The effects of minimalist or maximalist shoes on running biomechanics and injury risk – a physio point of view by Laurence Trachez
There is no topic that sparks more debate among runners than shoes! It almost feels like a risky territory to make definitive statements about. So instead, I will provide a nuanced overview of the influence of a few shoe properties on running biomechanics. While the shoe industry may promote specific types of running shoes, as runners, we should choose the most suitable shoe based on our needs, comfort, and scientific evidence, rather than simply following trends.
What are minimalist shoes?
Shoes can be broadly categorized as either minimal, traditional, or maximal. But what do these categories really mean? A group of 42 experts has developed and validated a rating scale called the Minimalist Index (MI) that determines the degree of minimalism in running shoes. The following definition of minimalist shoes was agreed upon by 95% of experts: „Footwear providing minimal interference with the natural movement of the foot due to its high flexibility, low heel to toe drop, weight and stack height, and the absence of motion control and stability devices„.
The standardized scale ranges from 0% to 100%, providing a more accurate assessment of a shoe’s minimalism. On one end of the scale, you have the heaviest and bulkiest shoes, scoring 0%, while the famous Vibram FiveFinger shoes have a MI score of 100%.
The MI percentage is calculated by considering five characteristics: weight, flexibility, heel-to-toe drop, stack height, and motion control/stability devices. Each characteristic carries an equal weight of 20% in the final score. Therefore, it’s important not to be misled by the sole consideration of a shoe’s heel-to-toe drop when determining whether it falls into the minimalist category.
The general consensus is that shoes with an MI score of 70% or higher can be considered minimal, as this threshold shows some biomechanical effects typically associated with minimalist shoes. „Traditional shoes“ are placed around the 50% mark on the scale.
Numerous variables have been studied and attributed to either maximalist or minimalist shoes. Although the list of studies is extensive and continually expanding, I will first provide a comprehensive overview of the research findings and then make some recommendations based on these findings.
Different characteristics, different effects
There are studies on minimal shoes as a group, as well as studies that solely look at one of the above mentioned characteristics of the MI. To be as precise as possible I decided to divide results by characteristics.
● Cushioning: Runners who wear maximal cushioning tend to overstride (landing with the foot in front of the knee), have a tendency for heel striking (initial contact with the ground), exhibit a lower cadence, experience longer ground contact times, and display higher vertical displacement.
Maximal cushioning increases ground impact and knee forces compared to more traditional shoes. Although there is no strong evidence that a higher vertical loading rate (VLR) leads to more running injuries (as the body is able to adapt to a given load), (specific) injuries are treated well by lowering VLR. On the other hand, minimal cushioning decreases knee joint forces, increases Achilles tendon forces and foot pressure, and reduces overall impact forces, resulting in less strain on the back, hips, and knees.
This occurs because when we wear less cushioned shoes, we tend to modify our impact behavior to land softly since a hard landing would be painful. However, this modification places additional workload on the Achilles tendon and the entire foot.
● Flexibility: Minimalist shoes contribute to strengthening of foot muscles. My belief is that this effect is related to the flexibility of a shoe. When a shoe is stiffer and slightly elevated at the front („toe spring“), the foot muscles are not activated substantially and may even weaken.
Minimalist shoes also enhance the tolerance of foot tissues: training with minimalist shoes has a positive effect on the achilles tendon stiffness and strength of the fascia plantaris.
Strong foot muscles have been linked to a reduced risk of foot injuries and improved symptom management if any injuries occur. Additionally, strong foot muscles positively impact speed and performance.
● The shoe’s drop: This refers to the difference in thickness between the front and back of the foot, measured in millimeters. It has received considerable attention recently. There are not many studies that have studied the effect of the shoe’s drop solely. Of the few studies there are, some found no difference in running biomechanics or running injuries, whereas a few studies found significantly higher joint stress on the kneecap joint with higher drops and a facilitation of a rearfoot striking pattern.
In the past, sports shoes typically had higher drops, and those who wore them became accustomed to it. Muscles can adapt in length when consistently used in a relatively shortened position to maintain an ideal length-force relationship. Rapidly transitioning from a high drop to a low drop can therefore overload the calves and tendons.
● Weight: Among all the MI subscales, weight likely has the most significant influence on speed and performance. For every 100 grams of added weight, there seems to be an impairment in running economy and performance.
● Motion control or stability devices: In the past, there was a belief that overpronated/flat feet or high arches put runners at risk of running-related injuries. However, several studies have undermined this claim. Unfortunately, this categorization is still being utilized, and feet still get categorized to sell „corrective“ shoes, which may impede the foot’s natural movement.
● Toe box: Although not rated in the MI, it is worth mentioning its importance. Often, we assume that a shoe is wide enough for our feet, but when we remove the insole and place our foot on it, we realize that it is actually too narrow. This can lead to an imbalance in foot muscles and the development of hallux valgus (the inward movement of the big toe, causing a bunion).
How can you utilize this information?
First of all, as the MI indicates, there is clearly no black and white: shoes are not either maximal or minimal, but there is a continuum. Minimalist shoes are those with a minimalist index of 70% or higher. This means it is not necessary to wear Vibram FiveFinger shoes to experience the benefits of minimalist shoes.
If you are a novice runner or have taken a long break from running and want to start again, my advice is to start out, at least partly, with minimalist shoes. Since you won’t be running high volumes initially, your feet will gradually adapt, and you will develop a favorable running style and strengthen your feet.
If you are an experienced runner who has been wearing maximal shoes for years without any issues, your muscles, tendons, joints, and cartilage have fully adapted to these loads and can handle them. Making any changes to your running style or shoes poses a risk of injury. This risk seems to be even higher if you are a heel striker (touching the ground with the heel first), trying to transition from maximal to minimalist shoes. Nevertheless, the lighter weight of shoes and the opportunity to develop stronger, healthier feet and a good running style with lower impact forces are of course compelling advantages. There are however other ways to train your feet (with exercises), and work on running style. It is an individual choice to make.
If you are motivated to start running with minimalist shoes: there are numerous studies that show that with a slow progression program, it is possible (even for experienced runners) to make a transition towards minimalist shoes. It is however generally advised to add foot and ankle exercises to prepare optimally. Regardless, it is crucial to start these training sessions very slowly and conservatively. Keep in mind that one minute of training translates to approximately 150-180 step repetitions, depending on your cadence. To be on the safe side, especially for heel strikers, training duration should therefore be increased by one minute per session only, or a one-month transition for every 10-20% difference on the MI. The important point is however to listen to your body! To ensure the change is not too drastic, a minimalist shoe with an MI score of around 70-80% could be chosen to start out with.
I have not considered other shoe selection aspects in this article, such as traction or specific needs for the trails you plan to do. Minimalist shoes might not be suitable for every race or trail. Some people argue you should race in the same shoes you train in. Of course it is debatable and an interesting question if it would be beneficial for runners to add some training with minimalist shoes, but run with shoes with more support for trails with higher demands. The intention of this article was solely to highlight some biomechanical effects of minimalist and maximal shoes, based on recent research.
This article has been written by Laurence Trachez, physiotherapist. www.trachezontrails.com
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