Prevalence of Abnormal Findings in the Posterosuperior Humeral Head of Asymptomatic Collegiate Baseball Pitchers Using Ultrasonography.

BACKGROUND: The posterosuperior humeral head contacts the glenoid during pitching. While magnetic resonance imaging (MRI) often detects abnormalities in the posterosuperior humeral head of baseball pitchers, ultrasonography may also be effective in identifying these abnormalities. However, studies on such abnormalities in asymptomatic players are limited. Thus, this study aimed to determine the prevalence of abnormal findings in the humeral head using ultrasonography in asymptomatic collegiate baseball pitchers. METHODS: We utilized ultrasonography to assess abnormal findings in the humeral head, defined as a break in continuity or an irregular surface around the infraspinatus insertion, in 33 college baseball pitchers (pitcher group) and 30 college students without experience in overhead sports (control group). For 11 of the 33 pitchers, computed tomography (CT)-like images were used to locate the abnormalities. The location was quantitatively identified in the axial plane using a clock system, with the bicipital groove designated as 12 o'clock, and qualitatively assessed in the sagittal plane. Shoulder internal and external rotation ranges of motion (IR and ER ROMs) and humeral retroversion were measured using an inclinometer. The prevalence of abnormalities among the four subgroups (throwing and non-throwing shoulders of the pitcher group and dominant and non-dominant shoulders of the control group) was compared using the Fisher's exact test. A paired t-test was also performed to compare the IR and ER ROMs, as well as the humeral retroversion between each group's throwing (dominant) and non-throwing (non-dominant) sides. RESULTS: The prevalence of abnormalities was significantly higher (76%) in the throwing shoulder of the pitcher group than in the other shoulder groups (< .001). The mean position of the humeral head abnormalities in the axial plane was 8:32 ± 0:21 in the clock system, with all abnormalities located at the infraspinatus insertion on the greater tuberosity in the sagittal plane according to CT-like image analysis. While ER ROM and humeral retroversion were greater in the throwing shoulder, IR ROM was less than that in the non-throwing shoulder in the pitcher group (< .001). CONCLUSION: Ultrasonographic assessments revealed a higher prevalence of abnormalities in humeral head for asymptomatic collegiate baseball pitchers. Repetitive throwing motions may lead not only to adaptations in the ROM of the shoulder joint but also to abnormalities in the humeral head. Thus, ultrasonography may help identify asymptomatic baseball players with physiological internal impingement.

Decreased moment of inertia of the lower limb facilitates a rapid hip internal rotation in a simulated foot impact maneuver. A laboratory-controlled biomechanical study for a precursor mechanism of noncontact anterior cruciate ligament injury.

BACKGROUND: Anterior cruciate ligament injury frequently occurs in the deceleration with the knee-extended position. In addition, a rapid hip internal rotation is concomitantly observed. However, how the extended knee position induces the hip internal rotation is unclear. METHODS: Sixteen healthy participants performed the simulated foot impact task on the experimental chair. To vary the knee flexion angle, the following four-foot placement positions relative to the pelvis segment, i.e.: 1) near; 2) middle; 3) far; and 4) far + heel strike, were tested. The reflective marker positions and the ground reaction force (GRF) data were collected. The moment of inertia of the entire lower limb around its long axis as well as the peak hip internal rotation angular velocity were calculated and compared among four conditions (Wilcoxon Signed-Rank Test with Bonferroni correction, P<0.0083). RESULTS: As the knee extended from the near to far + heel strike condition, the moment of inertia of the entire lower limb significantly decreased and hip internal rotation angular velocity significantly increased (P<0.001). CONCLUSIONS: The extended knee position with far foot placement from torso reduces the inertial resistance of the entire lower limb around its long axis and is vulnerable to the hip internal rotation.

Absorption function loss due to the history of previous ankle sprain explored by unsupervised machine learning.

