A. 30/20/10 cardio intervals
Warm up for five minutes. Do five minutes at your regular speed, then cycle through the following pattern for 10 minutes: 30 seconds at easy to regular speed, 20 seconds at a faster speed, and 10 seconds even faster. Cool down for five minutes.
B. Tabata intervals
One cycle of Tabata is comprised of eight sets alternating 20 seconds of work with 10 seconds of rest. Break for one minute after each cycle, then move on to your next exercise. A workout should include four to six exercises (pull-ups, burpees, and squats are a few ideas), plus a warm-up and cool-down.
C. Time-based strength sets
Instead of working towards a rep goal, fit as many reps as possible into a set time frame. After a warm-up, spend 45 seconds doing squat jumps. Take 15 seconds rest. Repeat that same 45-to-15-second ratio with four other exercises. After a one-minute break, repeat the cycle twice more.