Measuring myoelectric fatigue of the serratus anterior in healthy subjects and patients with long thoracic nerve palsy

Proper function of serratus anterior plays a vital role in the movement and stability of the scapula, and thus of the glenohumeral joint and the upper limb. The unique anatomy of this muscle makes direct measurements of its fatigue properties impossible. Here we describe for the first time indirect measurements of the myoelectric manifestations of fatigue in the serratus anterior. Eight healthy volunteers (29-35 years) were tested, four of them on two different occasions, using two exercise protocols (60 s isometric maximum upward force in 120 degrees arm flexion, and 60 s maximum forward force at 90 degrees arm flexion) with simultaneous recording by surface and wire electrodes applied according to established methods. Signals were analysed to obtain the rate of fall of median EMG frequency and the rate of rise of amplitude. Both exercise protocols gave similar results. Frequency-slope measurements (mean rate of fall 0.6+/-0.1% initial value per second (% s(-1)) with both surface and wire electrodes) were more precise than those of amplitude (mean rate of rise 2.6+/-0.3% s(-1) with surface electrodes, only 1.3+/-0.2% s(-1) with wire electrodes). Surface electrodes gave much lower variation than fine wires, the coefficient of variation of slopes for surface electrodes being approximately 20-40% both between studies in a single subject and between subjects. In 5 patients (aged 22-59 years) recovering from long thoracic nerve palsy studied using surface electrodes the frequency slopes was normal (0.6+/-0.1% s(-1)), while the amplitude slope was reduced (0.9+/-0.4% s(-1), P = 0.01). This shows abnormal fatigue properties of the reinnervated muscle and a dissociation between the frequency and amplitude manifestations of fatigue.

Predicting shoulder strength using allometry: implications for shoulder outcome assessments

INTRODUCTION

Shoulder strength is an integral component of shoulder function. In assessing shoulder function many functional scales rely on direct or indirect measures of strength. Strength, and thus these scales, is often highly correlated with age. We propose an allometric method for assessing shoulder strength. Allometric modeling has provided accurate predictions of biologic growth and physiologic function in both human and animal studies. Allometry utilizes the relationship between the two homologous structures on the left and right sides of the body, providing in effect an internal control and thus eliminating many confounding effects, e.g. age and level of activity.

METHODS

Twenty patients with unilateral shoulder dysfunction underwent strength testing of their affected and unaffected shoulder. Strength testing of the bilateral shoulders was also assessed in twenty people without shoulder pain in order to delineate the effect of hand dominance on strength in those without shoulder pain. Absolute and predicted strength deficits of the involved shoulder were calculated via regression analysis. Pearson's correlation coefficients were computed between age and strength.

RESULTS

Utilizing the contralateral extremity as an internal control eliminates age as a confounding variable in predicting strength outcomes (r = 0.093).

CONCLUSION

Allometric concepts, applied to shoulder strength assessment, eliminates age as a confounding variable. Strength testing of both shoulders should be considered in the development of future shoulder outcome scales in order to eliminate the strong influence of age.

The influence of different intermittent myofeedback training schedules on learning relaxation of the trapezius muscle while performing a gross-motor task

The aim of this study was to investigate the influence of different intermittent myofeedback training schedules, as provided by a Cinderella-based myofeedback system, on learning relaxation and resistance to extinction of the trapezius muscle, in subjects performing a unilateral gross-motor task. Eighteen healthy subjects performed the task without and with feedback to study baseline and learning relaxation. Subsequently, resistance to extinction was investigated by performing the task without feedback. The gross-motor task consisted of continuously moving the dominant arm between three target areas at a constant pace. Subjects were randomly assigned into three groups, characterized by the sequence of feedback schedules with which the task was performed on 3 consecutive days. Auditory feedback was provided after a 5-, 10-, or 20-s interval when a pre-set level of 80% rest was not reached. Bipolar surface electromyography recordings performed at the dominant upper trapezius muscle were quantified using relative rest time (RRT) and root mean square (RMS) parameters. Learning relaxation was defined as an increase in RRT and a decrease in RMS values. Results showed the highest RRT levels as well as a decrease in RMS for the 10-s schedule. Additionally, the 10-s schedule was unique in its ability to elevate muscular rest above the 20% level, which may be considered relevant in preventing myalgia. None of the three schedules showed resistance to extinction. It was concluded that the 10-s interval was preferred over the 5- and 20-s schedules in learning trapezius relaxation in subjects performing a unilateral gross-motor task.

