The recent NY Times article “For Runners, Soft Surfaces Can Be Just as Hard on the Body”, brings up three interesting points for me.
1. Author Bias
First off, always be wary of author bias: the actual conclusion of the article as I read it is that there is really no appreciable difference between surface and injury rate. But this doesn’t make for a good headline, so the story gets a spin put to it. As I read the story and the research, it is simply that different surfaces create different demands. The headline could have just as easily been “For runners, different surfaces are different”, but that really doesn’t attract one to read the article does it? I have to admit a bias; personally I prefer trails. Professionally, I believe that variability of physical task demand results in the end product of a more robust system and is therefore a desirable trait in any physical or mental training program. Soft or uneven surface will create more variability in the demands on the system. That being said, the most important take home point is probably that if you are going to make a change, you need to do it slowly and prepare for it. Interestingly, that is also a take home point of a similar ‘myth buster’ article, Skip the Pre-Run Stretch, it Doesn’t Prevent Injuries
2. Biomechanical Demands
Secondly, softer or uneven surfaces (trails) do present different biomechanical demands. This must be recognized and trained for. In running, generally softer surfaces will correlate with more uneven terrain. Even if a softer terrain is not uneven, the body still has to find minimum amount of stability in order to maintain balance. So, in either case, the dynamic balance demand is increased. Theoretically softer surfaces would require more mobility, neurological awareness and strength in the foot and ankle as well as increased strength at the hip in all ranges of motion. Harder surfaces will require more strength in the knee and hip muscles that cushion landing. Based on these assumptions, soft surfaces may yield more injuries to the ankle joint, knee joint ligaments or hip soft tissues. Hard surfaces may yield more injuries to the foot structures, knee joint and tendons, knee & hip cartilage and spinal discs. All of these are structures that could receive excessive pressure if sufficient dampening of ground impact shock is not achieved. I am not aware of studies that have looked for these long term correlations; this is just based on biomechanical theory.
A final thought, we do know from research that the body will adapt running mechanics around impact force, and this article references that concept. The research into barefoot running and minimalist shoe design supports this theory. It forms one of the underlying tenants of why minimalist shoes can prove beneficial to some individuals. We do not know what the ‘optimal force’ is for an individual, but we do know that people adjust to find what their body ‘needs’. As people go to less cushioning in a shoe, they generally adapt their running form to absorb more impact. Some people adapt well, others not so well. There is a lot of information about what the variables are that determine these adaptations and why the adaptations are needed. To fully explain would take a small book, not a short article. However, I take all of this information and reach a different conclusion than “But with no evidence that softer surfaces prevent injuries, there is no reason to run on softer ground unless you like to” I think there are many valid reasons; they just have to be done strategically with proper preparation.