Horizontal Flexion Research Articles

Relationship of Physical Factors to the Occurrence of Injuries in Young Gymnasts.

There is a large population of young athletes who participate in gymnastics, and the prevention of injury in junior athletes is considered important. However, few studies have prospectively investigated the relationship between physical factors and the occurrence of injury. To investigate the physical characteristics that are factors in the injury occurrence in elementary and junior high school gymnasts. Prospective observational study. A total of 36 healthy young gymnasts (at national competition level) were enrolled in the study. Once a week for 23 weeks, injuries were prospectively investigated using self-report questionnaires under the supervision of a research staff. Joint range of motion (hip, ankle, shoulder, and wrist), tightness (Thomas test, Ely test, straight leg raise [SLR], triceps surae, combined abduction test [CAT], horizontal flexion test [HFT]), and muscle elasticity (multifidus) were assessed to compare differences in physical function between injured and non-injured participants. Injuries occurred most commonly in the wrist (42.1%), lower back (30.2%), and foot (9.5%) among males, whereas heel (22.2%), knee (16.0%), and lower back (12.8%) were the most common injury sites among females. Wrist injuries in male athletes showed decreased shoulder joint range of motion, and lower back injuries showed decreased hip and shoulder joint range of motion. Lower back injuries in female athletes showed decreased hip extension mobility. Heel and knee joint injuries in females also showed increased range of motion and decreased tightness. The results of this study indicate that the factors related to flexibility differ according to injury location. Further studies are required to clarify the physical factors that influence injury occurrence by examining the effects of the gymnasts' muscle strength, age, individual factors, and left-right differences. 3.

The moment arms and lines of action of subscapularis after the Latarjet procedure.

The Latarjet procedure is an established surgical treatment for recurrent glenohumeral joint instability with glenoid bone loss. Intraoperatively, the conjoint tendon and its attachement on the coracoid bone graft is routedthrough a split in subscapularis where the graft is fixed to and augments the anteroinferior glenoid. The objective of this in vitro study was to quantify the influence of glenohumeral joint position and conjoint tendon force on the lines of action and moment arms of subscapularis muscle sub-regions after Latarjet surgery. Eight fresh-frozen, entire upper extremities were mounted onto a testing apparatus, and a cable-pulley system was used to apply physiological muscle loading to the major shoulder muscles. The lines of action and moment arms of four subregions of subscapularis (superior, mid-superior, mid-inferior, and inferior) were quantified radiographically with the conjoint tendon unloaded and loaded while the shoulder was in (i) 0° abduction (ii) 90° abduction (iii) 90° abduction and full external rotation (ABER), and (iv) the apprehension position, defined as ABER with 30° horizontal extension. Conjoint tendon loading after Latarjet surgery significantly increased the inferior inclination of the lines of action of the mid-inferior and inferior subregions of subscapularis in the scapular plane in ABER and apprehension positions (p < 0.001), as well as decreased the horizontal flexion moment arm of the inferior subscapularis (p = 0.040). Increased subscapularis inferior inclination may ultimately increase inferior joint shear potential, while smaller horizontal flexion leverage may reduce joint flexion capacity. The findings have implications for Latarjet surgical planning and postoperative rehabilitation prescription.

Quantifying the Effects of American Football Shoulder Pads on Reach Distance and Player Perception of Comfort and Fit

Background: The majority of sports equipment research to date has focused on their protective capabilities, and not on how they impact player performance and comfort while using them. Objective: The purpose of this study was to quantify the reach distances of players wearing different football shoulder pads and determine player perceptions of shoulder pad comfort and fit. Methods: Football players (n=10) underwent a standardized reach distance protocol comprised of three trials of repeated shoulder flexion, extension, abduction, horizontal flexion, and horizontal extension in each of the three shoulder pad conditions (no shoulder pad, standard shoulder pad, prototype shoulder pad). Player perceptions of shoulder pad comfort and fit, breathability, restrictiveness, and weight were also evaluated using a questionnaire. Reach distances were recorded using five GoPro Hero 9 cameras and analyzed using ProAnalyst®3D motion tracking software. Results: Reach distances were significantly affected during several movements, but especially in the vertical direction, for flexion and abduction, with mean differences between the prototype pad and standard pad of 10.3 cm and 23.1 cm, respectively (P = 0.007 and P = 0.003). Differences in reach distance were greater for the standard shoulder pad than the prototype shoulder pad on average. This indicates that the prototype shoulder pad was less restrictive, which aligned with what players reported. There was significantly more discomfort reported in the neck collar and armpit regions for the standard shoulder pad compared to the prototype pad. Participants also found the prototype shoulder pad to be lighter, and more breathable (P0.05). Conclusion: These results provide manufacturers with valuable insights from a design standpoint, and offer athletes who are looking for superior sport protective equipment key evidence regarding shoulder pad performance, fit, and comfort.

