How Running on Different Surfaces Affects Your Health
As a runner, you have many options when it comes to training surface. Road, bike path, snow, grass, treadmill, track, trails, dirt, asphalt, and sand are all common terrains. In fact, as long as there isn’t a sign that forbids your presence, you are pretty much free to run wherever you would like. How do these different surfaces affect your health as a runner? Is there any one “best” surface on which to run? Here, the science of running surfaces is discussed.
Physics of Running
Before we can understand the way running surface affects a person’s health, we must first understand the physics of running, particularly how the foot interacts with the ground.
There are three forces that act on both the runner and the ground. The first is a horizontal force that occurs due to contact between foot and ground. The second is a vertical force, also due to contact between foot and ground. The third force is gravity. During a run, the vertical force must be greater than the force of gravity in order to stay upright and with proper propulsion. The horizontal force is what propagates forward motion. This horizontal force also dictates speed; the average runner applies 500 – 600 lbs of peak force during a run. Usain Bolt? 1000 lbs.
Does this force affect our joints?
The next obvious question is whether the force we apply to the ground when running has any affect on injury rates. If so, how does the running surface affect the applied force? Although anecdotal evidence suggests otherwise, there is no scientific indication that the force applied to the ground when we run affects our rate of injury. A comprehensive review1 that looked at 2,016 references on vertical ground reactive force found no significant injury rate correlated with this factor.
However, loading rate2 was shown to play a role in injury, particularly in runners who had previously been injured. Loading rate refers to the speed at which you apply a force to your body. In running, the loading rate is dependent on where the runner’s foot makes contact with the ground in relation to the person’s center of mass. A higher loading rate is considered bad, while a lower loading rate is good.
Running also evolves eccentric contractions3, which occur when a muscle elongates in response to force. An example is the tibialis anterior muscle, which is located along the shin bone. An eccentric contraction in this muscle controls the positioning of a runner’s foot when contact is made with the running surface. Little is actually known about eccentric muscle contractions, other than they likely contribute to delayed onset muscle soreness.
Most pertinent to the question of how different surfaces affect the body’s health is the idea of shock adaptation. Bones and joints will require different amounts of shock absorption depending on the surface. Think of this as the difference between the shock absorbers in an all-terrain vehicle versus a sports car. Runners have been shown to make kinematic adjustments4 in order to mitigate the force on joints with respect to running surface.
Now that the physics of running is better understood, the way that varying surfaces affect the body can be explained. The surfaces will be discussed from softest to hardest.
Sand is the softest – and the most difficult – surface on which to run. Because sand shifts beneath a runner’s foot, much of the horizontal force a runner puts forth is absorbed the sand grains. While the force exerted on bones and joints is lowest for runners on sand, loading rate and injury risk may be higher. In fact, in one study running in sand5 was found to increase the risk of mid-portion tendinopathy in the Achilles tendon among master’s level runners. The benefit of this difficult activity is that sand can lead to all-around enhanced strength, thanks to the added stress on small stabilization muscles.
Running on grass is a favorite activity of cross country runners, and one that is dreaded by road racers. This surface is soft, has high absorption rates, but also presents hazards such as unseen holes or divots. From a performance perspective, running on grass is slower6 because the surface has a low energy return, particularly on rainy days.
From a health perspective, running on grass requires more energy in order to propel the body forward than is required on a track or road. This excessive use of energy can cause muscle fatigue, leading to increased loading rates and sub-optimal muscle control. However, the force placed on bones and joints is greatly decreased in grass. Due to the uneven surface of grass, more stabilization muscles are engaged, which is also beneficial.
Who doesn’t love a nice run on a beautiful dirt road or trail? Trail running has long been lauded for being better on joints than concrete or asphalt, as well as more stimulating for the mind. The biggest downside to running on dirt roads or trails is the uneven, and sometimes dangerous, surface. Tree roots, rocks, holes, and areas of erosion combined with a misstep or lapse in attention can lead to sudden and disastrous injury, such as a sprained ankle.
What are the benefits to running on dirt? Like sand and grass, dirt provides an uneven surface that allows the body to use a greater range of muscles and tendons. While exercise physiologists argue whether force and load rate are the major contributing factors to injuries, they may be overlooking the fact that strengthening key stabilization muscles can decrease injury risk.
Gravel roads and paths are popular for runners because they offer a softer surface without the uncertainty that grass and dirt trails often provide. A study performed in Slovenia compared grass, gravel, and road running and found that runners who exercised on gravel7 stressed the ankle joint and lower leg muscles the most, particularly the peroneus brevis. This study looked at gravel that ranged in size from 5 – 10 cm in diameter and was unevenly distributed. Homogenous gravel, such as crushed limestone, would likely cause less stress.
While tracks range in stiffness from very soft to very hard, the most common track surface that non-elite and non-university level competitors encounter is comprised of rubber. This surface is often prized for running the fastest times because it “gives back” by virtue of its elastic nature. One study found that the optimal surface for reaching peak speed and energy return is 2 – 4 times as stiff6 as the runner’s legs, which is true of most track surfaces. The downside to running on the track is the frequency of turns, which can place an uneven load on the left side of the body. As speeds increase, so does strain and injury risk for left ankle, knee, and hip.
