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Daniel E. Lidstone, Justin A. Stewart, Reed Gurchiek, Alan R. Needle, Herman van Werkhoven and Jeffrey M. McBride

development of muscular fatigue during heavy prolonged load carriage in an inexperienced population. Our results may not represent physiological and biomechanical responses in soldiers with experience carrying US military operational loads. Future studies should examine physiological and biomechanical

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Andrew R. Kemper, Joel D. Stitzel, Craig McNally, H. Clay Gabler and Stefan M. Duma

The purpose of this study was to determine the influence of loading direction on the structural response of the human clavicle subjected to three-point bending. A total of 20 clavicles were obtained from 10 unembalmed fresh-frozen postmortem human subjects ranging from 45 to 92 years of age. The right and left clavicles from each subject were randomly divided into two test groups. One group was impacted at 0° from the transverse plane, and the second group was impacted at 45° angle from the transverse plane. There was no statistically significant difference in peak force (p = .22), peak moment (p = .30), or peak displacement (p = .44) between specimens impacted at 0° versus 45° from the transverse plane. However, there was a significant difference in the structural stiffness (p = .01) and peak strain (p < .01) between specimens impacted at 0° versus 45° from the transverse plane. The peak strain, however, must be evaluated with caution because of the variation in fracture location relative to the strain gauge. Due to the controlled matched data set, the differences in the structural stiffness with respect to loading direction can be attributed to the complex geometry of the clavicle and not material differences.

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Yu Shu, Zongliang Jiang, Xu Xu and Gary A. Mirka

Stooping and squatting postures are seen in a number of industries (e.g., agriculture, construction) where workers must work near ground level for extended periods of time. The focus of the current research was to evaluate a knee support device designed to reduce the biomechanical loading of these postures. Ten participants performed a series of sudden loading tasks while in a semisquat posture under two conditions of knee support (no support and fully supported) and two conditions of torso flexion (45 and 60°). A weight was released into the hands of the participants who then came to steady state while maintaining the designated posture. As they performed this task, the EMG responses of the trunk extensors (multifidus and erector spinae) were collected, both during the “sudden loading” phase of the trial as well as the steady weight-holding phase of the trial. As expected, the effects of torso flexion angle showed significant decreases in the activation of the multifidus muscles with greater torso angle (indicating the initiation of the flexion–relaxation response). Interestingly, the results showed that the knee support device had no effect on the activation levels of the sampled muscles, indicating that the loss of the degree of freedom from the ankle joint during the knee support condition had no impact on trunk extensor muscle response. The a priori concern with regard to these supports was that they would tend to focus loading on the low back and therefore would not serve as a potential ergonomic solution for these stooping/semisquatting tasks. Because the results of this study did not support this concern, further development of such an intervention is underway.

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C. Roger James, Barry T. Bates and Janet S. Dufek

The purposes of this study were to (a) present a theoretical model to explain the methods by which individuals accommodate impact force in response to increases in an applied stressor, (b) use the model and a correlation procedure to classify a sample of individuals based on their observed response patterns, and (c) statistically evaluate the classification process. Ten participants performed landings from three heights while video and force platform data were being collected. Magnitudes of impact-force characteristics from ground reaction force and lower extremity joint moments were evaluated relative to changes in landing momentum. Correlation between impact force and landing momentum was used to classify participant responses into either a positive or negative biomechanical strategy, as defined by the model. Positive and negative groups were compared using the Mann-Whitney U test. Results indicated that all responses fit within the categories defined by the model. Some individuals preferred positive strategies while others preferred negative ones depending on the specific variable. Only one participant consistently exhibited the negative strategy for all variables. Positive and negative groups were determined to be statistically different, p ≤ 0.05, for 61% of the comparisons, suggesting actual differences between groups. The proposed model appeared robust and accounted for all responses in the current experiment. The model should be evaluated further using landing and other impact activities; it should be refined and used to help researchers understand individual impact-response strategies in order to identify those who may be at risk for impact related injuries.

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Victoria H. Stiles, Igor N. Guisasola, Iain T. James and Sharon J. Dixon

Integrated biomechanical and engineering assessments were used to determine how humans responded to variations in turf during running and turning. Ground reaction force (AMTI, 960 Hz) and kinematic data (Vicon Peak Motus, 120 Hz) were collected from eight participants during running (3.83 m/s) and turning (10 trials per condition) on three natural turf surfaces in the laboratory. Surface hardness (Clegg hammer) and shear strength (cruciform shear vane) were measured before and after participant testing. Peak loading rate during running was significantly higher (p < .05) on the least hard surface (sandy; 101.48 BW/s ± 23.3) compared with clay (84.67 BW/s ± 22.9). There were no significant differences in running kinematics. Compared with the “medium” condition, fifth MTP impact velocities during turning were significantly (RM-ANOVA, p < .05) lower on clay (resultant: 2.30 m/s [± 0.68] compared with 2.64 m/s [± 0.70]), which was significantly (p < .05) harder “after” and had the greatest shear strength both “before” and “after” participant testing. This unique finding suggests that further study of foot impact velocities are important to increase understanding of overuse injury mechanisms.

