Running Surfaces and Injury Risk: Does Softer Always Mean Safer?

Running Surfaces and Injury Risk

Does Softer Always Mean Safer?s.

Many runners in Sheffield will already know that the Woodbourne Road athletics track has recently been closed by Sheffield Hallam University after failing to meet the required standards for shock absorption. As a result, many local training groups have had to quickly find alternative venues for interval sessions.

Our own group — which my daughter and I have been part of since September — has moved our sessions onto grass, with an ongoing search for the flattest, smoothest, and most practical locations around the city. Other groups have shifted to doing intervals on the tarmac paths around the EIS.

Naturally, this sparked a conversation with our coach about whether running surface actually affects injury risk.

For years, runners have been told that harder surfaces increase the likelihood of injury. The logic seems straightforward: when your foot hits the ground while running, forces several times your body weight travel through the body. If the surface is hard, like concrete or tarmac, there is very little “give,” so the body must absorb more of that force through muscles, tendons, ligaments, and bones. Softer surfaces, such as grass or trails, are therefore often assumed to be kinder on the body.

But as with many topics in sports medicine, the reality is far more complicated.

The Body Adapts More Than We Think

Research over the last two decades has challenged the idea that softer automatically means safer. Studies have shown that runners instinctively adapt the stiffness of their legs depending on the surface they run on.

When runners move onto softer ground, the body often responds by increasing muscle tension and leg stiffness in order to maintain balance, posture, and running efficiency. On harder surfaces, the opposite tends to happen — the legs become slightly less stiff.

This adaptation is incredibly important. Rather than simply “taking impact,” the body constantly adjusts to keep the centre of mass stable and maintain efficient forward movement.

One influential study by Daniel Ferris and colleagues demonstrated that runners rapidly and subconsciously alter leg stiffness depending on the elasticity of the surface beneath them. Without this adjustment, maintaining a smooth running stride across different terrains would be extremely difficult.

Could Softer Surfaces Actually Increase Load?

Interestingly, some researchers now believe softer surfaces may increase load in certain tissues — particularly the calf muscles and Achilles tendon.

Because the ground absorbs more energy, the body may need to produce more force to maintain propulsion and stability. This increased demand appears especially relevant for runners with a history of Achilles problems or older athletes, who are already at higher risk of calf and tendon injuries.

There have even been studies showing higher tibial (shin bone) acceleration on softer surfaces compared with harder ones, suggesting that the relationship between surface and injury is far from straightforward.

What Does the Latest Research Say?

A recent study published in Sports Biomechanics has added further discussion to the debate around running surfaces and injury risk. The researchers compared runners on concrete, synthetic track, and grass, measuring the acceleration forces travelling through the lower leg on each surface.

The study found that running on concrete produced slightly higher impact accelerations than running on grass or synthetic track. On the surface, this appears to support the traditional belief that harder surfaces may place runners at greater risk of injury.

However, the conclusions need to be interpreted carefully.

Importantly, the study did not actually measure injuries — it only measured biomechanical variables such as acceleration and loading patterns over a short testing period. While these findings are interesting, higher measured impact does not automatically translate into higher injury rates in the real world.

The study also reinforces an important point seen repeatedly in biomechanics research: runners naturally adapt their movement depending on the surface beneath them. The body is not simply absorbing force like a rigid structure; it is constantly adjusting muscle activity, leg stiffness, and running mechanics to maintain efficiency and balance.

This is one reason why the relationship between surface and injury remains unclear. A softer surface may reduce one type of loading while increasing another.

So while this newer research suggests concrete may create higher impact accelerations, it still does not prove that harder surfaces cause more running injuries overall.

In many ways, the study highlights just how adaptable the human body is — and how difficult it is to reduce running injuries down to a simple “hard surface bad, soft surface good” explanation.

So What Can We Conclude?

At the moment, despite lots of theories and biomechanical research, there is still no strong evidence proving that one running surface consistently causes more injuries than another.

Studies  have generally failed to show lower injury rates on softer surfaces such as grass or trails. While softer ground may reduce load in some areas, it may simultaneously increase demand elsewhere.

In reality, injury risk is influenced by many factors beyond surface alone.

One of the strongest predictors of injury remains previous injury. Recent research has also highlighted sudden increases in long-run distance as a significant contributor.

What Does This Mean for Runners in Sheffield?

With some groups now training on grass and others on tarmac, it is impossible to confidently say one group is at greater injury risk than the other. The evidence simply is not strong enough.

The debate around surface and injury risk also raises an interesting question regarding the current track closure. If the scientific evidence remains unclear about whether grass, tarmac, or track surfaces meaningfully alter injury risk, can we really be certain that a relatively small reduction in track shock absorbency represents a major health and safety concern?

At present, sports science does not give us a definitive answer.

As researchers Malisoux et al. famously concluded:

“Running practice is a necessary cause for running-related injury and, in fact, the only necessary cause.”

In other words, the biggest risk factor for running injury is, ultimately, running itself! 

Ferris, D. P., Liang, K., & Farley, C. T. (1999). Runners adjust leg stiffness for their first step on a new running surface. Journal of Biomechanics, 32(8), 787–794.

van der Worp, M. P., ten Haaf, D. S. M., van Cingel, R., de Wijer, A., Nijhuis-van der Sanden, M. W. G., & Staal, J. B. (2015). Injuries in runners: A systematic review on risk factors and sex differences. PLOS ONE, 10(2), e0114937.

Colino, E., et al. (2021). Effects of running surface stiffness on neuromechanical behavior and shock transmission in endurance runners. Journal of Sports Sciences.

Ferro-Sánchez, A., Martín-Castellanos, A., de la Rubia, A., García-Aliaga, A., Hontoria-Galán, M., & Marquina, M. (2023). An Analysis of Running Impact on Different Surfaces for Injury Prevention. International Journal of Environmental Research and Public Health, 20(14), 6405.

Malisoux, L., et al. (2014). Running-related injuries and risk factors among recreational runners.