Biomechanical Characteristics of Scapular and Glenohumeral Movements during Pitching Motion in Injury-prone College Baseball Pitchers.

OBJECTIVES: The coordination of glenohumeral (GH) and scapular movements is central to the injury prevention of baseball pitchers. However, there is no objective data establishing the direct relationship between pitching injuries and associated GH and scapular movements. Therefore, this study demonstrated the biomechanical differences in the scapular and GH movements during pitching between injury-prone pitchers and healthy college baseball pitchers. METHODS: A total of 30 collegiate baseball pitchers were classified into two groups according to their injury status: injury-prone group (n = 15) and control group (n = 15). We obtained pitching motion data using three-dimensional motion analysis technique. RESULTS: The horizontal abduction angles of the GH joint during cocking and acceleration phases were considerably greater in the injury-prone pitchers (19.0° at stride foot contact [SFC], -4.0° at maximum external rotation [MER], and -0.3° at ball release) than those in healthy controls (11.7° at SFC, -10.0° at MER, and -6.9° at ball release). Additionally, in the cocking phase, the amount of angular change in the scapular external rotation (ER) was significantly smaller in the injury-prone group than that in the control group (mean difference, -13.0). CONCLUSION: These results suggest that the injury-prone pitchers have less internal rotation of the scapula and a more horizontal abduction of the GH joint during the cocking and acceleration phases. Therefore, sports medicine practitioners may need to pay considerable attention to the coordination of scapular and GH horizontal movements during pitching for prevention of shoulder injuries.

New method for liquid-medication filling systems.

For the systems used to fill large numbers of containers with liquid medication, a permissible relative error is ±1.0%. Here, a medication filling and estimating system was designed to improve cycle time. The nonlinear least squares (NLS) method was used with the proposed system, and the results succeeded in providing the medication fill ration meeting certain specifications and below the permissible relative error. The proposed method also realizes medication filling accuracy comparable to that achieved by the conventional method, but additionally made it possible to shorten the time needed to compute the weight value by approx 60%. Moreover, since a low-pass filter does not need to be used with the proposed method, the new method is not subject to the influence of a time delay.

Mechanisms of the anterior cruciate ligament injury in sports activities: a twenty-year clinical research of 1,700 athletes.

The mechanisms of anterior cruciate ligament (ACL) injuries are still inconclusive from an epidemiological standpoint. An epidemiological approach in a large sample group over an appropriate period of years will be necessary to enhance the current knowledge of the ACL injury mechanism. The objective of the study was to investigate the ACL injury occurrence in a large sample over twenty years and demonstrate the relationships between the ACL injury occurrence and the dynamic knee alignment at the time of the injury. We investigated the activity, the injury mechanism, and the dynamic knee alignment at the time of the injury in 1,718 patients diagnosed as having the ACL injuries. Regarding the activity at the time of the injury, "competition "was the most common, accounting for about half of all the injuries. The current result also showed that the noncontact injury was the most common, which was observed especially in many female athletes. Finally, the dynamic alignment of "Knee-in & Toe- out "(i.e. dynamic knee valgus) was the most common, accounting for about half. These results enhance our understanding of the ACL injury mechanism and may be used to guide future injury prevention strategies. Key pointsWe investigated the situation of ACL injury occurrence, especially dynamic alignments at the time of injury, in 1,718 patients who had visited our institution for surgery and physical therapy for twenty years.Our epidemiological study of the large patient group revealed that "knee-in & toe-out "alignment was the most frequently seen at the time of the ACL injury.From an epidemiological standpoint, we need to pay much attention to avoiding "Knee-in & Toe-out "alignment during sports activities.

Glenohumeral, scapular, and thoracic angles at maximum shoulder external rotation in throwing.

