Edited by: Olivier Girard, Murdoch University, Australia
Reviewed by: Alexandre Igor Araripe Medeiros, Universidade Federal Do Ceará, Brazil; Helen Bayne, University of Pretoria, South Africa
This article was submitted to Elite Sports and Performance Enhancement, a section of the journal Frontiers in Sports and Active Living
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The foot is a complex system with multiple degrees of freedom that play an essential role in running or sprinting. The intrinsic foot muscles (IFM) are the main local stabilizers of the foot and are part of the active and neural subsystems that constitute the foot core. These muscles lengthen eccentrically during the stance phase of running before shortening at the propulsion phase, as the arch recoils in parallel to the plantar fascia. They play a key role in supporting the medial longitudinal arch, providing flexibility, stability and shock absorption to the foot, whilst partially controlling pronation. Much of the foot rigidity in late stance has been attributed to the windlass mechanism – the dorsiflexion of the toes building tension up in the plantar aponeurosis and stiffening the foot. In addition, recent studies have shown that the IFM provide a necessary active contribution in late stance, in order to develop sufficient impedance in the metatarsal-phalangeal joints. This in turn facilitates the propulsive forces at push-off. These factors support the critical role of the foot in providing rigidity and an efficient lever at push-off. During running or sprinting, athletes need to generate and maintain the highest (linear) running velocity during a single effort in a sprinting lane. Acceleration and sprinting performance requires forces to be transmitted efficiently to the ground. It may be of particular interest to strengthen foot muscles to maintain and improve an optimal capacity to generate and absorb these forces. The current evidence supports multiple exercises to achieve higher strength in the foot, such as the “short foot exercise,” doming, toes curl, towing exercises or the more dynamic hopping exercises, or even barefoot running. Their real impact on foot muscle strength remains unclear and data related to its assessment remains scarce, despite a recognized need for this, especially before and after a strengthening intervention. It would be optimal to be able to assess it. In this article, we aim to provide the track and field community with an updated review on the current modalities available for foot strength assessment and training. We present recommendations for the incorporation of foot muscles training for performance and injury prevention in track and field.
The foot is a complex joint system with multiple degrees of freedom that play an important role in athletic tasks such as running or sprinting. The compliance of the foot is remarkable and its spring-like properties—in the medial longitudinal arch (MLA) – allow mechanical energy to be stored and returned at each step (Ker et al.,
The IFM are the main local stabilizers of the foot and are part of the active and neural subsystems that constitute the foot core (McKeon et al.,
Because the IFM are usually neglected in assessment and treatment, a key component of foot core stability is not considered. We aim to provide the track and field community an updated review on the current modalities available for foot strength assessment and training. Running or sprinting is a cyclic activity involving all joints and muscles groups in the lower limbs, including the IFM, and the metatarsophalangeal (MTP) joint. We believe that it is of interest to assess the MTP joint's role during sprinting, especially looking at the link between midfoot and plantar flexors' torque before considering the various strengthening modalities and protocols. We will present recommendations for the incorporation of foot muscles training or performance and injury prevention in track and field.
During running or sprinting, athletes need to generate and maintain the highest (linear) running velocity during a single effort in a sprinting lane. Acceleration and sprinting performance requires forces to be transmitted efficiently to the ground. In particular, the production of horizontal force during the acceleration, more than vertical force, is related to sprinting performance. Indeed, the fastest runners at the end of the acceleration phase are not those who produce the highest total force, but those who manage to orient the forces horizontally (Morin and Samozino,
To achieve this, the sprinter must accomplish a series of segment rotations (Krell and Stefanyshyn,
This longer lever arm requires increased strength from the plantar flexors, and running athletes can benefit from it: a larger and more efficient horizontal force production may enhance performance (Morin and Samozino,
Finally the MTP joint plays a key role during sprinting and that may result in the development of very strong foot muscles in sprinters population. However, Tanaka et al. (
Although toe flexors strength is generated by a simultaneous action of both intrinsic and extrinsic foot muscles, the IFM seem most likely to be the main contributors to MTP joints torque (Farris et al.,
The foot enjoys some flexibility characterized by the medial longitudinal arch (MLA) which compresses and recoils. This ability allows mechanical energy to be stored and then released sequentially with every running step. Previous studies have proposed that mobility of the MLA can partly enhance the triceps surae and longus flexor hallucis moment during the push-off (Leardini et al.,
This relationship between MLA and plantar flexor torque has been shown in one study where hyperpronated feet showed lower concentric force of the plantar flexors when compared to neutral feet (Snook,
Finally, a stiff MLA seems to play a key role in ensuring a stable stance phase, and facilitating its load-absorbing task, the one which mitigates the dissipation of the mechanical energy produced by plantar flexors at push-off. Takahashi et al. (
The assessment of foot muscle strength is addressed in the literature with magnetic resonance imaging (MRI) or ultrasound imaging (USI) (Soysa et al.,
This assessment performed during gait and/or standing phase requires the use of the Oxford Foot Model, a 3D multi-segment foot model with a good to excellent repeatability (Okamura et al.,
The arch rigidity index (ARI) is calculated by dividing the standing arch height index by the sitting arch height index and it represents the structural mobility of the MLA (Mulligan and Cook,
Measurement of the arch rigidity index.
