I know this post is old, but thought I'd like to add my two cents here.
I exercise quite a bit, both weight trianing and stamina training, and should have something to add to this discussion, as someone that has followed sports education for 10 years.
What I can say is: All exercise increase the hormone levels in your body and not just lifting weights. Testosterone is what they call an anabolic hormone i.e(repairs muscule). Their are many anabolic hormones, so many that it's difficult for me to go into all of them. At any rate the HGH hormone is also anabolic and is known to have a rejuvenating effect on alot cellular activity, possibly including hair cells. So any rise in testosterone levels would I'm sure be counter acted by rising levels of other hormones.
When you exercise, you produce what is called a catabolic hormone which basiclly tears muscule down. My point here is that your anabolic hormones are usedup repairing the fibres that exercise has tore down. Anabolic seroids maily the testosterone variety, allow you to rebuild muscule tear down quicker than the average person, thus counter acting the bodys catabolic hormones and allowing quicker recoveries.
As most of use know, introducing steroids into the body artificially is a mugs game. The hormonal balance is exteremly complex, and not completey understood as far as I know, most certainly the effects of all the hormones haven't been exmained in relation to hair.
I hope this helps a little bit, but again it's probally not the complete answer.