For a long time now there has been the thought process that running surfaces are directly linked to injury. The thought process has been harder surfaces mean more impact through the body which means more to absorb and more load for the body to take. We may in fact have this thought process wrong. The latest findings point toward leg stiffness actually being the cause of injury and this primarily comes from softer grounds as the body is forced to stabilise more.
The correlation between surface and injury
In the 1970s running volume was given a bad reputation for injuries, while this may be the case in many instances, the surface on which we run has now been given greater cause for concern.
The science behind hard ground causing injury as opposed to the softer ground made perfect sense. Sandkof words this point well when he says, "When you stride forward and land on your outstretched foot, the force coming down on your foot and leg is many times your body weight, which must be absorbed somewhere. If the running surface is hard (like pavement), then there is no give and all the force must be absorbed by your muscles, tendons, ligaments, and bones. Alternatively, softer running surfaces (like a dirt path) alleviate this impact so that less force needs to be absorbed by your leg." However, evidence is now putting towards stiffness and not necessarily the ground we are running on.
Muscle stiffness from different running surfaces
Some exercise scientists particularly those looking at the biomechanics of limbs when they are under stress have begun to question this narrative. A paper published in the "Journal of Biomechanics" researched how runners adapt their stride when moving from one type of running surface to another. The exercise scientists evaluated the stiffness of the runners’ legs, which has a direct correlation with impact absorption. The stiffer the legs, the less they are able to absorb force and this in fact is the problem at hand.
One thing that is known to reduce stiffness in the legs and the whole body is Pilates. Pilates emphasizes ideal posture, core strength, muscle balance, good footwork, and ideal foot/knee and hip alignment. These are all things that assist a runner’s efficiency, consistency and injury free. Stretching has many benefits for both the body and mind, including greater flexibility, better posture, and reduced emotional stress. It can be helpful to do dynamic (moving) stretching before running and static (held) stretching after a run to reduce soreness and tight muscles. Runners should be sure to stretch all muscle groups in the legs, hips, and back (especially the lower back). For exercises that you can do as a runner visit our other blogs for runners and join Pilates.
The study pointed out that when runners moved from a softer ground to a harder ground, they decreased the stiffness in their legs by more than 25%! A softer ground made runners much stiffer than harder ground due to the amount of stabilisation required. Therefore, when running on a softer surface, runners did so with more muscle tension and with stiffer legs.
The science behind this is also quite simple. When running on soft ground, a runner’s centre of gravity tends to lean back because of the lack of support from the ground and because the runner does not want to fall face forward. This means that a runner naturally needs to compensate and use more muscle strength to keep them moving forward. On harder surfaces, however, the ground supports a runner’s weight with more ease, this negates the need for extra muscle exertion which in turn decreases leg stiffness.
Muscle stiffness more injury
Researchers hypothesised that when running on softer ground, the leg stiffness needed for balance and propulsion would put more stress on all structures of the limb than when running on a harder surface. Additionally, as stated above, stiffer legs have much less ability to absorb impact than a relaxed limb. This means that all of the impact absorptions of the softer surface would be offset by the stiffer leg, also increasing the likelihood of injury. This is interesting research and, if true, would drastically alter the way we understand mobility, running, stretching and rehabilitation.
Conclusions
The research behind these studies is fascinating, although there haven’t been any well-designed studies designed yet on specific running injuries and the ground we run on. It is best not to conclude that surfaces cause injury, however, we can say that softer grounds make runners more stiff and fatigued and if left untreated this can potentially lead to injuries. It is also empowering to note that perhaps on more fatigued running days, running on harder grounds may elevate more stress and allow for a slightly faster recovery. Moreover, including stretching and Pilates would no doubt aid recovery, help muscle tightness and keep the body well-balanced.
References
Boey, H. et al. (2016, September 5). The effect of three surface conditions, speed and running experience on vertical acceleration of the tibia during running. Retrieved from https://pubmed.ncbi.nlm.nih.gov/27595311/
Davis, J. (n.d.). Running surface and injuries: The role of leg stiffness in running injuries. Retrieved from https://runnersconnect.net/running-surface/
Ferris, D.P. et al. (1999, August). Runners adjust leg stiffness for their first step on a new running surface. Retrieved from https://pubmed.ncbi.nlm.nih.gov/10433420/
Lawton, T. (2019, March 4). Do Running Injuries Depend on the Running Surface? Retrieved from http://sites.nd.edu/biomechanics-in-the-wild/2019/03/04/do-running-injuries-depend-on-the-running-surface/
Van Der Worp, M.P. et al. (2015, February 23). Injuries in runners; a systematic review on risk factors and sex differences. Retrieved from https://pubmed.ncbi.nlm.nih.gov/25706955/
Waite, N. et al. (2020, October 6). Effect of Grade and Surface Type on Peak Tibial
Acceleration in Trained Distance Runners. Retrieved from https://pubmed.ncbi.nlm.nih.gov/33022655/
Sankoff, J. (2023). Do Softer Running Surfaces Really Reduce Injury? Retrieved from https://www.trainingpeaks.com/blog/do-softer-running-surfaces-really-reduce-injury/