BACKGROUND: Ankle sprains are common and cause persistent ankle function reduction. To biomechanically evaluate the ankle function after ankle sprains, the ground reaction force (GRF) measurement during the single-legged landing had been used. However, previous studies focused on discrete features of vertical GRF (vGRF), which largely ignored vGRF waveform features that could better identify the ankle function. PURPOSE: To identify how the history of ankle sprain affect the vGRF waveform during the single-legged landing with unsupervised machine learning considering the time-series information of vGRF. METHODS: Eighty-seven currently healthy basketball athletes (12 athletes without ankle sprain, 49 athletes with bilateral, and 26 athletes with unilateral ankle sprain more than 6 months before the test day) performed single-legged landings from a 20 centimeters (cm) high box onto the force platform. Totally 518 trials vGRF data were collected from 87 athletes of 174 ankles, including 259 ankle sprain trials (from previous sprain ankles) and 259 non-ankle sprain trials (from without sprain ankles). The first 100 milliseconds (ms) vGRF waveforms after landing were extracted. Principal component analysis (PCA) was applied to the vGRF data, selecting 8 principal components (PCs) representing 96% of the information. Based on these 8 PCs, k-means method (k = 3) clustered the 518 trials into three clusters. Chi-square test assessed significant differences (p < 0.01) in the distribution of ankle sprain and non-ankle sprain trials among clusters. FINDINGS: The ankle sprain trials accounted for a significantly larger percentage (63.9%) in Cluster 3, which exhibited rapidly increased impulse vGRF waveforms with larger peaks in a short time. SIGNIFICANCE: PCA and k-means method for vGRF waveforms during single-legged landing identified that the history of previous ankle sprains caused a loss of ankle absorption ability lasting at least 6 months from an ankle sprain.

Individual Variation in Adaptive Ability of the Anticipated Postural Stability During a Dual-Task Single-Leg Landing in Female Athletes.

Background: Precise postural control helps prevent anterior cruciate ligament injury. However, it is unknown whether the anticipated postural stability can be improved during a physically uncertain and cognitively demanding task. Hypothesis: Anticipated postural stability will improve through unanticipated single-leg landing with a rapid foot placement target tracking. Study Design: Controlled laboratory study. Methods: A total of 22 healthy female university-level athletes performed a novel dual-task paradigm: an unanticipated single-leg landing with foot placement target tracking. In the normal condition (60 trials), the participants jumped from a 20 cm-high box onto the landing target with their dominant leg as softly as possible. In the subsequent perturbation condition (PC) (60 trials), the initially assigned landing target was abruptly switched randomly, requiring participants to modify their preplanned foot placement position to the newly assigned position. The center-of-pressure trajectory length within the first 100 ms after foot impact (CoP100) was calculated as a measure of anticipated postural stability for each trial. In addition, the peak vertical ground-reaction force (FzPeak) was quantified to assess landing load, and the degree of postural adaptation during PC was quantified by fitting an exponential function to trial-by-trial changes in CoP100. Participants were divided into 2 groups according to increase or decrease in CoP100, and results were compared between the groups. Results: The direction and magnitude of postural sway alterations of the 22 participants showed a spectrum-like variation during the repeated trials. Twelve participants (sway-decreased group) exhibited a gradual reduction in postural sway (CoP100) during the PC, while the remaining 10 participants (sway-increased group) showed a gradual increase in CoP100. The FzPeak during the PC was significantly less in the sway-decreased group compared with the sway-increased group (P < .05). Conclusion: Variation in the direction and magnitude of postural sway alteration among participants suggested that there was individual variation in an athlete's adaptive ability of the anticipated postural stability. Clinical Relevance: The novel dual-task paradigm described in this study may be useful for rating individual injury risk based on an athlete's postural adaptation ability and may aid in targeted prevention strategies.

The counteracting effect of the friction moment against the tibial rotational moment driven by the ground reaction force in an early stance phase of cutting maneuver among healthy male athletes.

The ground reaction force (GRF) is known to produce tibial internal rotation loading associated with the stress in the anterior cruciate ligament (ACL). However, it is unclear whether the friction moment (FM; the moment due to horizontal shoe-floor friction, acting around the vertical axis at the GRF acting point) facilitates or restrains the effect of GRF-driven tibial rotation loading during cutting. The 45° cutting motions with forefoot/rearfoot strikes were captured simultaneously with GRF and FM data from 23 healthy males. The FM- and GRF-driven tibial rotation moments were calculated. Time-series correlation between FM- and GRF-driven tibial rotation moments and the orientation relationship among those moment vectors was investigated. The FM-driven tibial rotation moment negatively correlated with the GRF-driven one within the first 10% of stance phase. The peak regression slope value was -0.34 [SD 0.33] for forefoot and -1.64 [SD 1.76] for rearfoot strikes, showing significant difference from zero (SPM one-sample t-test, p<0.05). The FM-driven tibial "external" rotation moment counteracted the GRF-driven tibial "internal" rotation moment within first 10% of the stance phase in most trials, suggesting that the FM-driven tibial rotation moment potentially diminishes the effect of GRF-driven one and may reduce ACL injury risk during cutting.

