Background/Purpose: 42 million Americans participate annually in running. In 2014, the half marathon was the most popular distance with a total of 61% females (1.2 million) finishing these races. Further, there has been a 2% increase annually in new female runners completing a half marathon. Because medial knee osteoarthritis (MOA) is more prevalent among women, it is reasonable to investigate the mechanical impact of females training for a half marathon. Knee stiffness is related to leg stiffness which is significantly greater in individuals with MOA during walking. However, it is currently unknown how knee mechanics may be impacted by running and training for a half marathon distance. Therefore, the purpose of this study is to determine the relationship between shear and compressive forces and torsional stiffness at the knee with training.

 Methods: A 16 week half-marathon training program was completed. Pre- and post-training analyses were completed. 3D gait analysis was performed during a 30-second treadmill run at self-selected pace.  Retroreflective markers were placed on bilateral lower extremities. Kinematic data were collected at 240 Hz with a 5-camera motion analysis system. Commercial software was used to reconstruct 3-D coordinates for each marker and generate kinematic and kinetic variables. Torsional stiffness was calculated as the slope between the net joint moment and the angular displacement at the knee joint in the sagittal plane. Univariate regression analyses were calculated for stiffness and shear, stiffness and compression (pre and post). Welch 2 sample t tests were used to compare pre and post stiffness and pre and post shear.

Results: 21 female recreational runners between 33-56 years. (µ=47.6±8.1 yrs).There were significant differences found between pre and post stiffness (p= 0.03), pre and post compression (p=0.01), pre and post joint moment (p=0.04) and pre and post stride frequency (p=0.02). Regression models predicted a significant relationship between joint moment and shear (pre) (p=<0.01,r²=0.19), and joint moment and compression (post) (p=<0.01,r²=0.44). In addition, stride frequency was increased after training.

Conclusion:

With training, torsional stiffness at the knee increased but shear and compressive forces decreased. The change in joint moment was significant but there was no change in joint angle.We suggest that the joint moment changes existed due to a different position of vertical ground reaction force (VGRF) relative to the knee joint center, as there were no changes in magnitude of VGRF. This change in position is likely related to the increase in stride frequency and subsequent decrease in stride length. The modulation of knee stiffness in women may be protective against passive joint loading (sparing the compressive and shear forces) by increasing quadriceps muscle activation (active generation of force). Quantification of quadriceps muscle activity may aid in development of adjunct training programs for female runners

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/effect-of-training-on-knee-torsional-stiffness-and-its-relationship-to-tibial-compressive-and-anterior-shear-forces-in-recreational-female-runners/