Changes in the P100 latency of the visual evoked potential and the saccadic reaction time during isometric contraction of the shoulder girdle elevators

We investigated changes in the P100 latency of the visual evoked potential (VEP) and the saccadic reaction time (SRT) in relation to the degree of activity of the shoulder girdle elevators. Muscle force was set in 10% increments from 0% to 50% of the maximal voluntary contraction (MVC). The VEP was derived from a midline occipital electrode with reference electrodes on the ears when the right retina was stimulated through the eyelid by light emitting diodes while the eyes were closed. The P100 latency of the VEP was defined as the time from the stimulus onset to the main positive peak. The SRT was defined as the latency until the beginning of eye movement toward the lateral target, which was moved at random time-intervals. P100 latency was shortened until 30% of the MVC, and which it lengthened. The SRT changed in a pattern similar to that observed for the P100 latency. The ratio of the shortening in P100 latency relative to that of the SRT was approximately 20%. All data is presented as the mean value, plus the standard deviation. We believe that the information processing time in the neural pathway from the retina to the visual cortex was shortened up to a certain muscle force of the shoulder girdle elevators, and then this processing time lengthened. These findings indicate that shortening of information processing time in the neural pathway beyond the visual cortex is included in the shortening of the SRT.

Relative shoulder flexor and handgrip strength is related to upper limb function after stroke

OBJECTIVE

To compare the relative strength of different muscle groups of the paretic upper limb and assess the relationship with motor performance.

DESIGN

Descriptive study.

SETTING

Secondary care rehabilitation centre.

SUBJECTS

A convenience sample of 13 chronic hemiparetic stroke subjects.

MAIN OUTCOME MEASURES

The maximal active torques of five muscle groups were measured in both upper limbs (UL) and converted into relative strength (paretic/nonparetic). The UL function was assessed using the Box and Block Test, the Finger-to-Nose Test, the Fugl-Meyer Test and the TEMPA (Test Evaluant les Membres supérieurs des Personnes Agées).

RESULTS

The Friedman two-way analysis of variance shows a significant difference across the relative strength of the different muscle groups (p = 0.017), but subsequent multiple comparisons indicate a significant difference between handgrip and elbow extension only (relative strength of 0.52 +/- 0.27 and 0.73 +/- 0.23 respectively). However, data show the presence of large intrasubject imbalances between muscle groups. The relative forces for shoulder flexion and handgrip are the best predictors of the UL function, the higher Spearman's rho correlation coefficients for each clinical test ranging from 0.70 to 0.81.

CONCLUSIONS

These results do not confirm classical clinical teaching regarding the distribution of weakness following stroke (e.g., proximal to distal gradient; extensors more affected than flexors) but support the hypothesis that strength is related to the function of the paretic upper limb.

Anatomie der Schulterregion?Klinisch relevante Aspekte f�r die Bildgebung und anatomische Variet�ten

Knowledge of anatomic details is important for interpretation of diagnostic imaging particularly MRI and CT. New findings even in macroscopy in the last years increased our knowledge significantly. In this article the findings are summarized with emphasis on clinical aspects.

Simultaneous modulation of the exteroceptive suppression periods in the trapezius and temporalis muscles by experimental muscle pain

OBJECTIVE

To investigate whether the exteroceptive suppression (ES) periods in the trapezius and temporalis muscles could be simultaneously modulated by either experimental trapezius muscle pain or temporalis muscle pain.

METHODS

Fourteen healthy volunteers participated in two sessions with randomised injections of either hypertonic or isotonic saline into the right trapezius muscle or right temporalis muscle. The pain intensity was continuously scored on a 10 cm electronic visual analogue scale. During muscle contraction, the early (ES1) and late (ES2) reflex in the temporalis and late (ES2) reflex in the trapezius elicited by electrical stimulation of the right infraorbital nerve were recorded pre-, during-, and post-injection.

RESULTS

Hypertonic saline injection induced local muscle pain and referred pain with the maximal pain intensity of 6.3+/-0.5 cm in the right trapezius and 6.7+/-0.6 cm in the right temporalis muscles. Injection of either hypertonic or isotonic saline into the right trapezius muscle was associated with significantly shortened ES2 duration and offset time in the injected right trapezius muscle. Only injection of hypertonic saline into the right trapezius muscle could significantly reduce the ES2 offset time and decrease the degree of suppression of ES2 in the right temporalis and left trapezius muscles. Injection of either hypertonic or isotonic saline into the right trapezius muscle evoked no changes in ES2 parameters in the left temporalis muscle. Injection of hypertonic saline, but not isotonic saline, into the right temporalis muscle caused a significantly shorter ES2 offset time and shorter ES2 duration bilaterally in the temporalis and trapezius muscles.

