I tried to follow the links in that article to primary sources and was not able to find a single one (though the article links to some blogspam for the Business Roundtable study).

A search for the title of the original study did turn up this meta-study:

http://www.danzpage.com/Construction-Management-Resources/Ca...

It has various narrow (i.e., really industry-specific) results that suggest you can have 6 week sprints of 50 hour weeks and gain productivity. Nearly all of it applies to construction.

Overall, I'm still not understanding why people are so confident that 40 hours is the True Answer across all industries and all people, as is commonly asserted.