Regardless of how the groups compared to the average joggers outside of the study, we still know that, within the study, the stretching group and non-stretching group had the same number of injuries. That still needs to be explained.

We still know the stretching group and non-stretching group had the same number of injuries. Regardless of difficulty during stretching, we still know the stretching group stretched before jogging. (B) doesn’t suggest that the stretching group didn’t actually stretch.

This supports the hypothesis that stretching doesn’t help prevent jogging injuries.

This raises the possibility that stretching might reduce jogging injuries, but the two groups had the same number of injuries because the stretching group began with a higher chance of injury than the non-stretching group.

The conclusion is about stretching before jogging, and it’s based on a study about stretching before jogging. Other studies about other kinds of exercise don’t affect how we should interpret the results of the jogging study described by the stimulus.