Three-dimensional kinematics of the scapula and trunk,and associated scapular muscle timing in individuals with stroke

Poor scapulothoracic control is a risk for developing shoulder pathology, but has received little attention so far in individuals with stroke (IwS). Trunk and scapular kinematics and surface muscle activity were measured in 15 healthy controls and 18 IwS during a low and high forward flexion (FF). Group-differences in trunk and scapular kinematics were assessed during low and high FF using a t-test (independent samples). Differences in muscle onset and offset time relative to movement start (both FF tasks) were determined using a mixed model taking into account the different groups and muscles. Recruitment patterns per group and task were described based on significant differences between muscles. In IwS, earlier lower trapezius and late infraspinatus offset were found during low FF, as well as a later onset and earlier offset of serratus anterior. For low FF, significantly more trunk axial rotation was found in IwS during both elevation and lowering. During high FF, IwS showed significantly less scapular posterior tilt during elevation and more scapular lateral rotation during lowering. IwS demonstrated adaptive muscle timing with earlier initiation and late inactivation of lower trapezius and infraspinatus, possibly to compensate for a late activation and early deactivation of the serratus anterior and to establish as such the correct pattern of scapulothoracic movement.     

Muscular contribution to low-back loading and stiffness during standard and suspended push-ups

Push-up exercises are normally performed to challenge muscles that span upper extremity joints. However, it is also recognized that push-ups provide an effective abdominal muscle challenge, especially when the hands are in contact with a labile support surface. The purpose of this study was to compare trunk muscle activation levels and resultant intervertebral joint (IVJ) loading when standard and suspended push-ups were performed, and to quantify and compare the contribution of trunk muscles to IVJ rotational stiffness in both exercises. Eleven recreationally trained male volunteers performed sets of standard and suspended push-ups. Upper body kinematic, kinetic, and EMG data were collected and input into a 3D biomechanical model of the lumbar torso to quantify lumbar IVJ loading and the contributions of trunk muscles to IVJ rotational stiffness. When performing suspended push-ups, muscles of the abdominal wall and the latissimus dorsi were activated to levels that were significantly greater than those elicited when performing standard push-ups (p<.05). As a direct result of these increased activation levels, model-predicted muscle forces increased and consequently led to significantly greater mean (p=.0008) and peak (p=.0012) lumbar IVJ compressive forces when performing suspended push-ups. Also directly resulting from the increased activation levels of the abdominal muscles and the latissimus dorsi during suspended push-ups was increased muscular contribution to lumbar IVJ rotational stiffness (p<.05). In comparison to the standard version of the exercise, suspended push-ups appear to provide a superior abdominal muscle challenge. However, for individuals unable to tolerate high lumbar IVJ compressive loads, potential benefits gained by incorporating suspended push-ups into their resistance training regimen may be outweighed by the risk of overloading low-back tissues.     

Impact of lumbar spine posture on thoracic spine motion and muscle activation patterns

Complex motion during standing is typical in daily living and requires movement of both the thoracic and lumbar spine; however, the effects of lumbar spine posture on thoracic spine motion patterns remain unclear. Thirteen males moved to six positions involving different lumbar (neutral and flexed) and thoracic (flexed and twisted) posture combinations. The thoracic spine was partitioned into three segments and the range of motion from each posture was calculated. Electromyographical data were collected from eight muscles bilaterally. Results showed that with a flexed lumbar spine, the lower-thoracic region had 14.83° and 15.61° more flexion than the upper- and mid-thoracic regions, respectively. A flexed lumbar spine significantly reduced the mid-thoracic axial twist angle by 5.21° compared to maximum twist in the mid-thoracic region. Functional differences emerged across muscles, as low back musculature was greatest in maintaining flexed lumbar postures, while thoracic erector spinae and abdominals showed bilateral differences with greater activations to the ipsilateral side. Combined postures have been previously identified as potential injury modulators and bilateral muscle patterns can have an effect on loading pathways. Overall, changes in thoracic motion were modified by lumbar spine posture, highlighting the importance of considering a multi-segmented approach when analyzing trunk motion.     

