms, and the presence of a midsagittal flange on the ventral surface of each external osteoderm that fits into grooves on the anterior and posterior edges of the neighbouring internal osteoderms. This configuration allowed vertical flexion of the vertebral column with little lateral flexion. The rod-like nature of osteoderms with the anterior three-quarters of the presacral vertebrae suggests a restricted form of forward movement for Cacops unlike that of other early tetrapods.     

Moment-rotation responses of the human lumbosacral spinal column

The objective of this study was to test the hypothesis that the human lumbosacral joint behaves differently from L1-L5 joints and provides primary moment-rotation responses under pure moment flexion and extension and left and right lateral bending on a level-by-level basis. In addition, range of motion (ROM) and stiffness data were extracted from the moment-rotation responses. Ten T12-S1 column specimens with ages ranging from 27 to 68 years (mean: 50.6+/-13.2) were tested at a load level of 4.0 N m. Nonlinear flexion and extension and left and right lateral bending moment-rotation responses at each spinal level are reported in the form of a logarithmic function. The mean ROM was the greatest at the L5-S1 level under flexion (7.37+/-3.69 degrees) and extension (4.62+/-2.56 degrees) and at the L3-L4 level under lateral bending (4.04+/-1.11 degrees). The mean ROM was the least at the L1-L2 level under flexion (2.42+/-0.90 degrees), L2-L3 level under extension (1.58+/-0.63 degrees), and L1-L2 level under lateral bending (2.50+/-0.75 degrees). The present study proved the hypothesis that L5-S1 motions are significantly greater than L1-L5 motions under flexion and extension loadings, but the hypothesis was found to be untrue under the lateral bending mode. These experimental data are useful in the improved validation of FE models, which will increase the confidence of stress analysis and other modeling applications.     

Brief communication: Three‐dimensional motion analysis of hindlimb during brachiation in a white‐handed gibbon (Hylobates lar)

In brachiating gibbons, it is thought that there is little movement in the hindlimb joints and that lateral body movement is quite limited. These hypotheses are based on naked‐eye observations, and no quantitative motion analyses of the hindlimbs have been reported. This study quantitatively describes the three‐dimensional movements of the lower trunk and distal thigh during continuous‐contact brachiation in a white‐handed gibbon (Hylobates lar) to evaluate the roles of the trunk and hindlimb. The results revealed that the lower trunk moved both laterally and vertically. The lateral movement of the lower trunk resulted from the lateral inclination of the trunk by gravity. The vertical movement of the trunk was converted into forward velocity, indicating an exchange between potential and kinetic energy. We also observed flexion and extension of the hip, although the excursion was within a small range. In addition, the lateral movement of the hindlimb in thedirection opposite to that of trunk movement helped to reduce the lateral sway of the body. These results suggest that during continuous‐contact brachiation a gibbon uses hip flexion and extension motions to increase the kinetic energy in the swing. In addition, fine motions of the hip may restrict the lateral sway of the center of body mass. Am J Phys Anthropol 142:650–654, 2010. © 2010 Wiley‐Liss, Inc.     

How effective are added constraints in improving TKR kinematics?

