How would you feel if a woman touched your arm?

I've been crushing on a guy for a year. Most of our interactions take place going into and out of the gym. Inside the gym, we do our own thing which I love as jogging is tough for me and he would be a big distraction. He is a lovely gentleman and we've had a few awkward chats as both of us are shy (lots of lovely shared smiles though). It took me a long time to realise he might be interested and I kinda feel like I may have missed the boat with him. This past week, he seems to be always passing behind my treadmill as I leave it. I'm in my own zone and only notice after he has passed so I don't make eye contact or smile. A friend suggested that I might try touching his arm if we are chatting outside the gym again to indicate some interest. I really don't know if that's a good idea. I don't want to make him uncomfortable. What would you think if an acquaintance touched your arm during a conversation? ... he really has lovely arms