There have always been a whole host of assumptions made by the average runner when it comes to the topic of prevention of injuries. Here’s a few common ones – see if you know which are true and which are false:
- The forces absorbed by the body during the landing phase of running are 2 to 3 times higher than during walking.
- These higher impact forces are associated with increased risk of injury.
- Enhancing the cushioning properties of running shoes (a) decreases impact forces and (b) thereby decreases
injury risk.
The correct answers, which may come as a mild surprise, are: true, true, false/false.
I found this out the hard way myself when I ran track in high school. As a sprinter, my school issued me a pair of flats for training and racing. They may as well have been a couple of layers of cardboard attached to a thin fabric with laces. It felt like I was running on concrete.
But, interestingly, I never sustained an injury during the entire season. After the season was over, however, a friend told me about a fantastic shoe – the Adidas Olympiad – that was supposed to be the state-of-the-art in cushioning and comfort. When I tried them on in the store, I thought I was on pillows; I immediately shelled out the exorbitant ($19.95) charge for a pair and within a few weeks experienced my first injury – shin splints. At the time, of course, I didn’t make the association between these occurrences. Even years later, and despite having treated hundreds of runners, I still did not think there was a causative relationship between highly cushioned running shoes and the onset of injuries – but I did start to consider it a few years ago when the barefoot/minimalist-shoe movement began to gain popularity, largely as a result of the book Born To Run, in 2010. The proponents of this movement advanced a number of theories to explain why running shoes caused, rather than prevented, injuries. At the time [Therapy Corner #101], I raised some questions regarding the validity of these beliefs.
One of the theories I listed back then stated —
Because running shoes provide so much cushioning and protection, runners adapt a different gait pattern that leads to increased contact of the heel, instead of at the mid- or forefoot, during the landing phase. This leads to increased impact forces which increases the incidence of injury.
— but as I noted at the time, this claim of how runners landed was not necessarily true, and this has been confirmed within the past few years by new research. Also, while laboratory studies on shoes alone indicated that highly cushioned models reduced impact forces, more recent studies using actual people surprisingly showed just the opposite: these shoes actually seemed to be causing higher impact loading.
A new study just published last month in the online, peer-reviewed journal Scientific Reports [Scientific Reports] takes some major steps toward helping us understand this counter-intuitive finding.
Researchers in Finland analyzed the impact forces in 12, healthy runners (all of whom ran with the “dreaded” heel strike pattern). First, they ran with conventional (CON) shoes, then with maximalist-cushioned (MAX) shoes. In addition to finding that impact forces with the latter were higher, especially with faster (10 mph vs. 6 mph) running speeds, they were also able to confirm differences in how their bodies absorbed impact with different shoes, thereby explaining the discrepancy in the expected results.
When a runner’s foot lands, the ground reaction forces are minimized by the actions of your leg muscles gradually allowing the hip, knee, and ankle to flex. Jump down from a one-foot high step and you’ll see for yourself that it would be more jarring if you tried to keep your legs stiff and straight than if you allow your legs to bend.
What the researchers found is that the MAX shoes cause runners to do just that! 3D imaging showed that these shoes increased leg muscle stiffness when landing compared to the CON shoes. They reasoned that the cushioning decreases the stability of the shoe, thereby forcing the muscles to compensate to improve balance and functional efficiency. (The same result was found in a previous study comparing leg stiffness standing on a solid floor vs. a compressed foam pad, such as a yoga or exercise mat. Again, try it yourself – I think you’ll feel immediately how
your muscles tense up more standing on one leg on such a compliant surface.)
These findings do not necessarily confirm the barefoot running advocates’ claims, but they do raise the question of whether highly cushioned shoes are of any benefit, since their main selling point is their supposed capacity to reduce impact forces. My advice has always been that you should not feel any discomfort when you first try on a new pair of running shoes. At the same time, you may want to avoid buying a shoe just because they feel like super-comfortable pillows.