HIIT stands for high intensity interval training. This involves repeated bouts of high intensity effort followed by a recovery period. The work and rest periods can vary from several seconds to several minutes each. The work to rest ratio length of time depends on the goals and training status of the individual. The overall goal is to achieve the benefits of an exercise training program within a shorter overall time commitment.
The American College of Sports Medicine published additional information on HIIT training.
Circuit Training is great way to incorporate aerobic and strength exercises, one right after another. There is usually minimal rest time in between exercises, which can help save time. You can rotate through as little as two exercises back and forth a couple times or set up a circuit with as many “stations” as you like and rotate through them several times! A different exercise will be at each “station”. You can choose to perform the exercise for a certain length of time or else a certain number of reps.
The American College of Sports Medicine has an example Fitness Circuit program that can be completed in a short amount of time.
Functional training challenges your body proprioceptively. Proprioception is sensing movement, location, and actions of the body with the goal of improving strength, balance, and coordination. Training in a functional way means you are performing exercises with complex movement tasks, as opposed to using a fixed motion piece of equipment. Consider exercises like step-ups, a farmer’s carry, or medicine ball throws. Practicing step ups on a box or bench challenges muscles in the lower body and core but also overall balance and motor control. A farmer’s carry is functionally practicing carrying a load while walking, keeping the core engaged and posture tall. Tossing a medicine ball laterally against a wall can improve movement coordination for generating power used in activities like tennis and golf. Functional exercises are completed without using fixed motion equipment. Fixed motion equipment takes the user on a set pathway and often provides support for posture. These factors must be considered when looking at exercise outcomes.