Shoulder Extensors Research Articles

Coordination of Activity of the Shoulder Belt and Shoulder Muscles in Humans During Bimanual Synchronous Two-Joint Movements

We examined coordination of EMG activity of flexors and extensors of the shoulder and elbow joints during realization of synchronous bimanual ramp-and-hold movements within a horizontal plane similar to those in the course of rowing. A tested subject moved handles of two levers rotating on the vertical axes and traced a trajectory of the command signal presented on a monitor. Test movements included displacements of the lever handles “to the chest” (TCh) and “from the chest” (FCh) (durations 0.4, 1.0, or 2.0 sec), separated by a phase of fixation of the extremum position after the first phase (duration 6.0 sec); the amplitude of turns of the levers was equal to 30 deg. The movements were realized under conditions of application of external loadings (33–28 and 19–15 N) having FCh or TCh directions. During realization of the movements, EMG activity of the shoulder belt and shoulder muscles was recorded bilaterally; patterns of rectified and integrated EMGs were considered correlates of the central motor commands (CMCs) coming to the corresponding muscles. Analysis of EMGs recorded from 12 muscles (six for each limb) demonstrated that the activity of the latter is coordinated in a rather complex mode. The peculiarities of functional interactions (synergies) of muscles during coordinated displacements of the shoulder links and forearms under conditions of realization of the above-mentioned test movements are described. Significant effects of the velocity factor on the dynamic components of CMCs addressed to the examined muscles were observed. In each muscle, statistically significant differences between the EMG amplitudes during realization of the TCh and FCh movements were found. Differences between the dynamic and static EMG components under the action of external loadings of opposite directions were also significant. It was found that, in the course of realization of the movements, CMCs coming to the elbow flexors were more variable (flexible) compared with CMCs directed toward shoulder extensors. With increase in the duration of active phases of the test movement, the amplitude of these phases (D1 and D2) in EMGs of all examined muscles decreased at both directions of the external loading. The dependence of stationary EMG levels on the direction of action of this loading has been also demonstrated. Static components of EMG activity of all muscles were considerably greater at extending loadings compared to those at flexing ones.

Effects of a Short Physical Exercise Intervention on Patients with Multiple Sclerosis (MS).

Background: The aim of this prospective randomized controlled trial was to investigate if a short-term endurance or combined endurance/resistance exercise program was sufficient to improve aerobic capacity and maximum force in adult patients (18–65 years) with multiple sclerosis (MS). Methods: All patients performed a three-month exercise program consisting of two training sessions per week, lasting 40 min each, with moderate intensity. All patients had a maximum value of 6 (low to moderate disability) on the Expanded Disability Status Scale (EDSS). One group (combined workout group (CWG); 15 females, 4 males) completed a combined endurance/resistance workout (20 min on a bicycle ergometer, followed by 20 min of resistance training), while the other group (endurance workout group (EWG); 13 females, 5 males) completed a 40 min endurance training program. Aerobic capacity was assessed as peak oxygen uptake, ventilatory anaerobic threshold, and workload expressed as Watts. Maximum force of knee and shoulder extensors and flexors was measured using isokinetic testing. Quality of life was assessed with the SF-36 questionnaire, and fatigue was measured using the Modified Fatigue Impact Scale. Results: Both training groups increased in aerobic capacity and maximum force. EWG, as well as CWG, showed improvement in several subscales of the SF-36 questionnaire and decrease of their fatigue. Conclusion: A short exercise intervention increased both aerobic capacity and maximum force independent of whether endurance or combined endurance/resistance workouts were performed.

Change in pitching biomechanics in the late-inning in Taiwanese high school baseball pitchers.

