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Lower Extremity Stiffness Predicts Ground Reaction Force Loading Rate in Heel Strike Runners


Medicine & Science in Sports & Exercise: August 2019 - Volume 51 - Issue 8 - p 1692–1697
doi: 10.1249/MSS.0000000000001963

Purpose High vertical ground reaction force (vGRF) loading rates are thought to contribute to lower extremity injuries in runners. Given that elevated lower extremity stiffness has been reported to be associated with increased GRFs, the purpose of the current study was to determine if overall lower extremity stiffness, individual joint angular excursions and/or torsional stiffness are predictive of the average vGRF loading rate during running.

Methods Forty heel strike runners (20 men and 20 women) ran overground at a speed of 3.4 m·s−1. Average vGRF loading rate, lower extremity stiffness, and hip, knee, and ankle joint excursions and torsional stiffness from initial contact to the first peak of the vGRF were quantified. Stepwise multiple linear regression was performed to determine the best predictor(s) of average vGRF loading rate.

Results Lower extremity stiffness was found to the best predictor of average vGRF loading rate (R2 = 0.68, P < 0.001). The second variable that entered the stepwise regression model of average vGRF loading rate was knee joint excursionR2 = 0.03, P = 0.023).

Conclusions Increased lower extremity stiffness immediately after initial contact may expose heel strike runners to higher vGRF loading rates.

1Jacquelin Perry Musculoskeletal Biomechanics Research Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA; and

2Department of Physical Therapy, California State University Long Beach, Long Beach, CA

Address for correspondence: Christopher M. Powers, Ph.D., P.T., Division of Biokinesiology and Physical Therapy, University of Southern California, 1540 Alcazar Street, CHP-155, Los Angeles, CA; E-mail:

Submitted for publication July 2018.

Accepted for publication February 2019.

Online date: February 26, 2019

© 2019 American College of Sports Medicine