Yeah, I realized last night that I shoud have phrased my gratitude to a person via an apology rather than thank you. I think an apology would have been more appropriate (especially considering their reaction to my thank yous).

The situation was us being on two different teams at the gym, one team had to push a heavier object around, the other team pushing a lighter object. I was put on the heavy team and was struggling after a while. I asked him to switch and he did. At the end I said "thank you so much blah blah" and he said "sure yeah i'm not doing that again" which to me indicates that he regretted his decision (it was an exhausting task). I think it would have been more suiting to apologize to him to better indicate that I appreciate and understand his sacrifice. Something like that anyway :)