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Tomoyuki Matsuo, Glenn S. Fleisig, Naiquan Zheng and James R. Andrews

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.

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Matej Daniel, Aleš Iglič and Veronika Kralj-Iglič

Hip contact stress is considered to be an important biomechanical factor related to development of coxarthrosis. The effect of the lateral coverage of the acetabulum on the hip contact stress has been demonstrated in several studies of hip dysplasia, whereas the effect of the anterior anteversion remains unclear. Therefore, the joint hip contact stress during normal level walking and staircase walking, in normal and dysplastic hips, for small and large acetabular anteversion angle was computed. For small acetabular anteversion angle, the hip contact stress is slightly increased (less than 15%) in staircase walking when compared with normal walking. In hips with large angle of acetabular anteversion, walking downstairs significantly increases the maximal peak contact stress (70% in normal hips and 115% in dysplastic hips) whereas walking upstairs decreases the peak contact stress (4% in normal hips and 34% in dysplastic hips) in comparison to normal walking. Based on the presented results, we suggest that the acetabular anteversion should be considered in biomechanical evaluation of the hips, especially when the lateral coverage of the acetabulum is small.

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Susanne Graner

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Regina R. Buccello-Stout, Ronita L. Cromwell, Jacob J. Bloomberg and Elbert B. Whorton

The goal of this study was to determine if exposure to sensorimotor adaptation training improved head stabilization in older adults. Sixteen participants, age 66–81 yr, were assigned at random to the control group (n = 8) or the experimental group (n = 8). Both groups first completed 6 trials of walking a foam pathway consisting of a moveable platform that induced a lateral perturbation during walking. Head-in-space and trunk-in-space angular velocities were collected. Participants from both groups then trained twice per week for 4 wk. Both groups walked on a treadmill for 20 min. The control group viewed a static scene. The experimental group viewed a rotating visual scene that provided a perceptual-motor mismatch. After training, both groups were retested on the perturbation pathway test. The experimental group used a movement strategy that preserved head stabilization compared with the controls (p < .05). This training effect was not retained after 4 wk.

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Rebecca J. Guthrie, Terry L. Grindstaff, Theodore Croy, Christopher D. Ingersoll and Susan A. Saliba

Context:

Individuals with low back pain (LBP) are thought to benefit from interventions that improve motor control of the lumbopelvic region. It is unknown if therapeutic exercise can acutely facilitate activation of lateral abdominal musculature.

Objective:

To investigate the ability of 2 types of bridging-exercise progressions to facilitate lateral abdominal muscles during an abdominal drawing-in maneuver (ADIM) in individuals with LBP.

Design:

Randomized control trial.

Setting:

University research laboratory.

Participants:

51 adults (mean ± SD age 23.1 ± 6.0 y, height 173.6 ± 10.5 cm, mass 74.7 ± 14.5 kg, and 64.7% female) with LBP. All participants met 3 of 4 criteria for stabilization-classification LBP or at least 6 best-fit criteria for stabilization classification.

Interventions:

Participants were randomly assigned to either traditional-bridge progression or suspension-exercise-bridge progression, each with 4 levels of progressive difficulty. They performed 5 repetitions at each level and were progressed based on specific criteria.

Main Outcome Measures:

Muscle thickness of the external oblique (EO), internal oblique (IO), and transversus abdominis (TrA) was measured during an ADIM using ultrasound imaging preintervention and postintervention. A contraction ratio (contracted thickness:resting thickness) of the EO, IO, and TrA was used to quantify changes in muscle thickness.

Results:

There was not a significant increase in EO (F 1,47 = 0.44, P = .51) or IO (F 1,47 = .30, P = .59) contraction ratios after the exercise progression. There was a significant (F 1,47 = 4.05, P = .05) group-by-time interaction wherein the traditional-bridge progression (pre = 1.55 ± 0.22; post = 1.65 ± 0.21) resulted in greater (P = .03) TrA contraction ratio after exercise than the suspension-exercise-bridge progression (pre = 1.61 ± 0.31; post = 1.58 ± 0.28).

Conclusion:

A single exercise progression did not acutely improve muscle thickness of the EO and IO. The magnitude of change in TrA muscle thickness after the traditional-bridging progression was less than the minimal detectable change, thus not clinically significant.