The sit-to-stand double-leg or single-leg navicular drop test is the most popular evaluation of longitudinal arch stability in the literature. The athlete sits with his hips, knees, and ankles bent to 90° and the feet resting on the floor. The inferior border of the prominent tuberosity of the navicular bone is palpated and marked with a pen, and the distance to the ground is measured using a steel ruler (resolution: 0.5 mm). At this point the tester asks the athlete to stand barefoot on a 4-in (10.16 cm) box, full weight on the foot being measured, while the other foot rests lightly on the box (Cote et al.,
The foot mobility measurement is a composite measure of vertical and medial to lateral mobility of the midfoot, whereas ND assess only vertical mobility. It has been described as a relevant technique for the assessment of foot mobility differences between non-weight bearing and weight bearing positions (McPoil et al.,
To measure the FMM, three instruments are needed: weight bearing and non-weight bearing arch height gauges and a device to measure midfoot width, both of which can be relatively easily manufactured, with the inclusion of a digital caliper (
where “Diff AH” and “Diff MFW” are the changes in dorsal arch height and in midfoot width between weight bearing and non-weight bearing, respectively.
Strengthening of the foot muscles responds to the same training principles as any other muscle group. IFM strengthening can be performed in isometric, concentric, eccentric or plyometric modes.
In isometric strengthening of the IFM, the most recognized exercise is the short foot exercise (SFE) (McKeon and Fourchet,
Short foot exercise.
It is also possible to combine the SFE with active and resisted activities of the upper body in order to create a cross-body inversion focus (i.e., trunk and pelvis medial rotation) and promote muscular chains facilitations (
Short foot exercise with cross-body inversion focus (with written informed consent obtained from the subject).
It is worth mentioning that numerous others exercises commonly referred to as “toe yoga” or “toe posture exercises” have been shown to activate the IFM in a isometric contraction (
Summarizes the recent studies on the topic.
Sulowska et al. ( |
Long distance runners |
Vele forward lean + Reverse tandem gait |
6 weeks |
↑ peak torque knee flexion (group 2) |
Unver et al. ( |
Pes planus |
Short Foot Exercise (SFE) group |
6 weeks |
↓ Navicular Drop (ND), Foot Posture Index (FPI), Pain and Disability Score |
Fraser and Hertel ( |
Healthy, recreationally active young adults |
IFM exercises program: |
4 weeks |
↑ IFM activation |
Taddei et al. ( |
Healthy long distance runners |
Foot and Ankle muscle strength training group |
8 weeks |
↑ cross sectional area (CSA) of AbH and FDB |
Sudhakar et al. ( |
Middle distance runners |
Vele forward lean + Walking backward |
4 weeks |
↑ of Functional Movement Screen (FMS) compared to VRF group |
Gooding et al. ( |
Healthy subjects |
Hallux extension Lesser toe extension Toe Spread Out (TSO) SFE | 1 set of 40 repetitions | SFE ↑ activation of AbH (29.7%) and FDB (29.8%) |
Kamonseki et al. ( |
Plantar fasciitis |
Foot exercise group |
Foot exercise group: |
All 3 exercise groups improve: |
Kim and Kim ( |
Flexible flat foot |
SFE group |
30 min per day |
↑ Y Balance test (both group) |
Sulowska et al. ( |
Long distance runners |
Vele forward lean + Reverse tandem gait + SFE | 6 weeks |
↓ FPI: item 1 et item 3 |
Kim et al. ( |
Mild and moderate hallux valgus |
Toe spread out + Orthosis | 20 min/days during 8 weeks |
↓ hallux valgus angle (HVA) + HVA during active abduction |
Panichawit et al. ( |
Flexible flat foot |
Calf muscles stretching exercise, strengthening of the tibialis posterior (TP), Peroneus Longus (PL), Flexor |
Stretching: 10 reps |
↑ TP and PL strength |
Hashimoto and Sakuraba ( |
Healthy male subjects |
Toe flexor strength | 8 weeks |
↑ vertical jump height + 50 m dash performance + IFM strength + 1 legged long jump |
Moon et al. ( |
Hyperpronated feet |
SFE | 1 session: 5 sets of 3 reps × 5 (2 min rest) with 5 s of contraction | ↑ dynamic balance |
Goldmann et al. ( |
Healthy subjects |
Toe flexor strength | 7 weeks (560 contractions) |
↑ toe strength |
Kim et al. ( |
Mild hallux valgus |
TSO group |
Practice for 2 weeks |
TSO exercise showed significantly greater activation of the AbdH than did SFE |
Mulligan and Cook ( |
Healthy subjects |
SFE | 4 weeks |
↓ navicular drop |
Lynn et al. ( |
Healthy subjects |
SFE group |
4 weeks |
NS difference in navicular height or static balance test |
Jung et al. ( |
Pes planus |
Foot orthosis + SFE group |
8 weeks |
↑ CSA AbH in foot orthosis + SFE group |
Jung et al. ( |
Normal feet |
SFE group |
SFE or Tower curl in maximal contraction (3 trials of 5 s = > muscular activation) 15 min/day during 2 weeks |
↑ AbH activity in SFE group in comparison to Tower curl group |
Toe spread out exercise, 1st toe extension and 2nd to 5th toe extension.
