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Rebecca J. Giorcelli, Richard E. Hughes, Richard S. Current and John R. Myers

This paper describes a procedure developed and validated to assess the accuracy of an infrared-based motion measurement system used to perform a kinematic analysis of the torso with respect to the pelvis during simulated lifting tasks. Two rigid reflective marker triads were designed and fabricated for attachment to the thorax over the 6th thoracic vertebra and the pelvis. System accuracy was assessed for planar rotation as well as rotations about multiple orthogonal axes. A test fixture was used to validate known triad orientations. The spatial coordinates of these triads were collected at 120 Hz using a ProReflex motion measurement system. Single value decomposition was used to estimate a rotation matrix describing the rigid body motion of the thorax triad relative to the sacral triad at each point in time. Euler angles corresponding to flexion, lateral bending, and twisting were computed from the rotation matrix. All measurement error residuals for flexion, lateral bending, and twisting were below 1.75°. The estimated mean measurement errors were less than 1° in all three planes. These results suggest that the motion measurement system is reliable and accurate to within approximately 1.5° for the angles examined.

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Rodrigo de M. Baldon, Daniel F.M. Lobato, Leonardo Furlan and Fábio Serrão

The purpose of this study was to compare lower limb kinematics between genders during stair descent. Fifteen females and fifteen males who were healthy and active were included in this study. The lower limb kinematics (pelvis, femur and knee) in the coronal and transversal planes were assessed during stair descent at 30°, 40°, 50° and 60° of knee flexion. The study found that females showed greater knee medial rotation for all the knee flexion angles (P = .02−.001), greater femoral adduction (P = .01 for all variables), with exception for 30° (P = .13), and greater femoral lateral rotation at 60° (P = .04). Females also showed a trend to have greater knee valgus at all the knee flexion angles (P = .06−.11) as well as less contralateral pelvis elevation at 50° and 60° (P = .10 and .12, respectively). This study showed that females carry out the stair descent with a lower limb alignment that might predispose them to develop overuse knee injuries, such as the iliotibial band syndrome and patellofemoral pain syndrome. Further prospective investigations should be carried out to verify whether these variables are factors that could predict these knee injuries.

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Aimée C. Smith, Jonathan R. Roberts, Eric S. Wallace, Pui Kong and Stephanie E. Forrester

Two-dimensional methods have been used to compute trunk kinematic variables (flexion/extension, lateral bend, axial rotation) and X-factor (difference in axial rotation between trunk and pelvis) during the golf swing. Recent X-factor studies advocated three-dimensional (3D) analysis due to the errors associated with two-dimensional (2D) methods, but this has not been investigated for all trunk kinematic variables. The purpose of this study was to compare trunk kinematic variables and X-factor calculated by 2D and 3D methods to examine how different approaches influenced their profiles during the swing. Trunk kinematic variables and X-factor were calculated for golfers from vectors projected onto the global laboratory planes and from 3D segment angles. Trunk kinematic variable profiles were similar in shape; however, there were statistically significant differences in trunk flexion (–6.5 ± 3.6°) at top of backswing and trunk right-side lateral bend (8.7 ± 2.9°) at impact. Differences between 2D and 3D X-factor (approximately 16°) could largely be explained by projection errors introduced to the 2D analysis through flexion and lateral bend of the trunk and pelvis segments. The results support the need to use a 3D method for kinematic data calculation to accurately analyze the golf swing.

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Alberto Ranavolo, Romildo Don, Angelo Cacchio, Mariano Serrao, Marco Paoloni, Massimiliano Mangone and Valter Santilli

Kinematic and kinetic methods (sacral marker, reconstructed pelvis, segmental analysis, and force platform methods) have been used to calculate the vertical excursion of the center of mass (COM) during movement. In this study we compared the measurement of vertical COM displacement yielded by different methods during able-bodied subjects’ hopping at different frequencies (varying between 1.2 and 3.2 Hz). ANOVA revealed a significant interaction between hopping frequency and method (p < 0.001), showing that increasing hopping frequency reduced the differences between methods. A post hoc analysis revealed a significant difference between all methods at the lowest hopping frequency and between the force platform and both the sacral marker and reconstructed pelvis methods at the intermediate hopping frequencies, with differences ranging from 16 to 67 millimeters (all p < 0.05). Results are discussed in view of each methods’ limits. We conclude that the segmental analysis and force platform methods can be considered to provide the most accurate results for COM vertical excursion during human hopping in a large range of hopping frequency.

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Shivam Bhan, Iris Levine and Andrew C. Laing

The biomechanical effectiveness of safety floors has never been assessed during sideways falls with human volunteers. Furthermore, the influence of body mass index (BMI) and gender on the protective capacity of safety floors is unknown. The purpose of this study was to test whether safety floors provide greater impact attenuation compared with traditional flooring, and whether BMI and gender modify their impact attenuation properties. Thirty participants (7 men and 7 women of low BMI; 7 men and 9 women of high BMI) underwent lateral pelvis release trials on 2 common floors and 4 safety floors. As a group, the safety floors reduced peak force (by up to 11.7%), and increased the time to peak force (by up to 25.5%) compared with a traditional institutional grade floor. Force attenuation was significantly higher for the low BMI group, and for males. Force attenuation was greatest for the low BMI males, averaging 26.5% (SD = 3.0) across the safety floors. These findings demonstrate an overall protective effect of safety floors during lateral falls on the pelvis, but also suggest augmented benefits for frail older adults (often with low body mass) who are at an increased risk of hip fracture.