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Kazem Malmir, Gholam Reza Olyaei, Saeed Talebian and Ali Ashraf Jamshidi

Context:

Cyclic movements and muscle fatigue may result in musculoskeletal injuries by inducing changes in neuromuscular control. Ankle frontal-plane neuromuscular control has rarely been studied in spite of its importance.

Objective:

To compare the effects of peroneal muscle fatigue and a cyclic passive-inversion (CPI) protocol on ankle neuromuscular control during a lateral hop.

Design:

Quasi-experimental, repeated measures.

Setting:

University laboratory.

Participants:

22 recreationally active, healthy men with no history of ankle sprain or giving way.

Interventions:

Participants performed a lateral hop before and after 2 interventions on a Biodex dynamometer. They were randomly assigned to intervention order and interventions were 1 wk apart. A passive intervention included 40 CPIs at 5°/s through 80% of maximum range of motion, and a fatigue intervention involved an isometric eversion at 40% of the maximal voluntary isometric contraction until the torque decreased to 50% of its initial value.

Main Outcome Measures:

Median frequency of the peroneus longus during the fatigue protocol, energy absorption by the viscoelastic tissues during the CPI protocol, and feedforward onset and reaction time of the peroneus longus during landing.

Results:

A significant fall in median frequency (P < .05) and a significant decrease in energy absorption (P < .05) confirmed fatigue and a change in viscoelastic behavior, respectively. There was a significant main effect of condition on feedforward onset and reaction time (P < .05). No significant main effect of intervention or intervention × condition interaction was noted (P > .05). There was a significant difference between pre- and postintervention measures (P < .0125), but no significant difference was found between postintervention measures (P > .0125).

Conclusions:

Both fatigue and the CPI may similarly impair ankle neuromuscular control. Thus, in prolonged sports competitions and exercises, the ankle may be injured due to either fatigue or changes in the biomechanical properties of the viscoelastic tissues.

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Maude Bastien, Hélène Moffet, Laurent Bouyer, Marc Perron, Luc J. Hébert and Jean Leblond

The Star Excursion Balance Test (SEBT) has frequently been used to measure motor control and residual functional deficits at different stages of recovery from lateral ankle sprain (LAS) in various populations. However, the validity of the measure used to characterize performance—the maximal reach distance (MRD) measured by visual estimation—is still unknown.

Objectives:

To evaluate the concurrent validity of the MRD in the SEBT estimated visually vs the MRD measured with a 3D motion-capture system and evaluate and compare the discriminant validity of 2 MRD-normalization methods (by height or by lower-limb length) in participants with or without LAS (n = 10 per group).

Results:

There is a high concurrent validity and a good degree of accuracy between the visual estimation measurement and the MRD gold-standard measurement for both groups and under all conditions. The Cohen d ratios between groups and MANOVA products were higher when computed from MRD data normalized by height.

Conclusion:

The results support the concurrent validity of visual estimation of the MRD and the use of the SEBT to evaluate motor control. Moreover, normalization of MRD data by height appears to increase the discriminant validity of this test.

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Renato Claudino, Marcio José dos Santos and Giovana Zarpellon Mazo

muscles. For instance, erector spinae longus, external oblique (EO), and RA played an important role in stabilizing hip and trunk during perturbation at the shoulder level ( Kanekar & Aruin, 2014b ; Santos & Aruin, 2008 , 2009 ; Santos, Kanekar, & Aruin, 2010a ). In addition, during lateral

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Sheng Li, Frederic Danion, Mark L. Latash, Zong-Ming Li and Vladimir M. Zatsiorsky

One purpose of the present study was to compare indices of finger coordination during force production by the fingers of the right hand and of the left hand. The other purpose was to study the relation between the phenomena of force deficit during multifinger one-hand tasks and of bilateral force deficit during two-hand tasks. Thirteen healthy right-handed subjects performed maximal voluntary force production tasks with different finger combinations involving fingers of one hand or of both hands together. Fingers of the left hand demonstrated lower peak forces, higher indices of finger enslaving, and similar indices of force deficit. Significant bilateral effects during force production by fingers of both hands acting in parallel were seen only during tasks involving different fingers or finger groups in the two hands (asymmetrical tasks). The bilateral deficit effects were more pronounced in the hand whose fingers generated higher forces. These findings suggest a generalization of an earlier introduced principle of minimization of secondary moments. They also may be interpreted as suggesting that bilateral force deficit is task-specific and may reflect certain optimization principles.

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M. Scott Fitzgerald

Column-editor : Marjorie J. Albohm