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Loren Z.F. Chiu and Amy N. Moolyk

Joint kinematics differ between jump and drop landings and there is evidence that segment kinematics may also be different. The purpose of this research was to compare lower extremity segment kinematics for jump and drop landings, and to examine if multiple days of practice would influence these kinematics. Men (n = 9) and women (n = 15) performed 4 sessions of jump and drop landings (40 cm and 60 cm) in a motion-capture laboratory. Segment kinematics at initial contact, foot flat, and peak knee flexion were compared between landing types and across visits. At initial contact, foot plantar flexion was greater in jump versus drop landings (P < .05). At initial contact and foot flat, forward leg inclination and pelvis flexion were greater in jump landing (P < .05), while thigh flexion was greater in drop landings (P > .05). The differences in leg and thigh angles at initial contact and foot flat altered lower extremity posture. These results are in contrast to a previous study; this suggests that drop landing can be modified to have the same mechanics as jump landing. As practice did not influence drop landing mechanics (P > .05), specific control strategies and instructions need to be identified.

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Yoichi Iino, Atsushi Fukushima and Takeji Kojima

The purpose of this study was to investigate the relevance of hip joint angles to the production of the pelvic rotation torque in fast-pitch softball hitting and to examine the effect of ball height on this production. Thirteen advanced female softball players hit stationary balls at three different heights: high, middle, and low. The pelvic rotation torque, defined as the torque acting on the pelvis through the hip joints about the pelvic superior–inferior axis, was determined from the kinematic and force plate data using inverse dynamics. Irrespective of the ball heights, the rear hip extension, rear hip external rotation, front hip adduction, and front hip flexion torques contributed to the production of pelvic rotation torque. Although the contributions of the adduction and external rotation torques at each hip joint were significantly different among the ball heights, the contributions of the front and rear hip joint torques were similar among the three ball heights owing to cancelation of the two torque components. The timings of the peaks of the hip joint torque components were significantly different, suggesting that softball hitters may need to adjust the timings of the torque exertions fairly precisely to rotate the upper body effectively.

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Jennifer E. Earl

Context:

Gluteus medius (GM) contraction during single-leg stance prevents the contralateral pelvis from “dropping,” providing stability for lower extremity motion.

Objective:

To determine which combination of hip rotation and abduction exercise results in the greatest activity of the GM and whether the GM responds to increased loads in these exercises.

Design and Setting:

Repeated measures, laboratory.

Subjects:

20 healthy volunteers.

Interventions:

Resistance (2.26 and 4.53 kg) was provided to 3 variations of a single-leg-stance exercise: hip abduction only, abduction-internal rotation (ABD-IR), and abduction-external rotation.

Measurements:

Muscle activity was recorded from the anterior and middle portions of the GM using surface electromyography.

Results:

ABD-IR produced the most activity in the anterior and middle sections of the GM muscle. The 4.53-kg load produced significantly more activity than the 2.26-kg load (P < .05).

Conclusions:

The GM is most active when performing abduction and internal rotation of the hip. This information could be used to develop GM-strengthening exercises.

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Rose M. Angell, Stephen A. Butterfield, Shihfen Tu, E. Michael Loovis, Craig A. Mason and Christopher J. Nightingale

Object control skills (OCS) provide children the means to be physically active. However, gender equality in some OCS remains elusive. Particularly troublesome is the basic throwing pattern and, by extension, the striking pattern, both of which rely on forceful, rapid rotation of the pelvis, trunk, and shoulders. Some scholars argue that sex differences in throwing and striking are rooted in human evolution. The purpose of this study was to examine development of throwing and striking at the fundamental movement level. The design was multi-cohort sequential: 280 boys and girls grades K–8 (ages 4–15) were tested up to three times per year for 5 years on the Test of Gross Motor Development (TGMD-2). Hierarchical linear modeling (HLM) was applied to analyze individual growth curves. As anticipated, significant (p < .001) age-related gains were found for throwing and striking. In terms of sex (biology) or gender (sociocultural) differences, boys performed better longitudinally at throwing (p < .05) and striking (p < .05). These results reinforce theories that girls may be disadvantaged in achieving proficiency in throwing and striking. Interventions designed to enhance development of these skills should be in place long before grade 4, when most physical education curricula transitions to games and sports.

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Maureen I. Ogamba, Kari L. Loverro, Natalie M. Laudicina, Simone V. Gill and Cara L. Lewis

During pregnancy, the female body experiences structural changes, such as weight gain. As pregnancy advances, most of the additional mass is concentrated anteriorly on the lower trunk. The purpose of this study is to analyze kinematic and kinetic changes when load is added anteriorly to the trunk, simulating a physical change experienced during pregnancy. Twenty healthy females walked on a treadmill while wearing a custom made pseudo-pregnancy sac (1 kg) under 3 load conditions: sac-only condition, 10-lb condition (4.535 kg added anteriorly), and 20-lb condition (9.07 kg added anteriorly), used to simulate pregnancy in the second trimester and at full-term pregnancy, respectively. The increase in anterior mass resulted in kinematic changes at the knee, hip, pelvis, and trunk in the sagittal and frontal planes. In addition, ankle, knee, and hip joint moments normalized to baseline mass increased with increased load; however, these moments decreased when normalized to total mass. These kinematic and kinetic changes may suggest that women modify gait biomechanics to reduce the effect of added load. Furthermore, the increase in joint moments increases stress on the musculoskeletal system and may contribute to musculoskeletal pain.