Electromechanical delay in ballistic movement of superior limb: comparison between karate athletes and nonathletes

The aim of the study was to analyze electromechanical delay in a ballistic movement of the superior limb. 10 male karate athletes and 9 nonathletes (without karate experience) performed a motor skill as fast and powerfully as possible, with impact on a makiwara (karate training instrument). For each participant, 10 choku-zuki performances were analyzed. Kinematics and surface electromyographic (EMG) activity of the anterior and posterior portions of deltoid, pectoralis major, latissimus dorsi, triceps brachii, and biceps brachii were recorded. Athletes had significantly shorter delay in arm flexion agonist muscles and significantly higher delay in arm flexion antagonist muscles and in forearm extension agonists. Results suggest that enhanced performance in athletes was mainly due to motor learning.     

Comparative study of the differences in shoulder muscle activation according to arm rotation angle

BackgroundScapular muscle exercise is important for patients with shoulder disorders. Distal variance leads to changes in shoulder muscle activation. Here, we aimed to determine whether scapular muscle activation is affected by different arm rotation angles.MethodsOverall, 30 healthy men participated in this study. The subjects were asked to keep their arms at 120 degrees of shoulder flexion while holding a 1.0-kg dumbbell in palms down (pronation) and palms up (supination) positions. Electromyography was used to measure anterior, middle, posterior deltoid, serratus anterior, upper, and lower trapezius muscle activation during the task. The muscle activations of each shoulder were compared between the pronation and supination positions.ResultsAnterior deltoid and serratus anterior activations were significantly higher in supination than in pronation (p < .05). Alternatively, posterior deltoid and lower trapezius muscles were significantly more activated in pronation than in supination (p < .05).ConclusionScapular muscle activation changed with arm rotation angle. Arm rotation angle should be assessed to estimate scapular muscle activation during exercise and motion analysis in clinical practice.     

Exploring the geometric and mechanical characteristics of the spine musculature to provide rotational stiffness to two spine joints in the neutral posture

Joint stiffness is inherently linked to both performance and injury. Muscular activation is the predominant provider of stiffness to the lumbar spine, and is essential to ensure optimal spine performance. The purpose of the current paper was to examine the potential of the trunk muscles to provide rotational joint stiffness at two spine joints in the neutral posture, and to demonstrate the sensitivity of this stiffening potential to various muscle orientation and stiffness assumptions. Two separate anatomical models were utilized to analyze the muscular contributions to the 3-dimensional rotational stiffness about each of the L1-L2 and L4-L5 spine joints. Total muscular stiffening potentials, for both joints in each anatomical model, were found to be highest about the global lateral bend axis, and lowest about the global axial twist axis. The stiffening potential was found to depend highly on both the assumed muscle stiffness coefficient (q value) and the moment arm of the muscle about the joint in question. Analyses of spine stiffness were found to be greatly affected by both the anatomical representation of the surrounding musculature and the selection of the q value in the determination of muscular stiffness. Inappropriate choices of either of these factors could lead to errors in stiffness and subsequently stability estimates, and in the interpretation and possible clinical recommendations stemming from such estimates.     

Concurrent verbal interference of right and left proximal and distal upper extremity tapping

The purpose of this study was to investigate crossed and uncrossed control of the proximal (upper arm and shoulder) and distal (lower arm and hand) musculature of the arms using the dual-task paradigm. Forty-one strongly right-handed men performed a tapping task using primarily the musculature of the upper or lower arms, with and without concurrent verbal processing demands. The results showed that the left distal region was distinguished from the other three effector locations by its relative insensitivity to the demands of the dual-task (verbal processing) condition. Rapid alternating movements of the left arm were functionally independent from the left index finger location in response to dual-task demands. Dual verbal and tapping demands at this effector produced greater interference on both the primary and secondary task. The results preclude the attribution of interference effects to manual dominance factors alone. The results generally support anatomical accounts of increased ipsilateral control over left side arm but not hand movements. Neither the traditional cognitive hemispheric model nor the manual dominance hypothesis were adequate in accounting for the results. An alternative generalized capacity hypothesis was required to account for performance at the LE.     

