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Michael Lyght, Matthew Nockerts, Thomas W. Kernozek and Robert Ragan

Achilles tendon (AT) injuries are common in runners. The AT withstands high magnitudes of stress during running which may contribute to injury. Our purpose was to examine the effects of foot strike pattern and step frequency on AT stress and strain during running utilizing muscle forces based on a musculoskeletal model and subject-specific ultrasound-derived AT crosssectional area. Nineteen female runners performed running trials under 6 conditions, including rearfoot strike and forefoot strike patterns at their preferred cadence, +5%, and –5% preferred cadence. Rearfoot strike patterns had less peak AT stress (P < .001), strain (P < .001), and strain rate (P < .001) compared with the forefoot strike pattern. A reduction in peak AT stress and strain were exhibited with a +5% preferred step frequency relative to the preferred condition using a rearfoot (P < .001) and forefoot (P=.005) strike pattern. Strain rate was not different (P > .05) between step frequencies within each foot strike condition. Our results suggest that a rearfoot pattern may reduce AT stress, strain, and strain rate. Increases in step frequency of 5% above preferred frequency, regardless of foot strike pattern, may also lower peak AT stress and strain.

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Bryan Sorenson, Thomas W. Kernozek, John David Willson, Robert Ragan and Jordan Hove

Context:

Hip- and knee-joint kinematics during drop landings are relevant to lower-extremity injury mechanisms. In clinical research the “gold standard” for joint kinematic assessment is 3-dimensional (3D) motion analysis. However, 2-dimensional (2D) kinematic analysis is an objective and feasible alternative.

Objective:

To quantify the relationship between 2D and 3D hip and knee kinematics in single-leg drop landings and test for a set of 3D hip and knee kinematics that best predicts 2D kinematic measures during single-leg drop landings Design: Descriptive, comparative laboratory study.

Participants:

31 healthy college-age women (65.5 kg [SD 12.3], 168.1 cm [SD 6.7]).

Methods:

Participants performed five 40-cm single-leg landings during motion capture at 240 Hz. Multiple regressions were used to predict relationships for knee and hip between 2D frontal-plane projection angles (FPPA) and 3D measurements.

Results:

2D knee FPPA had a strong relationship with 3D frontal-plane knee kinematics at initial contact (IC) (r 2 = .72), which was only minimally improved with the addition of knee sagittal-plane and hip transverse-plane positions at IC (r 2 = .77). In contrast, 2D knee FPPA had a low relationship with 3D knee-abduction excursion (r 2 = .06). The addition of knee sagittal-plane and hip transverse-plane motions did not improve this relationship (r 2 = .14). 2D hip FPPA had a moderate relationship with 3D frontal-plane hip position at IC (r 2 = .52), which was strengthened with the addition of hip sagittal-plane position (r 2 = .60). In addition, hip 2D FPPA into adduction excursion had a strong association with 3D hip-adduction excursion (r 2 = .70).

Conclusion:

2D kinematics can predict 3D frontal-plane hip and knee position at IC during a single-leg landing but predict 3D frontal-plane knee excursion with far less accuracy.