Variability in Physical Inactivity Responses of University Students during COVID-19 Pandemic: A Monitoring of Daily Step Counts Using a Smartphone Application.

This study investigated the changes in physical inactivity of university students during the COVID-19 pandemic, with reference to their academic calendar. We used the daily step counts recorded by a smartphone application (iPhone Health App) from April 2020 to January 2021 (287 days) for 603 participants. The data for 287 days were divided into five periods based on their academic calendar. The median value of daily step counts across each period was calculated. A k-means clustering analysis was performed to classify the 603 participants into subgroups to demonstrate the variability in the physical inactivity responses. The median daily step counts, with a 7-day moving average, dramatically decreased from 5000 to 2000 steps/day in early April. It remained at a lower level (less than 2000 steps/day) during the first semester, then increased to more than 5000 steps/day at the start of summer vacation. The clustering analysis demonstrated the variability in physical inactivity responses. The inactive students did not recover daily step counts throughout the year. Consequently, promoting physical activity is recommended for inactive university students over the course of the whole semester.

Consistent Hand Dynamics Are Achieved by Controlling Variabilities Among Joint Movements During Fastball Pitching.

This study aimed to determine whether covariations among joint movements are utilized to stabilize hand orientation and movement and to determine which of the upper or lower extremities make effective use of the covariation. Joint angles during pitching were measured in 12 skilled baseball pitchers, using a motion capture system. The joint angles in 10 successful trials were used for the reconstructed motions. The reconstructed motion in the first condition was the same as for the measured motion. In the second condition, the reconstructed motion was generated with joint angles that were pseudo-randomly selected to artificially break off covariation in the measured joint-angle combination. In the third and fourth conditions, the reconstructed motions were generated with the same joint-angle combinations as the measured angles in the throwing arm and the stride leg, respectively, but pseudo-randomly selected in the other joint angles. Ten reconstructed motions were generated for each condition. Standard deviations (SDs) of hand orientation and movement direction were calculated and compared among the conditions. All SDs for the first condition were the smallest among the conditions, indicating that the movements in the measured condition used the covariation in joint angles to make the hand movement stable. The results also illustrated that some SDs in the fourth condition were smaller than those in the third condition, suggesting that the lower extremity made effective use of the covariation. These results imply that it is necessary not only to reduce variability in each joint but also to regulate joint movements to stabilize hand orientation and movement.

Middle finger and ball movements around ball release during baseball fastball pitching.

The objectives of this study were to investigate middle finger movements and dynamics of ball movements around the instant of ball release during baseball pitching. Baseball pitching from an indoor mound among 14 semi-professional pitchers was captured using a motion capture system with 16 high-speed cameras (1,000 Hz). Kinematics of middle finger joints, ball rotation, and force applied to the ball were calculated. The proximal and distal interphalangeal joints continued to extend until the instant of ball release, then abruptly flexed. The abrupt flexion lasted for only several milliseconds, followed by a short extension phase. The finger made a quick double cycle of extension-flexion movement, suggesting that it attained high stiffness resulting from co-contraction. The ball began to roll up to the tip of the finger 8 ± 1 ms before ball release owing to the start of extension or the increased angular velocity of extension for the proximal interphalangeal joint. A mean force of 195 ± 27 N was applied in the proximal direction of the hand at the same time as the beginning of ball rolling, and a mean force of 109 ± 22 N was applied to the throwing direction just before ball release.

Finger forces in fastball baseball pitching.

