This is actually pretty comforting (at least for me). It means you can significantly alter your attractiveness, and you're not stuck with what you have!
"Contrary to popular theories of men's physical attractiveness, there was no evidence of a nonlinear effect; the strongest men were the most attractive in all samples"
But in the real world women don't judge men by looking at photographs of their bodies. They interact with them and make an assessment based on many dimensions like handsomeness, physique, wealth, education, personality, etc.
"In both sets of photographs, the subjects' faces were obscured. See figure 1 for sample photographs. Set 1 photos included both front and side views; Set 2 photos had only front views."
So far, it seems like the conclusion should be that upper body strength accounts for variance in attractiveness when the only available information is visual imagery of a man's body, with the face obscured.. That's a big enough qualifier that I think the conclusion in the title is misleading, and claims a broader conclusion than can be justified from this study.
The study authors did address this somewhat in question d:
"Research on facial attractiveness reveals that some women prefer more feminized and less dominant faces". It sounds like they way they studied this was to see if preference for more feminized faces might translate into a similar preference for bodies, and they found that it did not. However, this doesn't address the possibility that faces might count for more variance if the raters had seen them, right? Again, I may be missing something here, but I'm not seeing it so far from the study.
Lastly, does anyone know how the study specifically controlled for upper body strength? Were there any images of men who were athletic but had most of their strength in their lower body? I'm not seeing it here, may have missed it.
At this point, I do think that the claim in the title is too substantial given then evidence from this study. I'd say that there certainly does appear to be evidence that upper body strength accounts for variance in attractiveness when a rater has access only to non-facial physical features, but even then, I'm not entirely sure the study adequately controlled for other athletic physical traits.
This measures two self assessed factors so it's very well possible that at least some of the correlation runs in the opposite direction. That is, more attractive people, all else being equal, are rated as being more physically strong.
"Contrary to popular theories of men's physical attractiveness, there was no evidence of a nonlinear effect; the strongest men were the most attractive in all samples"