EMG scanning: Normative data

Surface EMG was recorded from both right and left aspects of 18 muscle groups for the purpose of establishing a data base of normative EMG levels. A scanning electrode permitted easy and rapid EMG measurement from 52 male and 51 female college students, both sitting and standing. Several a posteriori analyses of variance revealed sex differences in the masseter, occipital, posterior cervical, upper trapezius, latissimus dorsi, and anterior tibialis. Similarly, there were side differences for the anterior temporalis, occipitalis, splenius capitus, trapezius, paraspinalis, and soleus. The analyses also revealed interactions among sex, position, and side for various measures on the trapezius. The data show that females tend to muscle brace more than males in the upper extremities. The study provides data for normative comparisons and helps to plan and interpret future EMG studies.     

Starting position of movement and perception of angle of trunk flexion while standing with eyes closed.

The present study attempted to investigate the effect of position on the perception of angle of trunk flexion while standing. For this purpose, the range effect was factored out by setting the constant target angle at 10 degrees, with varied starting positions of trunk flexion. We found that subjects underestimated angle of trunk flexion when the starting position was close to a quiet standing posture, overestimated when close to maximum trunk flexion, and correctly perceived it when at the middle position. Less perceptual distortion was observed at the positions close to maximum trunk flexion in the present study than in our previous one, in which various target angles of trunk flexion were reproduced from a quiet standing posture. The reduced distortion in the present study was believed to have resulted from factoring out the range effect. The flexion angle of the hip joint changed in tandem with that of the trunk, while very little movement was observed in the ankle, knee, and neck joints. Judging from the changing pattern of hip-joint angle, the muscle activity of the erector spinae and biceps femoris increased gradually to 90 degrees trunk flexion. In contrast, the actual increment of muscle activity reached zero or a minimum value at the middle angles as the angle of trunk flexion increased. It was assumed that the abrupt change in kinesthetic information associated with muscle activity exerted a great influence on the perception of trunk flexion.     

The effects of trunk extensor and abdominal muscle fatigue on postural control and trunk proprioception in young,healthy individuals

The purpose of this study was to induce both trunk extensor and abdominal muscle fatigue, on separate occasions, and compare their effects on standing postural control and trunk proprioception, as well as look at the effects of a recovery period on these outcome measures. A total of 20 individuals participated, with 10 (5 males and 5 females) completing either a standing postural control or lumbar axial repositioning protocol. Participants completed their randomly assigned protocol on two occasions, separated by at least 4 days, with either their trunk extensor or abdominal muscles being fatigued on either day. Postural control centre of pressure variables and trunk proprioception errors were compared pre- and post-fatigue. Results showed that both trunk extensor and abdominal muscle fatigue significantly degraded standing postural control immediately post-fatigue, with recovery occurring within 2 min post-fatigue. In general, these degradative effects on postural control appeared to be greater when the trunk extensor muscles were fatigued compared to the abdominal muscles. No statistically significant changes in trunk proprioception were found after either fatigue protocol. The present findings demonstrate our body’s ability to quickly adapt and reweight somatosensory information to maintain postural control and trunk proprioception, as well as illustrate the importance of considering the abdominal muscles, along with the trunk extensor muscles, when considering the impact of fatigue on trunk movement and postural control.     