Newer designs of total knee arthroplasty (TKA), through the use of added degrees of constraint, attempt to provide a "guided motion" to restore more normal and predictable kinematics. Two such design philosophies are the posterior stabilised (PS) using a cam-post and the medial pivot (MP) concepts. Knee kinematics of 12 patients with a PS TKA, 13 subjects with a MP TKA and 10 normal subjects were compared. For kinematic assessment, patients underwent fluoroscopic assessment of the knee during a step-up exercise and deep knee bend. Fluoroscopic images were corrected for distortion and assessed using 3D model fitting to determine relative 3D motion, and a 2D method to measure the patellar tendon angle (PTA) as function of knee flexion. For the PS design the cam-post mechanism engaged between 70 degrees and 100 degrees flexion. Between extension and 50 degrees there was forward motion of the contact points. Beyond 60 degrees both condyles rolled moved posteriorly. The majority of the external rotation of the femur occurred between 50 degrees and 80 degrees . The PTA was lower than normal in extension and higher than normal in flexion. The MP exhibited no anterior movement throughout the rage of motion. The medial condyle moved minimally. The lateral contact point moved posteriorly from extension to flexion. The femur rotated externally throughout the range of flexion analysed. The PTA was similar to normal from extension to mid flexion and then higher than normal beyond to high flexion. The PS design fails to fully restrain paradoxical anterior movement and although the cam engages, it does not contribute significantly to overall rollback. The MP knee does not show significant anterior movement, the medial pivot concept appears to achieve near normal kinematics from extension to 50 degrees of knee flexion. However, the results show that at high flexion this design does not achieve normal knee kinematics.     

Cervical helical axis characteristics and its center of rotation during active head and upper arm movements-comparisons of whiplash-associated disorders, non-specific neck pain and asymptomatic individuals

The helical axis model can be used to describe translation and rotation of spine segments. The aim of this study was to investigate the cervical helical axis and its center of rotation during fast head movements (side rotation and flexion/extension) and ball catching in patients with non-specific neck pain or pain due to whiplash injury as compared with matched controls. The aim was also to investigate correlations with neck pain intensity. A finite helical axis model with a time-varying window was used. The intersection point of the axis during different movement conditions was calculated. A repeated-measures ANOVA model was used to investigate the cervical helical axis and its rotation center for consecutive levels of 15 degrees during head movement. Irregularities in axis movement were derived using a zero-crossing approach. In addition, head, arm and upper body range of motion and velocity were observed. A general increase of axis irregularity that correlated to pain intensity was observed in the whiplash group. The rotation center was superiorly displaced in the non-specific neck pain group during side rotation, with the same tendency for the whiplash group. During ball catching, an anterior displacement (and a tendency to an inferior displacement) of the center of rotation and slower and more restricted upper body movements implied a changed movement strategy in neck pain patients, possibly as an attempt to stabilize the cervical spine during head movement.     

Characteristics and lateral dominance of hand grip and elbow flexion powers in young male adults

This study aimed to clarify the characteristics and the lateral dominance of hand grip power and elbow flexion power. The subjects were 15 healthy young males (mean age 22.1+/-0.7 yr, mean height 171.3+/-3.4 cm, mean mass 64.5+/-4.1 kg). All subjects were right-handed. Peak power was measured by both hands with 6 different loads of 20%-70% of maximum voluntary contraction. The maximum voluntary contraction of hand grip movement and elbow flexion movement was significantly larger in the dominant hand. Peak power of the dominant hand was larger in all loads in hand grip movement and in loads of 20% and 30% of maximum voluntary contraction in elbow flexion movement. In short, lateral dominance was confirmed. Peak power was significantly larger in hand grip movement than in elbow flexion movement in both hands. Peak velocity decreased with increasing loads in both movements, but peak power increased until about 50% of maximum voluntary contraction and then decreased. The peak power ratio of the dominant hand to the nondominant hand was significantly larger in hand grip movement than in elbow flexion movement in all loads and the peak power ratio in elbow flexion movement was more marked in light loads. In conclusion, both powers showed lateral dominance. Lateral dominance is more marked in hand grip power.     

