High Intensity Interval Training (HIIT or known as High Intensity Training--HIT) is a popular component of several workout regimens. It can been seen in programs such as Shaun T's Insanity, Fartlek or "speed play" in runners, The Tabata Method, and CrossFit. As a disclaimer, these are programs and systems for clients that have already built a substantial fitness base and not necessarily the weekend warrior this article is to improve your knowledge of these programs out there and are not meant as a recommendation for clients.
The benefits of HIIT training are improvements in physique, athletic ability, and aerobic conditioning (increased fat burning and utilization). For persons with Diabetes and those without the condition, there are improvements in glucose metabolism.
For active persons with Diabetes, they may want to monitor their carbohydrate consumption and blood glucose levels to avoid a hypoglycemic episode.
Crossfit is a combination of sprints, weight lifting, gymnastics, and calisthenics. Please note that they do have a segment on nutrition and advocate a Paleolithic Diet (40% carbohydrate, 30% protein and fat) that you may want to be aware of if you are counseling clients in CrossFit.
The Tabata Method has roots in HIIT. The program came from Izumi Tabata and uses short bursts of all out intensity of 20 seconds (roughly 170% of VO2max) then 10 seconds of rest. This is repeated for a total of 4 minutes or 8 cycles. This shorter/higher intensity program done four times per week gave a group of athletes the same benefit as another group that trained five times per week at a steady state of 70% VO2max). The Tabata group also had gained anaerobic capacity benefits.
Fartleks are not something that can send a classroom of 10 year-olds giggling but is a training method that continuously blends continuous training with intervals and intensity. The exercise places stress on the aerobic and anaerobic systems. Most sessions are typically 45 minutes and can work with cycling and other sports.