CONCLUSIONS

The findings of the present study provide evidence for a bi-directional effects reflecting convergence of muscle afferents from the trigeminal and upper cervical neural systems in humans, which may partly underlie the manifestations of pain referral between these two areas.

A comparison of a triple-injection axillary brachial plexus block with the humeral approach

BACKGROUND AND OBJECTIVES

This prospective, randomized, and single-blind study compared effectiveness, performance, onset, and total anesthetic time and complications of the multiple axillary block (median, radial, and musculocutaneous nerves) with the humeral approach.

METHODS

One hundred patients were randomly assigned to 2 groups. In group A (axillary) median, radial, and musculocutaneus nerves were located by a nerve stimulator and injections were made. In group H (humeral) all 4 terminal nerves of the brachial plexus were located and injections were made. A total of 40 mL mepivacaine of 1% was used.

RESULTS

Complete sensory block of all 6 peripheral nerves occurred in 94% and 79% of patients in groups A and H, respectively (P < .05). The time to perform the block was shorter in group A (8 +/- 4 minutes v 11 +/- 4 minutes; P < .001); onset time was shorter in group A (16 +/- 8 minutes v 21 +/- 9 minutes; P < .05); total anesthetic time was shorter in group A (24 +/- 8 minutes v 33 +/- 10 minutes; P < .0001). Complete motor block was greater in group A (88% v 66%; P < .05). More vascular punctures occurred in group A (22% v 8%, P < .05).

CONCLUSION

The triple-injection axillary block was more effective than the humeral approach as it was associated with more cases of sensory and complete motor block and gave shorter performance and onset times.

Referent configuration of the body: a global factor in the control of multiple skeletal muscles

In addition to local biomechanical and reflex factors influencing muscle activation, global factors may be used by the nervous system to control all muscles in a coherent and task-specific way. It has been hypothesized that a virtual or referent (R) configuration of the body determined by muscle recruitment thresholds specified by neural control levels is such a factor. Due to the threshold nature of the R configuration, the activity of each muscle depends on the difference between the actual (Q) and the R configuration of the body. The nervous system modifies the R configuration to produce movement. One prediction of this hypothesis is that the Q and R configurations may match each other, most likely in movements with reversals in direction, resulting in a minimum in the electromyographic (EMG) activity level of muscles involved. The depth of the minima is constrained by the degree of coactivation of opposing muscle groups. Another prediction is that EMG minima in the activity of multiple muscles may occur not only when the movement is assisted but also when it is opposed by external forces (e.g., gravity). To verify these predictions, we analyzed EMG patterns of 16-21 functionally diverse muscles of the legs, trunk, and arms during jumping and stepping in place. One EMG minimum in the activity of all muscles regularly occurred near the apex of the jump. A minimum was also observed near the point of transition of the body from flexion to extension leading to a jump. During stepping in place, the activity of muscles of each side of the body was usually minimized near the beginning and near the end of the stance phase as well as during the maximum elevation of the foot. Since EMG minima occurred not only during gravity-assisted but also gravity-opposed movement reversals, it is concluded that neural factors (such as matching between the Q and R) rather than mechanical factors are responsible for minimizing the EMG activity in these movements.

Motor outputs from the primate reticular formation to shoulder muscles as revealed by stimulus-triggered averaging