Repetitive overhead throwing may result in overuse injuries and a change in the pitching mechanics of a baseball pitcher. Accordingly, the purpose of this study is to quantify the changes in the muscle strength and pitching motion kinematics in the late-innings stage of a baseball game. Sixteen healthy baseball pitchers (16.77 ± 0.73 years) recruited from a high school, which won the National High School Baseball Championship in Taiwan in 2011; each performed 100 pitches in a bullpen throwing session. Isometric muscle strength measurements and joint kinematic data were obtained before and after the throwing session. The mean Borg's Rating of Perceived Exertion index was found to have a value of 14.14, indicating a medium-to-large degree of perceived tiredness. The results showed that the ball velocity and horizontal abduction angle decreased significantly as the pitchers became tired. Moreover, the upper torso forward tilt and knee flexion angle both increased significantly at the moment of ball release. Finally, the muscle strength of the upper extremity remained decreased 2 days after the bullpen throwing session. Overall, the results suggest that an adequate amount of rest and specific strengthening programs for the shoulder external rotator, shoulder internal rotator, shoulder flexor, shoulder extensor, shoulder adductor, and shoulder abductor muscles are recommended to the coaches and for adolescent baseball pitchers. In addition, the changes in pitching mechanics noted in this study should be carefully monitored during the course of a baseball game to minimize the risk for overuse injuries.

Muscle Activation Pattern During Isometric Ab Wheel Rollout Exercise in Different Shoulder Angle-Positions

OBJECTIVE: To investigate muscle activation of the shoulder extensors and trunk stabilizers by surface electromyography (sEMG) activity during the isometric Ab Wheel Rollout exercise in different shoulder joint positions. METHOD: We recruited 8 young, healthy, resistance trained men (age: 25 ± 3 years, height: 178 ± 5 cm, and total body mass: 81 ± 2 kg). All subjects performed two sets of 10 sec. maximal isometric contractions of the Ab Wheel Rollout exercise keeping the knees fixed on the floor and the arms taut. To perform the exercise, all subjects were randomly assessed in the following three positions related to the angle between the arms and trunk, in random order: arms aligned vertically with the Ab Wheel Rollout exercise (neutral); 90o and 150o. A rest period of 5 minutes was provided between tests. The sEMG signals were recorded in the following muscles: Latissimus Dorsi; Pectoralis Major; Erector Spinae; Rectus Abdominis. RESULTS: There were significant increases in Rectus Abdominis muscle activity between: neutral vs. 90o, neutral vs. 150o and 90o vs. 150o. There was a significant increase in Pectoralis Major muscle activity between neutral x 150o. CONCLUSION: The present findings indicate that (a) Ab Wheel Rollout exercise emphasizes the muscle action of the Pectoralis Major and Rectus Abdominis more than the Latissimus Dorsi and Erector Spinae; (b) the level of muscle activation depends on the external force created by the body mass and lever arm from the center of mass.

Fast feedback control involves two independent processes utilizing knowledge of limb dynamics

Corrective muscle responses occurring 50-100 ms after a mechanical perturbation are tailored to the mechanical features of the limb and its environment. For example, the evoked response by the shoulder's extensor muscle counters an imposed shoulder torque, rather than local shoulder motion, by integrating motion information from the shoulder and elbow appropriate for their dynamic interaction. Previous studies suggest that arm muscle activity within this epoch, alternately termed the R2/3 response, or long-latency reflex, reflects the summed result of two distinct components: an activity-dependent component which scales with the background muscle activity, and a task-dependent component which scales with the required vigor of the behavioral task. Here we examine how the knowledge of limb dynamics expressed during the shoulder muscle's R2/3 epoch is related to these two functional components. Subjects countered torque steps applied to their shoulder and/or elbow under different conditions of background torque and target size to recruit the activity-dependent and task-dependent component in varying degrees. Experiment 1 involved four torque perturbations, two levels of background torques and two target sizes; this design revealed that both background torque and target size impacted the shoulder's R2/3 activity, indicative of knowledge of limb dynamics. Experiment 2 involved two perturbation torques, five levels of background torque and two target sizes; this design demonstrated that the two factors had an independent impact on the R2/3 activity indicative of knowledge of limb dynamics. We conclude that a sophisticated feature of upper limb feedback control reflects the summation of two processes having a common capability.