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Alexander Tsouknidas, Nikoalos Michailidis, Savvas Savvakis, Kleovoulos Anagnostidis, Konstantinos-Dionysios Bouzakis and Georgios Kapetanos

This study presents a CT-based finite element model of the lumbar spine taking into account all function-related boundary conditions, such as anisotropy of mechanical properties, ligaments, contact elements, mesh size, etc. Through advanced mesh generation and employment of compound elements, the developed model is capable of assessing the mechanical response of the examined spine segment for complex loading conditions, thus providing valuable insight on stress development within the model and allowing the prediction of critical loading scenarios. The model was validated through a comparison of the calculated force-induced inclination/deformation and a correlation of these data to experimental values. The mechanical response of the examined functional spine segment was evaluated, and the effect of the loading scenario determined for both vertebral bodies as well as the connecting intervertebral disc.

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Max R. Paquette and Daniel A. Melcher

reported in the other. 13 Sex differences may exist with regard to the biomechanical response from runs of different intensities and distances, but since peak hip adduction is generally greater in rearfoot strike female runners compared to rearfoot strike male runners, 31 it may be difficult to observe

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Liam D. Harper, Adam Field, Liam D. Corr and Robert J. Naughton

The aim of this investigation was to profile the physiological, physical, and biomechanical responses during walking football. A total of 17 male participants (aged 66 ± 6 years) participated. Heart rate; blood lactate; accelerometer variables (biomechanical load [PlayerLoad], changes of direction); and rating of perceived exertion were measured. Participants mean percentage of maximum heart rate was 76 ± 6% during the sessions, with rating of perceived exertion across all sessions at 13 ± 2. Blood lactate increased by ∼157% from presession (1.24 ± 0.4 mmol/L) to postsession (3.19 ± 1.7 mmol/L; p ≤ .0005). PlayerLoad values of 353 ± 67 arbitrary units were observed, as well as ∼100 changes of direction per session. In conclusion, walking football is a moderate- to vigorous-intensity activity. The longitudinal health benefits of walking football remain to be elucidated, particularly on bone health, cardiovascular fitness, and social and mental well-being.

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Øyvind Sandbakk, Matt Spencer, Gertjan Ettema, Silvana Bucher Sandbakk, Knut Skovereng and Boye Welde

Purpose:

To investigate performance and the associated physiological and biomechanical responses during upper-body repeated-sprint work.

Methods:

Twelve male ice sledge hockey players from the Norwegian national team performed eight 30-m sprints with start every 30 s and an active recovery between sprints. Time was captured every 10 m by photocells, cycle length and rate were determined by video analyses, and heart rate and blood lactate concentration were measured by conventional methods.

Results:

The percentage sprint decrement was 7% over the 8 trials, with significant reductions in performance from the previous trial already on the second trial (all P < .05). Furthermore, cycle rate was reduced by 9% over the 8 trials (P < .05). Similar changes in performance and kinematic patterns were evident for all 10-m phases of the sprints. Heart rate gradually increased to 94% of maximal (178 ± 10 beats/min) over the 8 trials, and the mean reduction in heart rate was 7 ± 2 beats/min during the 22–24 s of active recovery for all trials (all P < .05). The blood lactate concentration increased to the athletes’ maximal levels over the 8 sprints (P < .05).

Conclusions:

This is the first study to investigate performance, physiological, and biomechanical aspects of self-propelled upperbody repeated-sprint work. The observed sprint decrement over the 8 trials was associated with reductions in cycle rates and high physiological demands. However, no kinematic and physiological characteristics were significantly correlated to repeated-sprint ability or the sprint decrement.

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Hong-Wan Ng, Ee-Chon Teo and QingHang Zhang

Posterior decompressive techniques including one- and two-level laminotomies and laminectomies are often used in treating cervical stenosis. Previously, several in vitro studies were conducted to help us understand the biomechanical changes occurring in the cervical spine after these surgical techniques. However, changes in the intersegmental flexibility under combined flexion-extension remain unclear. In this study, a 3-D nonlinear intact model of the C2–C7 was developed to evaluate the influence of one- and two-level laminotomies and laminectomies on the intersegmental moment rotational responses and internal stresses. The intact model was validated by comparing the predicted responses against experimental data. The validated model was then modified to simulate various surgical techniques for finite element analysis. Results showed that one- and two-level laminectomies increase the C2–C7 rotation motions by about 15% and 20%, respectively. The predicted increase in rotational motions also correlated well with the published data. Furthermore, results indicated that laminectomies would influence the biomechanical responses on both the affected and adjacent motion segments. In contrast, laminotomies have no significant effects on cervical biomechanics. To conduct a one-level laminectomy study, current findings indicate that it takes at least five motion segments to capture the immediate postsurgical biomechanical changes accurately and realistically. Minimally invasive cervical spine surgeries with one- or two-level laminotomies are preferred over one- and two-level laminectomies. Also, there is no consideration as to the efficacy of the two techniques in decompressing the spinal cord or nerve roots, which is the goal of the surgery, but is not examined in this study.