'You Must Have Good Tyres' - Why and How to Train the Foot

Aside from serving as the point of weight-bearing for all activities performed in standing, the foot represents the terminal link in the kinetic chain where forces generated by the athlete are transmitted to the ground beneath them. The action of the foot is integral to all modes of gait, from walking to sprinting. During sprinting, for example, the athlete's technical proficiency in how they apply force during each foot contact is recognised as paramount. Despite the integral role of the foot in locomotion and a host of athletic activities common to the majority of sports, training to develop this critical link is often overlooked in the physical preparation undertaken by athletes. This post examines the role of the different muscle groups involved in the dynamic function of the foot. We will explore different training modalities to develop the respective muscle groups, and also discuss the applications of this form of training, from both sports injury and performance perspectives.

You Must Have Good Tyres
— Jacques Piasenta

Jacques Piasenta may not be name known to many outside of France, and the sport of track and field athletics, but he boasts a long and distinguished career as a highly successful coach and trainer to multiple medallists (sprints and hurdles) at Olympic games, World Champs, and European Champs.

Piasenta's quote captures the importance of the foot - the analogy of the tyres of a race car, or perhaps a motorcycle, is well chosen. The dynamic function of the foot is critical in relation to balance, traction and propulsion. Likewise, just as a racing team would not concentrate their efforts on the engine and neglect the tyres, it follows that it makes little sense to train each of the proximal links in the lower limb kinetic chain and then ignore the terminal segment that connects with the ground.

The functional anatomy of the foot is adapted to its various functions in standing and during gait, from balance and weight-bearing to shock absorption and force transmission during locomotion. The specialised architecture of the foot comprises arches of bones (longitudinal, or front-to-back, and transverse, or side-to-side), reinforced by both passive ligamentous structures and the dynamic support provided by myofascial structures (notably the plantar fascia) and a variety of muscles.

These ligament springs and elastic myofascial components allows the foot to function in a 'sprung' manner - deforming under load before springing back to its original shape. This compression and recoil action is important as it serves to first store and then return elastic energy during locomotion and other activities, such as jumping. The contribution of this elastic energy return to the overall mechanical energy expended during running for example is significant

The muscles of the foot include both the intrinsic muscles, which originate and insert at the foot, and extrinsic muscles that cross multiple lower joints with the belly of the muscle above the ankle.

Different portions of the intrinsic muscles provide both dynamic support and stability to the foot and contribute to force generation during gait. For instance, the recruitment of plantar intrinsic muscles increases under conditions that demand additional stabilisation - for example when standing on one leg. By developing these muscles it is therefore possible to reduce stresses placed upon bone and ligament structures, and potentially also alter the functional architecture of the foot - such as height or length of the foot arches.

The extrinsic muscles of the foot originate above the ankle and so cross multiple joints. As such these muscles essentially operate as long pulleys and their action produces movement at the foot and ankle. The extrinsic muscles are considered the prime movers of the foot, and the long toe flexors in particular are important in generating propulsion during locomotion. Equally the extensors of the toes - particularly the big toe - serve a critical role during gait, first preparing the foot for ground contact and then in the recovery action after 'toe-off'.

Given the roles of these muscle groups it is easy to make the case for training to develop the intrinsic muscles, the toe flexors and the extensors of the toes, respectively. These muscles are not only integral to normal function, they are also important from an injury perspective. Impaired or altered function of the intrinsic plantar muscles particularly is linked to abnormal foot mechanics, which in turn implicated in different overuse injuries - particularly those suffered by runners. For instance, atrophy (wasting) of the intrinsic plantar muscles has been found in runners suffering with chronic plantar fasciitis 

But are these muscle groups responsive to training? Well, importantly, the answer to this is a firm 'yes'.

A range of studies has reported significant effects in response to a variety of training interventions for the plantar intrinsic muscles, the toe flexor muscles, and toe extensors. The muscles of the foot are shown to be highly responsive to training, and strength scores for the respective muscle groups increase with short-term training interventions. The various positive outcomes also include changes in static and dynamic foot posture - i.e. changes in arch height and length.

Perhaps more striking is that a range of improvements in athletic performance measures have been reported following different foot training modalities. Improvements in vertical and horizontal jump height and distance have been reported, and sprint times have also been improved following foot training interventions.

So, we have established that developing the muscles of the foot is important, and that these muscles are responsive to training. The question that remains is how practically should we approach training for the respective muscle groups of the foot?

One approach might be to simply train barefoot or wearing 'minimalist' footwear. Indeed there is some preliminary evidence that performance athletic activity in minimalist footwear might elicit some training adaptation in the foot muscles. One approach might be to perform a portion of the strength training workout barefoot - particularly for exercises that involve single-limb support, in view of the finding that plantar muscle activity is higher during such exercises due to the greater postural stability demands involved.