Relationship between muscle strength and front crawl swimming velocity

PurposeCompetitive performance in swimming depends on a number of factors including, among others, the development of relevant muscle groups. The aim of the study was to clarify the relationship between muscle strength and swimming velocity and the role of individual muscle groups in front crawl swimming.MethodsSixteen physical education university students participated in the study. The strength values, defined as torque produced during isometric contractions, of eight upper and lower extremity muscle groups were measured. Data were compared with participants' front crawl swim times in the 25m and 50m distances.ResultsCorrelation analysis demonstrated a relationship between muscle strength and swimming velocity. statistically significant relationships were observed between swimming velocity and the torque values of the elbow flexor and shoulder extensor muscles as well as the sum of upper extremity muscle torque values (<i>p</i> < 0.05).ConclusionsThe results indicate the need for a focus on training those muscle groups identified as having a statistically significant relationship with swimming velocity for a given distance, as the sample showed deficiencies in the strength of those muscle groups responsible for generating propulsive force in the front crawl. Additionally, the collected data can serve as a diagnostic tool in evaluating the development of muscle groups critical for swimming performance.

Assessment of function in patients with rotator cuff tears: Functional test versus self-reported questionnaire.

Purpose:The rotator cuff tears (RCT) are a well-known cause of shoulder pain and loss of upper extremity function. The purpose of this study was to evaluate the upper extremity function using two different methods in patients with RCT and to determine the parameters that influence the upper extremity function.Materials and Methods:A sample of 38 patients (27-76 years; 10 men and 28 women) who were diagnosed with a chronic full-thickness RCT, confirmed by magnetic resonance imaging (MRI), was studied. Upper extremity function was determined using Western Ontario Rotator Cuff Index (WORC) and 9 Hole Peg Test (9PEG). Other assessments included active range of motion (ROM), muscle strength, shoulder pain, and scapular dyskinesis.Results:There was a weak association between WORC scores and 9PEG. A statistically significant, negative relationship was found between 9PEG and ROM in supination, as well as muscle strength of shoulder extensors, adductors, internal and external rotators.Conclusions:In addition to the weak association between WORC and 9PEG, the difference between the parameters related to each method suggests that they should not be used interchangeably to determine the upper extremity function. We recommend the utilization of 9PEG instead of WORC in assessing the upper extremity function in the setting of loss of muscle strength.Level of Evidence:Level IV, Therapeutic study.

Cerebellar damage diminishes long-latency responses to multijoint perturbations

Damage to the cerebellum can cause significant problems in the coordination of voluntary arm movements. One prominent idea is that incoordination stems from an inability to predictively account for the complex mechanical interactions between the arm's several joints. Motivated by growing evidence that corrective feedback control shares important capabilities and neural substrates with feedforward control, we asked whether cerebellar damage impacts feedback stabilization of the multijoint arm appropriate for the arm's intersegmental dynamics. Specifically, we tested whether cerebellar dysfunction impacts the ability of posterior deltoid to incorporate elbow motion in its long-latency response (R2 = 45-75 ms and R3 = 75-100 ms after perturbation) to an unexpected torque perturbation. Healthy and cerebellar-damaged subjects were exposed to a selected pattern of shoulder-elbow displacements to probe the response pattern from this shoulder extensor muscle. The healthy elderly subjects expressed a long-latency response linked to both shoulder and elbow motion, including an increase/decrease in shoulder extensor activity with elbow flexion/extension. Critically, cerebellar-damaged subjects displayed the normal pattern of activity in the R3 period indicating an intact ability to rapidly integrate multijoint motion appropriate to the arm's intersegmental dynamics. However, cerebellar-damaged subjects had a lower magnitude of activity that was specific to the long-latency period (both R2 and R3) and a slightly delayed onset of multijoint sensitivity. Taken together, our results suggest that the basic motor pattern of the long-latency response is housed outside the cerebellum and is scaled by processes within the cerebellum.

