That conclusion was bolstered by the fact that only hamstring grafts tore among the Delaware subjects. Those with that type of graft had been allowed to return to sport four months sooner than those whose graft came from the patellar tendon. The latter traditionally takes longer because it is often more painful. Yet, that extra time probably allows the graft to more fully mature.
In short, at least for the females in the Delaware study, the culprit was incomplete rehabilitation.
A study just released online by Sports Health blamed the same for poor performance upon return to sport after a hamstring strain. Conducted by Australian investigators, the study looked at professional soccer, rugby, and Australian Rules football players who suffered hamstring strains over the course of one season and who had played at least five games prior to injury and at least five games after returning.
The researchers were motivated by a hamstring injury rate of 17% in all of those sports in Australia each year, the highest rate for any lower extremity muscle group.
A total of 15 players qualified for the study and the focus of the study was on their ability to sprint upon returning to play. The study determined that seven of the 15 could run just as fast for just as long after the injury but seven others were significantly impaired in their ability to maintain top speed for the remainder of the season. One of the subjects was actually better.