High-intensity interval training (HIIT) is a type of workout that alternates between short bursts of intense exercise and periods of low-intensity activity.
Sprint Interval Training (SIT) is a type of high-intensity interval training that involves short, maximal-effort sprints interspersed with periods of rest.
Both methods have benefits including improved cardiovascular health, increased calorie burn, improved insulin sensitivity, and enhanced muscle strength and power.
These workouts can stand alone if you are running short on time, or they can be performed at the end of a resistance training session.
Here is a link to a great video about HIIT and how to implement it. Dr. Berg suggests 30-60 seconds of the intense part of the workout, and 1-5 minutes of rest. If I am doing something like a punching bag, I will perform 20-30 seconds of all-out effort + 1 minute rest, for 8-12 rounds