Effect of Strengthening Exercises of Shoulder Muscles on Hand Functions in Spastic Hemiplegic Cerebral Palsied Children

Objective: To determine the effect of strengthening exercises of shoulder muscles on hand functions in spastic hemiplegic cerebral palsied children. Methods: The study was carried out on thirty spastic hemiplegic children of both sexes (15 females and 15 males) divided into equal groups A and B. Their age ranged from six to ten years old. The muscular strength of shoulder flexors and extensors were evaluated by Biodex isokinetic dynamometer. Their hand functions were evaluated by using Peadody developmental motor scales(PDMS).prior and after six months of rehabilitation program. Group A received the traditional physiotherapy program. While group B received strengthening exercises program for shoulder muscles in addition to the traditional physiotherapy program . Results: Patients of group (B) improved in age equivalent of grasping by 42.4% with SD 1.27±0.46, Values of peak torque (flexion) improved 8.9 with SD 10.29±1.04 and values of peak torque (extension) improved 1.57 with SD 9.92±0.63 Conclusion: The study showed significant improvement in group B more than group A. for age equivalent of grasping and peak torque of flexors and extensors of shoulder muscles.

Deliberate utilization of interaction torques brakes elbow extension in a fast throwing motion

We tested the hypothesis that in fast arm movements the CNS deliberately utilizes interaction torques to decelerate (brake) joint rotations. Twelve subjects performed fast 2-D overarm throws in which large elbow extension velocities occurred. Joint motions were computed from recordings made with search coils; joint torques were calculated using inverse dynamics. After ball release, a large follow-through shoulder extension acceleration occurred that was initiated by shoulder extensor muscle torque. This shoulder acceleration produced a flexor interaction torque at the elbow that initiated elbow deceleration (braking). An instantaneous mechanical interaction of passive torques then occurred between elbow and shoulder, i.e., elbow extension deceleration produced a large shoulder extensor interaction torque that contributed to the shoulder extension acceleration which, simultaneously, produced a large elbow flexor interaction torque that contributed to elbow extension deceleration, and so on. Late elbow flexor muscle torque also contributed to elbow deceleration. The interaction of passive torques between shoulder and elbow was braked by shoulder flexor muscle torque. In this mechanism, shoulder musculature contributed to braking elbow extension in two ways: shoulder extensors initiated the mechanical interaction of passive torques between shoulder and elbow and shoulder flexors dissipated kinetic energy from elbow braking. It is concluded that, in fast 2-D throws, the CNS deliberately utilizes powerful interaction torques between shoulder and elbow to brake motion at the elbow.

Individual muscle contributions to push and recovery subtasks during wheelchair propulsion

Manual wheelchair propulsion places considerable physical demand on the upper extremity and is one of the primary activities associated with the high prevalence of upper extremity overuse injuries and pain among wheelchair users. As a result, recent effort has focused on determining how various propulsion techniques influence upper extremity demand during wheelchair propulsion. However, an important prerequisite for identifying the relationships between propulsion techniques and upper extremity demand is to understand how individual muscles contribute to the mechanical energetics of wheelchair propulsion. The purpose of this study was to use a forward dynamics simulation of wheelchair propulsion to quantify how individual muscles deliver, absorb and/or transfer mechanical power during propulsion. The analysis showed that muscles contribute to either push (i.e., deliver mechanical power to the handrim) or recovery (i.e., reposition the arm) subtasks, with the shoulder flexors being the primary contributors to the push and the shoulder extensors being the primary contributors to the recovery. In addition, significant activity from the shoulder muscles was required during the transition between push and recovery, which resulted in increased co-contraction and upper extremity demand. Thus, strengthening the shoulder flexors and promoting propulsion techniques that improve transition mechanics have much potential to reduce upper extremity demand and improve rehabilitation outcomes.

Feasibility and reproducibility of muscular strength measures in gymnastics-specific body positions using hand-held dynamometry