The equine neck and its function during movement and locomotion

During both locomotion and body movements at stance, the head and neck of the horse are a major craniocaudal and lateral balancing mechanism employing input from the visual, vestibular and proprioceptive systems. The function of the equine neck has recently become the focus of several research groups; this is probably also feeding on an increase of interest in the equine neck in equestrian sports, with a controversial discussion of specific neck positions such as maximum head and neck flexion. The aim of this review is to offer an overview of new findings on the structures and functions of the equine neck, illustrating their interplay. The movement of the neck is based on intervertebral motion, but it is also an integral part of locomotion; this is illustrated by the different neck conformations in the breeds of horses used for various types of work. The considerable effect of the neck movement and posture onto the whole trunk and even the limbs is transmitted via bony, ligamentous and muscular structures. Also, the fact that the neck position can easily be influenced by the rider and/or by the employment of training aids makes it an important avenue for training of new movements of the neck as well as the whole horse. Additionally, the neck position also affects the cervical spinal cord as well as the roots of the spinal nerves; besides the commonly encountered long-term neurological effects of cervical vertebral disorders, short-term changes of neural and muscular function have also been identified in the maximum flexion of the cranial neck and head position. During locomotion, the neck stores elastic energy within the passive tissues such as ligaments, joint capsules and fasciae. For adequate stabilisation, additional muscle activity is necessary; this is learned and requires constant muscle training as it is essential to prevent excessive wear and tear on the vertebral joints and also repetitive or single trauma to the spinal nerves and the spinal cord. The capability for this stabilisation decreases with age in the majority of horses due to changes in muscle tissue, muscle coordination and consequently muscle strength.     

Orientation of tendons in vivo with active and passive knee muscles

Tendon orientations in knee models are often taken from cadaver studies. The aim of this study was to investigate the effect of muscle activation on tendon orientation in vivo. Magnetic resonance imaging (MRI) images of the knee were made during relaxation and isometric knee extensions and flexions with 0 degrees , 15 degrees and 30 degrees of knee joint flexion. For six tendons, the orientation angles in sagittal and frontal plane were calculated. In the sagittal plane, muscle activation pulled the patellar tendon to a more vertical orientation and the semitendinosus and sartorius tendons to a more posterior orientation. In the frontal plane, the semitendinosus had a less lateral orientation, the biceps femoris a more medial orientation and the patellar tendon less medial orientation in loaded compared to unloaded conditions. The knee joint angle also influenced the tendon orientations. In the sagittal plane, the patellar tendon had a more anterior orientation near full extension and the biceps femoris had an anterior orientation with 0 degrees and 15 degrees flexions and neutral with 30 degrees flexions. Within 0 degrees to 30 degrees of flexion, the biceps femoris cannot produce a posterior shear force and the anterior angle of the patellar tendon is always larger than the hamstring tendons. Therefore, co-contraction of the hamstring and quadriceps is unlikely to reduce anterior shear forces in knee angles up to 30 degrees . Finally, inter-individual variation in tendon angles was large. This suggests that the amount of shear force produced and the potential to counteract shear forces by co-contraction is subject-specific.     

An improved method for measuring tibiofemoral contact areas in total knee arthroplasty: a comparison of K-scan sensor and Fuji film.

A computerised, real time, thin-film pressure transducer method is used to measure tibiofemoral contact area in total knee arthroplasty (TKA) devices that is easier and more reliable and reproducible as compared to the Fuji pressure-sensitive film technique. Many authors have suggested that contact areas and pressures within TKA devices can be a predictor of wear and failure of the ultra-high molecular weight polyethylene (UHMWPE) tibial insert. In this study, two contact area measurement techniques (Fuji pressure-sensitive Film and K-scan sensor system) were compared using a custom TKA testing jig designed for freedom of movement so that in any loading configuration the component found and seated in its own "home" position. The K-scan system was used to measure contact areas of one TKA design at several angles from 0 to 110 degrees flexion with loads equating to 4, 4.5, and 5 times body weight. For comparison, four ranges of Fuji film were used to measure areas at the same flexion angles but at 5 times body weight only. Contact areas measured with the Fuji films were 11-36% (p < 0.05) lower than those measured by the K-scan sensor.     

