The glass-is-always-half-empty angle of losing weight is worrying about gaining it back. This hobgoblin of the mind assails you most notably before a vacation, where you might not be able to exercise in the mode to which you have grown accustomed (read: addicted), and where you will probably eat and drink more than you would at home.

This happened to me for the first time when I started cycling; I knew I wasn’t going to take my bike on vacation back then, and was loathe to disappear for the 90 minutes to two hours most rides take.

The second time this happened, I had gotten into rowing, and again, knew that I wouldn’t be able to row. I did get a list of bodyweight exercises to try and did those on the beach.

This summer I once again found myself worrying about giving up my hard-won gains: would not exercising cause me to gain weight? Would I lapse into old habits?

Happily, though, I managed to do two things: keep it light on the food and drink, and exercise.

For the latter, each morning began with a walk, up the beach, then back up to the hotel. That was usually 2.5 miles. So 300-400 calories to start the day, minus some coffee on the way back. Easy and not surprising.

But the new discovery for me, thanks to the Apple Watch: swimming. Specifically, treading water.

In the hotel pool, on the first day of swimming, I saw that my watch was trying to record an outdoor swim. Once I told to watch to go ahead and record, I learned that just putzing around in the pool was burning around 100 calories every ten minutes. So a half hour was 300 calories, and you can do the math.

I actually got more exercise on vacation. Fear: unfounded.

I came home after one week in Ocean City, NJ, and after a hard 10k row, I weighed exactly what I weighed when I left.