The preferable shoulder position can isolate supraspinatus activity superior to the classic empty can test: an electromyographic study

BackgroundSupraspinatus (SSP) strength tests are an important shoulder examination tool for clinical evaluations of patients with a suspected SSP tear. While the empty can (EC) test is widely used to diagnose SSP dysfunction, the test cannot selectively activate SSP activity. The aim of this study was to access the electromyographic (EMG) activity within SSP, deltoid, and surrounding periscapular muscles after resisted abduction force to determine which shoulder position helps best isolate SSP from deltoid activity.MethodsA controlled laboratory EMG study was conducted. Specifically, we conducted an EMG analysis of the seven periscapular muscles (i.e., the middle deltoid, anterior deltoid, SSP, upper trapezius, posterior deltoid, infraspinatus, and pectoralis major) in 21 healthy participants, without any history of shoulder disorder, aged 29 ± 0.9 years old with a dominant-right arm. EMG activities were measured during resisted abduction force according to comprehensive shoulder positions in abduction, horizontal flexion, and humeral rotation. The supraspinatus to middle deltoid (S:D) ratio was calculated using the standardized weighted EMG and the maximum voluntary isometric contraction of the SSP and middle deltoid muscles, for each shoulder position to determine the best isolated SSP muscle strength test position. Results were analyzed with the Kruskal–Wallis test for non-normally distributed data.ResultsShoulder abduction, horizontal flexion, and humeral rotation significantly affected the activity of the middle deltoid, SSP, and S:D ratio (P < 0.05). The S:D ratio increased significantly in lower degrees of shoulder abduction, lower degrees of horizontal flexion, and external humeral rotation over internal rotation. The greatest S:D ratio (3.4 (0.5–9.1)) occurred at the shoulder position of 30° shoulder abduction combined with 30° horizontal flexion and external humeral rotation. Conversely, the classic EC position manifested nearly the smallest S:D ratio (0.8 (0.2–1.2)).ConclusionApplication of the SSP strength test in the shoulder position of 30 degrees abduction, 30 degrees horizontal flexion, and external humeral rotation offers the best position to isolate the abducting activity of the SSP from that of the deltoid, which could help with diagnosis among patients with chronic shoulder pain with a suspected SSP tear condition.

Numerical and Experimental Investigations of Humeral Greater Tuberosity Fractures with Plate Fixation under Different Shoulder Rehabilitation Activities

The incidence of humerus greater tuberosity (GT) fractures is about 20% in patients with proximal humerus fractures. This study aimed to investigate the biomechanical performances of the humerus GT fracture stabilized by a locking plate with rotator cuff function for shoulder rehabilitation activities. A three-dimensional finite element model of the GT-fracture-treated humerus with a single traction force condition was analyzed for abduction, flexion, and horizontal flexion activities and validated by the biomechanical tests. The results showed that the stiffness calculated by the numerical models was closely related to that obtained by the mechanical tests with a correlation coefficient of 0.88. Under realistic rotator cuff muscle loading, the shoulder joint had a larger displacement at the fracture site (1.163 mm), as well as higher bone stress (60.6 MPa), higher plate stress (29.1 MPa), and higher mean screw stress (37.3 MPa) in horizontal flexion rehabilitation activity when compared to that abduction and flexion activities. The horizontal flexion may not be suggested in the early stage of shoulder joint rehabilitation activities. Numerical simulation techniques and experimental designs mimicked clinical treatment plans. These methodologies could be used to evaluate new implant designs and fixation strategies for the shoulder joint.

Evaluation of Upper Limb Joint Contribution to Racket Head Speed in Elite Tennis Players Using IMU Sensors: Comparison between the Cross-Court and Inside-Out Attacking Forehand Drive.