This study aimed to determine feasibility and reproducibility of muscular strength measurements in young gymnasts, using hand-held dynamometry in gymnastics-specific body positions. A group of 32 male and female young gymnasts 8-11 years-old, performed different strength tests using a Nicholas Manual Muscle Tester (NMMT). The measurements were collected in 4 major muscle groups (shoulder flexors and extensors, hip flexors and extensors) at 22 different joint angular positions, with the active elbow or knee joint in full extension. The maximal strength was obtained by placing the NMMT in a distal forearm or shank position, with the gymnast in supine or prone position stabilized on a vault. A Myrin goniometer, attached on the sagittal plane near elbow or knee joint, was used to specify the shoulder and hip joint angular positions. In the majority of the measurements (18 out of 22 angular positions) the intra-class correlation coefficients revealed a good level of test-retest reliability (R = 0.80-0.88). In four cases (3 in shoulder flexors and 1 in shoulder extensors) intra-class reliability was fair, with R-values ranging from 0.70 to 0.78. The low coefficients of variation and standard errors of measurements affirmed the reproducibility of measurements. In conclusion, this study showed the feasibility and the reproducibility of shoulder and hip flexor and extensor muscles maximal strength measurements using NMMT in gymnastics-based settings.

Within-day and between-days reproducibility of isokinetic parameters of knee, trunk and shoulder movements

The purpose of this study was to examine the within-day and between-days reproducibility of isokinetic parameters of knee, shoulder and trunk movements. Ten healthy males (age 30 ± 8 years, height 1.79 ± 0.05 m, body mass 79.4 ± 8.3 kg) performed isokinetic concentric contractions (knee: 60 and 180 ◦ /s; shoulder: 60 and 180 ◦ /s: and; trunk: 15 and 60 ◦ /s) at 0 (baseline), 2, 24, 48 and 72 hours. Reproducibility of the baseline peak moment, mean peak moment and maximum work was assessed using Bland and Altman limits of agreement and pre-planned paired t-tests ( P< 0.05). Peak moment of knee, trunk and shoulder extensors at low velocities had highest reproducibility within and between days over a time period of 3 days. Peak moment at high and low velocities of knee extensors was consistently the most reliable parameter over a 3 day period. It is concluded that isokinetic parameters can be reproducibly measured in a combined session of knee, shoulder and trunk movements in healthy male subjects over a 3-day time period.

Long-Latency Responses During Reaching Account for the Mechanical Interaction Between the Shoulder and Elbow Joints

Although considerable research indicates that reaching movements rely on knowledge of the arm's mechanical properties and environment to anticipate and counter predictable loads, far less research has examined whether this degree of sophistication is present for on-line corrections during reaching. Here we examine the R2/3 response to mechanical perturbations (45-100 ms, also called the long-latency reflex), which is highly flexible and includes the fastest possible contribution from primary motor cortex, a key neural substrate for self-initiated action. Torque perturbations were occasionally and unexpectedly applied to the subject's shoulder and/or elbow in the course of performing reaching movements. Critically, these perturbations would evoke different patterns of feedback corrections from a shoulder extensor muscle if it countered only the local shoulder displacement relative to unperturbed motion or accounted for the mechanical interactions between the shoulder and elbow joints and countered the underlying shoulder torque. Our results show that the earliest response (R1: 20-45 ms) reflected local shoulder displacement, whereas the R2/3 response (45-100 ms) reflected knowledge of multijoint dynamics. Moreover, the same pattern of feedback occurred whether the shoulder muscle helped initiate the movement (during its agonist phase) or helped terminate the movement (during its antagonist phase). These results contribute to the accumulating evidence that highly sophisticated feedback control underlies motor behavior and are consistent with a shared neural substrate, such as primary motor cortex, for feedforward and feedback control.

Earth-Referenced Handrail Contact Facilitates Interlimb Cutaneous Reflexes During Locomotion

The purpose of this study was to investigate whether the gating of interlimb cutaneous reflexes is altered by holding an earth-referenced handrail during locomotion. In the first experiment, subjects performed locomotor tasks of varying difficulty (level walking, incline walking, and stair climbing) while lightly holding an earth-referenced rail. In the second experiment, the extent of rail contact and nature of the rail stability (e.g., fixed vs. mobile rail) were varied while subjects performed incline walking. Cutaneous reflexes were evoked by delivering trains of electrical stimulation to the sural nerve at the ankle. EMG data were collected continuously from muscles in the upper and lower limbs and trunk. Results showed that modulation of reflexes across the body changed when the rail was held. Most interestingly, a facilitatory reflex in the shoulder extensor posterior deltoid emerged during swing phase only when subjects held a rail. This facilitatory reflex was largest during the more challenging tasks of incline walking and stair climbing, A similar reflex facilitation was observed in the elbow extensor triceps brachii. The observed facilitation of reflexes in triceps brachii and posterior deltoid was specifically expressed only when subjects held an earth-referenced rail. This suggests that interlimb reflexes in arm extensors may be enhanced to make use of a supportive handrail for stability during gait. Therefore, holding a rail may cause global changes in reflex thresholds across the body that may have widespread functional relevance for assisting in the maintenance of postural stability during locomotion.

