When will the U.S. regain dominance in the sprints?

4 or 8 years. Maybe tomorrow (today). There are still races left! The performance patterns in this year's sprints look too fishy for the kind of changes that have been happening. When you behave like Usain Bolt did (like the 2000 US Sprint Relay team) everyone is going to find some way to get you positive for something. It may take a few years, but the performance or recovery enhancement drugs will be found out.