Forces imparted by the fingers onto a baseball are the final, critical aspects for pitching, however these forces have not been quantified previously as no biomechanical technology was available. In this study, an instrumented baseball was developed for direct measurement of ball reaction force by individual fingers and used to provide fundamental information on the forces during a fastball pitch. A tri-axial force transducer with a cable having an easily-detachable connector were installed in an official baseball. Data were collected from 11 pitchers who placed the fingertip of their index, middle, ring, or thumb on the transducer, and threw four-seam fastballs to a target cage from a flat mound. For the index and middle fingers, resultant ball reaction force exhibited a bimodal pattern with initial and second peaks at 38-39ms and 6-7ms before ball release, and their amplitudes were around 97N each. The ring finger and thumb produced single-peak forces of approximately 50 and 83N, respectively. Shear forces for the index and middle fingers formed distinct peak at 4-5ms before release, and the peaks summed to 102N; a kinetic source for backspin on the ball. An additional experiment with submaximal pitching effort showed a linear relationship of peak forces with ball velocity. The peak ball reaction force for fastballs exceeded 80% of maximum finger strength measured, suggesting that strengthening of the distal muscles is important both for enhancing performance and for avoiding injuries.

Radio-ulnar joint supinates around ball release during baseball fastball pitching.

This study was conducted to determine whether a supination phase of the forearm exists around ball release (BRL), and, if present, to determine whether this supination is explained by a reaction force or by the body configuration required for this task. A 16-camera motion analysis system with a sampling frequency of 1,000 Hz recorded 20 healthy male semi-professional pitchers pitching from an indoor pitching mound. A short supination phase around BRL was confirmed for all participants in the current study. Correlation analyses revealed that the supination angle at BRL had significant relationships with several measurements of shoulder movement kinematics. Mechanical work analysis of the forearm's longitudinal axis revealed several variations in joint power curve and various patterns of mechanical work among the participants, suggesting that a reaction force originating from accelerating a ball might not be the main cause of supination. The raw data also were down-sampled to a sampling frequency of 250 Hz, to match previous studies and to investigate the discrepancy among previous studies concerning the existence of the supination phase. The experience of participants and methodological differences, such as the definition of BRL and the time-normalisation technique, influenced whether the supination phase was observed.

Two types of motor strategy for accurate dart throwing.

This study investigated whether expert dart players utilize hand trajectory patterns that can compensate for the inherent variability in their release timing. In this study, we compared the timing error and hand trajectory patterns of expert players with those of novices. Eight experts and eight novices each made 60 dart throws, aiming at the bull's-eye. The movements of the dart and index finger were captured using seven 480-Hz cameras. The data were interpolated using a cubic spline function and analyzed by the millisecond. The estimated vertical errors on the dartboard were calculated as a time-series by using the state variables of the index finger (position, velocity, and direction of motion). This time-series error represents the hand trajectory pattern. Two variables assessing the performance outcome in the vertical plane and two variables related to the timing control were quantified on the basis of the time-series error. The results revealed two typical types of motor strategies in the expert group. The timing error of some experts was similar to that of novices; however, these experts had a longer window of time in which to release an accurately thrown dart. These subjects selected hand trajectory patterns that could compensate for the timing error. Other experts did not select the complementary hand trajectories, but greatly reduced their error in release timing.

Asymmetric load-carrying in young and elderly women: relationship with lower limb coordination.

This study investigates balance during asymmetric load-carrying and how asymmetric loading affects lower limb coordination during gait. Walking with and without a hand-held bag was analyzed in five young and six elderly women using a 6-camera VICON system and two force plates. Balance and lower limb coordination were compared when walking with and without a bag and also between age groups. While carrying a bag, the trunk, head, and upper arm were recruited in both young and elderly women. With the load, the contralateral hip abduction torque increased, whereas the ipsilateral hip torque decreased. Intralimb and interlimb coordinations did not vary with the different load conditions. The only difference observed between the groups was the contralateral shoulder abduction. The elderly group abducted their shoulders to a greater extent, even when walking without a bag.

Bat speed, trajectory, and timing for collegiate baseball batters hitting a stationary ball.

The aims of this study were to examine whether batters hit stationary balls at the time of peak speed of the bat head and whether the impact occurs at the lowest point of the bat trajectory. Eight university baseball players hit three balls, each hung with a string; each ball was made of a different material and was different in weight. Bat movement was captured by four 240-Hz infrared cameras and analysed three-dimensionally. Time for peak speed of the bat head varied according to the conditions. When stationary balls of standard weight were used, the bat head was at maximum speed at impact with the ball; then, it decelerated drastically owing to the impact. In contrast, maximum speed was obtained after impact when lightweight stationary balls were used. The time-speed profile of the bat head before impact in the lightweight ball condition was identical with that in the standard weight ball condition. Regardless of conditions, the timing of the lowest point of the bat head was nearly identical for each batter and most participants hit the stationary balls at about the lowest point of the bat trajectory.

