retro space images

Important Tumblr NASA News: A friend of mine shared this Retro Space Images photo of a shirtless Deke Slayton training for his ASTP mission sometime in the mid-70s.

I have no idea where to start with this picture. Were shirtless simulator runs a thing at NASA? Was Deke trying to prove something as the soon-to-be oldest person to travel into space at age 51? Whatever the case, as a Deke girl, I greatly appreciate this photo.