Indoor cycling, often also called spinning, as an organized activity, is a form of exercise with classes focusing on endurance, strength, intervals, high intensity (race days) and recovery, and involves using a special stationary exercise bicycle with a weighted flywheel in a classroom setting. Classes generally use specialized stationary bicycles. Features include a mechanical device to modify the difficulty of pedalling, specially shaped handlebars, and multiple adjustment points to fit the bicycle to a range of riders. Many have a weighted flywheel, which simulates the effects of inertia and momentum when riding a real bicycle. The pedals are equipped with toe clips as on sports bicycles to allow one foot to pull up when the other is pushing down.