arobic - noun
(Health and Fitness) (Lifestyle and Leisure) A form of physical exercise designed to increase fitness by any maintainable activity that increases oxygen intake and heart rate. Etymology: A plural noun on the same model as mathematics or stylistics, formed on the adjective aerobic ('requiring or using free oxygen in the air'), which has itself been in use since the late nineteenth century. History and Usage: The word was coined by Major Kenneth Cooper of the US Air Force as the name for a fitness programme developed in the sixties for US astronauts. In the early eighties, when fitness became a subject of widespread public interest , aerobics became the first of a string of fitness crazes enthusiastically taken up by the media. The fashion for the aerobics class, at which aerobic exercises were done rhythmically to music as part of a dance movement called an aerobics routine, started in California, soon spread to the UK, Europe, and Australia, and even reached the Soviet Union before giving way to other exercise programmes such as Callanetics. Although a plural noun in form, aerobics may take either singular or plural agreement . Aerobics have become the latest fitness craze . Observer 18 July 1982, p.
25 The air-waves of the small, stuffy gym reverberated with the insistent drum notes as thirty pairs of track shoes beat out the rhythm of the aerobics routine. Pat Booth Palm Beach (1986), p.
31 See also Aquarobics

arobic - n.pl. vigorous exercises designed to increase the body's oxygen intake.