F45 cardio sessions include explosive exercises like the box jump. Tom Werner / Getty Images F45 is a fitness program that focuses on cardio, resistance-based strength training, or a hybrid of both. The sessions last 45 minutes and are done in a group setting at studios around the country. F45 has been around for more than 10 years, with the first studio opening in Australia in 2012, but its popularity has seemed to grow recently on social media.