Changing step width alters lower extremity biomechanics during running.

The Cross over gait. We have been talking about this for years, our theories have been supported by the available research and years of patient care.
Here is another study that goes with our ideas, which gives it deeper clinical relevance.

Changing step width alters lower extremity biomechanics during running. Brindle RA1, Milner CE, Zhang S, Fitzhugh EC. Gait Posture. 2014

"Step width is a spatiotemporal parameter that may influence lower extremity biomechanics at the hip and knee joint. Peak hip adduction and rearfoot eversion angles decreased as step width increased from narrow to wide."
Step width influences lower extremity biomechanics in healthy runners. "When step width increased from narrow to wide, peak values of frontal plane variables decreased.

The Fredericson paper (Hip Abductor weakness in distance runners with iliotibial band syndrome) is also supportive. That paper found that increasing step width reduced the strain on the iliotibial band during running. Greater ITB strain and strain rate were found in the narrower step width condition.

We have said it, and will say it again, because someone will post here, "maybe, but all the pros when you watch then and see photos of them, they all have a very narrow step width, basically qualifying for what you guys call a Cross Over gait. So how can you make such bold statements?"
Our response would be, "every attempt at squeezing out more economy in ones gait, walking that fine line of riskier gait mechanics, is a game of playing ECONOMY vs. LIABILITY. And if you have built enough durability and conditioning into your system that you can nudge right up to that fence of RISK, you can play with those liabilities and squeeze out the economy of your gait (like the pros) with that narrower step width. Just be aware and careful, that when you are losing control, as the runs lengthen, that the LIABILITIES are increasing and thus so is the RISK for injury. Just remember, you are likely not a pro, and have not spend the time building a safe zone of durability on your system to endure narrow step width for 26 miles.

A good runner will train the frontal and rotational planes regularly as they engage in their sagittal sport of running. So that as fatigue sets in and the step width begins to narrow, they have some durability of the lower limb to sustain the risky mechanics of the narrow step width. There is a limit for everyone, when the well goes dry.