As you noted, the project was fun to undertake, even though it was only a sub-component to a much larger endeavor. I may yet go back, visit it, and submit an extension as a nice stand-alone article.
To answer your questions, though, I relied on a pool of around seventy subjects, equally distributed across genders and with a tri-modal distribution for age, many of whom were nudists that had heard about the data collection through some friends of mine. I also had a couple of adventurous fellow students and peers sign up to contribute; even my girlfriend at the time had no qualms about being filmed.
In any event, while there was some inherent selection bias in who I chose, mainly because I needed footage of as many different body types as I could capture, so as to allow the underlying model to generalize well, I do admit to being elated whenever people with certain body types were incredibly eager to help. Granted, I did, at the later stages, have to turn some people away, since I was spending too much time acquiring data.
For the experiments themselves, people had multiple options for what to wear for the various training phases, aside from the different changes of loose- and tight-fitting clothes that I'd ask them to bring and don. I did my best to provide multi-sex body suits of different sizes, which provided more than sufficient constraints when coupled with manually-derived measurements of quantities such as chest circumference, stomach circumference, and so forth. Others opted to strip down to their undergarments and a fair amount, surprisingly many of them women, wore nothing at all.
Regardless of what they wore or didn't wear, each subject executed a series of actions, such as walking, sitting down, standing up, skipping, and climbing. I used six pairs of stereo vision cameras to record the events. I had hoped to use Vicon cameras for the ground truth, but the professor that had them in her lab, even though they hadn't been turned on in a year or so, was aghast over my intended application and barred me from borrowing them.