All-out effort at 170 percent of your VO2 max is the criterion of the protocol. If you feel OK afterwards you've not done it properly. The first three repetitions will feel easy but the last two will feel impossibly hard. In the original plan the aim was to get to eight, but some only lasted six or seven.
DR IZUMI TABATA
The Guardian March 24, 2013: “The Tabata workout programme: harder, faster, fitter, quicker?”
The Tabata Protocol was developed in Japan in 1996 by scientist Dr. Izumi Tabata and his team from the National Institute of Fitness and Sport in Tokyo. It uses high-intensity interval training (HIIT) with the following structure: 20 seconds maximum exercise, with ten seconds rest, repeated eight times and totalling four minutes. Dr. Tabata's study showed noticeable increases in both aerobic and anaerobic capacity of the test subjects. It should be noted, however, that in order to gain the benefits outlined by Dr. Tabata, participants need to work at 170% VO2 Max in each and every cycle. That’s very intense.
Improve aerobic (cardio) and anaerobic (weight training) endurance
Boost cardiovascular resistance and stamina
Increase muscle resistance to fatigue
Release greater amounts of testosterone and growth hormone
Produce higher muscular endurance and anaerobic capacity
Increase metabolism and burn more fat while you rest