Arm adductor with arm abduction in rotator cuff tear patients vs. healthy--design of a new measuring instrument

The incidence of (a)symptomatic rotator cuff tears is high, but etiologic mechanisms are unclear and treatment outcomes vary. A practical tool providing objective outcome measures and insight into etiology and potential patient subgroups is desirable. Symptomatic cuff tears coincide with humerus cranialization. Adductor co-activation during active arm abduction has been reported to reduce subacromial narrowing and pain in cuff patients. We present an easy-to-use method to evaluate adductor co-activation. Twenty healthy controls and twenty full-thickness cuff tear patients exerted EMG-recorded isometric arm abduction and adduction tasks. Ab- and adductor EMG's were expressed using the "Activation Ratio (AR)" (-1 ≤ AR ≤ 1), where lower values express more co-activation. Mean control AR's ranged from .7 to .9 with moderate to good test-retest reliability (ICC: .60-.74). Patients showed significantly more adductor co-activation during abduction, with adductor AR's ranging between .3 (teres major) and .5 (latissimus dorsi). In conclusion, the introduced method discriminates symptomatic cuff tear patients from healthy controls, quantifies adductor co-activation in an interpretable measure, and provides the opportunity to study correlations between muscle activation and humerus cranialization in a straightforward manner. It has potential as an objective outcome measure, for distinguishing symptomatic from asymptomatic cuff tears and as a tool for surgical or therapeutic decision-making.     

Effects of scapular retraction/protraction position and scapular elevation on shoulder girdle muscle activity during glenohumeral abduction

According to scapulohumeral rhythm, shoulder abduction is followed through scapular upward rotation to ensure joint mobility and stability. Of interest, the shoulder abduction can be performed holding the scapula in different positions and in association with scapular elevation, with possible effects on shoulder muscle activity. Therefore, the aim of the study was to analyze the activity of relevant shoulder muscles and the activity ratios between the scapulothoracic muscles, during shoulder abduction performed in different combinations of scapular position (neutral, retracted, protracted) and scapular elevation.The electromyographic activity of middle deltoid, serratus anterior, upper, middle and lower fibers of trapezius was recorded during shoulder abduction movements executed holding the scapula in neutral, retracted and protracted position, and subsequently a shoulder elevation movement. The activation of each muscle and the scapulothoracic muscles activity ratios were determined every 15 degrees, from 15° to 120° of abduction.Scapular retraction led to higher activation of the entire trapezius muscle, whereas protraction induced higher upper trapezius, middle deltoid and serratus anterior activity, along with lower activity of middle and lower trapezius. Shoulder elevation led to higher activity of the upper trapezius and middle deltoid. Moreover, it induced lower activation of the serratus anterior and middle and lower trapezius, thus leading to high ratios between the upper trapezius and the other scapulothoracic muscles, especially between 15 and 75 degrees of abduction.This study highlights that shoulder abduction performed with scapular protraction and in combination with scapular elevation leads to increased activity of the middle deltoid and upper trapezius, resulting in imbalances between the scapulothoracic muscles that could hamper the optimal scapulohumeral rhythm. The abduction performed in the aforementioned scapular conditions also induce potential reciprocal inhibition effects between the movers and stabilizers muscles of scapula, suggesting different motor control strategies of integrating a common shoulder movement with various modification of the scapular position.     

Comparison of trunk muscle reflex activation patterns between active and passive trunk flexion–extension loading conditions

The aim of the present study was to determine the effects of trunk flexion–extension loading on the neuromuscular reflexive latencies and amplitude responses of the trunk musculature. Eighteen male and female subjects (18–27 yrs) participated in active and passive trunk flexion extension, performed ∼7 days apart. Subjects performed 60 trunk flexion–extension repetitions. Surface electromyography (EMG) was collected bilaterally from paraspinal and abdominal muscles. In the active condition, subjects volitionally moved their trunks, while in the passive condition the dynamometer controlled the movements. The trunk was perturbed before and immediately after 30 repetitions. Latency of muscle onset, latency of first peak, latency of maximum peak, and peak EMG amplitude were evaluated. No differences between conditions, sides, or perturbation session were apparent. Overall latencies were shorter in females (p < .05) and abdominal muscles compared to paraspinals (p < .05). Thoracic paraspinal muscle amplitudes were greater than all other muscles (p < .05). Based upon the present results, the neuromuscular system engages trunk flexor muscles prior to the paraspinals in order to provide possible stabilization of the trunk when flexor moments are generated. Overall, the results indicate no difference in response of the neuromuscular system to active or passive repetitive loading.     