The motor output of the medial pontomedullary reticular formation (mPMRF) was investigated using stimulus-triggered averaging (StimulusTA) of EMG responses from proximal arm and shoulder muscles in awake, behaving monkeys (M. fascicularis). Muscles studied on the side ipsilateral (i) to stimulation were biceps (iBic), triceps (iTri), anterior deltoid (iADlt), posterior deltoid (iPDlt), and latissimus dorsi (iLat). The upper and middle trapezius were studied on the ipsilateral and contralateral (c) side (iUTr, cUTr, iMTr, cMTr). Of 133 sites tested, 97 (73%) produced a poststimulus effect (PStE) in one or more muscles; on average, 38% of the sampled muscles responded per effective site. For responses that were observed in the arm and shoulder, poststimulus facilitation (PStF) was prevalent for the flexors, iBic (8 responses, 100% PStF) and iADlt (13 responses, 77% PStF), and poststimulus suppression (PStS) was prevalent for the extensors, iTri (22 responses, 96% PStS) and iLat (16 responses, 81% PStS). For trapezius muscles, PStS of upper trapezius (iUTr, 49 responses, 73% PStS) and PStF of middle trapezius (iMTr, 22 responses, 64% PStF) were prevalent ipsilaterally, and PStS of middle trapezius (cMTr, 6 responses, 67% PStS) and PStF of upper trapezius (cUTr, 46 responses, 83% PStS) were prevalent contralaterally. Onset latencies were significantly earlier for PStF (7.0 +/- 2.2 ms) than for PStS (8.6 +/- 2.0 ms). At several sites, extremely strong PStF was evoked in iUTr, even though PStS was most common for this muscle. The anatomical antagonists iBic/iTri were affected reciprocally when both responded. The bilateral muscle pair iUTr/cUTr demonstrated various combinations of effects, but cUTr PStF with iUTr PStS was prevalent. Overall, the results are consistent with data from the cat and show that outputs from the mPMRF can facilitate or suppress activity in muscles involved in reaching; responses that would contribute to flexion of the ipsilateral arm were prevalent.

Body-centered visuomotor adaptation

Previous research has shown that humans generalize distortions of visuomotor feedback in terms of egocentric rotations. We examined whether these rotations are linked to the orientation of the eyes or of the shoulder of the arm that was used. Subjects moved a hand-held cube between target locations in a sequence of adaptation and test phases. During adaptation phases, subjects received either veridical or distorted visual feedback about the location of the cube. The distortions were changes in azimuth either relative to the eyes or to the shoulder. During test phases subjects received no visual feedback. Test phases were performed either with the arm that was exposed to the distorted feedback or with the unexposed arm. We compared test movement endpoints after distorted feedback with ones after veridical feedback. For the exposed arm, the spatial layout of the changes in endpoints clearly reflected the small differences between a rotation around the shoulder and around the eyes. For the unexposed arm, the changes in endpoints were smaller for both types of distortions and were less consistent with the distortions. Thus although the adaptation closely matches the imposed distortion, it does not appear to be directly linked to the orientation of the eyes or of the exposed arm.

Accuracy and validity of observational estimates of shoulder and elbow posture

This study investigated the accuracy of video-based observational posture analysis for the elbow and shoulder. Posture analyses were conducted by 28 ergonomists for four jobs presented on a traditional VHS format video recording. Estimates of posture from the observational-based methods were compared with values measured directly with an optical motion capture system. Ergonomists used categorical posture scales and a continuous visual analog scale to estimate the peak and most frequently occurring or average posture for each job. Use of a three-category scale resulted in misclassifications of peak and most frequently occurring elbow and shoulder posture with a probability averaging 30.1%. With the six-category posture scale this average probability of misclassification increased to 64.9%. Using a continuous visual analog scale peak shoulder elevation was the only posture for which the average error among ergonomists' estimates was significantly different from zero (p<0.05). Correlations between the estimated postures and measured postures were higher and statistically significant (p<0.05) for elbow flexion and shoulder elevation (r2 between 0.45 and 0.66) but were considerably lower and not significant (r2 between 0.03 and 0.18) for the peak and average horizontal shoulder abduction. Ergonomists' estimates of the temporal distribution of shoulder posture, indicating the duration severity of the posture, appeared to be biased such that the percentage of the cycle time in each posture category was estimated as more uniformly distributed than the measured values indicated.

Three-dimensional clavicular motion during arm elevation: reliability and descriptive data

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To determine the reliability of a surface sensor measurement of clavicular motion during arm elevation and to describe 3-dimensional clavicular motion in an asymptomatic population.

BACKGROUND

Abnormal scapular motion on the thorax has been implicated in shoulder pathology. Without the ability to measure clavicular motion, it is not possible to identify if abnormal scapular motions derive from the sternoclavicular or acromioclavicular joints.

METHODS AND MEASURES

Thirty-nine subjects participated in the investigation, including an asymptomatic group (n = 30) and a group with a history or current symptoms of shoulder pathology (n = 9). Clavicular angles relative to the thorax were tracked with surface electromagnetic sensors on the thorax, clavicle, and humerus as subjects completed humeral flexion, scapular plane abduction, and abduction. Within-day reliability was assessed using intraclass correlation coefficients and SEM. Descriptive statistics quantified sternoclavicular joint motions for the various arm movements.

