What does Mihaly Csikszentmihalyi mean by Nautilus? I'm not sure that this is the best site for the question but given it is a psychology book I figured better here than nowhere.

I'm reading flow by Mihaly Csikszentmihalyi and on page 47 the following quote is made:

“they will go on diets, join health clubs, do aerobics, buy a Nautilus, or undergo plastic surgery.”

What i meant by "Buy a Nautilus"? I've never heard of someone acquiring the shelled invertebrate as a response to stresses of life, in my entire existence, and based on my research a $10,000+ watch isn't a "normal" response either so i'm not sure what is being communicated in this sentence.
There is lots of opportunity here for jokes about generational differences, as both Csikszentmihalyi and I were born before generational names were even invented, but I will go straight to the answer. It was probably in the 1960s that Nautilus was the brand name of one of the first manufacturers of home exercise/weight machines. In those days there weren't any exercise clubs to join, and, if you didn't like the YMCA scene, then the only option was to buy a set of barbells, which were clumsy and not well adapted to many muscle groups. The Nautilus machine filled that economic gap and became very popular; you see their many descendants in all the exercise clubs today.