The argument started in 1967. Judge Roy Hofheinz had built the Astrodome two years prior. Some called it the eighth wonder of the world — 18 stories high, air conditioned — the first indoor stadium to hold thousands for both football and baseball. Grass was planted. Some speculated the building was so big that clouds may form; it might even rain. But the grass didn’t grow and the search was on for an alternative surface. The judge decided to install Chemgrass, a product from Monsanto, but didn’t like the name. Astroturf was born.

Astroturf, a nylon monofilament carpet rolled out on dirt, was used for baseball and football. First reports were that it was rough on the skin, often leaving rashes, but the main problem was that it was hard. When footballers hit the ground, it hurt. More injuries occurred on Astroturf and the argument regarding the injury rate between natural grass and turf began.

The grass/turf argument hasn’t stopped but it renewed this fall when Aaron Rodgers, the New York Jets hope for the future, ruptured his Achilles tendon on the fourth play of the game. Like Achilles’ heel after being dipped in the river Styx, Rodgers’ tendon was vulnerable. Will Rodgers recover? Return to play? It takes months to rehabilitate this large tendon. Complete recovery is questionable.

Was it because the Jets were playing on turf? Playing surface is only one factor related to injury as injury is related to many variables including the age of the player and surface, conditioning, temperature, footwear, moisture, and a host of other variables. Rodgers is not a young man and tendon stiffness is related to age. Was Rodgers in top shape for the first game of the year? We will never know if Rodgers’ tendon rupture was related to playing surface.

Interestingly, when sports writers talk about turf they almost exclusively refer to the hardness of the surface. Although hardness is highly related to the force on the body, such as the head, when falling, it is primarily surface friction, the resistance to movement between foot and surface, that affects the force on joints. For example, if you watch a tennis match on clay, players often slide after planting their foot. The foot slides as a result of the reduced surface friction. Clay is the safest tennis surface. Meanwhile, if friction is high, such as the original Astroturf, the foot stops abruptly resulting in significant forces applied to the foot, knee, hip, and back.

Injuries to the knee and foot are the most common injuries in football, and in most sports. Data comparing all the stadiums in the NFL show that the injury rate to knees and ankles are the same for grass and turf. Today, Astroturf is gone but several generations of turf have been developed. Manufacturers attempt to develop that perfect combination of hardness and friction. Football players uniformly prefer grass but grass surfaces need maintenance, something the NFL can easily afford. But what about ill-kept grass surfaces such as high schools and playgrounds? School playgrounds are notoriously hard. Further, grass fields are often irregular, possibly leading to missteps.

A rarely mentioned property of turf fields is they can be used all year. Athletes preparing for spring sport in northern climate often have to train indoors in small gyms. But turf fields can be plowed and spring sport athletes can train in winter. Athletes who are fit and trained prior to the season suffer less injuries. Many large schools have indoor turf fields for off-season conditioning.

Today, there is another argument regarding artificial surfaces. In 2009 a soccer coach in Washington raised concerns that the rate of cancer in soccer players seemed abnormally high. Most artificial surfaces contain a layer of crumb rubber at the base. Crumb rubber is made from virgin rubber or from old tires. Some contain chemicals that are toxic. Since artificial surfaces cover playing fields and playgrounds all over the country, there was cause for concern. To date, research by the Washington State Department of Health and scientists at the New Jersey Institute of Technology found no association between crumb rubber and the incidence of cancer.

So is grass or turf better? I love watching football played outside on a grass field, but not all grass fields are the same. I like to see a dirty uniform. Turf fields wear as well and are expensive. It’s a toss-up but research will continue and new materials will be developed. My advice, stop worrying. Play.

Jim Johnson is a retired professor of exercise and sport science after teaching 52 years at Smith College and Washington University in St. Louis. He comments about sport, exercise, and sports medicine. He can be reached at jjohnson@smith.edu