RESULTS

Reliable measurements were obtained, with intraclass correlation coefficients ranging from 0.93 to 0.99, and SEMs from 0.9 degrees to 1.8 degrees. Between-day reliability SEM values were generally 2 degrees to 4 degrees. During elevation of the arm, the clavicle with respect to the thorax generally undergoes elevation (11 degrees-15 degrees maximum), retraction (15 degrees-29 degrees maximum), and posterior long-axis rotation (15 degrees-31 degrees maximum), with variability between subjects and planes of motion regarding the magnitude of motion.

CONCLUSION

Rehabilitation approaches attempting to improve shoulder motion should benefit from improved knowledge of 3-dimensional contributions of the clavicle to normal and abnormal scapular kinematics.

Muscle activity during patient transfers: a preliminary study on the influence of lift assists and experience

The purpose of this study was to examine muscle activity patterns during patient handling during manual transfers, and transfers using floor and ceiling lifts. EMG patterns during transfers from bed to wheelchair and wheelchair to bed as well as patient repositioning in novices and experienced participants were examined. Surface EMG was recorded from the upper and lower erector spinae, latissimus dorsi and trapezius muscles bilaterally. Overall, normalized mean and peak muscle activity were lowest using the ceiling lift, increasing with the floor lift, which were lower than manual transfers (novices: all p < 0.01). Experienced patient handlers demonstrated approximately two times greater trapezius and latissimus dorsi activity than novices, combined with lower mean erector spinae activity (p < 0.05, for most tasks). Integrated EMG for all muscles was directly proportional to the transfer time and was lowest during the manual transfer followed by the ceiling lift, with the floor lift being highest. The difference between the muscle activity patterns between the experienced and novice patient handlers may suggest a learned behaviour to protect the spine by distributing load to the shoulder. Further examination of the muscle activation patterns differences between experience levels could improve training techniques to develop better patient handling strategies.

Determination of worker physiological cost in workspace reach envelopes

Oxygen uptake (VO2), heart rate (HR) and myoelectric activity (EMG) were measured while performing a repetitive task in the normal, maximum and extreme workspace reach envelopes. The VO2 and HR increased significantly from the normal to the maximum to the extreme workspace reach envelope. The average increases in VO2 when compared to the normal workspace were 19 and 52%, respectively. The corresponding average increases in HR were 6 and 14%, respectively. The increase in EMG for anterior deltoid, upper trapezious and erector spinae showed a significant increase from normal to maximum and from maximum to extreme workspaces. The average increases in EMG for anterior deltoid, upper trapezious and erector spinae, compared to the normal workspace were 96, 37 and 48% respectively for the maximum workspace and 193, 95 and 106% for the extreme workspace, respectively. The research indicated for the first time that during task performance, worker physiological cost would increase significantly with the increase in workspace reach levels.

Physical workload during use of speech recognition and traditional computer input devices

Musculoskeletal symptoms among computer users are frequently found. The aim was to investigate the musculoskeletal workload during computer work using speech recognition and traditional computer input devices (keyboard/mouse). Ten experienced computer users (nine female, one male) participated. They performed three different computer tasks: (1). text entry and (2). text editing of a standard text and (3). a self-selected work task. These tasks were performed twice using speech recognition and traditional computer input devices (keyboard/mouse). Additionally, a task consisting of reading aloud of the standard text was performed. Surface EMG from the forearm (m. extensor carpi ulnaris, m. extensor carpi radialis), the shoulder (m. trapezius) and the neck extensor muscles was recorded, in addition to the voice-related muscles (m. scalenii, m. cricothyroideus). Using speech recognition during text entry and text editing reduced the static muscle activity of the forearm, neck and to some extent the shoulder muscles. Furthermore, tendencies to longer periods of muscle activity pause (relative time with EMG gaps) in the forearm and shoulder muscles were found. This was seen at the expense of a tendency to an increased static activity and a decreased relative time with EMG gaps in m. cricothyroideus. Finally, during use of speech recognition the hand was tied to the keyboard/mouse for a shorter period of time, while the eyes were viewing the screen for a longer period of time compared to the condition with traditional computer input devices. It is recommended to use speech recognition as a supplementary tool to traditional computer input devices.