This study aimed to quantify and compare the upper limb angular kinematics and its contributions to the racket head speed between the cross-court (CC) and inside-out (IO) attacking tennis forehand of elite tennis players in a competitive environment. A new approach was used to study the forehand drive with mini-inertial sensors of motion capture to record the kinematic data. Six strokes in each direction per participant (72 shots in total) were chosen for analysis. Upper limb kinematics were calculated in the Visual 3D platform (Visual 3D Professional V5.01.21, C-motion, Germantown, MD, USA). The method used to calculate the upper limb’s contributions was performed with MATLAB software and used the segment’s (upper arm, forearm and hand) angular velocities and their respective displacement vectors obtained through the inertial sensors. Upper limb kinematics demonstrated a higher shoulder rotation in the IO direction with significant differences at the end of the backswing, which could be a key factor in distinguishing the two directions of the shot. Results also demonstrated that the horizontal flexion of the upper arm (around the shoulder joint) was primarily responsible for the racket velocity in the anteroposterior direction (48.1% CC and 45.2% IO), followed by the extension of the forearm (around the elbow joint) (17.3% CC and 20.9% IO) and the internal rotation of the upper arm (around the shoulder joint) (15.6% CC and 14.2% IO). No significant differences were shown in the contributions of upper limbs to the racket head velocity between the two directions of the shot. Tennis coaches and players should develop a specific training programme to perform higher angular velocities in these specific joint rotations.

Differential regional pectoralis major activation indicates functional diversity in healthy females

Pectoralis major activation enables the performance of several upper extremity movements. Its regional activation, however, is not documented in healthy females. This work used high-density surface electromyography to investigate regional pectoralis major activation in twenty-nine healthy young females across two independent experiments in several ramp and hold isometric tasks and force levels. Regional mean root mean square amplitudes (normalized to the task-specific maxima) were quantified for the clavicular, superior, and middle sternocostal regions. Two-way ANOVAs were used to determine if differences in normalized regional activation exist within each task and force level. The middle sternocostal region activated 12–108% more than the clavicular and the superior sternocostal region in extension, adduction with external rotation, and high elevation internal rotation. In high elevation adduction, the middle sternocostal region activated more (7–22%) than the superior sternocostal region. In low elevation, internal rotation (60°), the clavicular and middle sternocostal regions activated more (9–13%) than the superior sternocostal region, while in adduction 60°, the clavicular region activated 9–19% more than the superior sternocostal region. Lastly, in forward and horizontal flexion, all three regions activated similarly irrespective of the force level, except at 25% MVF in forward flexion, where the clavicular region activated 21% more than the superior sternocostal region. This work provides a first comprehensive evaluation of the normalized regional pectoralis major activation in healthy females. The present findings indicate that the performance of isometric tasks in different directions activates different pectoralis major regions in healthy females, suggesting regional specificity to functional actions.

An analysis of whole-body kinematics, muscle strength and activity during cross-step topspin among table tennis players

ABSTRACT This study examined the differences of muscle strength, electromyography (EMG) and whole-body kinematics during maximum cross-step table tennis topspin between advanced and intermediate players. Ten advanced and ten intermediate players performed both voluntary isokinetic contraction test and forehand topspin strokes with maximum-effort towards cross-court target zone. The results indicated that advanced players generated significantly greater maximum racket speeds during forward swing phase (P < 0.05). At the instant of the topspin stroke, significantly smaller shoulder horizontal flexion and elbow flexion angles, but larger joint angular velocities in advanced players (P < 0.05). Moreover, advanced players exhibited longer muscle firing duration of anterior deltoid and biceps brachii as well as higher root mean squares and EMG integrals of the abdominal external oblique, anterior deltoid and biceps brachii muscles than the intermediate players (P < 0.05). Furthermore, the isokinetic results showed higher shoulder abduction/adduction, hip flexion/extension and knee flexion torques at fast speed (240°/s) and higher elbow flexion torque at medium speed (120°/s) in advanced players (P < 0.05). The findings suggest that higher activation of the deltoid, biceps and abdominal external oblique muscles as well as larger muscle strength under higher speed conditions would be the plausible key factors to maximise racket and joint angular velocities in forehand topspin.

Age and Not the Preferred Limb Influences the Kinematic Structure of Pointing Movements.

In goal-directed movements, effective open-loop control reduces the need for feedback-based corrective submovements. The purpose of this study was to determine the influence of hand preference and aging on submovements during single- and two-joint pointing movements. A total of 12 young and 12 older right-handed participants performed pointing movements that involved either elbow extension or a combination of elbow extension and horizontal shoulder flexion with their right and left arms to a target. Kinematics were used to separate the movements into their primary and secondary submovements. The older adults exhibited slower movements, used secondary submovements more often, and produced relatively shorter primary submovements. However, there were no interlimb differences for either age group or for the single- and two-joint movements. These findings indicate that open-loop control is similar between arms but compromised in older compared to younger adults.

