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Rafael F. Escamilla, Glenn S. Fleisig, Coop DeRenne, Marcus K. Taylor, Claude T. Moorman III, Rodney Imamura, Edward Barakatt and James R. Andrews

We propose that learning proper hitting kinematics should be encouraged at a young age during youth baseball because this may help reinforce proper hitting kinematics as a player progresses to higher levels of baseball in their adult years. To enhance our understanding between youth and adult baseball hitting, kinematic and temporal analyses of baseball hitting were evaluated with a high-speed motion analysis system between 12 skilled youth and 12 skilled adult baseball players. There were only a small number of temporal differences between youth and adult hitters, with adult hitters taking significantly greater time than youth hitters during the stride phase and during the swing. Compared with youth hitters, adult hitters a) had significantly greater (p < .01) lead knee flexion when the hands started to move forward; b) flexed the lead knee over a greater range of motion during the transition phase (31° versus 13°); c) extended the lead knee over a greater range of motion during the bat acceleration phase (59° versus 32°); d) maintained a more open pelvis position at lead foot off ground; and e) maintained a more open upper torso position when the hands started to move forward and a more closed upper torso position at bat-ball contact. Moreover, adult hitters had greater peak upper torso angular velocity (857°/s versus 717°/s), peak left elbow extension angular velocity (752°/s versus 598°/s), peak left knee extension angular velocity (386°/s versus 303°/s), and bat linear velocity at bat-ball contact (30 m/s versus 25 m/s). The numerous differences in kinematic and temporal parameters between youth and adult hitters suggest that hitting mechanics are different between these two groups.

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Ram Haddas, Steven F. Sawyer, Phillip S. Sizer, Toby Brooks, Ming-Chien Chyu and C. Roger James

Introduction:

Recurrent lower back pain (rLBP) and neuromuscular fatigue are independently thought to increase the risk of lower extremity (LE) injury. Volitional preemptive abdominal contraction (VPAC) is thought to improve lumbar spine and pelvis control in individuals with rLBP. The effects of VPAC on fatigued landing performance in individuals with rLBP are unknown.

Objectives:

To determine the effects of VPAC and LE fatigue on landing performance in a rLBP population.

Design:

Cross-sectional pretest-posttest cohort control design.

Setting:

A clinical biomechanics laboratory.

Subjects:

32 rLBP (age 21.2 ± 2.7 y) but without current symptoms and 33 healthy (age 20.9 ± 2.3 y) subjects.

Intervention(s):

(i) Volitional preemptive abdominal contraction using abdominal bracing and (ii) fatigue using submaximal free-weight squat protocol with 15% body weight until task failure was achieved.

Main Outcome Measure(s):

Knee and ankle angles, moments, electromyographic measurements from semitendinosus and vastus medialis muscles, and ground reaction force (GRF) were collected during 0.30 m drop-jump landings.

Results:

The VPAC resulted in significantly earlier muscle onsets across all muscles with and without fatigue in both groups (mean ± SD, 0.063 ± 0.016 s earlier; P ≤ .001). Fatigue significantly delayed semitendinosus muscle onsets (0.033 ± 0.024 s later; P ≤ .001), decreased GRF (P ≤ .001), and altered landing kinematics in a variety of ways. The rLBP group exhibited delayed semitendinosus and vastus medialis muscle onsets (0.031 ± 0.028 s later; P ≤ .001) and 1.8° less knee flexion at initial contact (P ≤ .008).

Conclusion:

The VPAC decreases some of the detrimental effects of fatigue on landing biomechanics and thus may reduce LE injury risk in a rLBP population.

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Sébastien Viel, Marianne Vaugoyeau and Christine Assaiante

In the current study, we adopted the hypothesis that the body scheme disturbances occurring during adolescence might lead subjects to transiently neglect proprioceptive information and that adolescents might rely more strongly on vision to control their orientation and stabilize their body. To check this point, we asked adolescents 14–15 years to maintain vertical stance while very slow sinusoidal oscillations in the frontal plane were applied to the supporting platform at 0.01 Hz (below the detection threshold of the semicircular canal system) and at 0.06 Hz (above) with the eyes open and closed. Two postural components, orientation and segmental stabilization, were analyzed at the head, shoulder, trunk, and pelvis levels. At the lowest frequency without vision, the performances of adolescents were much less efficient than those of adults. Moreover, this study showed that vision plays a predominant role in adolescents’ control of orientation and body stabilization. At 0.06 Hz without vision, a clearcut difference was observed between the strategies used by girls and boys; specifically, the maturation of the segmental stabilization processes was found to be more advanced in girls than in boys. However, no such difference was observed at 0.01 Hz. Lastly, comparisons between the data obtained in adolescents and those previously obtained in young adults (Vaugoyeau, Viel, Amblard, Azulay, & Assaiante, 2008) clearly show that adolescents use different postural strategies and that they are not yet capable of reaching comparable postural performance levels to those observed in adults. Because adolescents were not able to use the proprioceptive information available to improve their postural control, we concluded that they showed a maturational lag in comparison with adults. This suggests that the mechanisms underlying postural control are still maturing during adolescence, which might constitute a transient period of proprioceptive neglect in sensory integration of postural control.

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Noah X. Tocci, David R. Howell, Dai Sugimoto, Corey Dawkins, Amy Whited and Donald Bae

-related injury. 9 , 11 , 18 Lower extremity movement, in particular pelvis movement, is one fundamental aspect to proper pitching mechanics. 9 , 19 , 20 Specifically, the pelvis acts as the foundation to the throwing motion, and serves an integral role in the transfer of energy during a pitch. 21

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Nicole C. George, Charles Kahelin, Timothy A. Burkhart and David M. Andrews

anatomical landmarks Measurements Segment Description and landmarks Lengths Pelvis (A) Vertical distance between the pubic symphysis and the level of the most prominent ridge on the superior aspect of the iliac crest Pelvis (L) ‡ Vertical distance between the

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Erin Macaronas, Shannon David and Nicole German

or effusion”, and “chronic expanding hematoma.” 1 Morel-Lavallée lesions are most commonly a result of severe trauma occurring at the greater trochanter and other parts of the pelvis. 1 – 3 Although the greater trochanter is the most common location for Morel-Lavallée lesions to occur, cases of the

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Hae-rim Han, Chung-hwi Yi, Sung-hyun You, Heon-seock Cynn, One-bin Lim and Jae-ik Son

Biomechanically, the gluteus medius (GMED) controls femoral motion during dynamic lower-extremity motion, and counteracts gravity to stabilize the pelvis in a single-leg stance. 1 , 2 However, when the GMED becomes weak, numerous neuromuscular problems including hip joint pathology, lateral hip

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Alyssa C. Adams, Kelly B. Fleming and Patricia M. Tripp

athletic training staff with pain in her left hip at the beginning of competition season. She reported no previous history of hip, groin, or pelvis pathology, but did have a history of a pars fracture at L2 and L5 and a herniated disc at T12. Her chief complaint was left hip pain initially originating

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Osamu Yanagisawa, Kenta Wakamatsu and Hidenori Taniguchi

The importance of lower-extremity function in baseball pitching is well recognized. In particular, the concern with hip function of baseball pitchers has been growing recently. The hip function is involved in the motion and stability of the pelvis, weight shift from a pivot leg (leg on the same

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Christian A. Clermont, Sean T. Osis, Angkoon Phinyomark and Reed Ferber

recreational runners according to differences in gait kinematics at the ankle, knee, and hip joints as well as the foot and pelvis segments in all 3 planes of motion. We hypothesized that we could separate and classify competitive and recreational runners and that the projected differences between groups would