Muscle architecture of biceps brachii, triceps brachii and supraspinatus in the horse

Three muscles from the proximal equine forelimb were dissected in order to investigate their potential to contribute to proximal limb mechanics. Muscle mass, fibre length, tendon mass and tendon length were measured from biceps brachii, triceps brachii, supraspinatus and lacertus fibrosus (biceps lateral head mass 171-343.4 g and fibre length 0.5-0.8 cm; biceps medial head mass 283-500 g and fibre length 2.2-4 cm; biceps tendon mass 121.8-260 g and tendon length 35-44 cm; triceps long head mass 3200-6663 g and fibre length 19-26.3 cm; triceps lateral head mass 513.8-1240 g and fibre length 17.5-24 cm; triceps medial head mass 85.2-270.6 g and fibre length 9-16.8 cm; supraspinatus mass 793-1546 g and fibre length 4.7-12.4 cm; lacertus fibrosus mass 4.6-12.4 g and length 10-16 cm). Physiological cross-sectional area (PCSA) and maximum isometric force were estimated for each muscle, and moment arm measurements were taken at the shoulder and elbow joints. Biceps has a greater isometric force-generating capacity than supraspinatus. It also appears to have a larger shoulder moment arm, so could therefore have the potential to make a greater contribution to the shoulder moment than supraspinatus. Supraspinatus is likely to function primarily as a shoulder stabilizer rather than a shoulder extensor. Biceps also functions as an elbow flexor and data here indicate that it has a greater PCSA and isometric force-generating capacity than its antagonist triceps brachii. Calculation of tendon forces showed that the biceps tendon can withstand much greater forces than lacertus fibrosus. This study will enable further investigation into the interaction between energy recycling in elastic tissues and the generation and absorption of mechanical work by adjacent muscle groups in the equine forelimb.

Reliability of the Modified Tardieu Scale and the Modified Ashworth Scale in adult patients with severe brain injury: a comparison study

To assess and to compare the reliability of the Modified Tardieu Scale with the Modified Ashworth Scale in patients with severe brain injury and impaired consciousness. Cross-sectional observational comparison study. An early rehabilitation centre for adults with neurological disorders. Thirty patients with impaired consciousness due to severe cerebral damage of various aetiologies. MEASUREMENT PROTOCOL: Four experienced physical therapists rated each patient in a randomized order once daily for two consecutive days. Shoulder, elbow, wrist, hip, knee and ankle spasticity were assessed by the use of Modified Tardieu Scale and Modified Ashworth Scale data collection procedures. Test-retest and inter-rater reliability (kappa = kappa value) of the Modified Tardieu Scale and the Modified Ashworth Scale. The test-retest reliability of the Modified Ashworth Scale was moderate to good (kappa = 0.47-0.62) and of the Modified Tardieu Scale moderate to very good (kappa = 0.52-0.87). Test-retest reliability was significantly higher within the Modified Tardieu Scale in comparison with the Modified Ashworth Scale (Z > 1.96; p < 0.05) except for shoulder extensor and internal rotator muscles (Z < 1.96; p > 0.05). Although inter-rater reliability of both scales was poor to moderate (Modified Ashworth Scale: kappa = 0.16-0.42; Modified Tardieu Scale: kappa = 0.29-0.53), significantly higher K-values were revealed with the Modified Tardieu Scale for all tested muscle groups (Z > 1.96; p < 0.05) except for wrist extensors (Z < 1.96; p > 0.05). In patients with severe brain injury and impaired consciousness the Modified Tardieu Scale provides higher test retest and inter-rater reliability compared with the Modified Ashworth Scale and may therefore be a more valid spasticity scale in adults.