The effect of the point of application of anterior tibial loads on human knee kinematics

Coupled axial tibial rotation in response to an anterior tibial load has been used as a common diagnostic measurement and as a means to load the ligamentous structures during laboratory tests. However, the exact location of the point of application of these loads as well as the corresponding sensitivity of the coupled tibial rotation to this point can have an effect on the function of the soft tissues at the joint. Therefore, the purpose of this study was to determine the effects of four different points of application of the anterior tibial load on the anterior tibial translation and coupled axial tibial rotation. The four points include: (1) geometric point - midway between the collateral ligament insertion sites on the tibia, (2) clinical point - a position that attempts to simulate clinical diagnostic tests, (3) medial point - a position medial to the geometric point and (4) lateral point - a position lateral to the clinical point. A robotic/universal force-moment sensor testing system was used to apply the anterior tibial load at the four points of application and to record the resulting joint motion. Anterior tibial translation in response to an anterior tibial load of 100N was found not to vary between the four points of application of the anterior tibial load at all flexion angles examined. However, internal tibial rotation was found for the lateral point (13+/-10 degrees at 30 degrees of knee flexion) in all specimens and clinical point (8+/-10 degrees at 30 degrees of knee flexion) while external rotation resulted when the load was applied at the medial point (-8+/-7 degrees at 30 degrees of knee flexion). Both internal and external tibial rotations occurred throughout the range of flexion when the tibial load was applied at the geometric point. The results suggest that the clinical point should be used as the point of application of the anterior tibial load whenever clinical examinations are simulated and multi-degree-of-freedom joint and soft tissue function are examined.     

Passive feeding in spiriferide brachiopods: an experimental approach using models of Devonian Paraspirifer and Cyrtospirifer

Shiino, Y. 2009: Passive feeding in spiriferide brachiopods: an experimental approach using models of Devonian Paraspirifer and Cyrtospirifer. Lethaia, Vol. 43, pp. 223–231. Passive feeding flows of two Devonian spiriferide brachiopods, Paraspirifer bownockeri and Cyrtospirifer sp., were examined experimentally using transparent hollow models and a flowing water tank. The models were constructed with polycarbonate plates using a vacuum heat press method. Another model of Paraspirifer with a spiral brachidium was constructed for the visualization of passive flow. The results of the ventral and dorsal directions of the hollow models suggest that outflow was generated through lateral gapes in the shell, while intake may have occurred through a sulcus gape. The passive internal flow inside the models invariably exhibited gyrating behaviour, and the axis of the rotation was similar to that of the spiral lophophore in spiriferides. Comparing the results using the hollow and backbone models indicates that the internal structures, which consisted mostly of the spiral brachidium, aided in adjusting the gyrating flows around the brachidium, even when the lateral region of the shell faced upstream. Extant terebratulides are known to generate gyrating flows around the median coils of the major feeding area, and this model best fits the relationship between the passive internal flows and the form of the lophophore. As a consequence, the shell forms of spiriferides could generate passive feeding flows from the gyrating movement surrounding the lophophore that are effective for feeding by the spiral lophophore. □Brachiopoda, flume experiment, functional morphology, impingement feeder, physiology, suspension feeder.     

Nuchal ligament reconstructions in diplodocid sauropods support horizontal neck feeding postures

Historically, sauropods have been largely perceived as having vertical, ‘S’-curved necks which were hypothesised to allow them to feed from the canopy of trees. Within the past two decades, this popular perception has been questioned, resulting in a debate over neck posture. The osteological differences between sauropods with horizontal neck posture (Diplodocus), and less horizontally inclined necks (Brachiosaurus) suggest differing life and feeding styles. One differing vertebral feature between these polarised bauplans is the bifurcated neural spine. Regardless of the spine condition, sauropods with and without bifurcated spines have been reconstructed exhibiting the same neck posture. Corroborating histology and morphology in extant taxa highlights the presence of modified vertebral ligaments associated with bifurcated spines. Using these extant taxa to better understand the biomechanics of bifurcated spines, this study proposes alternative soft tissue reconstructions. Previous depictions had the bifurcation trough entirely open or harbouring pneumatic diverticula or muscles; conversely this study proposes that the apices of the bifurcated spines were the anchoring points for a split nuchal ligament, and that the trough of bifurcation was predominantly filled with interspinal ligaments. Ligaments provide energy-efficient elastic rebound, and a paired ligament in the cervical series would aid in prolonged, lateral movement in a horizontal plane (i.e. feeding).     