Reciprocal inhibition improves posterior shoulder tightness and shoulder range of motion in youth baseball players.

BackgroundThe aim of this study was to evaluate the efficacy of reciprocal inhibition for posterior shoulder tightness (PST), internal rotation at 90° abduction (ABIR) limitation, and subacromial impingement in elementary and junior high school baseball players.MethodsThe present study included 290 elementary school and junior high school baseball players who were members of an organized baseball team and attended a medical checkup in 2014. Seventeen participants were excluded because they were left-handed. We applied a sit-up exercise as a tool of reciprocal inhibition to all participants. Before and after the sit-up exercise, we evaluated the shoulder range of motion (ROM) in external rotation at 90° abduction (ABER), ABIR, and horizontal flexion (HF) in both shoulders and the prevalence of subacromial impingement in the dominant shoulder. We defined PST as a ≧15°decrease in the HF angle of the dominant shoulder in comparison to the nondominant shoulder before the sit-up exercise and divided participants into two groups (the PST group and the non-PST groups). An independent t-test was performed to compare the shoulder ROM, and a chi-squared test was performed to compare the prevalence of subacromial impingement between the two groups. A dependent t-test was performed to compare intragroup changes in the shoulder ROM. The McNemar test was performed to compare intragroup changes in the prevalence of subacromial impingement.ResultsFifty-six of 273 participants had PST in the initial examination. The initial examination revealed that the ROM of ABIR and HF in the dominant shoulder were significantly lower in the PST group than those in the non-PST group, whereas the ROM of ABER and total arc were significantly higher in the PST group. The prevalence of subacromial impingement in the PST group was significantly higher than that in the non-PST group. The sit-up exercise improved ABER, ABIR, total arc, HF, and the prevalence of subacromial impingement in both groups. However, the amount of ROM change did not differ between the two groups for any parameter with the exception of HF.ConclusionThe presence of PST affects the prevalence of subacromial impingement but was not related to the loss of ABIR or the prevalence of pathological glenohumeral internal rotation deficit. The sit-up exercise, as reciprocal inhibition, can transiently improve the prevalence of subacromial impingement via the improvement of PST.

Intra-Rater and Inter-Rater Reliability of Hand-Held Dynamometry for Shoulder Strength Assessment in Circus Arts Students.

Over two testing sessions, two experienced physiotherapists assessed the shoulder strength of 24 student circus artists with clinically diagnosed atraumatic shoulder instability. Both the symptomatic and asymptomatic shoulder was assessed using a HHD in 10 functional positions. Intra-class correlation coefficients (ICCs) were calculated to determine the reliability of strength measurements. All examined positions showed moderate-high intra-rater and inter-rater reliability. External rotation at 0° and internal rotation in horizontal flexion at 45° revealed the most reliable results, and the shrug position the least reliable. Inter-rater and intra-rater reliability was high and demonstrated similar results in symptomatic and asymptomatic shoulders by both raters. This study demonstrated clinical applicability in reliably measuring functional strength in symptomatic atraumatic instability or asymptomatic shoulders when assessed by experienced therapists using an HHD.

Shoulder ranges of motion and humeral torsions of injured baseball players have different characteristics depending on their pitching sides.

BackgroundRight- and left-side throwers in baseball may have different shoulder conditions and throwing biomechanics. This study aimed to compare the passive range of motion, humeral torsion, and clinical findings between right- and left-handed throwers who sustained throwing shoulder injuries and confirm the differences in the characteristics between throwing sides.MethodsA total of 52 pitchers diagnosed with throwing shoulder injuries were included in this study: 27 patients were right-side throwers (R group), and 25 were left-side throwers (L group). We measured the bilateral passive external and internal rotation angles in abduction position (ABIR) and total arc at their first visit. To assess posterior shoulder tightness, the internal rotation angles in forward flexion (FIR), and the abduction angle (AA) and horizontal flexion angle (HFA) without scapula motion were measured. The bilateral humeral torsion angles were also measured using ultrasonography. These values were compared between the participants' throwing and non-throwing sides and between the R and L groups' throwing sides. Furthermore, several physical findings in the shoulders were assessed, and the positive ratio was compared between the R and L groups.ResultsOn comparing the throwing and non-throwing sides, the R group had significantly greater external rotation angles in the abduction position and humeral torsion angle, and smaller ABIR, total arc, FIR, AA, and HFA in the throwing side, while the L group showed no significant differences, except for a smaller ABIR and larger HFA in the throwing side. On comparing the throwing side between the R and L groups, the R group had a smaller FIR, AA, and FHA than the L group. Regarding the physical findings, the posterior jerk test, Kim test, anterior and posterior drawer sign, sulcus sign, and scapular winging in the L group were significantly more positive than in the R group.ConclusionThe range of motion and humeral torsions differed between the left- and right-side throwers, as did the pathology between their throwing sides. Clinicians should consider the possibility that the pathological condition differs between left- and right-side throwers.

