Harder surfaces surely subject the body to higher forces, right?

Initially, I thought the obvious answer was that harder surfaces would be responsible for developing injuries, due to the excessive ground reaction force that can occur when running on them. I mean, Newton’s Third Law states that a force on one object will produce a reactional force on the other object (i.e. the reaction of force into a footpath will produce a reactional force back up the limb). And while this is true, studies have actually found that harder surfaces produce less ground reaction force than softer ones.

Study Examples:

• Barefoot Running: “The maximum peak GRF (ground reaction force) was found highest…when barefoot running on rubber, followed by artificial grass and concrete. It seems that the increase of surface hardness reduced the GRF response.” (Yamin et al, 2017)

• With Footwear: “the peak GRF response on artificial grass was found higher compared to running on rubber and concrete.” (Yamin et al, 2017)

How is this all possible?

Studies have found that human running gait will adapt to the surface that we are running on, which is remarkable in itself, and a testament to the subconscious mechanics of the human body. However, this leaves me with a few questions: If my body adapts its running gait on harder surfaces and ground reaction force is lower, then why do I still pull up much worse after running on concrete or bitumen? And why have I been more prone to overuse injuries when I run on harder surfaces?

Well, research suggests that although ground reaction force is lessened on more rigid surfaces, peak pressures are increased as the surface gets harder. Which is why my body will adjust its running gait, and most likely, why the risk of injury for me is greater on a harder surface.

Study Examples:

• “Running on grass produced peak pressures 9.3% to 16.6% lower than the other surfaces (asphalt, concrete & rubber) in the rearfoot and 4.7% to 12.3% lower in the forefoot...running on grass may reduce the total stress on the musculoskeletal system compared with the total musculoskeletal stress when running on more rigid surfaces, such as asphalt & concrete.” (Tessutti et al, 2012)

• “These results suggest that natural grass may be a surface that provokes lighter loads on the rearfoot and forefoot in runners.” (Tessutti et al, 2008)

• “Compared with running on concrete…natural grass showed a lower magnitude of maximum plantar pressure at the total foot.” (Wang et al, 2012)

• “The values of shock absorption averaged 0.0% (asphalt), 37.4% (tartan athletics track), and 71.3% (treadmill).” (Colino et al, 2020)

What does it all mean?

In summary, running is great for your body and has a variety of benefits, both physically and mentally. Simply, be mindful of your body and the stress placed on it. Go for a run at an athletics track or an oval once in a while, or use the treadmill at the gym to give your body a bit of respite, rather than continually pounding the footpath. It will reduce the strain placed on your body and keep you running for longer as age progresses.