Mechanical power flow changes during multijoint movement acquisition.

We investigated the differences in mechanical power flow in early and late practice stages during a cyclic movement consisting of upper arm circumduction to clarify the change in mechanical energy use with skill acquisition. Seven participants practiced the task every other day until their joint angular movements conformed to those of an expert. During the practice sessions, participants' motions were digitally recorded once a week using four high-speed infrared cameras, and the joint kinematics and joint powers of the right arm were calculated. With practice, the inflow power derived from the net joint force increased at the hand, forearm, and upper arm segments by 143.1 +/- 17.2%, 57.1 +/- 7.3%, and 198.1 +/- 35.4%, respectively. In contrast, the power caused by the muscle joint moments was not significantly increased. These results suggested that participants acquired a motor pattern promoting transfer of the joint reaction forces. Results may provide some support for Bernstein's (1967) ideas that skill acquisition involves improving movement efficiency by greater use of nonmuscular forces.

Influence of shoulder abduction and lateral trunk tilt on peak elbow varus torque for college baseball pitchers during simulated pitching.

Elbow varus torque is a primary factor in the risk of elbow injury during pitching. To examine the effects of shoulder abduction and lateral trunk tilt angles on elbow varus torque, we conducted simulation and regression analyses on 33 college baseball pitchers. Motion data were used for computer simulations in which two angles-shoulder abduction and lateral trunk tilt-were systematically altered. Forty-two simulated motions were generated for each pitcher, and the peak elbow varus torque for each simulated motion was calculated. A two-way analysis of variance was performed to analyze the effects of shoulder abduction and trunk tilt on elbow varus torque. Regression analyses of a simple regression model, second-order regression model, and multiple regression model were also performed. Although regression analyses did not show any significant relationship, computer simulation indicated that the peak elbow varus torque was affected by both angles, and the interaction of those angles was also significant. As trunk tilt to the contralateral side increased, the shoulder abduction angle producing the minimum peak elbow varus torque decreased. It is suggested that shoulder abduction and lateral trunk tilt may be only two of several determinants of peak elbow varus torque.

Temporal and spatial factors reflecting performance improvement during learning three-ball cascade juggling.

Beek and van Santvoord [Beek, P. J., & van Santvoord, A. A. M. (1992). Journal of Motor Behavior, 24, 85-94] proposed a three-stage model of learning to juggle based on group analyses of temporal measures. Here, we examined in detail how the temporal and spatial features of juggling evolved in eight individual participants progressing from the second to the third stage of learning. During the second stage, the dwell ratio, defined as the ratio of the time that the juggler holds a ball between catch and toss and the hand cycle time (HCT), was stable when it was about 0.83. The subjects with a dwell ratio near this value and controlled throws exhibited stable juggling, whereas the subjects with a dwell ratio of 0.80 or smaller exhibited unstable juggling. Compared to the former group, the latter group had a longer time from the throw of a ball to the arrival at its zenith (TZ), and a shorter time between the arrival of an airborne ball at its zenith and the subsequent throw (IZR). The latter group also exhibited larger variability in the dwell ratio and IZR. With practice, the subjects appropriated, on average, the duration of TZ and IZR to the dwell ratio and improved the ability to accurately throw balls by changing the motions of the limb segments involved. Although these changes helped to stabilize the performance during the second stage, the variability problem was not sufficiently resolved. Only two out of eight subjects passed on to the third stage by the last (10th) Session. They achieved small variability in IZR, dwell ratio, and flight paths of the ball while juggling with short HCTs and small dwell ratios. These results suggest that the reduction of variability in these variables was essential to pass on to the third stage.

Practice changes the usage of moment components in executing a multijoint task.

We examined changes in the usage of muscular and motion-dependent moments during the long-term practice of a complex, multijoint movement. Seven participants practiced a cyclic movement of the upper limbs until their joint angular movements conformed to those of an expert. The motions of the participants were digitally recorded using four high-speed infrared cameras, and the joint kinematics and kinetics of the right arm were calculated. Practice brought about changes in the patterns of the net joint moment and in the contributions of the muscular and motion-dependent moments to the net moments. Practice also brought about a growing opposition between the directions of the two moments. These changes seemed to be important for improving the dynamic equilibrium of the movements.