If you live in Ireland, it’s no secret we have frequent rainfall.

From Jan-Apr 2024 we seen the highest amount of rainfall (mm) year to date across the last 4 years. I’ve never seen as much disruption to field sports, namely GAA, Rugby and Soccer (as they are pre-season/in-season Jan-Apr) causing prolonged season timelines and ultimately crossovers.

When teams did get access to pitches, be it grass or sand-based, they were soft/muddy which can be compared to running on a wet sponge. You don’t move as well on soft ground, we don’t need biomechanists to tell us that but there is a lot of value in knowing how different surface type can impact us.

Why do we feel less comfortable on soft ground?  Our mechanics adapt to the surface.

When you think about running, an oversimplified view is to think about our ability to put force into the ground to move our bodies. Soft ground is less responsive to these forces, which demands a series of compensatory adjustments in our running mechanics (1) .

Greater leg stiffness, reduced muscle-tendon efficiency, greater ranges of motion and reduced percentage of ground forces reaction coupled with longer ground contact times are what many studies found when comparing our running on firm to soft surfaces (i.e. sand, wet muddy fields etc).

Leg stiffness is a major contributor in how we respond to a surface. This can even be seen in the first single step, by up to 30% reduced leg stiffness when transitioning onto a hard surface from a soft surface (2).

How does this softer ground affect us? We don’t change so much about how we move, what changes is how we achieve similar movement.

Soft surfaces show less friction and less rotational traction achieved compared to firm ground and this causes less muscle-tendon efficiency (3) and on average a greater hip and knee range of motion (predominantly via flexion) requirements.

I recall a small-sided game where a head coach decided to even the player count by adding me into the drill, the term “slip n’slide” doesn’t do justice the amount of times I ended up on the ground – sidenote: Wear appropriate footwear.

Is soft ground always a bad thing? This depends on what you want out of it.

Soft ground ca be seen as a positive with reduced impact forces / greater impact absorption, something in biomechanics referred to as percentage of ground reaction forces (GRF).

GRF can be defined as the force exerted by the ground on a body in contact with it (4).

Think about when doing plyometrics (for a workable definition – a series of jumps/landings) would you rather we land on concrete or astroturf surface?

Astroturf, as this is a softer, more compliant surface and absorbs a greater %GRF and lowers our mechanical load compared to concrete.

As such soft ground can be a good thing through the lens of mechanical load. However, when we are talking about a muddy field (very soft surface) and viewed as a running surface where we are looking for high levels of efficiency in our movement (i.e. a training session or match) it can be a negative and come at additional tax on our system.

In general, we are faster on firmer surfaces than softer surfaces due to the better “responsiveness” of the surface to our forces (5).

Due to reduced impact forces (%GRF forces) when running on soft ground we need to create longer contact times and greater joint stiffness as well as greater ranges of motion in our run at both the knee and hip. With greater range of motion requirements this inevitably leads to greater joint angles that perhaps you are not adequately exposed to which can be a risk factor for injuries.

While there is individual variability to running techniques, and muscle activation levels, various studies investigated the muscle activation levels in the legs across the duration of a stride. On average, the hamstrings showed up to x1.7 the magnitude of activation when on soft surfaced compared to firm surfaces, quadriceps activation was 44% greater on soft surface compared to firm surfaces (6). Therefore, as you can see, running on soft surfaces can “tax” our systems more.

What can we do about it?

The reality is we often don’t get to choose what surface we compete on, given a lot of this is out of our control (weather impacting the firmness of pitches, pitch base variances such as grass, sand, astroturf, etc). We can choose what surfaces (given the luxury and facilities to do so) we train on and how much of training we do on each across a session / week / phase.

Something of great benefit that I do with a number of my athletes/teams is train on softer ground (i.e. astro) to reduce the mechanical loads when needed and return to the pitch to simulate likely match day surface conditions.

Moral of the story, we must become robust enough to tolerate the continuum of mechanical loads we are exposed to with the various surfaces we find ourselves on. We can achieve this with carefully planned training and closely monitored/ managed training loads where surface selection can be impactful to manipulate mechanical loads.

It is unfortunate though, that for some people (be it athletes or coaches) training load only becomes a priority when injuries occur.

If you need help with you/your team’s performance – to reach out.

Train with purpose, not habit.

References

  1. Burillo P, Gallardo L, Felipe JL, Gallardo AM. Artificial turf surfaces: perception of safety, sporting feature, satisfaction and preference of football users. European journal of sport science. 2014;14:S437-S47.
  2. Ferris DP, Louie M, Farley CT. Running in the real world: adjusting leg stiffness for different surfaces. Proc Biol Sci. 1998;265(1400):989-94.
  3. Lejeune TM, Willems PA, Heglund NC. Mechanics and energetics of human locomotion on sand. J Exp Biol. 1998;201(Pt 13):2071-80.
  4. Kim J, Kang H, Lee S, Choi J, Tack G. A Deep Learning Model for 3D Ground Reaction Force Estimation Using Shoes with Three Uniaxial Load Cells. Sensors. 2023;23(7):3428.
  5. Sanchez-Sanchez J, Martinez-Rodriguez A, Felipe JL, Hernandez-Martin A, Ubago-Guisado E, Bangsbo J, et al. Effect of Natural Turf, Artificial Turf, and Sand Surfaces on Sprint Performance. A Systematic Review and Meta-Analysis. International Journal of Environmental Research and Public Health. 2020;17(24):9478.
  6. Pinnington HC, Lloyd DG, Besier TF, Dawson B. Kinematic and electromyography analysis of submaximal differences running on a firm surface compared with soft, dry sand. European Journal of Applied Physiology. 2005;94(3):242-53.