More than 2,700 people who run 10 or more miles per week were recruited for the research.
Half stretched before exercise. The other half did not.
After three months, researchers found there was no difference in injury rates, but there was a 40 percent increase in injury rates among runners who normally stretch but were assigned to the no-stretch group.
This suggests switching from a pre-run stretching routine to non-stretch could cause trouble.
These results were also presented at the American Academy of Orthopedic Surgeons meeting.