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Foot Angle and Loading Rate during Running Demonstrate a Nonlinear Relationship

STIFFLER-JOACHIM, MIKEL R.1,2; WILLE, CHRISTA M.1,2,3; KLIETHERMES, STEPHANIE A.1; JOHNSTON, WILLIAM4,5; HEIDERSCHEIT, BRYAN C.1,2,3

Medicine & Science in Sports & Exercise: October 2019 - Volume 51 - Issue 10 - p 2067–2072
doi: 10.1249/MSS.0000000000002023
APPLIED SCIENCES
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Vertical loading rates are typically found to be lower in forefoot compared to rearfoot strikers, promoting the idea that forefoot striking is desirable and may reduce running injury risk. However, prior work using linear models has shown that foot inclination angle (FIA) at initial contact is a poor predictor of vertical loading rate, suggesting a more complex association exists.

Purpose To determine if a nonlinear model superiorly describes the relationship between FIA and average vertical loading rate (AVLR). Secondary analyses assessed the influence of sex and sport on the association between FIA and AVLR.

Methods Whole body kinematics and vertical ground reaction forces were collected for 170 healthy National Collegiate Athletic Association Division I athletes (97 males; 81 cross-country runners) during treadmill running at 2.68, 3.35, and 4.47 m·s−1. Foot inclination angle and AVLR were calculated for 15 strides and averaged across strides for each limb. Polynomial mixed effects models assessed linear and nonlinear trends in the relationship between FIA and AVLR across the entire sample and accounting for sex and sport participation.

Results Average vertical loading rate was lowest at the extremes of FIA (i.e., −15°, 20°), whereas greater AVLR were observed between 5° and 10°. The cubic model resulted in a significantly better fit than the linear model (P < 0.001). Average vertical loading rate was also more variable among FIA associated with rearfoot and midfoot strike than forefoot strike. Adding sex to the model did not influence model fit; though, controlling for sport minimally improved model fit.

Conclusions The relationship between FIA and AVLR is best represented by a cubic model. Consequently, FIA should be treated as a continuous variable. Reducing FIA into categories may misrepresent the relationship between FIA and other gait variables.

1Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, WI

2Badger Athletic Performance Program, University of Wisconsin-Madison, Madison, WI

3Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI

4School of Public Health, Physiotherapy and Sports Science, University College Dublin, Dublin, IRELAND

5Insight Centre for Data Analytics, University College Dublin, Dublin, IRELAND

Address for correspondence: Bryan C. Heiderscheit, P.T, Ph.D., 1685 Highland Ave, 6136 Medical Foundation Centennial Building, Madison, WI 53705; E-mail: heiderscheit@ortho.wisc.edu.

Submitted for publication January 2019.

Accepted for publication April 2019.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.acsm-msse.org).

Online date: May 4, 2019

© 2019 American College of Sports Medicine