By Dev K. Mishra, M.D., President, Sideline Sports Doc
In last week’s post we discussed how there isn?t conclusive evidence about injury rates as an effect of the type of field surface (grass vs. artificial turf). To recap: I don’t think there’s any better playing surface than a well-maintained grass field, but I’d prefer one of the newer varieties of turf fields over a poorly-maintained grass field any day. Some people have also suggested that the interaction between the athlete’s shoe and the playing surface can have some effect on injury rates. It turns out that this is an issue that’s been studied pretty extensively in the scientific literature for older artificial surfaces like AstroTurf? and there’s some good information relating to the newer surfaces that use soft rubber infill like FieldTurf’ too.
There are two competing issues at work here, and both come down to friction. From a performance perspective athletes like a lot of friction between their shoe/cleat and the playing surface- it results in what we’d commonly call ‘traction’. A lot of traction allows them to start and stop very quickly and also to turn on a dime. As you can imagine, if you’re slipping (less friction) it will have a negative effect on your quickness and cutting ability. But from a medical standpoint friction can lead to injury. Injuries to the ankle, knee, and hip often are the result of forces created on the joints when the foot stays planted firmly on the playing surface and the body goes another way. The engineering term for this is a ‘rotational moment’ and the higher the rotational moment the greater is the potential for injury.
From the more recent published scientific studies, I found that this one (Am J Sports Med 2009 37: 518-525) titled ‘Football Playing Surface and Shoe Design Affect Rotational Traction’ was a well-designed study that yielded some practical information. The investigators studied four different surfaces (two types of infill-type artificial turf, and two types of natural grass), and five different types of cleat configurations (7-stud removable, 12 stud molded, 15 stud hybrid, blade style molded, and multiple stud turf shoes). Two common brands of shoes were used to give us a total of 10 shoe types.
The main points they found were that for the field surface, the infill-type artificial turf surfaces all had higher rotational traction values than grass, regardless of shoe type. For the shoe types they found no differences in rotational torques for the 7-stud, 12-stud, hybrid, or blade types; but the turf shoes had significantly less rotational torque than any of the other cleat types.
So what can I recommend based upon the studies I’ve looked at (there are many more than just the one above)? Remember that my viewpoint for this post is biased towards player safety, and as discussed above this could affect performance.
- If you’re playing on turf the data would indicate that a turf shoe could very well be the ‘safest’ type of shoe, but you might find that you slip a bit too much in these. If possible I’d recommend that you test a turf shoe out on your field. If it allows you to perform the way you’d like I’d recommend that you wear it. If the turf shoe causes too much slipping your next choice should likely be a firm ground cleat.
- If you’re playing on grass the data doesn’t show a difference in traction amongst cleat types. In spite of that I wouldn’t ever recommend a soft ground cleat on firm grass.
- The study also shows that the type of upper material will affect the rotational traction too, for very complex reasons. A stiff non-yielding upper (like a hard synthetic material) might produce higher rotational traction. So if possible I would recommend a soft leather upper material.
Field surfaces and shoe types change frequently, so I hope to see additional studies performed to help us with future decisions.