At RhythmCycle, exercisers pedal on modern stationary bikes in sync to a soundtrack of dance- and pop-music beats. Riders only sit for approximately 10 percent of the time during classes, with workouts that target the thighs, glutes, and hamstrings and jump-start the metabolism. They can also be adapted to the fitness level of each student, which means the classes are appropriate whether you're ready to complete the Tour de France or struggling to finish your paper route before the writing staff makes up more news.