BACKGROUND: Because a majority of throwing injuries occur near the maximum external rotation (MER) of the throwing shoulder, sports medicine practitioners and researchers have paid special attention to the shoulder kinematics at the MER in throwing. However, little is known about the individual kinematics of the glenohumeral, scapulothoracic, and thoracic joints at the MER. Purpose To demonstrate the glenohumeral, scapulothoracic, and thoracic joint movements and their contribution to the MER in throwing for baseball players. STUDY DESIGN: Descriptive laboratory study. METHODS: We collected throwing motion data for 20 collegiate baseball players by using 3 high-speed cameras and established 3-dimensional coordinates of each landmark with a direct linear translation method. We then obtained the MER of the shoulder complex, the external rotation angle of the glenohumeral joint, the posterior tipping angle of the scapula, and the thoracic extension angles at the MER in throwing. RESULTS: The mean (+/- standard deviation) value of the MER was 144.2 degrees +/- 11.0 degrees . The mean (+/- standard deviation) values of the glenohumeral external rotation, the scapular posterior tipping, and the thoracic extension angles at the MER were 105.7 degrees +/- 15.5 degrees , 23.5 degrees +/- 13.9 degrees , and 8.9 degrees +/- 7.3 degrees , respectively. CONCLUSION: Our results indicate that not only the glenohumeral joint movement but also the scapular and thoracic movements make major contributions to the MER angle. CLINICAL RELEVANCE: To better understand the pathomechanics of the shoulder complex in throwing, we need to take into account the individual contributions of the glenohumeral, scapulothoracic, and thoracic extension movements to the MER.

How back-muscle fatigue influences lumbar curvature.

CONTEXT: Back-muscle fatigue and lumbar curvature are related to low back pain, but the relation between them is unknown. OBJECTIVE: To clarify whether lumbar curvature changes with back-muscle fatigue. DESIGN: Prospective pseudorandomized. SETTING: Laboratory. PARTICIPANTS: 13 healthy men without low back pain. INTERVENTION: To induce back-muscle fatigue, subjects performed a repetitive prone back-extension exercise from 45 degrees to 0 degrees until exhaustion and then rested 10 min. They performed this exercise 3 times. MAIN OUTCOME MEASURES: Before the trial and after each exercise, lumbar curvature was measured with a Spinal Mouse. RESULTS: After back-muscle fatigue, lumbar curvature decreased significantly (P < .01). This decrease occurred at L4-S1, which was defined as the lower spine. On the contrary, curvature of the upper lumbar spine, at Th12-L4, did not decrease. CONCLUSION: Lumbar curvature, especially the lower portion, decreased with back-muscle fatigue induced by prone back-extension exercise.

Muscular outputs during dynamic bench press under stable versus unstable conditions.

Previous studies have suggested that resistance training exercise under unstable conditions decreases the isometric force output, yet little is known about its influence on muscular outputs during dynamic movement. The objective of this study was to investigate the effect of an unstable condition on power, force, and velocity outputs during the bench press. Twenty male collegiate athletes (mean age, 21.3 +/- 1.5 years; mean height, 167.7 +/- 7.7 cm; mean weight, 75.9 +/- 17.5 kg) participated in this study. Each subject attempted 3 sets of single bench presses with 50% of 1 repetition maximum (1RM) under a stable condition with a flat bench and an unstable condition with a Swiss ball. Acceleration data were obtained with an accelerometer attached to the center of a barbell shaft, and peak outputs of power, force, and velocity were computed. Although significant loss of the peak outputs was found under the unstable condition (p < 0.017), their reduction rates remained relatively low, approximately 6% for force and 10% for power and velocity outputs, compared with previous findings. Such small reduction rates of muscular outputs may not compromise the training effect. Prospective studies are necessary to confirm whether the resistance training under an unstable condition permits the improvement of dynamic performance and trunk stability.

Characteristics of trunk lean motion during walking in patients with symptomatic knee osteoarthritis.

