If your knee hurts, you might want to try strengthening your hips, working out your abs, and improving your jumping form.
The recommended exercises, presented at the American College of Sports Medicine's annual meeting in Orlando, Fla., in late May, reflect a new understanding of how people get hurt playing games like soccer, basketball, and volleyball—games that involve lots of jumping and sudden turns.
Researchers have learned that doing a few toe touches, or even strengthening muscles around the knee itself, won't protect it, said Maria Clara Carrelli, a physical therapy researcher at Georgia State University in Atlanta, who reviewed all the studies she could find on runner's knee. However, "if your hip gets weak, there will be weird forces on your knee," she said.
For many years, high school athletic teams have warmed up with a light jog and a few hamstring stretches. The theory made sense: If your muscles were cold and tight, they might snap, like frozen meat. But no one really knew how well the stretching and running worked.
"I think back to when I played football and the warm-ups we did," said Eric Robertson, a professor of physical therapy at Regis University in Colorado. "They were just 'lean over and stretch this muscle, and then come up and skip.' I think the coach was just pulling them out of thin air."
But starting in the 1990s, researchers began to notice which athletes were most likely to injure their knees.
Females, for example, are three to 10 times more likely to tear their anterior cruciate ligaments (ACLs) than males. When boys jump, they are more likely to land with their knees aligned over their feet. Girls' knees sometimes land knock-kneed or bow-legged, putting strain on their ACLs.
Other research has led to the principle that core muscles—generally speaking, those that make up the torso—hold the rest of the body together like a hub holding the spokes of a wheel. If the core isn't strong, the other parts can't hold their proper positions and, as a result, undergo strain they weren't designed to withstand.
A Better Way to Warm Up
Various researchers have created exercises aimed at correcting these weaknesses. They tested them by assigning some teams to do the exercises and others to do traditional warm-ups.
In review of these studies, a group of researchers in Ireland and England looked at 23 controlled trials with a total of 21,479 participants playing soccer, basketball, Australian football, handball, floorball, and volleyball.
Twelve of the trials tested programs that combined exercises to strengthen hips, hamstrings, and core muscles, improving balance and teaching proper jumping technique.
The Irish and English researchers reported that, put together, the studies showed that these programs reduced total injuries by 35 percent, knee injuries by 21 percent, ACL injuries by 49 percent, and ankle injuries by 28 percent.
Another seven studies examined exercises that train athletes on balance boards, improving the way they control their legs and feet in space and time. These exercises reduced the risk of hamstring injury by 78 percent and ankle injury by 36 percent.
Three studies targeted hamstring muscle training with no significant effect. And some exercises actually did harm. In one study, researchers tried training just the Achilles and patellar tendons and actually increased the risk of injury by 150 percent.
A Happier Future for the World's Knees
Overall, the research shows that science-based warm-ups can make an important difference.
"I think it's a direction we should be moving in as a profession in athletic training and sports medicine," said Jim Thornton, president of the National Athletic Trainers' Association.
He offered the caveat that athletes are better off if they can work one-on-one with a professional who can assess their weaknesses and prescribe the best exercises to address them. "Any type of prevention programming, as opposed to not doing one, would help," he said. "But the gold standard would be to evaluate the individuals on the team."
That makes intuitive sense, Robertson agreed. But he said there is no evidence yet to show that individualized training works better or worse than the group approach.
"Coaches [and athletes] and people who are responsible for those types of things are not patient when it comes to exercises that prevent injury," said Thornton. "They are kind of boring and tedious. But we know they work."