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Randy J. Schmitz, Bryan L. Riemann and Timothy Thompson

Objective:

To determine whether gluteus medius (GM) activity increases in response to isometric closed-chain external hip rotation.

Design:

Subjects performed single-leg stances in 3 different conditions: 0° knee flexion, 0° hip flexion (C1); 0° knee flexion, 20° hip flexion (C2); and knee flexed 20–30°, 20° hip flexion (C3). Posteriorly directed forces of 8.9 N (F1), 17.8 N (F2), and 26.7 N (F3) were applied at the lateral pelvis of the nonstance side during each condition.

Subjects:

20 college students.

Measurements:

Surface EMG RMS amplitude from the GM and kinematic data from the trunk, hip, and knee.

Results:

Statistical analyses revealed a significant Condition 3 Force interaction and significant increases of EMG activity from C1F1 and C1F2 to C1F3 and from C3F1 to C3F2 and C3F3. F2 and F3 of C2 were significantly less than F2 and F3 of both C1 and C3.

Conclusions:

GM activity increases in response to isometric, closed-chain, external hip-rotation forces, and forward movement of the upper body with respect to the base of support decreases GM activity.

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Ya-Ting Yang, Yasuyuki Yoshida, Tibor Hortobágyi and Shuji Suzuki

We determined the angular range of motion and the relative timing of displacement in the thorax, lumbar spine, and pelvis in the transverse plane during treadmill walking at three velocities. Nine healthy young females walked on a treadmill for three minutes at 0.40, 0.93, and 1.47 m/s. The position of seven reflective markers and three rigs placed on the thorax, lumbar spine, and pelvis were recorded at 200 Hz by an eight-camera motion capture system. As gait velocity increased, stride length increased, cycle time decreased, and angular displacement in the thorax and L1 decreased but increased at the pelvis and L5 (all P < .05). The time of maximal angular rotation occurred in the following sequence: pelvis, L5, L3, L1, and thorax (P < .001). The thorax and L1 and L3 were in-phase for shorter duration as gait velocity increased, and this reduction was especially large, approx. 32% (P < .05), between thorax and pelvis. As gait velocity increased, the pelvis rotated earlier, causing the shortening of in-phase duration between thorax and pelvis. These data suggest that, as gait velocity increases, pelvis rotation dictates trunk rotation in the transverse plane during gait in healthy young females.

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David F. Stodden, Glenn S. Fleisig, Scott P. McLean, Stephen L. Lyman and James R. Andrews

Generating consistent maximum ball velocity is an important factor for a baseball pitcher’s success. While previous investigations have focused on the role of the upper and lower extremities, little attention has been given to the trunk. In this study it was hypothesized that variations in pelvis and upper torso kinematics within individual pitchers would be significantly associated with variations in pitched ball velocity. Nineteen elite baseball pitchers were analyzed using 3-D high-speed motion analysis. For inclusion in this study, each pitcher demonstrated a variation in ball velocity of at least 1.8 m/s (range: 1.8–3.5 m/s) during his 10 fastball pitch trials. A mixed-model analysis was used to determine the relationship between 12 pelvis and upper torso kinematic variables and pitched ball velocity. Results indicated that five variables were associated with variations in ball velocity within individual pitchers: pelvis orientation at maximum external rotation of the throwing shoulder (p = .026), pelvis orientation at ball release (p = .044), upper torso orientation at maximum external rotation of the throwing shoulder (p = .007), average pelvis velocity during arm cocking (p = .024), and average upper torso velocity during arm acceleration (p = .035). As ball velocity increased, pitchers showed an increase in pelvis orientation and upper torso orientation at the instant of maximal external rotation of the throwing shoulder. In addition, average pelvis velocity during arm cocking and average upper torso velocity during arm acceleration increased as ball velocity increased. From a practical perspective, the athlete should be coached to strive for proper trunk rotation during arm cocking as well as strength and flexibility in order to generate angular velocity within the trunk for maximum ball velocity.

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Edited by Richard Ray

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Rebecca L. Carl

Edited by Verle Valentine

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Heather VanOpdorp, Bonnie Van Lunen and James Swanson

Context:

Hip and pelvic injuries are often associated with direct trauma, but spe-cific fractures to the acetabulum are rare. The signs and symptoms of an acetabular fracture can mimic those of conditions that are more common at the hip area, and therefore the specificity of the diagnostic testing is crucial.

Objective:

To present the case of a female Division I college field-hockey player who developed a superomedial acetabular fracture.

Background:

The athlete’s initial complaint of intolerable hip pain decreased after a 3-week rest period but persisted with passive internal and external hip rotation. Additional diagnostic testing was needed to differentiate the various pathologies that were associated with her symptoms.

Conclusions:

Clinicians should be aware of the potential differential diagnoses of the hip and should investigate all potential possibilities even though they might not coincide with the initial injury.

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Micheal J. Luera, Brittany Dowling, Tyler W.D. Muddle and Nathaniel D.M. Jenkins

pitch where a pitcher intends, the ability to optimize velocity is likely influenced directly by a pitcher’s mechanics. Proper motion and timing of the lower body, pelvis, trunk, and throwing arm are crucial for developing the necessary velocity required for proficient pitch performance. 1 – 4

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Anna Bjerkefors, Johanna S. Rosén, Olga Tarassova and Anton Arndt

paddle stroke force and a 16% reduction in kayak speed. The rotation of the trunk and pelvis is also factors contributing to kayaking performance, 1 – 3 , 6 and results have shown that trunk 6 and pelvis 3 rotations are significantly greater in elite paddlers compared with nonelite paddlers indicating

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Sophie Speariett and Ross Armstrong

pelvis rotation speed, and swing sequence which may potentially increase methodological rigor. The aim of the current study was to investigate the relationship between the GSFMS composite and individual element scores and the golf performance measures of player’s handicap, clubhead speed, side accuracy

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Yumeng Li, Rumit S. Kakar, Marika A. Walker, Yang-Chieh Fu, Timothy S. Oswald, Cathleen N. Brown and Kathy J. Simpson

move the upper and middle trunk more synchronously in time than healthy individuals. 9 For adolescent girls with untreated mild to severe idiopathic scoliosis, the upper trunk and pelvis have been observed to move in the same direction (in-phase coordination pattern) for greater periods of time and