Anticipatory and compensatory postural adjustments in sitting in children with cerebral palsy

The aim of this study was to examine postural control in children with cerebral palsy performing a bilateral shoulder flexion to grasp a ball from a sitting posture. The participants were 12 typically developing children (control) without cerebral palsy and 12 children with cerebral palsy (CP). We analyzed the effect of ball mass (1 kg and 0.18 kg), postural adjustment (anticipatory, APA, and compensatory, CPA), and groups (control and CP) on the electrical activity of shoulder and trunk muscles with surface electromyography (EMG). Greater mean iEMG was seen in CPA, with heavy ball, and for posterior trunk muscles (p < .05). The children with CP presented the highest EMG and level of co-activation (p < .05). Linear regression indicated a positive relationship between EMG and aging for the control group, whereas that relationship was negative for participants with CP. We suggest that the main postural control strategy in children is based on corrections after the beginning of the movement. The linear relationship between EMG and aging suggests that postural control development is affected by central nervous disease which may lead to an increase in muscle co-activation.     

The effect of trunk flexion angle on lower limb mechanics during running

Trunk flexion is an understudied biomechanical variable that potentially influences running performance and susceptibility to injury. We present and test a theoretical model relating trunk flexion angle to stride parameters, joint moments and ground reaction forces that have been implicated in repetitive stress injuries. Twenty-three participants (12 male, 11 female) ran at preferred trunk flexion and three more flexed trunk positions (moderate, intermediate and high) on a custom built Bertec™ instrumented treadmill while kinematic and kinetic data were simultaneously captured. Markers adhered to bony landmarks tracked the movement of the trunk and lower limb. Stride parameters, moments of force and ground reaction force were calculated using Visual 3D (C-Motion ©) software. From preferred to high trunk flexion, stride length decreased 6% (P < 0.001) and stride frequency increased 7% (P < 0.001). Extensor moments at the hip increased 70% (P < 0.001), but knee extensor (P < 0.001) and ankle plantarflexor moments (P < 0.001) decreased 22% and 14%, respectively. Greater trunk flexion increased rate of loading by 29% (P < 0.01) and vertical ground reaction force impact transients by 20% (P < 0.01). Trunk flexion angle during running has significant effects on stride kinematics, lower extremity joint moments and ground reaction force and should be further investigated in relation to running performance and repetitive stress injuries.     

Physicians' H]ead and Body Positions as Determinants of Perceived Rapport

The relationship between physicians' b]ody movement and judgments of rapport was examined in this study. One-hundred eighteen observers rated physicians' b]ehavior on 14 bipolar scales assessing dimensions of empathy. Physicians' n]onverbal behavior was manipulated so that there were three levels of trunk angle (forward, straight, backward), two levels of arm position (open, folded), two levels of leg position (open, crossed), and two levels of head attitude (nodding, not-nodding). Significant effects were found for trunk angle, head attitude, and arm posture; physicians who leaned forward with open arm positions and nodded their head were judged more positively. Discussion focuses on the reinforcing valuc of nodding, judges' p]erceptions of physicians' a]ccessibility conveyed by trunk and arm postures, and expressions of dominance in physician-patient encounters.     

Pathomechanisms of cervical headaches

Various types of disorders of the cervical region may produce headache. In many of these increased tension of the neck musculature plays an important role. The following mechanisms underlying headache are described and differentiated: 1. Headache due to faulty muscle pattern (stereotype) resulting in overstrain of the upper fixators of the shoulder girdle (upper part of the m.trapezius and levator scapulae); faulty respiration with the aid of the upper auxillary muscles even at rest is pointed out. 2. A forward drawn head position producing static overstrain in the posterior neck muscles and compensatory retroflexion of the cranio-cervical junction resulting in blockage in this region. 3. Anteflexion and ligament pain mainly due to faulty position at work and jolting. 4. Static disturbance in the frontal plain due to obliquity producing asymmetrical strain in the neck musculature. 5. Increased muscular tension due to psychological stress. 6. Blockage in the regions of the cervical spine, shoulder girdle and upper ribs with reflex muscular spasm. 7. Reflex spasm of the neck musculature in visceral disorders causing in addition blockage of the cervico-thoracic junction (heart, gall bladder). 8. Pain arising from the posterior arch of the atlas (here described for the first time). 9. Headache due to vertebral artery involvement. The type of headache seems to be determined rather by the individual mode of reaction than by the mechanism underlying it. As a rule a combination of mechanisms is actually found.     

