Basically, someone asked for specific studies to prove it. People came up with all the various ways it affects health and fitness, and the person still went away with his previous opinions b/c I don't believe anyone could find a specific study that said weed prevented muscle growth.
Just got back from a little rooting around and found an equal measure of sites that claimed that weed either did or didn't reduce Testosterone levels. The sites that said it didn't though were basically all written by pot-heads.