While other strengthening and flexibility programs have been found to reduce injuries to the ligament, known as the A.C.L., they often require special equipment. The researchers said they wanted one that could be easily incorporated into regular team practices.

A co-author of the study, Holly J. Silvers of the Santa Monica Orthopedic and Sports Medicine Research Foundation, said the new program took only about 20 minutes three times a week.

For the study, the researchers worked with 61 women’s soccer teams in the N.C.A.A. and more than 1,400 athletes. Some teams were asked to use the new program for the fall season, while the others were asked to follow their usual routine.

The study, published in the latest issue of The New England Journal of Medicine, examined heart attack trends among Germans during the 2006 tournament compared to other times of the year. They found that on days the German team played, cardiac emergencies more than tripled for men and nearly doubled for women.

How the team played, the overall importance of the match and whether the winner was determined by a shootout all affected fans’ heart risks. When Germany beat Costa Rica on June 9 of that year, cardiac emergencies rose. The effect was even more pronounced in the second preliminary match, when Germany defeated Poland in a dramatic contest, with the winning goal scored in the last minute. But notably, after Germany had already qualified for the next round, a less important match with Ecuador didn’t have much effect on the rate of heart attacks.

So-called knockout games, which determine whether a team stays in the tournament, appeared to provoke the highest level of emotional stress and resulting cardiac events. The quarterfinal during which Germany beat Argentina after a dramatic penalty shootout was associated with a major increase in the number of heart attacks. On the day of the semifinal, in which Germany lost to Italy and failed to reach the final, the number of events also surged.

Once Germany was out of the finals, the effects of the tournament on German fans’ hearts virtually disappeared. On the day of the match that determined third place, in which Germany beat Portugal, the number of heart attacks didn’t increase. The final match between Italy and France triggered only a moderate increase in cardiac events.

“Apparently, of prime importance for triggering a stress-induced event is not the outcome of a game — a win or a loss — but rather the intense strain and excitement experienced during the viewing of a dramatic match, such as one with a penalty shootout,” the study authors wrote.

The risk was highest for fans who already had heart disease. Their chance of having a heart attack or other cardiac events during the tournament was four times higher, while risk doubled for those who didn’t have a prior history of heart problems.

The researchers noted that the higher risk of viewing stressful soccer matches should be taken into consideration by doctors treating patients with known heart disease. Not only should doctors counsel patients about stress, but they may consider increasing a patient’s medication dose during stressful sports events.

Although European soccer fans are unique in the sports world for their intense loyalty and passionate reactions to game results, the findings likely translate to fans of other major sporting events, the authors noted.

“I know a little bit about the Super Bowl,” study author Dr. Gerhard Steinbeck of Ludwig Maximilians University in Munich told the Associated Press. “It’s reasonable to think that something quite similar might happen.”