OBJECTIVE: Trunk lean motion on the frontal plane shifts the pressure across the medial-lateral cartilage of the stance limb's knee. The purpose of this study was to investigate trunk lean motion during walking in patients with knee osteoarthritis. MATERIALS AND METHODS: The study involved five healthy normal controls and 12 patients with symptoms of knee osteoarthritis (six with unilateral and six with bilateral). The trunk lean angle and the direction during one stride cycle of walking were calculated using a three-dimensional gait analysis. RESULTS: There was no significant difference between the three groups (normal, unilateral knee OA, and bilateral knee OA group). However, patients with bilateral limb knee osteoarthritis displayed a tendency to lean their trunk toward the swing side. CONCLUSION: This study determined that bilateral OA patients exhibit the characteristic gait which may progress knee OA.

The role of shoulder maximum external rotation during throwing for elbow injury prevention in baseball players.

The objective of the present study was to examine whether the passive range of shoulder external rotation (ER), the maximum shoulder external rotation angle (MER) during throwing, and the ratio of MER to ER are related to the incidence of the elbow injury. A mixed design with one between-factor (a history of the elbow injury) and two within-factors (ER and MER) was used to analyze the difference between baseball players with and without a history of medial elbow pain. Twenty high school baseball players who had experienced the medial elbow pain within the previous month but who were not experiencing the pain on the day of the experiment were recruited (elbow-injured group). Another twenty baseball players who had never experienced the medial elbow pain were also used for testing (control group). MER during throwing, ER, and the ratio of MER to ER were obtained in both of the group. A Mann-Whitney test was used for the group comparison (p < 0.05). The ratio of MER to ER was significantly greater in the elbow-injured group (1.52 ± 0.19) than that in the control group (1.33 ± 0.23) (p = 0.008). On the other hand, there was no statistical significance in MER and ER between two groups. The findings of the study indicate that MER/ER relation could be associated with the incidence of the elbow injury in baseball players. Key pointsIt is accepted that the greatest elbow valgus stress appears at the position of shoulder maximum external rotation (MER) in the acceleration phase of the throwing movement. As a consequence, shoulders with restricted range of motion of external rotation (ER) compensate with a valgus stress on their elbow joints.In this study, we evaluated the relation between MER and ER of shoulder in players with/without elbow injuries.The result of this study demonstrated that the elbow injured group showed significantly greater MER/ER relation than the control group.The current finding suggests that great MER combined with the ROM restriction may be one of the risk factors to cause medial elbow pain in baseball players.

Relationship between maximum shoulder external rotation angle during throwing and physical variables.

The amount of stress imposed on shoulder and elbow appears to be directly correlated with the degree of maximum shoulder external rotation (MER) during throwing motions. Therefore, identifying risk factors contributing to the increase of MER angle may help to decrease the throwing injuries occurrence in baseball players. The purpose of the present study was to demonstrate the correlation between MER and the kinematic variables at stride foot contact (SFC) during the early cocking phase, the passive range of motion (ROM), and the shoulder strength. The subjects were 40 high school baseball players. Each subject carried out five throwing tasks with his maximum effort. A three-dimensional analysis was performed to obtain the MER, and the shoulder angles of external rotation (ER), extension and abduction at SFC in the early cocking phase. The ROM and muscle strength of the shoulder ER and internal rotation (IR) were also measured. Significant moderate linear correlations were found between the MER and the ER (r = -0.32, p = 0.04) at SFC, extension angle ( r= 0.35, p = 0.03) at SFC, IR strength (r = -0.30, p = 0.04) and passive ROM of ER (r = 0.46, p = 0.01). The shoulder IR and extension angles at SFC may determine the degree of the MER angle. Furthermore, weak IR muscle strength and excessive ROM of ER might be risk factors for shoulder and elbow injuries. The finding will enable us to establish better prevention and rehabilitation strategies for throwing injuries in baseball players. Key pointsIt has been reported that the amount of stress imposed on shoulder and elbow joints is correlated with the degree of maximum shoulder external rotation angle (MER) during throwing. Therefore, controlling MER within a normal range plays a key role in the prevention for throwing-related injuries in baseball players.Physical and biomechanical factors related to the degree of MER must be addressed to advance the current prevention and rehabilitation strategies for the shoulder and elbow injuries.The current finding demonstrated that there was a significant moderate leaner correlation between shoulder internal rotation angle at the initial foot contact in the early cocking phase and MER.