BACKGROUND: In distance running, stride rate has received a lot of attention. Many studies focus on separating runners into groups based on their stride rate, however, stride rate seems to not be a style of running, rather a byproduct of different running styles. Hip kinematics are not often used to create such groups, in this study, we use the hip to determine what groups to separate runners into and determine if this affects knee kinematics and stride rate. PURPOSE: Compare runners who extend the hip after toe-off to runners who cease hip extension at toe-off and determine if there are significant differences in overall kinematics. METHODS: The participants were 20 Division I cross-country runners (19.5±1.2 years; 40+ miles per week). For the data collection, participants ran 3 minutes on the laboratory treadmill at an 8-minute/mile pace (data collected at 3-minutes). The motion-capture data was collected at 200Hz using 6 Vicon Bonita motion-capture cameras and 3DGAIT software. Ten strides were used to generate average plots (normalized to 101 data points) for the hip and knee motion in all three planes. The 10 plots were averaged to generate an overall waveform for the hip and knee in each plane. The joint motion, in each plane, was determined by calculating the range of each waveform. One-way ANOVAS were used to test for significant differences among the three planes (p=0.05). Bonferroni post-hoc analysis was used for follow-up testing. RESULTS: The group of runners who pulled the hip forward at toe off (11.23°±7.67°) were consistent with how fast the knee was pulled forward as well (27.18°±12.12°). While the group who extended the hip past toe-off (17.05°±6.4°) were also consistent on how far back the knee went before coming forward (11.88°±3.34). There was a significant difference when looking at what runners pulled their knee forward and which ones did not (p=0.001). For the hip, the result approached a significant difference when looking at how far back the runners extended it (p=0.08). Stride rate was significantly greater (p=0.002) in runners who did not extend the hip past toe off (176spm°±10steps) in comparison to the runners who did extend past toe-off (162spm°±4.14). CONCLUSION: the amount of motion the hip has in the sagittal plane is directly corelated to the amount of motion the knee has in the sagittal plane. Stride rate also is significantly greater if the hip is pulled back immediately.

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