Use of a triaxial magnetometer for respiratory measurements

We describe a triaxial magnetometer (Tri-mag) system, which consists of a transmitter, four sensors, a processing unit, and a personal computer (PC). The Tri-mag processing unit outputs the position of each sensor relative to the transmitter in three orthogonal coordinates, and this information is communicated to the PC. First, we demonstrated that within a defined octant of a sphere in which the center is the transmitter, we can measure radial distances with an accuracy of +/- 1 mm over a range extending from 10 to 70 cm from the transmitter. Second, we recorded the three-dimensional movement of sensors on the anterior and posterior surfaces of the chest wall during maximum voluntary ventilation in four normal men; all sensors were placed in the midsagittal plane of the body. Anterior sensors were located on the sternum at the level of the third intercostal space and at 2 cm above the umbilicus, whereas posterior sensors were located on the posterior spine at the same vertical levels as the anterior sensors. In all subjects the following was found. 1) Both anterior sensors moved anterior and cephalad during inspiration. The anterior thoracic sensor showed greater vertical than anteroposterior (A-P) movement, whereas the anterior abdominal sensor showed greater A-P than vertical movement. 2) Inspiration was associated with spinal extension, whereas expiration was associated with spinal flexion. Third, we used Tri-mag information to 1) measure tidal volume (VT) over a range extending from 500 ml to inspiratory capacity and 2) measure the change in end-expiratory lung volume (EELV) over a range extending from FRC to FRC plus a minimum of 1.5 liters. Our results indicate that greater than 96% of the changes in VT and greater than 82% of the changes in EELV can be accounted for by changes in A-P, vertical, and lateral dimensions of the chest wall.     

Electromyography of superficial and deep neck muscles during isometric, voluntary, and reflex contractions

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) from the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.     

Relationship between active cervical range of motion and flexion-relaxation ratio in asymptomatic computer workers

A high prevalence and incidence of neck and shoulder pain is present in the working population, especially sedentary workers. Recent findings have indicated that the flexion-relaxation (FR) ratio in the cervical erector spinae (CES) muscles might be a significant criteria of neuromuscular impairment and function. Additionally, the active cervical range of motion (ROM) is frequently used for discriminating between individuals with pain and those who are asymptomatic. The purpose of the present study was to examine the relationship between the active cervical ROM and the FR ratio in a sample of regular visual display terminal (VDT) workers. In total, 20 asymptomatic male VDT workers were recruited. Active cervical ROM was measured by a cervical ROM (CROM) instrument. Surface electromyography (EMG) was used to collect myoelectrical signals from the CES muscles, and the FR ratio was calculated for statistical analysis. Pearson correlation coefficients were used to quantify the linear relationship between the active cervical ROM and the FR ratio. The values obtained for the FR ratio in the right CES muscles correlated significantly with the active cervical ROM measured in flexion (r=0.73, p<0.01), left lateral flexion (r=0.64, p<0.01), and left rotation (r=0.60, p<0.01). Flexion (r=0.74, p<0.01) and right lateral flexion (r=0.61, p<0.01) positively correlated with the left FR ratio. Extension and right rotation showed either a very weak or no correlation with the mean value of the right and left FR ratio. Our findings suggested that the cervical FR ratio had a positive correlation with cervical movements, and that changes of the activation patterns in CES demonstrated as cervical FR ratio are associated with reduction of the cervical range of motion including flexion and lateral flexion. In addition, muscular dysfunction of the CES could occur in regular computer workers prior to occurrence of pain; this means that the FR ratio could be used to evaluate the potential risk of neck discomfort in computer workers.