The Influence of Foot-Strike Technique on the Neuromechanical Function of the Foot

Luke A. Kelly; Dominic J. Farris; Glen A. Lichtwark; Andrew G. Cresswell

Disclosures

Med Sci Sports Exerc. 2018;50(1):98-108. 

In This Article

Abstract and Introduction

Abstract

Purpose: The aim of this study was to investigate the influence of foot-strike technique on longitudinal arch mechanics and intrinsic foot muscle function during running.

Methods: Thirteen healthy participants ran barefoot on a force-instrumented treadmill at 2.8 ms−1 with a forefoot (FFS) and rearfoot (RFS; habitual) running technique, whereas kinetic, kinematic, and electromyographic data from the intrinsic foot muscles were collected simultaneously. The longitudinal arch was modeled as a single "midfoot" joint representing motion of the rearfoot (calcaneus) relative to the forefoot (metatarsals). An inverse dynamic analysis was performed to estimate joint moments generated about the midfoot, as well as mechanical work and power.

Results: The midfoot was more plantar flexed (higher arch) at foot contact when running with a forefoot running technique (RFS 0.2° ± 1.8° vs FFS 6.9° ± 3.0°, effect size (ES) = 2.7); however, there was no difference in peak midfoot dorsiflexion in stance (RFS −11.6° ± 3.0° vs FFS −11.4° ± 3.4°, ES = 0.63). When running with a forefoot technique, participants generated greater moments about the midfoot (27% increase, ES = 1.1) and performed more negative work (240% increase, ES = 2.2) and positive work (42% increase, ES = 1.1) about the midfoot. Average stance-phase muscle activation was greater for flexor digitorum brevis (20% increase, ES = 0.56) and abductor hallucis (17% increase, ES = 0.63) when running with a forefoot technique.

Conclusions: Forefoot running increases loading about the longitudinal arch and also increases the mechanical work performed by the intrinsic foot muscles. These findings have substantial implications in terms of injury prevention and management for runners who transition from a rearfoot to a forefoot running technique.

Introduction

The orientation of a runner's foot at the moment of foot-ground impact is often used as a method to classify running technique.[1–4] Foot-strike patterns are generally classified into three groups: 1) runners who land in a heel-first manner (rearfoot strike), 2) runners who land on the forefoot (forefoot strike (FFS)), and 3) runners who land with a simultaneous heel and forefoot contact (midfoot strike).[2,5] Although the majority (>75%) of distance runners adopt a rearfoot running technique,[6,7] it has been suggested that a forefoot running technique is mechanically advantageous, because it affords the runner greater opportunity to recycle the energy associated with foot–ground impact via elastic stretch and recoil of the tendons and ligaments of the ankle and foot.[4,8,9] Consequently, the popularity of running "retraining" programs that promote a forefoot landing pattern to reduce injury risk and improve running performance has surged.[5,10,11]

The longitudinal arch (LA) of the human foot behaves in a springlike manner when running, temporarily storing and then subsequently returning a considerable portion of the mechanical energy required for each stride.[12–14] Compression (lowering and lengthening) of the LA during the first half of stance phase allows mechanical energy to be temporarily stored within the stretched ligaments, muscles, and tendons that span this structure.[12,14,15] This energy is subsequently returned in late stance, because the resultant ground reaction force (GRF) declines and the stretched elastic structures shorten to allow the LA to recoil (rise and shorten).[4,12,15]

Recently, studies have explored the hypothesis that a forefoot running technique enhances foot-spring function by allowing a greater proportion of mechanical energy to be recycled during each stride.[4,14,16] Consistent with the hypothesis of enhanced foot-spring function, these studies have all reported an increase in LA compliance with a forefoot technique compared with a rearfoot technique when running at matched velocities. However, the increased compliance seems to be due to a higher LA at foot contact, rather than an increase in peak LA compression in midstance.[4,14,16] A key finding in each of these studies was that peak LA compression and model-derived plantar aponeurosis strains were similar, regardless of foot-strike technique.[4,14,16] Given that peak strain primarily determines the magnitude of stored elastic energy, this finding suggests no energetic benefits to a forefoot running technique. The studies by McDonald et al.[16] and Wager and Challis[14] provide valuable insight into the biomechanics of the LA when running with rearfoot and forefoot running techniques. However, these studies have a methodological limitation in their assumption that the foot is a passive structure with no active muscular control of its biomechanical function.

Forefoot running is characterized by the center of pressure (COP) being located further anterior in the foot and higher peak GRF.[2,5,17,18] Thus, in a similar manner to the ankle joint,[19] an increase in the length of the GRF moment arm, combined with the higher peak GRF, will likely increase loading of the LA when running with a forefoot technique. Given that the intrinsic foot muscles have similar anatomical pathways to the plantar aponeurosis[20–22] and have the capacity to alter the stiffness of the LA,[15,23] it is highly likely that these muscles also contribute to the observed alterations in LA mechanics between foot-strike techniques. An increase in activation of the intrinsic foot muscles when running with a forefoot technique could potentially reduce excessive LA compression and reduce plantar aponeurosis strain, providing an explanation for the lack of difference in plantar aponeurosis strain observed in previous studies.[14,16] Furthermore, these muscles are also known to display preparatory activation before foot contact;[15,24] thus, it is conceivable that increased activation of these muscles in late swing may also explain the increased LA height at foot contact when running with a forefoot technique.

It is currently unknown if the intrinsic foot muscles contribute to the regulation of LA motion when switching from a rearfoot to a forefoot running technique. It is also unknown if loading of the LA changes when converting to forefoot running technique. Therefore, the aim of this study was to test the hypothesis that a forefoot running technique results in higher magnitudes of activation in the intrinsic foot muscles during the stance and swing phases while running, because of the higher mechanical loading occurring about the LA.

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