Why is it that in the past two days, on two separate occasions, I've gotten weird thumbs up and what seemed like condescending mouthed encouragement from random middle-aged men at the gym while I'm working out on the weight machines? What is this shit?

I thought the unstated social rule of the gym was that you do not talk to other people unless you absolutely must, or you know them. I'm trying to strengthen my back, because it's the only way I can deal with this seriously fucked up back pain I have. I just want to be left alone. I do not need some grimy sleaze giving me "you go girl" thumbs up. Anyone else have this happen to them?