Shoulder Rotation Characteristics in Professional Tennis Players

Aim of this study was to assess the glenohumeral joint internal and external rotational range of motion using an ultrasound based kinematic measurement device. Twenty-seven male professional tennis players were bilaterally measured for internal and external rotation at 90 degrees of shoulder abduction while avoiding scapulothoracic motion. The control group consisted of 20 asymptomatic volunteers not involved in overhead sports activities. The dominant arm (playing arm) had a significantly greater range of external rotation than the non-dominant arm, while their internal rotation showed a significant deficit as compared to the non-dominant arm. The dominant arm total rotational range of motion was also significantly reduced in comparison to the non-dominant arm and to the controls. No significant difference was found between the dominant and non-dominant extremity in the control group. For objective measurement of glenohumeral rotational range of motion ultrasound based real time motion analysis is a new application for the diagnostic testing of specific shoulder parameters in orthopedics and sports physical therapy. It is therefore concluded that the specific methodology aiming at isolated glenohumeral motion may have clinical application for the development of rehabilitation and preventative programs.

Outcome following nonoperative treatment of brachial plexus birth injuries

Ninety-one infants who sustained a brachial plexus birth injury were treated with only physical and occupational therapy. The children were evaluated at 3-month intervals and followed for a minimum of 2 years. Sixty-three children with an upper or upper-middle plexus injury recovered good to excellent shoulder and hand function. In all of these children, critical marker muscles recovered M4 by 6 months of age. Twelve infants sustained a global palsy, with critical marker muscles remaining at M0-M1 at 6 months, resulting in a useless extremity. Sixteen infants with upper and upper-middle plexus injuries failed to recover greater than M1-M2 deltoid and biceps by 6 months, resulting in a very poor final outcome. These data provide useful guidelines for selection of infants for surgical reconstruction to improve ultimate outcome.

Rhythmic and discrete elements in multi-joint coordination

Everyday actions invariably consist of a combination of discrete and rhythmic elements within or across joints. The study investigated constraints arising from the co-occurrence of the two actions in a two-joint task and how endpoint trajectories are shaped due to these action elements at the joint level. The task consisted of an elbow oscillation in the plane that was to be merged with a fast discrete adduction or abduction in the shoulder triggered by an auditory signal. The task was performed with and without explicit instruction about the joint involvement. Two hypotheses were tested: (1) kinematic constraints for the coupling of discrete and rhythmic elements arise at the neuro-muscular level, such that EMG bursts of the discrete and rhythmic movement have a tendency to synchronize. This effect was documented previously in a comparable single-joint task. (2) The merging of the two elements is constrained by intersegmental torques such that initiation and performance of the discrete movement utilizes interaction torques. This hypothesis rests on the assumption that the CNS has an internal model of the limb dynamics and exploits passive torques. Key results support hypothesis 1: (i) the discrete action's initiation at the shoulder was constrained to a preferred phase of the ongoing elbow oscillation. (ii) The rhythmic elbow movement showed a systematic phase advance during the discrete shoulder shift, similar to those reported for the single-joint variant of the task. Reaction times of the discrete movement were longer and peak velocities slower than reported for isolated discrete movements, due to the simultaneous presence of the oscillation. (iii) Interaction torques acting from the elbow onto the shoulder joint were not selectively exploited for the acceleration of the discrete shoulder movement. Indirectly however, hypothesis 2 also found support: torques at the elbow generated compensatory muscle activity in the shoulder that stabilized the stationary joint. It was this rhythmic activity that posed the direct constraints on the initiation of the discrete movement.

Mechanical loading of the low back and shoulders during pushing and pulling activities

The objective of this study was to quantify the mechanical load on the low back and shoulders during pushing and pulling in combination with three task constraints: the use of one or two hands, three cart weights, and two handle heights. The second objective was to explore the relation between the initial and sustained exerted forces and the mechanical load on the low back and shoulders. Detailed biomechanical models of the low back and shoulder joint were used to estimate mechanical loading. Using generalized estimating equations (GEE) the effects were quantified for exerted push/pull forces, net moments at the low back and shoulders, compressive and shear forces at the low back, and compressive forces at the glenohumeral joint. The results of this study appeared to be useful to estimate ergonomics consequences of interventions in the working constraints during pushing and pulling. Cart weight as well as handle height had a considerable effect on the mechanical load and it is recommended to maintain low cart weights and to push or pull at shoulder height. Initial and sustained exerted forces were not highly correlated with the mechanical load at the low back and shoulders within the studied range of the exerted forces.

