Can minimalist footwear prevent injury in runners?
Wearing minimalist footwear is a way to closely replicate the barefoot condition without risking the dangers of the urban environment and is an alternative to shod (trainers/sneakers). It must be noted that minimalist footwear is not the same as barefoot in that, although there is no mid-sole, there is still a rubber outer-sole that will limit sensory feedback between your foot and the ground (Bonacci et al., 2013) and potentially restrict some of the more intricate mechanics of the foot.
Minimalist shoes display certain distinguishing characteristics, these include:
– A thin rubber outer-sole (usually less than 7mm thick)
– Minimal toe-to-heel elevation (ramp)
– Lack of a heel wedge
– No cushioning
– They are lightweight
– They are flexible width-ways and length-ways
– Possess a wide toe box/forefoot
This type of footwear has recently been marketed as a way to reduce the incidence of running injuries, however no scientific study has ever explicit said or proven this – thus resulting in vibram five fingers being sued.
Where did it come from?
As humans we have evolved as runners, having to chase our prey over longer distances in order to eat it (persistence hunting) and whilst doing this we would have been barefoot or wearing thin moccasin footwear (Bramble & Lieberman, 2004). This thin style of footwear prevailed until the 1970’s when traditional running trainers/sneakers were invented.
Running itself has a high incidence of injury, particularly to the lower limbs (and most commonly the knee joint; van Gent et al., 2007), and it is the modern belief of many that trainers are responsible for these injury rates due to the cushioning, stiffness and the fact that they force you to adopt a certain running style.
Adding to this are studies such as one by Lieberman et al. (2010) that have shown minimalist footwear and barefoot running to reduce areas of the force trace associated with injury, and in addition several books have been published advocating the barefoot running style. These books and studies increase the popularity of barefoot/minimalist running.
Key Biomechanical Effects
All the potential injury mechanisms of minimalist footwear are results of changes in the gait cycle, with the biggest distinction in the stance phase or the ‘single limb support phase’ where the most ground reaction forces are present (Murphy, Curry, & Matzkin, 2013).
The most prominent difference during this stance phase is the foot strike pattern, where runners in minimalist footwear most likely to adopt a forefoot strike pattern (A) as opposed to a midfoot (B) or rearfoot (C) strike .
This likelihood of a forefoot strike is probably due to the lack of cushioning and heel wedge found in common trainers/sneakers (that encourages you to rearfoot strike and make it comfortable to do so).
Characteristics of the forefoot strike
During the landing phase of a forefoot strike there is more plantar-flexion at the ankle and flexion at the knee, resulting in changes in muscle activity (Stockton & Dyson, 1998) – the gastrocnemius and soleus (calf muscles) will pre-activate in order to resist a high velocity dorsi-flexion of the ankle (heel slapping down).
Secondly, there is a flatter foot placement during the stance phase which increases the surface area and thus allowing greater distribution of impact forces (Hasegawa, Yamauchi, & Kraemer, 2007).
Finally, the foot strikes closer to the centre of mass, reducing the moment arms of the knee and the hip (Altman & Davis, 2012).
Possible Mechanisms of Injury Prevention
Stride Length, Stance Time and Cadence
A study by Willson et al. (2014) looked at 19 female runners who underwent a two week transition into minimalist running shoes, which involved three 20-minute runs each week (volume was limited due to injury risk).
Five of these runners immediately switched to a forefoot strike pattern (the others maintained a rearfoot strike or more of a midfoot strike), and when re-tested had altered their running style considerably.
There was an average of a 5cm decrease in stride length, an 11ms shorter stance time and, subsequently, an increase cadence/frequency.
Heiderscheit (2011) found that a shorter stride length and faster cadence resulted in less stress to the knees and hips, meaning these running style alterations may well have an injury prevention effect.
The impact transient is the short ‘peak’ of force that is noticed during a stiff landing on a small surface area.
Lieberman et al. (2010) did a study on American and Kenyan runners who were a mixture of habitually shod (wore trainers/sneakers) and habitually barefoot and looked at footstrike patterns in both groups when shod and barefoot. He found that when shod the runners mostly had a rearfoot strike pattern and there was a distinct impact transient, however those who ran barefoot adopted a forefoot strike and did not have an impact transient.
This has clear implications on injury risk as a large impact transient is correlated to a greater risk of tibial stress injuries such as medial tibial stress syndrome (“shin splints”; Zadpoor & Nikooyan, 2011). Knee injuries are common due to the rearfoot strike also due to the tibia being loaded directly through the calcaneus.
Loading rate is the speed at which a limb is stressed with force and is represented by the ‘steepness’ of the curves above – with A being a rearfoot strike and B a forefoot strike.
Shih, Lin, and Shiang (2013) took 12 male habitually shod runners and looked at their loading rates in all conditions (shod, barefoot, minimalist, rearfoot strike, midfoot strike, forefoot strike) and found that forefoot strikers experience a significant reduction in loading rates.
High loading rates are implicated in tibial stress fractures and other lower limb soft tissue dysfunctions (Milner et al., 2006).
Negative Aspect of Minimalist Footwear
So does minimalist footwear prevent all injuries?
The answer is likely no, as when there is a reduction in load/stress in one area (i.e. the knee) it often increases elsewhere (i.e. the ankle).
When forefoot striking, the increased plantar-flexion at the ankle causes the gastrocnemius and soleus to do more work eccentrically to control the dorsi-flexion moment occurring at the ankle upon impact. This leads to the potential for Achilles tendinopathies and gastrocnemius strains if those tissues are unable to handle this increases stress (Tam, Wilson, Noakes, & Tucker, 2014).
Another common injury is metatarsal stress fractures, specifically to the second metatarsal (presumably because its the longest). This is due to the higher peak pressures that occur under the metatarsal heads (forefoot) during the impact and propulsion phases (Giuliani, Masini, Alitz, & Owens, 2011; Tam, Wilson, Noakes, & Tucker, 2014).
So should we all wear minimalist footwear?
The answer is – it depends.
As evidenced by Giuliani et al. (2011) and Wilson et al (2014) not everyone will instantly transition to a forefoot strike pattern (which has been shown to be the ‘safe’ way to run barefoot/minimalist if you are going to). If you rearfoot strike when barefoot/minimalist you are likely to experience debilitating injury to the knee due to extremely high loading rates/shock.
Additionally, running minimalist requires considerably eccentric control/strength in the gastrocnemius and soleus in order to resist dorsi-flexion, a lack of this required strength may result in overuse injuries to the Achilles tendon or acute strains to the gastrocnemius.
Finally, are we designed to run long distance races in minimalist footwear/barefoot?
It’s true we ran after our prey when we were cavemen, however although we ran fair distances we didn’t race long distances, therefore it’s debatable as to whether we are meant to run marathons at speed in minimalist footwear or barefoot.
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