When it comes to running on the roads, asphalt is a slightly more forgiving surface than its concrete counterpart. Asphalt is comprised of pitch and sand or gravel, giving the finished road a surface that is not entirely uniform. Air pockets form on the surface, which can provide slight cushion for a runner. However, despite its hard surface, asphalt does not provide a high energy return, as might be assumed. Instead, asphalt reduces the ability of the legs to gain vertical force. Anecdotally, runners prefer asphalt to concrete because it “feels” softer, but no studies have shown that asphalt lessens a runner’s injury risk versus concrete. On the contrary, a runner is less likely to experience a sudden injury on asphalt, such as a sprained ankle or a stress fracture. You can read more about the latter on Jessica Natalie’s blog, where she discusses a healthy lifestyle through running. Her years of training as well as coaching and inspiring others help her provide genuine value.
Concrete is by far the hardest surface for runners, and indeed has been shown to increase the risk of plantar fasciitis in both runners9 and construction workers8. The unyielding surface may cause greater wear and tear on muscles, joints, and tendons. Despite the extreme density of concrete, it actually has the lowest energy return of all surfaces listed here. In addition to skeletal stress, concrete may also be to blame for issues such as “footstrike anemia10,” where foot strike force is so great that red blood cells lyse, or rupture, causing anemia.
The treadmill is either loved or hated by runners from a mental perspective, but how does it affect the runner physically? There are many benefits to running on the treadmill; avoidance of extreme temperatures, controllable pace and surface, and the ability to direct your focus solely on your running form.
However, running form may be compromised on the treadmill. Researchers from East Carolina University in North Carolina found that treadmill running resulted in greater loading11 on the Achilles tendon than did running outdoors. The increases were significant, with treadmill runners experiencing 12.5% greater Achilles tendon peak force and 15.6% greater Achilles tendon loading rate.
Where Should You Run?
Now that you are armed with this new information, where should you run? First and foremost, the majority of your training (60 – 70%) should be performed on the surface on which you are planning to race. This will help your body create necessary adaptations that will help you perform your best on race day. Next, you should vary the terrain as much as possible for the additional 30 – 40% of your mileage.
Exercise scientists theorize that continual use of the same muscles contributes to injury more than vertical force. As we have shown, each surface stresses the body in a unique way, which can be beneficial to training. If varying your training surface is not plausible, seek to make changes in topography, such as switching between hilly and flat routes.
1. Worp, H. V., Vrielink, J. W., & Bredeweg, S. W. (2016). Do runners who suffer injuries have higher vertical ground reaction forces than those who remain injury-free? A systematic review and meta-analysis. British Journal of Sports Medicine, 50(8), 450-457. doi:10.1136/bjsports-2015-094924 Link
2. Davis, I. S., Bowser, B. J., & Mullineaux, D. R. (2015). Greater vertical impact loading in female runners with medically diagnosed injuries: a prospective investigation. British Journal of Sports Medicine, 50(14), 887-892. doi:10.1136/bjsports-2015-094579 Link
3. Eston, R. G., Mickleborough, J., & Baltzopoulos, V. (1995). Eccentric activation and muscle damage: biomechanical and physiological considerations during downhill running. British Journal of Sports Medicine, 29(2), 89–94. Link
4. Dixon, S. J., Collop, A. C., & Batt, M. E. (2000). Surface effects on ground reaction forces and lower extremity kinematics in running. Medicine & Science in Sports & Exercise, 32(11), 1919-1926. doi:10.1097/00005768-200011000-00016 Link
5. Knobloch, K., Yoon, U., & Vogt, P. M. (2008). Acute and Overuse Injuries Correlated to Hours of Training in Master Running Athletes. Foot & Ankle International, 29(7), 671-676. doi:10.3113/fai.2008.0671 Link
6. Kim, W., & Voloshin, A. S. (1991). Evaluation of running surfaces: The in vivo approach. Journal of Biomechanics, 24(3-4), 244. doi:10.1016/0021-9290(91)90208-5 Link
7. Ales D., Igor S., Vojko S. Activation Pattern of Lower Leg Muscles in Running on Asphalt, Gravel and Grass. Collegium antropologicum 39(suppl 1):167-172 Link
8. Werner, R. A., Gell, N., Hartigan, A., Wiggerman, N., & Keyserling, W. M. (2010). Risk Factors for Plantar Fasciitis Among Assembly Plant Workers. Pm&r, 2(2), 110-116. doi:10.1016/j.pmrj.2009.11.012 Link
9. William G Clancy, Tendinitis and Plantar Fasciitis in Runners. Orthopedics. DOI: 10.3928/0147-7447-19830201-12 Link
10. Eichner ER. Runner’s macrocytosis: a clue to footstrike hemolysis. Runner’s anemia as a benefit versus runner’s hemolysis as a detriment. Am J Med. 1985;78:321–325. Link
11. Willy, R. W., Halsey, L., Hayek, A., Johnson, H., & Willson, J. D. (2016). Patellofemoral Joint and Achilles Tendon Loads During Overground and Treadmill Running. Journal of Orthopaedic & Sports Physical Therapy, 46(8), 664-672. doi:10.2519/jospt.2016.6494 Link