Figure Skating

The purpose of this study was to compare triple (T) and quadruple (Q) toe-loop figure skating jumps and quantify basic characteristics of these jumps to provide information to coaches that will assist them in teaching quadruple toe-loops to elite figure skaters. High-speed video was taken during men's practice and competition sessions at the 2002 Salt Lake City Winter Olympics; three-dimensional analyses of selected triple and quadruple jumps were completed. The most significant difference between triple and quadruple toe-loops was an increase in rotational velocity in the air. Additionally, increased vertical velocity at take-off and subsequent time in the air were also observed. Three main conclusions were developed: 1) The timing of rotation of the hips and shoulders was different for quadruple toe-loops compared to triples with the differences being observed before toe-pick; 2) Increases in rotational velocity occurred primarily as a result of the skaters assuming different body positions from take-off through landing which resulted in tighter rotating positions for longer durations of the jump; 3) Greater vertical velocity was gained during the propulsive phase due to the extension of the legs during the press off the ice.

Baseball

Efficient, sequential timing is essential for upper level pitching. Interestingly, pitchers vary considerably in timing related elements of pitching style including pelvis rotation, arm cocking, stride leg behaviour, and pitch delivery time. The purpose of this study was to determine whether relationships exist among these elements by examining the overall style of pitchers exhibiting different pelvis rotation patterns. Pitching styles were defined by pelvis orientation at the instant of stride foot contact. Pitchers demonstrating a pelvis orientation greater than 30 degrees were designated as 'early rotators', while pitchers demonstrating a pelvis orientation less than 30 degrees were designated as 'late rotators'. Kinematic and temporal differences were associated with the two styles. During the arm cocking phase, early rotators showed significantly greater shoulder external rotation at the instant of stride foot contact, earlier occurrence of maximum pelvis rotation angular velocity, and shorter time taken to complete the phase. However, by the instant of maximum shoulder external rotation, early and late rotators appeared remarkably similar as no significant difference occurred in pelvis and arm orientations. Therefore, it appears that early and late rotators used different methods to achieve similar results, including throwing velocity. Significant differences in throwing arm kinetics were also found for 10 of the 11 measures in the study. As the pelvis assumed a more open position at stride foot contact, maximum kinetic values were found to both decrease in magnitude and occur at an earlier time within the pitch.

A biomechanical evaluation of the role of labrum on anterior/posterior translation of shoulders at different degrees of abduction

The objective of the study was to investigate the effects of anterior and posterior labrums on the anterior/posterior translations of shoulders. Thirteen cadaver shoulders were arthroscopically evaluated and nine were selected based on the absence of any pathological findings. These shoulders were tested intact, vented and after sequential arthroscpoic incision of the anterior and posterior labrums. The anterior/posterior translations were measured in a specially designed apparatus. The loads vs. displacement curves were obtained. The loads vs. displacement curves of the shoulders before and after labrum incision did not show any appreciable differences. Moreover the measured loads at 6 mm displacement did not show any statistically significant differences due to labrum incision. It was concluded that both anterior and posterior labrum incisions of the shoulders did not show any appreciable differences in anterior/posterior laxity. An arthroscopic technique was successfully developed to isolate the effect of labrum on the shoulder laxity.

Scoring systems for the functional assessment of the shoulder

A number of instruments have been developed to measure the quality of life in patients with various conditions of the shoulder. Older instruments appear to have been developed at a time when little information was available on the appropriate methodology for instrument development. Much progress has been made in this area, and currently an appropriate instrument exists for each of the main conditions of the shoulder. Investigators planning clinical trials should select modern instruments that have been developed with appropriate patient input for item generation and reduction, and established validity and reliability. Among the other factors discussed in this review, responsiveness of an instrument is an important consideration as it can serve to minimize the sample size for a proposed study. The shoulder instruments reviewed include the Rating Sheet for Bankart Repair (Rowe), ASES Shoulder Evaluation Form, UCLA Shoulder Score, The Constant Score, Disabilities of the Arm, Shoulder and Hand (DASH), the Shoulder Rating Questionnaire, the Simple Shoulder Test (SST), the Western Ontario Osteoarthritis of the Shoulder Index (WOOS), the Western Ontario Rotator Cuff Index (WORC), the Western Ontario Shoulder Instability Index (WOSI), Rotator Cuff Quality of Life (RC-QOL), and the Oxford Shoulder Scores (OSS).