The tireless 71-year-old designer, best known for punky prom dresses and a lot of pink, introduced her fall collection as a theatrical exercise video for the Style Network program Betsey and Lulu, which follows the lives of Johnson and her daughter. It was a catwalk of energetic, giggly models in active wear chatting on mobile phones as they waved to attendees, then an exercise routine led by the designer that included running in place, yoga and pull-ups. Rows of pink yoga mats were strewn on the runway, each accompanied by a pair of high-top sneakers, towels and wine bottles. The collection, named BJ Kicks A, veered from the high school dance party looks that she has championed for decades, running toward a junior high school gym class with a lot of cheek. It was an explosion of neon pink and yellow, animal prints and plaids on mini dresses worn over leggings, a veritable visual feast piled over one another.