I don't think I'd call it sexy. When someone makes something difficult look effortless I would call it graceful. I can appreciate grace without getting turned on. Ha!
Depends what they are doing?
What would be sexy about watching someone doing manual labor.
Down vote? Really?
Sexy? No, but I do get envious that they make it look so easy and I know better.
It can be, but it depends what it is. The sexiest thing I've seen in a woman is confidence, especially calmly and politely rejecting a guy who's hitting on her in a sleezy kind of way.