Identifying coordination between joint movements during a throwing task with multiple degrees of freedom.

It is known that coordination between joint movements is crucial for the achievement of motor tasks and has been studied extensively. Especially, in sports biomechanics, researchers are interested in determining which joint movements are coordinated to achieve a motor task. However, this issue cannot be easily addressed with the methods employed in previous studies. Therefore, we aimed to propose a method for identifying joint coordination. Subsequently, we examined which joint movements were coordinated using accurate overhead throwing, which required reduction in vertical hand velocity variability. Fourteen baseball players participated by attempting throwing using a motion capture system. The index of coordination for each joint movement and the effect of deviation of one joint movement on vertical hand velocity were quantified. Our results showed that the shoulder internal/external rotation angle (θ1-IE) and the other joint movements or the shoulder horizontal flexion/extension angular velocity (ω1-FE) and the other joint movements were coordinated. These results could be explained by the fact that the effects of the deviation of the shoulder internal rotation angle (θ1-I) and shoulder horizontal flexion angular velocity (ω1-F) on vertical hand velocity were larger than those of the other joint movements. This meant that it was necessary to cancel the deviations of θ1-IE and ω1-FE by the other joint movements. These findings indicate that the method proposed in this study enables the identification of which joint movements are coordinated in multiple degrees of freedom.

Effects of joint capsular release on range of motion in patients with frozen shoulder

A thickened joint capsule is believed to be one of the most specific manifestations of and the primary restraint against range of motion (ROM) in frozen shoulders. The purpose of this study was to evaluate the relationship among ROMs under general anesthesia before surgery and the effects of each joint capsular release on ROM. ROM was measured using a goniometer with scapular fixation. Arthroscopic pan-capsular release was performed with the patient in the beach-chair position in the following order: (1) rotator interval, (2) coracohumeral ligament, (3) superior capsule, (4) middle glenohumeral ligament, (5) anterior inferior glenohumeral ligament, and (6) posterior inferior glenohumeral ligament. ROMs in forward flexion (FF), lateral elevation (LE), external rotation with the arm at the side (ER1), external rotation at 90° of LE (ER2), internal rotation at 90° of LE (IR2), horizontal flexion, external rotation at 90° of FF (ER3), and internal rotation at 90° of FF (IR3) were evaluated before and after each release. A total of 32 consecutive shoulders were included. After each capsular release, the ROM recovered; the final ROM was significantly greater on the affected side than on the unaffected side. Significant correlations were found between FF and LE, FF and ER1, ER1 and ER2, ER1 and ER3, ER2 and ER3, and IR2 and IR3 on both sides, regardless of surgery. Each segment of the joint capsule affected ROM in all directions, supporting the need for whole-joint capsular release; ROM was significantly greater on the affected side than on the unaffected side after surgery.

P46 Swimmer’s thoracic outlet: it doesn’t have quite the same ring as tennis elbow!

