Benefits of spanking adults

Here is the lastest research on spanking therapy:

Spanking is stressful at first, but it could bring consenting couples closer together. That's the implication of two studies of hormonal changes associated with sadomasochistic (S&M) activities including spanking, bondage and flogging. ...

Nick Neave, a psychologist at the University of Northumbria, UK, says the results are interesting, but future studies should control for whether participants experienced orgasm, ...

I guess Neave wants to know whether the benefit comes from the spanking or the orgasm. I will be looking for the followup research.