One caveat is that, as has been reported recently with barefoot running interventions, training responses are likely to be somewhat mixed. The effectiveness of simply training barefoot or in minimalist footwear is likely to vary according to the individual; this will depend on their morphology, but also their understanding of what they are attempting to achieve - i.e. what constitutes proper foot mechanics. 

A major factor with the latter is the level of instruction or coaching input provided. For instance, this is a likely explanation for the differences between 'responders' and 'non-responders' when barefoot running programmes are implemented without instruction. The neuromuscular skill component of training the foot is something we will return to later in the post.

With respect to targeted training interventions, we can employ a functional distinction so that the four toes outside the big toe are treated as a functional unit, and then deal with the movers of the big toe as a separate entity for training purposes.

Arguably this makes more sense than separating the intrinsic versus extrinsic muscles. Whilst some investigations have attempted to isolate the intrinsic muscles without extrinsic muscle activity, the merit and utility of this practice in a real-world setting is perhaps questionable. The 4-toe grouping was also employed in a recent study that combined flexor strength scores of the outer four toes (without big toe).

Just as foot training in general is often overlooked, the outer four toes in particular are frequently ignored during training. This is somewhat baffling given their integral role in supporting the dynamic function of the foot, especially during gait.

During running gait for example, it is the lateral part of the forefoot, or 5th metatarsal, that should ideally contact the ground first, before a medial shift onto the 1st metatarsal at weight acceptance. This initial contact and subsequent transition or weight shift is key to the transfer of energy between the metatarsal phalangeal (MTP) joints and the arch during the stance phase. The plantar muscles of the outer four toes help to control this initial contact and transition. Moreover, these muscles contribute to regulating the arch compression or deformation that occurs during ground contact.

The practical importance of this is reinforced by the aberrant findings reported among those with running overuse injuries. The mechanics of initial contact and transition during ground contact are different to healthy runners, and the degree of arch deformation is similarly greater in those suffering with chronic medial tibial stress syndrome. 

Relevant exercises in the literature are typically variations of the 'short foot' exercise, performed with the foot planted. These exercises are essentially isometric - i.e. involve static contractions with relatively little movement. A suggested modification involves the addition of a heavy band to apply resistance in medial direction. This variation still involves quasi isometric contraction, but the muscles must work to oppose the resistance applied in order to maintain the shape of the foot arch.

More dynamic exercises include single-leg 'pogo' bounds in a lateral direction. The aim is for a rolling contact, using the plantar muscles of the outer four toes to generate propulsion. Progression can be achieved by extending the distance for repetitions and/or incorporating an incline slope. Resistance can also be added, for example holding a medicine ball. 

Moving onto the big toe, training the short and long flexors of the big toe perhaps represents a more straightforward proposition. Often studies in the literature have employed body weight resistance only, performing exercises such as 'toe raises' and/or 'toe lowers'. A suggested variation employs either light resistance band or elastic tubing positioned under the big toe to augment the degree of loading placed upon the toe flexors.

An alternative approach once again employs a heavy band. The athlete performs isometric efforts, first in the initial position and then in the terminal position, with concentric and eccentric efforts in the transition movements in between.

In contrast to the standard toe raise exercise described previously, in which the ankle travels through a range of plantarflexion motion, in this exercise the ankle joint remains within a similar range (from neutral to slight dorsiflexion) throughout. Within these ranges the toe flexors are able to work at more of a mechanical advantage; it is also more similar to the joint angles that occur during the stance phase when running.

Finally, the extensor muscles of the big toe can similarly be trained using equivalent exercises involving resistance bands or elastic tubing to provide resistance to the top surface of the big toe joint. Essentially there are two main variations of toe extensor exercises. The first are isolation exercises that simply involve extending the big toe under resistance. The second approach involves compound movements where the emphasis is maintaining the big toe in a flexed position as the lower limb moves through a range of movement.

Aside from resistance exercises, a variety of drills and low-amplitude plyometrics can also be employed to train the foot. These drills are performed either barefoot or with minimalist footwear. Broadly, there are two main categories of foot conditioning activities. The first essentially involve a bounce action with a rigid foot/ankle position at foot strike that is maintained on contact.

In contrast, the second category employs drills which simulate more of a running gait pattern. The focus here is on a rolling foot contact, whereby the initial contact at the forefoot occurs at the 5th metatarsal, before moving medially to the first metatarsal during subsequent weight-acceptance. As such, the intention of the athlete is a large part of the neuromuscular training effect derived, so it is vital that they are instructed properly and executed correctly.

So, there you have it - the 'why' and 'how' of training the various muscles of the foot, with a selection of examples and suggestions for training modes. As we have outlined, for athletes who run and jump it is critical to take account of foot strength and control in your training - after all, developing a big engine is ultimately futile if the tyres fail.

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