Time to task failure of trunk extensor muscles differs with load type

Time to task failure of trunk extensor muscles during seated submaximal isometric exertions was assessed in 18 healthy participants using 2 different load types. One required supporting an inertial load (position-matching task) whereas the 2nd required maintaining an equivalent torque against a rigid restraint (force-matching task). Time to task failure was significantly longer for position-matching tasks compared to the force-matching tasks. This finding is opposite to that reported for the appendicular muscles. A subset of 4 individuals completed a 2nd experiment to test the time to task failure of the elbow flexors in the position- and force-matching tasks. Time to task failure of the elbow flexors was significantly longer for the force-matching tasks compared to position matching. Thus, the same population shows that the effects of load type on time to task failure are opposite for the appendicular and axial muscles. This could be an important issue in understanding the mechanisms of task failure, and the endurance capacity of the trunk extensor muscles.     

Kinematic descriptions of upper limb function using simulated tasks in activities of daily living after stroke

Assessment of upper limb function poststroke is critical for clinical management and determining the efficacy of interventions. We designed a unilateral upper limb task to simulate activities of daily living to examine how chronic stroke survivors manage reaching, grasping and handling skills simultaneously to perform the functional task using kinematic analysis. The aim of the study was to compare the motor strategies for performing a functional task between paretic and nonparetic arms. Sixteen chronic stroke survivors were instructed to control an ergonomic spoon to transfer liquid from a large bowl to a small bowl using paretic or nonparetic arm. Kinematic data were recorded using a Vicon motion capture system. Outcome measures included movement duration, relative timing, path length, joint excursions, and trial-to-trial variability. Results showed that movement duration, spoon path length, and trunk path length increased significantly when participants used paretic arm to perform the task. Participants tended to reduce shoulder and elbow excursions, and increase trunk excursions to perform the task with paretic arm and altered the relative timing of the task. Although participants used different motor strategies to perform the task with their paretic arms, we did not find the significant differences in trial-to trial variability of joint excursions between paretic and nonparetic arms. The results revealed differences in temporal and spatial aspects of motor strategies between paretic and nonparetic arms. Clinicians should explore the underlying causes of pathological movement patterns and facilitate preferred movement patterns of paretic arm.     

Posture-movement responses to stance perturbations and upper limb fatigue during a repetitive pointing task

Localized muscle fatigue and postural perturbation have separately been shown to alter whole-body movement but little is known about how humans respond when subjected to both factors combined. Here we sought to quantify the kinematics of postural control and repetitive upper limb movement during standing surface perturbations and in the presence of fatigue. Subjects stood on a motion-based platform and repetitively reached between two shoulder-height targets until noticeably fatigued (rating of perceived exertion = 8/10). Every minute, subjects experienced a posterior and an anterior platform translation while reaching to the distal target. Outcomes were compared prior to and with fatigue (first vs. final minute data). When fatigued, regardless of the perturbation condition, subjects decreased their shoulder abduction and increased contralateral trunk flexion, a strategy that may relieve the load on the fatiguing upper limb musculature. During perturbations, kinematic adaptations emerged across the trunk and arm to preserve task performance. In contrast to our expectation, the kinematic response to the perturbations did not alter in the presence of fatigue. Kinematic adaptations in response to the perturbation predominantly occurred in the direction of the reach whereas fatigue adaptations occurred orthogonal to the reach. These findings suggest that during repetitive reaching, fatigue and postural perturbation compensations organize so as to minimize interaction with each other and preserve the global task characteristics of endpoint motion.