In terms of repetitive stress injuries involved with bicycling, one type of injury that we are encountering with increased frequency is the “neck strain.”
Take a look at the relative positions of both the head and neck in the photo on the right.
Note that this person’s neck has to extend quite a bit in order for him to right his head. Although the horizontal positions of his middle and lower back are aerodynamic, it places significant stress on the muscles and vertebrae of the neck. If this man’s neck muscles were not working overtime to keep his head up, he would be looking straight down at the ground. That would indeed be dangerous.
For those of us who are not professional racers, there is an easy solution to this problem. Raising the handlebars of your bicycle will allow you to ride in a more upright position. The lower and middle back is in a more vertical position, and the head can look forward without as much neck strain. Most bicycle shops are happy to make this adjustment for you!