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This article is from the In-Depth Report Science and Soccer's World Cup

Does Extreme Heat Boost Your Chances of Pulling a Hamstring?

Pulled hamstrings took out two U.S. players at the World Cup. Why?


United States' Jozy Altidore was injured during the World Cup soccer match between Ghana and the U.S. at the Arena das Dunas in Natal, Brazil
AP Photo/Dolores Ochoa

It was some 22 minutes into the first U.S. match of the 2014 World Cup when U.S. forward Jozy Altidore suddenly grimaced, clutched the back of his left leg and dropped to the ground in agony. He had pulled his left hamstring. Later that game U.S. team central defender Matt Besler was also replaced due to a hamstring injury. The U.S. still beat Ghana 2–1, but those players were placed at least temporarily out of commission. Altidore still has not recovered.
 
At game time, the temperature at the match in Natal, Brazil, was upwards of 82 degrees Fahrenheit. The scorching heat during the World Cup matches even led to a recent Brazilian court decision ordering FIFA (International Federation of Association Football) to include mandatory water breaks for players during a game if temperatures climb to 89.6 degrees F or more. (The World Cup’s first-ever water break took place during the June 22 U.S.–Portugal match).
 
A pulled hamstring is a common sports injury—with roughly one such incident per 1,000 hours of playing or training in soccer—but do the extreme temperatures and humidity in Brazil amplify that risk?
 
Scientific American spoke with Thomas Trojian, director of the Injury Prevention and Sports Outreach Programs at the New England Musculoskeletal Institute, about hamstring injuries and how such high temperatures may impact player injury.
 
[An edited transcript of the conversation follows.]
 
Is a pulled hamstring more common in extreme heat?
Not necessarily. It’s more related to the overuse of the muscles and the prolonged playing season. Players, like Altidore for the U.S., had been playing since last fall and been playing all the way through. When he injured it he was in an awkward position and mis-stepped. People saw a number of hamstring injuries on the U.S. team but [researchers] haven’t found a correlation directly to the warm temperature. Obviously, if it’s hot and you are not able to stay hydrated you’ll be more fatigued, and then muscles don’t fire at the right rate—perhaps making you more prone to injury—but in general researchers haven’t seen a direct correlation.
 
What are the other risk factors?
Once you have hurt your hamstring you are much more likely to hurt your hamstring. The muscle doesn’t repair like bone and go back to normal—it lays down scar tissue. When you get into a situation of maximum load it won’t be able to handle it as well. Not knowing if he had a hamstring injury recently or not, that would play into his injury.
 
When you hurt your hamstring it’s a mis-timing of a stride—the stride is awkward. Usually when people tear it they are striding, and as they go to stride their muscle fires as the leg is extending and it’s that lengthening of the muscle while it’s trying to tighten that tears it.
 
Altidore happened to be heading the ball as well when he injured himself. He was leaning forward, so that would stretch his hamstring even more—like he was going to touch his toes as he was running.
 
What is a pulled hamstring?
When the connection between the tendon and the muscle is injured or partially separates. For a complete tear it actually fully separates.
 
[The hamstring is] not like a biceps tendon muscle, which is only attached at one spot. The hamstring is attached to bone all along the muscle and that’s why people hurt the hamstring in the middle of the leg as well. The hamstring extends from ischial tuberosity, the bone you sit on, and attaches to the femur behind the knee, the fibula [smaller bone in lower leg] and the tibia [bigger bone]. The tendon, which is the rope part of the muscle, is attached to the muscle, which is the engine that pulls the bone.
 
What can be done to prevent hamstring injuries?
Strengthening and eccentric training exercises. In soccer there have been a number of studies that prove doing something called Nordic exercises—also called Russian hamstring exercises—can strengthen the hamstring in a particular way to make it less likely they are injured.
 
In these a player kneels on the ground with someone holding the ankles. The player then leans forward at the knees with the player’s upper leg and torso in a straight line, all while the player tries to hold the position with his or her hamstrings.
 
It looks very difficult if you have never tried them. And if you try it, it is very difficult the first times you do them. It’s usually very common in soccer to add it as part of the training program because of the high instance of hamstring injuries and the effectiveness of preventing those injuries with these exercises.
 
What do we know about how much exercises help prevent this injury?
One randomized controlled trial published in The American Journal of Sports Medicine in 2011 found that among players who did not do the Nordic Hamstring issues there were about two hamstring injuries per Danish professional team in a season. Among a group of teams that did do the Nordic hamstring exercises they saw a reduction in the injuries by almost two thirds. They had 27 Danish professional teams in their control group [that didn’t do the exercises] with 52 hamstring injuries. In the group who did Nordic hamstring exercises, which had 23 teams, there were only 15 injuries.
 
Should we be on the lookout for more pulled hamstrings at the World Cup?
Well, I think no U.S. player [pulled a hamstring] at this last game [versus Portugal on June 22]. Sometimes two people get injured at the same time, as happened during that first game. It’s an unlucky coincidence. That’s the difficulty in trying to find a trend—sometimes it’s just by chance.
 
How long does it typically take to rehab from a pulled hamstring?
If it’s a mild hamstring, it’s about 10 days and a player would be back and ready to play. If you get a grade 2, where you start to get separation from muscle, that takes four to six weeks to get better and you’re out for the tournament.
 
It’s good that [Altidore] stopped. You don’t want to push through it. If you hurt your hamstring you’re much more likely to reinjure it, especially acutely or right away.
 
Do you have any financial ties to the Nordic exercises or any exercise company in any way?
No. No, other than taking care of soccer players—that’s the only financial tie I have. I’m a state employee of the University of Connecticut.
 
Overall, what are the biggest health concerns at the World Cup as far as its climate?
Heat stroke and dehydration.
 

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