Abstract Background We present a case that was referred and seen in our chronic pain clinic, and highlight the importance of keeping an open mind about alternative diagnoses when reviewing these patients. Methods Please refer to the results section. Results A 12 year-old girl was referred with right sided neck and shoulder pain associated with occasional pins and needles. The patient was a competitive swimmer, training and competing five times a week at her peak. She did not have a history of mottling or colour change, and clinically she had full range of motion of her joints and no neurological deficit. On repeated assessments, she had reproducible pain on horizontal flexion and reduced muscle bulk of the right shoulder, although power was preserved. Functionally the patient had to reduce her participation in swimming due to pain, and found it difficult to carry or lift things, brush or wash her hair, or write for extended periods of time. Imaging with shoulder X-ray and shoulder and cervical spine MRI did not reveal a cause, and she did not have an anatomical variation such as a thoracic rib. Due to the reproducibility on swimming, an ultrasound looking at the insertion of the biceps insertion during dynamic movements was arranged and was also normal with no subluxation noted. As she failed to improve with chronic pain education, chronic pain approach to physiotherapy sessions and graded reintroduction of swimming, ultrasound angiology was arranged. This showed minor disease in the right subclavian, axillary, brachial, radial and ulnar arteries, with significant reduction in right brachial arterial flow with the patient supine, right arm in horizontal flexion and contralateral head turn. This suggested arterial thoracic outlet syndrome (TOS). All other positions resulted in no significant difference in arterial flow. TOS is traditionally broken into two categories – neurogenic and vascular, the latter can be broken down further into arterial or venous. While in adults, the vast majority (90-95%) present as neurogenic, in the paediatric population there is a higher proportion of vascular cases. This has implications, as vascular TOS can be complicated by vessel disease and thrombus formation. There are a number of case reports in which management is reported as decompression of the thoracic outlet with partial first rib resection, with or without scalene muscle resection. Consideration of hypercoagulable states is also warranted. We have referred our patient to the vascular team for an urgent review and await their assessment and feedback about management. Conclusion A proportion of patients managed with chronic pain syndrome will have an alternative explanation for their pain. In particular, if a patient has focal pain or pain that is reproducible on a particular movement or activity, consider alternate diagnoses. Conflicts of Interest The authors declare no conflicts of interest.

In Which Arm Position Is a Hill-Sachs Lesion Created?

Background: It has been believed that a Hill-Sachs lesion (HSL) is created with the arm in abduction and external rotation at the time of dislocation. However, no studies have clarified the arm position in which an HSL is created. Purpose: To determine the arm position in which an HSL is created. Study Design: Descriptive laboratory study. Methods: The computed tomography images of 100 shoulders of 100 patients (72 males and 28 females; mean age, 30 years old) with recurrent anterior dislocation of the shoulder were investigated using an image analyzing software. Three-dimensional surface bone models of the scapula and humerus were created separately. The humerus was moved so that the HSL perfectly fit the anterior rim of the glenoid. This arm position was recorded 3-dimensionally. Results: Considering the scapulohumeral rhythm, the average arm position in which the HSL and the anterior glenoid rim best fit was 74° of abduction, 27° of external rotation, and 3° of horizontal flexion relative to the trunk. Conclusion: The arm position when an HSL and the anterior glenoid rim best fit is 74° of abduction, 27° of external rotation, and 3° of horizontal flexion, which seems to be the arm position when the HSL has been created. This result suggests 2 possibilities: dislocation occurred in this midrange position or HSL was not created at the time of dislocation but later in the mid–range of motion. However, as we have no information on the arm position at the time of dislocation, we cannot conclude which of these possibilities is true in our study. Clinical Relevance: This study gives us a better understanding of the timing of HSL occurrence. Shoulder dislocation may occur at the end range of motion or in the mid–range of motion, but an HSL is created in the mid–range of motion.

Postural differences in shoulder dynamics during pushing and pulling

Assessments of shoulder dynamics (e.g. the inertial, viscous, and stiffness properties of the joint) can provide important insights into the stability of the joint at rest and during volitional contraction. The purpose of this study was to investigate how arm posture influences shoulder dynamics while generating pushing or pulling torques in the horizontal plane. Sixteen healthy participants were examined in seven postures encompassing a large workspace of the shoulder. At each posture, the participant’s shoulder was rapidly perturbed while measuring the resultant change in shoulder torque about the glenohumeral axis. Participants were examined both at rest and while producing horizontal flexion and extension torques scaled to 15% of a maximum voluntary contraction. Shoulder stiffness, viscosity, and damping ratio were estimated using impedance-based matching, and changes in these outcome measures with torque level, elevation angle, and plane of elevation angle were explored with a linear mixed effects model. Shoulder stiffness was found to decrease with increasing elevation angles (p < 0.001) without subsequent changes in viscosity, leading to a greater damping ratios at higher elevation angles (p < 0.001). Shoulder stiffness, viscosity, and damping ratio (all p < 0.05) were all found to significantly increase as the plane of elevation of the arm was increased. The relationship between the viscosity, stiffness and the damping ratio of the shoulder is one that the central nervous system must regulate in order to maintain stability, protect against injury, and control the shoulder joint as the inertial and muscle contributions change across different arm postures.

