So I played tennis again yesterday... with the same person as last time.
What's amazing is how quickly the human body adapts. Last time, I was so out of shape that I was way too winded after only a couple of games in.
This time though, I felt a noticeable increase in endurance from the previous match, just a few days earlier. I even had enough energy to play a second set, which I wasn't able to pull off the first time around.
Final score: 6-2, 6-1