4-Week Cardio Boost with HIIT

Put some heart into your routine with this collection for boosting cardio fitness. The high-intensity intervals and recovery breaks are the perfect match for helping you gradually increase your strength and stamina one short energy burst at a time. Do a different workout every other day in the order shown—no equipment needed. Feel free to follow the trainer doing modifications for low-impact and less-intense options. Once you have done all three workouts in a section, keep building your cardio fitness and stamina by moving on to the next week. Follow that pattern until you have completed all four weeks. Who knows, you might just boost your fondness for HIIT—if you don’t love it already.