Imagine this. A group of adults convene in a dark room. They are seated on what looks like a bike with no wheels. Their feet are in shoes that are attached to pedals. They are required to pedal for 45 minute stretches of time at various intensities. Sometimes they are freewheeling at great speed, sometimes pushing against great resistance. Hip hop music is played as a superhuman at the front exhorts them to greater effort. Most are in their 20s or 30s, but occasionally people who should be old enough to know better take part. That is spinning. People actually pay for this.