A Mechanism for Power Output of the Upper Limbs During Overhead Throw with Stretch-Shortening Cycle

The purpose of this study was to investigate the effect of the stretch-shortening cycle (SSC) on power output in overhead throwing and on the behavior of shoulder extensor muscles by means of kinematics, kinetics and EMG. Thirteen healthy men performed two kinds of medicine ball throw; concentric throw (CT) without SSC and rebound throw (RT) with SSC. All throws were videotaped using a high-speed camera. Kinematics and kinetics such as joint angle, joint torque and joint torque power of the upper limbs were calculated utilizing the inverse dynamics approach. The EMG activities of trapezius, latissimus dorsi, deltoid, pectoralis major and triceps brachii muscles were recorded using surface electrodes. Mean ball power in RT was significantly higher than that in CT. There was a significant correlation between augmentation of mean ball power and that of mean shoulder joint torque power in RT compared with CT. The EMG activities of pectoralis major and triceps brachii muscles showed nearly no activity during the shoulder flexion phase. These results suggest that although enhancement of power by overhead throwing using upper limb muscles was mainly caused by the enhancement of shoulder joint torque power, the shoulder extensor muscles are not eccentrically contracted but passively stretched during shoulder flexion phase in throwing. This finding contradicts a previously proposed mechanism of power enhancement in SSC.

Target-dependent differences between free and constrained arm movements in chronic hemiparesis.

This study compares the kinematic and kinetic characteristics of constrained and free upper limb movements in eight subjects with chronic hemiparesis. Movements of the dominant and nondominant limbs were also examined in five control subjects. Rapid movements were performed in the horizontal plane from a central starting point to five targets located to require various combinations of flexion/extension rotations at the elbow and shoulder. Support of the upper limb against gravity loading was provided either by a low-friction air-bearing apparatus (constrained condition) or by voluntary generation of abduction and external rotation torques at the shoulder (free condition). Data analysis focused on the peak joint torques generated during the acceleratory phase of movement, and on the net change in joint angles at the elbow and shoulder. We found that movement parameters were broadly invariant with support condition for either limb of control subjects, as well as for the nonparetic limb of hemiparetic subjects. In contrast, support condition had a target-dependent effect on movements of the paretic limb. Relative to the constrained condition, peak torques for free arm movements were significantly reduced for distal targets requiring elbow extension and/or shoulder flexion torques. However, peak elbow flexion and shoulder extension joint torques for proximal targets were relatively unaffected by support condition. Of perhaps more functional importance, free movements were characterized by a target-dependent restriction in the hand's work area that reflected a reduced range of active elbow extension, relative to constrained movements. The target-dependent effects of support condition on movements of the paretic limb are consistent with the existence of abnormal constraints on muscle activation patterns in subjects with chronic hemiparesis, namely an abnormal linkage between activation of the elbow flexors and shoulder extensors, abductors, and external rotators.

Gymnastics

The purpose of the study was to quantify the muscle torques required in the performance of an optimised Yurchenko layout vault based on a five‐segment rigid link model and using input data from an elite female gymnast. At impact, the wrist torque trajectory indicated an extension‐flexion action while the shoulder was characterised by extension. The approximate 100 Nm (wrist flexor) and 125 Nm (shoulder extensor) respective peak torque magnitudes indicated that the impact action is not passive in nature. The contribution of joint torques to the adjoining segments was apportioned to the relative components namely; centripetal, gravity and net joint torque components. Despite the presence of both large wrist and shoulder joint torques, the net turning effect on the upper limb and hand segments about their centre of mass (CM) was small. The principal role of the upper limb joint torques was therefore to effect the appropriate joint motions and to support the weight of the gymnast. The performance of the optimum vault was primarily the result of the interplay between the centripetal and the net joint torque components at the wrist, hip and shoulder joints. This has implications to the performer in that successful execution of the vault is principally concerned with the ability to create a high angular momentum for horse impact and to then apply an appropriate level of joint torques that will make optimal use of the initial kinetic condition.