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Shane J. Gore, Brendan M. Marshall, Andrew D. Franklyn-Miller, Eanna C. Falvey and Kieran A. Moran

When reporting a subject’s mean movement pattern, it is important to ensure that reported values are representative of the subject’s typical movement. While previous studies have used the mean of 3 trials, scientific justification of this number is lacking. One approach is to determine statistically how many trials are required to achieve a representative mean. This study compared 4 methods of calculating the number of trials required in a hopping movement to achieve a representative mean. Fifteen males completed 15 trials of a lateral hurdle hop. Range of motion at the trunk, pelvis, hip, knee, and ankle, in addition to peak moments for the latter 3 joints were examined. The number of trials required was computed using a peak intraclass correlation coefficient method, sequential analysis with a bandwidth of acceptable variance in the mean, and a novel method based on the standard error of measurement (SEMind). The number of trials required across all variables ranged from 2 to 12 depending on method, joint, and anatomical plane. The authors advocate the SEMind method as it demonstrated fewer limitations than the other methods. Using the SEMind, the required number of trials for a representative mean during the lateral hurdle hop is 6.

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Li-Xin Guo, Zhao-Wen Wang, Yi-Min Zhang, Kim-Kheng Lee, Ee-Chon Teo, He Li and Bang-Chun Wen

The aim of this study is to investigate the effect of material property changes in the spinal components on the resonant frequency characteristics of the human spine. Several investigations have reported the material property sensitivity of human spine under static loading conditions, but less research has been devoted to the material property sensitivity of spinal biomechanical characteristics under a vibration environment. A detailed three-dimensional finite element model of the human spine, T12– pelvis, was built and used to predict the influence of material property variation on the resonant frequencies of the human spine. The simulation results reveal that material properties of spinal components have obvious influences on the dynamic characteristics of the spine. The annulus ground substance is the dominant component affecting the vertical resonant frequencies of the spine. The percentage change of the resonant frequency relative to the basic condition was more than 20% if Young’s modulus of disc annulus is less than 1.5 MPa. The vertical resonant frequency may also decrease if Poisson’s ratio of nucleus pulposus of intervertebral disc decreases.

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Haidzir Manaf, Maria Justine and Hui-Ting Goh

Attentional loadings deteriorate straight walking performance for individuals poststroke, but its effects on turning while walking remain to be determined. Here we compared turning kinematics under three attentional loading conditions (single, dual-motor, and dual-cognitive task) between stroke survivors and healthy controls. Nine chronic stroke survivors and 10 healthy controls performed the Timed Upand- Go test while their full-body kinematics were recorded. Onset times of yaw rotation of the head, thorax and pelvis segments and head anticipation distance were used to quantify turning coordination. Results showed that stroke survivors reoriented their body segments much earlier than the controls, but they preserved the similar segmental reorientation sequence under the single-task condition. For the healthy controls, attentional loading led to an earlier axial segment reorientation, but the reorientation sequence was preserved. In contrast, the dual-cognitive task condition led to a disrupted reorientation sequence in stroke. The results indicate that turning coordination was altered in individuals poststroke, especially under the dual-task interference.

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Kurt L. Mudie, Amitabh Gupta, Simon Green, Hiroaki Hobara and Peter J. Clothier

This study assessed the agreement between Kvert calculated from 4 different methods of estimating vertical displacement of the center of mass (COM) during single-leg hopping. Healthy participants (N = 38) completed a 10-s single-leg hopping effort on a force plate, with 3D motion of the lower limb, pelvis, and trunk captured. Derived variables were calculated for a total of 753 hop cycles using 4 methods, including: double integration of the vertical ground reaction force, law of falling bodies, a marker cluster on the sacrum, and a segmental analysis method. Bland-Altman plots demonstrated that Kvert calculated using segmental analysis and double integration methods have a relatively small bias (0.93 kN⋅m–1) and 95% limits of agreement (–1.89 to 3.75 kN⋅m–1). In contrast, a greater bias was revealed between sacral marker cluster and segmental analysis (–2.32 kN⋅m–1), sacral marker cluster and double integration (–3.25 kN⋅m–1), and the law of falling bodies compared with all methods (17.26–20.52 kN⋅m–1). These findings suggest the segmental analysis and double integration methods can be used interchangeably for the calculation of Kvert during single-leg hopping. The authors propose the segmental analysis method to be considered the gold standard for the calculation of Kvert during single-leg, on-the-spot hopping.

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Trent M. Guess, Swithin Razu, Amirhossein Jahandar, Marjorie Skubic and Zhiyu Huo

The Microsoft Kinect is becoming a widely used tool for inexpensive, portable measurement of human motion, with the potential to support clinical assessments of performance and function. In this study, the relative osteokinematic Cardan joint angles of the hip and knee were calculated using the Kinect 2.0 skeletal tracker. The pelvis segments of the default skeletal model were reoriented and 3-dimensional joint angles were compared with a marker-based system during a drop vertical jump and a hip abduction motion. Good agreement between the Kinect and marker-based system were found for knee (correlation coefficient = 0.96, cycle RMS error = 11°, peak flexion difference = 3°) and hip (correlation coefficient = 0.97, cycle RMS = 12°, peak flexion difference = 12°) flexion during the landing phase of the drop vertical jump and for hip abduction/adduction (correlation coefficient = 0.99, cycle RMS error = 7°, peak flexion difference = 8°) during isolated hip motion. Nonsagittal hip and knee angles did not correlate well for the drop vertical jump. When limited to activities in the optimal capture volume and with simple modifications to the skeletal model, the Kinect 2.0 skeletal tracker can provide limited 3-dimensional kinematic information of the lower limbs that may be useful for functional movement assessment.