Elsevier

Journal of Biomechanics

Volume 76, 25 July 2018, Pages 1-7
Journal of Biomechanics

Acute changes in foot strike pattern and cadence affect running parameters associated with tibial stress fractures

https://doi.org/10.1016/j.jbiomech.2018.05.017Get rights and content

Abstract

Tibial stress fractures are a common and debilitating injury that occur in distance runners. Runners may be able to decrease tibial stress fracture risk by adopting a running pattern that reduces biomechanical parameters associated with a history of tibial stress fracture. The purpose of this study was to test the hypothesis that converting to a forefoot striking pattern or increasing cadence without focusing on changing foot strike type would reduce injury risk parameters in recreational runners. Running kinematics, ground reaction forces and tibial accelerations were recorded from seventeen healthy, habitual rearfoot striking runners while running in their natural running pattern and after two acute retraining conditions: (1) converting to forefoot striking without focusing on cadence and (2) increasing cadence without focusing on foot strike. We found that converting to forefoot striking decreased two risk factors for tibial stress fracture: average and peak loading rates. Increasing cadence decreased one risk factor: peak hip adduction angle. Our results demonstrate that acute adaptation to forefoot striking reduces different injury risk parameters than acute adaptation to increased cadence and suggest that both modifications may reduce the risk of tibial stress fractures.

Introduction

Long distance running is plagued with high injury rates; in one study, 79% of long distance recreational runners experienced an injury that required training adjustments (Lun et al., 2004). Tibial stress fractures, one of the most common running injuries (Taunton et al., 2002), are the most common stress fracture in athletes (Matheson et al., 1987) and require an average recovery time of 12 weeks (Beck et al., 2008). Biomechanical parameters associated with a history of tibial stress fracture suggest possible mechanisms of injury. Higher average and peak loading rates and peak tibial accelerations may contribute to stress fracture development (Milner et al., 2006b). Runners with a history of tibial stress fractures tend to have higher peak hip adduction angles and peak absolute free moments than runners with no prior fracture (Pohl et al., 2008); these parameters are thought to increase fracture risk due to poor alignment during running (Milner et al., 2005) and excessive torques (Milner et al., 2006a), respectively. Although we cannot directly determine changes to injury risk, it is possible to investigate the effects of changing running pattern on parameters associated with tibial stress fractures.

A small retrospective study showed that habitual forefoot striking runners had a lower incidence of tibial stress fractures than rearfoot striking runners (Daoud et al., 2012), suggesting that converting to forefoot striking may reduce tibial stress fracture risk. Converting from rearfoot striking to forefoot striking is associated with lower average and peak loading rates (Boyer et al., 2014, Shih et al., 2013), but can increase tibial accelerations near the time of foot contact (Laughton et al., 2003). Forefoot striking is typically taught to habitual rearfoot strikers through verbal explanation (Giandolini et al., 2013, Laughton et al., 2003, Olin and Gutierrez, 2013) or video (Boyer and Derrick, 2015). Adjusting to forefoot striking is associated with changes in kinematics – e.g., higher cadence (Arendse et al., 2004), a more plantarflexed ankle (Lieberman et al., 2010) and flexed knee (Laughton et al., 2003) at foot contact – and changes in muscle activity (Landreneau et al., 2014, Shih et al., 2013, Yong et al., 2014). It is unclear which kinematic and kinetic differences associated with forefoot striking contribute to the potential decrease in injury rate, and whether injury risk parameters can be reduced with a different adaptation, such as increasing cadence.

Increasing cadence may reduce the risk of tibial stress fractures, but, unlike forefoot striking, does not require major adjustments to running style. Increasing cadence while rearfoot striking was shown to lower peak tibial accelerations during overground running (Derrick et al., 1998) and lower peak hip adduction angle during treadmill running (Heiderscheit et al., 2011, Willy et al., 2016a). Previous studies increased subjects’ cadence during overground running by using tape marks on the floor to shorten stride length (Boyer and Derrick, 2015, Edwards et al., 2009), but this method does not ensure the ability to recreate the motion without visual feedback. Cadence has been successfully increased using a metronome during treadmill running (Giandolini et al., 2013, Hamill et al., 1995, Heiderscheit et al., 2011, Hobara et al., 2012, Snyder et al., 2012), overground running (Lyght et al., 2016), and during in-field gait retraining (Willy et al., 2016a, Willy et al., 2016b). It remains unknown, however, if changes to parameters associated with tibial stress fracture, which were previously observed during treadmill running, translate to overground running without visual feedback.

The effectiveness of reducing injury risk parameters by increasing cadence alone compared to that of forefoot striking during overground running is unclear. Studies that compared the effects of foot strike type and increased cadence on tibial stress fracture risk parameters were either restricted to treadmill running (Giandolini et al., 2013) or investigated a limited set of parameters (Boyer and Derrick, 2015, Giandolini et al., 2013). Previous work comparing these acute adaptations independently assessed the effects of foot strike or cadence by having subjects run using a forefoot striking pattern without adjusting cadence and changing cadence while maintaining a rearfoot striking pattern (Boyer and Derrick, 2015, Giandolini et al., 2013, Lyght et al., 2016). In our study, we aimed to capture how runners naturally adjusted their running pattern when being asked to only focus on changing foot strike or increasing cadence. Our goal was to study how natural adaptations to changing foot strike or increasing cadence affects tibial stress fracture risk during overground running in a single population by analyzing the following set of injury risk parameters: peak tibial acceleration, peak absolute free moment, peak hip adduction angle, and average and peak loading rates.

To achieve this goal, we first demonstrated that training runners with visual feedback of foot pressure allows them to perform a forefoot striking pattern, and providing runners with auditory cueing allows them to increase cadence while running overground. We then tested the hypotheses that in comparison to rearfoot striking, (1) average and peak loading rate decrease during forefoot striking, (2) peak tibial acceleration and free moment decrease during increased cadence, and (3) peak hip adduction angle decreases during both forefoot striking and increased cadence.

Section snippets

Subjects

Seventeen healthy, habitual rearfoot striking recreational runners (11 females, 6 males; age: 32.1 ± 9.8 years; height: 168 ± 11 cm; mass: 64.9 ± 12.5 kg), participated in this study. We ensured subjects landed on their heels using a high speed camera (Casio Exilim Pro Ex-F1, Casio Computer Co., Ltd., Shibuya-ku, Tokyo, Japan) during overground running (≥120 frames/s). All subjects were experienced long distance runners who reported running a minimum of 10 km/week (33.5 ± 17.5 km/week). Each

Results

Individuals were able to perform forefoot striking and increased cadence running patterns while running overground after practicing with feedback on a treadmill. We confirmed runners converted foot strike pattern while running overground, and observed significant differences in foot orientation at foot contact between rearfoot striking and forefoot striking (p < 0.001) (Fig. 2a). We also found 4.0 ± 3.3% greater cadence in forefoot striking compared to overground rearfoot striking trials

Discussion

This study’s findings suggest that parameters associated with tibial stress fractures can be reduced by altering running pattern; forefoot striking with free cadence reduces loading rates, and increasing cadence with free foot strike decreases peak hip adduction angle. In our study, we independently evaluated both running pattern modifications in the same population, which allowed us to compare changes to injury risk parameters and improve understanding of differences between the two

Conflict of interest statement

None of the authors had any financial or personal conflict of interest with regard to this study.

Acknowledgements

The authors thank Christopher Dembia, Johann Simpson, Apoorva Rajagopal, and Carmichael Ong. This work was supported by a Stanford Bio-X Graduate Student Fellowship and NIH grants U54 EB020405, P2C HD065690.

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