Dry swing training with a light bat increases bat speed

Baseball training usually includes dry swing training to improve batting ability. However, no consensus has been reached on the relationship between bat weight and the increase in post-dry swing training bat speed. We hypothesized that dry swing training with a light bat would increase post dry swing training bat speed. Therefore, the purpose of this study was to examine the effect of dry swing training with a light bat on post dry swing training bat speed by comparing a light bat group with a heavy bat group. A total of 34 healthy male students from a university baseball team were randomly divided into a light bat group (n = 17) and a heavy bat group (n = 17). Subjects performed 100 dry swings per day, twice a week for eight weeks. The light bat group performed dry swing training with a 10.6 oz bat and the heavy bat group with a 38.8 oz bat. Bat speed and muscle power were measured before and after the intervention. There was no interaction between the intervention and post dry swing training bat speed, knee extension strength, shoulder horizontal flexion, or hand grip strength. There was a main effect of the intervention on post dry swing training bat speed and shoulder horizontal flexion. Bat speed increased in both groups, but without significant group differences in intervention effects. Since light bat loads in this study were very low, dry swing training with a light bat may be more effective and less strenuous.

Directionally compensated mechanical work provided by the shoulder leads to similar racket velocities during open and square stance forehand groundstrokes in tennis

The differences between the racket-arm acceleration mechanisms during open and square stance forehand groundstrokes in tennis were examined by quantifying the mechanical work done on the racket arm. We studied 13 advanced tennis players as they performed these strokes at maximum effort and calculated the work using inverse dynamics. The racket head speed was similar between the open and square stances. In the open stance, the lack of weight shifting towards the hitting direction resulted in a lower velocity for the shoulder joint centre in the hitting direction than in the square stance, and less work was done by the shoulder joint force in the hitting direction in the open stance than in the square stance (0.30 ± 0.11 J·kg-1 vs. 0.38 ± 0.16 J·kg-1; p = 0.005). However, in the open stance, the torso rotated more towards the hitting direction and had more upward acceleration, which resulted in more work done by the sideways and upward shoulder joint forces than in the square stance (sideways: 0.07 ± 0.09 J·kg-1 vs. 0.05 ± 0.09 J·kg-1, p = 0.046; upward: 0.08 ± 0.09 J·kg-1 vs. 0.04 ± 0.07 J·kg-1, p = 0.002). Thus, the greater work done by the sideways and upward shoulder joint forces compensated for the lesser work done by the shoulder joint force in the hitting direction in the open stance. In both stances, mainly the horizontal flexion torque and internal rotation torque at the shoulder increased the energy of the racket arm.

Effects of triple-treatment trunk stretching on physical fitness and curvature of the spine

BackgroundResearch on the effectiveness of treatment for low back disorders has been made, however yet no established method has been found. Therefore, we devised a triple-treatment trunk stretching program comprising the following three trunk stretching exercises: stretching using an unstable flex chair; stretching using a stretching bench; and stretching using a stretch pad. Our three-treatment trunk stretching program is based on the principles of static muscular stabilization of the spine and uses well-known physiological strength-training principles. In this study, we investigated the effects of triple-treatment trunk stretching on physical fitness levels and curvature of the spine measured by X-ray photographs. MethodsThirteen healthy male subjects (mean age, 26.3 ± 4.0 years; height, 173.5 ± 4.9 cm; weight, 64.9 ± 5.7 kg; BMI 21.6 ± 1.7) were enrolled in this study. In consideration of safety and simplicity, we applied the physical fitness test introduced by the Ministry of Education, Culture, Sports, Science and Technology of Japan for 65- to 79-year-olds. ResultsTriple-treatment trunk stretching led to significant improvements in sit-and-reach flexibility, 10-m obstacle course walking time, standing forward flexion, thoracolumbar extension and horizontal flexion. Significant improvements were also observed in the neutral angle of the curvature of the lower thoracic spine and the neutral angle of the curvature of the lower lumbar spine. ConclusionsSignificant improvements were evident in the neutral angles of both the curvature of the lower thoracic spine and the curvature of the lower lumbar spine after triple-treatment trunk stretching. This suggests that triple-treatment trunk stretching can help improve the curvature of the spine and physical fitness.