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Jongseong An, Gabriele Wulf and Seonjin Kim

We examined the effects of attentional focus instructions on the learning of movement form and carry distance in low-skilled golfers. The X-factor describes the rotation of the shoulders relative to the pelvis, and its increase during the downswing (so-called X-factor stretch) is associated with the carry distance of the ball. X-factor stretch and carry distance have been shown to be associated with an early weight shift toward the front leg during the downswing. In our study, one group (internal focus, IF) was instructed to focus on shifting their weight to their left foot while hitting the ball, whereas another group (external focus, EF) was instructed to focus on pushing against the left side of the ground. A control (C) group was not given attentional focus instructions. Participants performed 100 practice trials. Learning was assessed after a 3-day interval in a retention test without focus instructions. The EF group demonstrated a greater carry distance, X-factor stretch, and higher maximum angular velocities of the pelvis, shoulder, and wrist than both the IF and C groups, which showed very similar performances. These findings demonstrate that both movement outcome and form can be enhanced in complex skill learning by providing the learner with an appropriate external focus instruction. Moreover, they show that a single external focus cue can be sufficient to elicit an effective whole-body coordination pattern.

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Lee Herrington

Context:

Hamstring muscle length is commonly measured because of its perceived relationship to injury of both the hamstrings themselves and the pelvis and lumbar spine. The popliteal (knee-extension) angle measured from the starting position hip and knee at 90° is a commonly used indirect measure of hamstring muscle length. When this measure has been undertaken in the literature previously, little attention was paid to the position of the pelvis, which may significantly influence measurements taken.

Design:

Repeated-measures.

Setting:

University human performance laboratory.

Participants:

60 healthy physically active males (mean age 20.1 ± 1.8 y, range 18–24 y).

Intervention:

The 2 extremes of pelvic position (anterior and posterior).

Main Outcome Measure:

Popliteal angle (with maximal knee extension) was measured in 2 positions, 1 of full anterior and 1 of full posterior pelvic tilt.

Results:

The mean difference in popliteal angle between anterior to posterior pelvic positions was 13.4° ± 9° (range 0–26°); this was statistically significant (P = .0001).

Conclusion:

The findings of the study indicate that pelvic position has a significant effect on popliteal angle and therefore should be taken into account when measuring hamstring muscle length.

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Gilles Dietrich, Alan Mark Wing, Martine Gilles and Ian Nimmo-Smith

This paper presents a conceptual model for studying the contribution of each leg to sideways stability of a four-link biped. It was assumed that a linear feedback controller maintained balance with torque related to the deviation from a reference value of the angle made by the trunk with the vertical. Predictions for ground reaction forces produced in resisting sideways push at the pelvis, based on simulation using a simple linear controller, are presented for two special cases (using one or both legs). This simple model was then compared to experimental data in which participants were asked to resist a sideways push. It was observed that all participants employed a strategy in which one leg was used to develop the force response. With this simple model, it was possible to simulate different kinds of responses to the balance perturbation. This model could be considered the first step of a more complex model in order to include specific components related to physiological parameters.

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Philippe C. Dixon and David J. Pearsall

The purpose of this study was to determine the effect of cross-slope on gait dynamics. Ten young adult males walked barefoot along an inclinable walkway. Ground reaction forces (GRFs), lower-limb joint kinematics, global pelvis orientation, functional leg-length, and joint reaction moments (JRMs) were measured. Statistical analyses revealed differences across limbs (up-slope [US] and down-slope [DS]) and inclinations (level; 0°; and cross-sloped, 6°). Adaptations included increases of nearly 300% in mediolateral GRFs (p < .001), functional shortening the US-limb and elongation of the DS-limb (p < .001), reduced step width (p = .024), asymmetrical changes in sagittal kinematics and JRM, and numerous pronounced coronal plane differences including increased US-hip adduction (and adductor moment) and decreased DS-hip adduction (and adductor moment). Data suggests that modest cross-slopes can induce substantial asymmetrical changes in gait dynamics and may represent a physical obstacle to populations with restricted mobility.

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Yungchien Chu, Glenn S. Fleisig, Kathy J. Simpson and James R. Andrews

The purpose of the current study was to identify the biomechanical features of elite female baseball pitching. Kinematics and kinetics of eleven elite female baseball pitchers were reported and compared with eleven elite male pitchers. Results suggested that females share many similarities with males in pitching kinematics, with a few significant differences. Specifically, at the instant of stride foot contact, a female pitcher had a shorter and more open stride and less separation between pelvis orientation and upper torso orientation. From foot contact to ball release, a female pitcher produced lower peak angular velocity for throwing elbow extension and stride knee extension. Ball velocity was lower for the female. Foot contact to ball release took more time for a female pitcher. Maximal proximal forces at the shoulder and elbow joints were less for a female pitcher.