The “First-Toe Extension” or “Hallux-Extension” exercise is performed by extending the first metatarsophalangeal joint while maintaining the lesser toes (Second To Fifth) in contact with the floor (
We have stressed the importance of the MTP joint for sprint performance and some MTP strength exercises can be discussed. Previously used techniques that attempted to strengthen the IFM involved toe-flexion exercises (Hashimoto and Sakuraba,
Tower curl (Toe flexor exercise).
From a biomechanical perspective, isometric exercises are not reflective of how foot muscles work during locomotion (Farris et al.,
Short foot exercise in rotation (with written informed consent obtained from the subject).
Short foot exercise during propulsion (with written informed consent obtained from the subject).
The literature on the effects of running on foot muscular adaptations is relatively scarce and somewhat contradictory. Nevertheless, it does suggest that running could improve the cross-sectional area and the volume of foot muscles, and that this may be modulated by running mileage and experience (Miller et al.,
Johnson et al. (
An additional modality for the volitional strengthening of foot muscles is neuromuscular electrical stimulation (NMES) of the IFM. The aim is to strengthen the foot lever as the first interface between the ground and the athlete (Fourchet and Gojanovic,
Scientific findings suggest that using NMES on foot muscles can decrease navicular drop after a 3-weeks programme (three sessions a week). In another study, we showed that combining NMES with other exercises during 5 weeks shifted plantar foot pressure distribution laterally, which resulted in a reduction of loads under the medial midfoot during running (Fourchet et al.,
Practically speaking, the set-up is very simple: the athlete stands with feet on the ground whilst the stimulator delivers NEMS as for 15 min, and a total of ~75 contractions completed per training session. The two electrodes are placed behind the head of the first metatarsal to stimulate the medial arch intrinsic muscles (
Placement of electrodes for NMES on medial arch intrinsic foot muscles (McKeon and Fourchet,
We recommend that the athletes performs an average of 9 to 12 NMES sessions through 3–5 weeks, as this will bring effective improvements. The athlete begins in bipodal stance during the first sessions and then progresses to single-leg stance and plyometric activities such as hopping.
The biomechanical specificities at the forefoot and the midfoot regions during running or sprinting require a high level of strength from the small foot muscles. The foot core system must act as a strong and rigid lever in order to best transfer lower limbs forces during propulsion, and it must also cope with significant amounts of constraints at the absorption phase, in the sense of impact attenuation.
The existing medical and scientific literature can help coaches and athletes to set up the most adapted exercises in order to strengthen their feet: variation and progression is necessary and ranges from isometric, concentric to eccentric contraction modes, from analytic to functional exercises, from volitional to electrically-assisted (NMES).
In order to track foot strength development and response to training, the athletic community can rely on several reliable and field-friendly assessments modalities.
This paper discusses aspects that are more performance-oriented or training-oriented, but the readers should keep in mind that the optimal control of the foot at stance phase is essential for the athlete's health as well. Overuse injuries linked to the control of the arch of the foot may be related to deficits in active foot stabilization during running, which may lead to increased tissue stresses. Medial tibial stress syndrome or Achilles tendinopathy are often linked to a lack of stiffness in the medial arch of the foot and its ability to cope with the changing demands for dynamic foot control.
We fully acknowledge that expert track and field coaches already apply a large body of the knowledge described in this article in their daily work with athletes. We do believe that for optimal health and performance outcomes, a close collaboration between coaches, sport scientists and medical staff is of primary interest and enables all parties to keep learning from each other.
All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.