Why Do So Many NFL Players Go Down With Hamstring Injuries Every Pre-season?

A study found that more than half of all reported hamstring injuries in the NFL occur in the pre-season. Here's why.

During every NFL pre-season, it seems like half of the league goes down with hamstring injuries. Pick any team and you'll likely find at least one player—often a high-profile skill position player—nursing a bad hammy.

Barely halfway through the 2015 pre-season, guys like LeSean McCoy, Dez Bryant and Mike Evans—key cogs in their respective team's offenses—have all missed time due to some type of hamstring ailment. In fact, if you do a quick scan of teams' news feeds this season, you'll find at least 15 players who've recently suffered or currently have a hamstring issue.

That's a lot of players, although if you look at injury history in the league, it should come as no surprise.

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A 2011 study examining 10 years of injury data found that hamstring injuries are the most common injury in the NFL, occurring, on average, 172 times per season. More than half of those injuries (51.3 percent) took place during the 7-week pre-season.

Frustrating for coaches and players alike is the fact that 68.2 percent of the time, the injury is caused by "non-contact sprinting,"— i.e., it's not the result of a player hitting or getting hit too hard, but simply from running.

How the Injury Occurs

The hamstrings are comprised of three individual muscles on the back of the thigh: the biceps femoris, semitendinosus and semimembranosus. Each one attaches to the hip bone and just below the knee with hamstring tendons. The hamstrings are responsible for flexing the knee and extending the hip.

A hamstring strain—often referred to as a pulled or torn hamstring—is when the muscle fibers of one of the hamstring muscles are actually torn. This causes a sharp pain, weakness, swelling and bruising within the injured muscle. Hamstring injuries most often occur where the biceps femoris transitions to the hamstring tendon.

Hamstring injuries can happen any time you rapidly accelerate, decelerate or change directions. However, they most frequently occur when an athlete is running—especially near top speed. The hamstrings act to decelerate knee extension as the lower leg swings from back to front during the stride. During this movement, any one of four issues can cause an injury:

Poor Eccentric Strength — Eccentric strength refers to when the muscle lengthens under tension (e.g., the lowering portion of a Bicep Curl). This is the action your hamstring undergoes as it decelerates your lower leg when you sprint. If the hamstring lacks sufficient strength, then the muscles are too weak to slow down your lower leg, causing an injury.

Muscle Imbalances — Many athletes are quad dominant, meaning their quads are significantly stronger that their hamstrings. This increases the ability of the lower leg to swing forward at speeds the hamstrings might not be able to handle.

Weak or Inactive Glutes — The largest muscle group in the body, the glutes are responsible for extending the hips. This is where the majority of your power comes from during athletic movements. If your glutes are underdeveloped—meaning you probably don't do enough Squats and Deadlifts—the hamstrings pick up some of the slack.

"Your glutes should be a dominant and powerful hip extensor," says Nick Rosencutter, owner of Rosencutter Ultra Fitness & Performance. "If you are not using them, your hamstrings will be overused and strain easily."

Tight Hip Flexors — Tight hip flexors are also problematic. Typically caused by sitting too much, they can cause anterior pelvic tilt, inhibiting the function of the glutes. "If your pelvis is tilted forward, your hamstrings will be overstretched and overworked, since your glutes are not in a good position to work," explains Rosencutter.

Insufficient Flexibility — Damage to the hamstrings occurs when they're stretched beyond their capacity. It's thought that if the hamstrings are tight, they're more likely to tear. That's why dynamic warm-up routines performed before workouts and games are important. They are designed to warm up and lengthen the hamstrings—among other muscles—reducing the chance that a muscle will be rapidly stretched too far.

Other issues can exacerbate these problems once training camp starts. They include:

Overuse — NFL teams practice five or six times a week during training camp, and wide receivers and defensive backs (who suffer 40 percent of all NFL hamstring injuries) are constantly moving. With all the starting, stoppping and changing direction on a dime, their hamstrings can be overworked, leading to injury.

Players out of shape or in the wrong shape — NFL athletes are left to fend for themselves when it comes to training during the off-season, and when they arrive back at training camp, their bodies aren't ready for the grind ahead of them.

Mark Roozen, former NFL strength and conditioning coach and owner of Coach Rozy Performance, says that the new collective bargaining agreement, which limits contact between teams and players during the off-season, has contributed to the rash of hamstring injuries. He says, "From April until June, they are with their strength coach, and then from June until training camp starts, they can't have any contact with them. So from January to July, they are only with their strength coach for eight to 10 weeks."

This lack of contact with the guys who set their training programs can lead NFL athletes to train the wrong way during the off-season. "A lot of guys would come back into camp, and they'd have done a lot of running and straight ahead stuff, but they didn't really ever plant or cut or anything like that," Roozen says.

Recovery Can Take Longer Than You Think

Even when athletes feel they've given their hamstring enough time to heal, it's probably not fully recovered. A 2007 study that performed MRIs on sprinters with moderate hamstring strains showed that 20 to 55 percent of the original injuries had not properly healed after six weeks. For professional football players, that's more than a third of the regular season—a veritable lifetime.

Most NFL players feel they can't miss that amount of time, especially guys on the bubble who are fighting for a roster spot. They return to the field before their hamstring is fully healed. That's one reason why 16.2 percent of NFL players with hamstring injuries re-injure themselves.

This season, Cleveland Browns wide receiver Terrelle Pryor has missed almost all of his team's training camp with a hamstring injury. He suffered the strain prior to the team's first pre-season game, missed time, then returned to the field a few weeks later, only to immediately pull the same hamstring again..

"I think everybody in the league is trying to solve the soft-tissue riddle," Browns head coach Mike Pettine said at the time. "It is a source of frustration. Sometimes you have it where you want guys to push through, but you don't want to worsen it, so usually you err on the side of caution and you end up holding guys out."

Following an injury, the hamstring first goes through an inflammatory period, in which fluid rushes to the area to protect it. Eventually, the inflammation settles down and you reach a crucial point in the process—one that can make all the difference in whether you can come back from a hamstring strain at 100 percent. The hamstrings can completely recover. But if the process gets rushed, the risk of future injuries increases, because the muscle doesn't get to fully repair itself. This can lead to a cycle of chronic injury, in which a player constantly re-aggravates a problem that was never allowed to heal fully in the first place.

After Tampa Bay wide receiver Mike Evans went down with a hamstring injury during his team's second pre-season game, head coach Lovie Smith acknowledged that the recovery process is a long one. "If a guy has a hamstring injury, he's going to be out a while," Smith told ESPN. "I could have come up here and said 'day-to-day,' which most people do with hamstring injuries. It doesn't work like that."


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