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Smita Rao, Fred Dietz and H. John Yack

The purpose of this study was to compare estimates of gastrocnemius muscle length (GML) obtained using a segmented versus straight-line model in children. Kinematic data were acquired on eleven typically developing children as they walked under the following conditions: normal gait, crouch gait, equinus gait, and crouch with equinus gait. Maximum and minimum GML, and GML change were calculated using two models: straight-line and segmented. A two-way RMANOVA was used to compare GML characteristics. Results indicated that maximum GML and GML change during simulated pathological gait patterns were influenced by model used to calculate gastrocnemius muscle length (interaction: P = .004 and P = .026). Maximum GML was lower in the simulated gait patterns compared with normal gait (P < .001). Maximum GML was higher with the segmented model compared with the straight-line model (P = .030). Using either model, GML change in equinus gait and crouch with equinus gait was lower compared with normal gait (P < .001). Overall, minimum GML estimated with the segmented model was higher compared with the straight-line model (P < .01). The key findings of our study indicate that GML is significantly affected by both gait pattern and method of estimation. The GML estimates tended to be lower with the straight-line model versus the segmented model.

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Brian J. O'Connor, H. John Yack and Scott C. White

A strategy is presented for temporally aligning ground reaction force and kinematic data. Alignment of these data requires marking both the force and video records at a common event. The strategy uses the information content of the video signal, which is A/D converted along with the ground reaction force analog signals, to accomplish this alignment in time. The vertical blanking pulses in the video signal, which define the start of each video field, can be readily identified, provided the correct A/D sampling rate is selected. Knowledge of the position of these vertical blanking pulses relative to the synchronization pulse makes it possible to precisely align the video and analog data in time. Choosing an A/D sampling rate of 598 Hz would enable video and analog data to be synchronized to within 1/1,196 s. Minimizing temporal alignment error results in greater accuracy and .reliability in calculations used to determine joint kinetics.

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Vanessa R. Yingling, H. John Yack and Scott C. White

This study investigated whether rearfoot motion at heel contact during running attenuates the magnitude of the impact force traveling through the body. Fifteen subjects completed running trials for two conditions:(a) running on a treadmill at a self-selected speed and a cadence of 160 steps/min and (b) running at the same speed and cadence but with rearfoot motion limited by a medial wedge inserted into the subject's shoe. A paired t test was used to test for differences between conditions in the peak accelerations of each accelerometer and the time to peak of the tibia acceleration. The predominant impact frequency and amplitude of the frequency peak were also tested for significant differences. No significant difference was found in the variables compared between the two conditions. The results demonstrated that restriction of rearfoot motion using a medial wedge during the initial 15% of the stance phase has no effect on the characteristics of the impulse wave at the tibia.

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Bhupinder Singh, Thomas D. Brown, John J. Callaghan and H. John Yack

During seated forward reaching tasks in obese individuals, excessive abdominal tissue can come into contact with the anterior thigh. This soft tissue apposition acts as a mechanical restriction, altering functional biomechanics at the hip, and causing difficulty in certain daily activities such as bending down, or picking up objects from the floor. The purpose of the study was to investigate the contact forces and associated moments exerted by the abdomen on the thigh during seated forward-reaching tasks in adult obese individuals. Ten healthy subjects (age 58.1 ± 4.4) with elevated BMI (39.04 ± 5.02) participated in the study. Contact pressures between the abdomen and thigh were measured using a Tekscan Conformat pressure-mapping sensor during forward-reaching tasks. Kinematic and force plate data were obtained using an infrared motion capture system. The mean abdomen-thigh contact force was 10.17 ± 5.18% of body weight, ranging from 57.8 N to 200 N. Net extensor moment at the hip decreased by mean 16.5 ± 6.44% after accounting for the moment generated by abdomen-thigh tissue contact. In obese individuals, abdomen-thigh contact decreases the net moment at the hip joint during seated forward-reaching activities. This phenomenon should be taken into consideration for accurate biomechanical modeling in these individuals.