Mia Trevillion's GrooveBounceFun exercise class captures the essence of trampoline bouncing, adding cardio moves for a hardcore, but low-impact workout. When I arrived at Mix Fit on T.C. Jester, one of two places Trevillion teaches, nearly 30 women were stretching in Kangoo Jumps rebound boots. Developed in the 1990s by Swiss entrepreneur Denis Naville, the boots were initially made for runners and other athletes to help reduce the impact from vigorous athletic activity. Trevillion, a trained dancer and veteran certified fitness instructor, started teaching the class in 2013 after injuring her knee in a car accident.