What is TRUE about group exercise?

It gained popularity in the 1980s with the aerobics craze
It is generally less effective for people than exercising alone.
It is most successful when negative social reinforcement is used
It was created by Otto Kohler in Germany in the 1920s

The statement "It gained popularity in the 1980s with the aerobics craze" is true about group exercise. It refers to the surge in popularity of group exercise classes, particularly aerobics, during the 1980s.