What is HIIT workout?

What is HIIT workout?

HIIT is high intensity interval training which involves short bursts of intense physical activity training alternated with recovery periods. Any of the aerobic exercises like running, climbing stairs, rowing or skipping can be used for HIIT. But the workout is fast and very intense followed by a slowing down period. This is followed by another round of high intensity workout. It is a time saving strategy for those who can’t find enough time for the usual type of steady, more prolonged exercise schedules. Body will continue to burn extra calories during the recovery phase for up to 2 hours so that weight loss is significant. You would have noted excessive sweating for a variable period after intense physical activity. Muscle building is another advantage. A short preceding warm up period is there like other exercise programs.

Several HIIT protocols are available, which can be broadly classified into aerobic HIIT and anaerobic HIIT. Anaerobic HIIT is also called sprint interval training (SIT). HIIT can be an alternative and more efficient protocol than the usual moderate intensity continuous training protocol which is the gold standard recommended by several guidelines from medical societies. Aerobic capacity of the individual is measured as maximal oxygen consumption during exercise (VO_2peak). This is measured using a test known as CPET. Aerobic capacity is the strongest predictor of future health and all-cause death rate. Even in persons with risk factors for heart disease like high body mass index (BMI), blood pressure or diabetes, high level of fitness reduces the risk of heart and blood vessel disease and early death. Increasing aerobic capacity has a major role in those with lifestyle related diseases as well as in preventing them.

Most guidelines on physical activity for adults from medical societies recommend at least 150 minutes of moderate intensity physical activity or 75 minutes of vigorous intensity physical activity per week or an equivalent combination of physical activities. Moderate intensity continuous training protocols are generally used in cardiac rehabilitation for those with heart disease. Some of the latest guidelines have started including HIIT as an alternative, though there is some disagreement among experts regarding the inclusion of HIIT in cardiac rehabilitation. This is mainly due to the absence of as many large scales studies on HIIT as is available on the conventional moderate intensity continuous training.

Two popular protocols for HIIT are 4 x 4 and 10 x 1 minute protocols. Protocols vary in the workout duration, rest interval, work/rest ratio, workout intensity and frequency of workout. As the name indicates, HIIT involves brief intermittent bursts of activity which is less than the peak aerobic capacity (70-90% of VO_2peak), with intervening active rest periods. A popular protocol for SIT is Wingate protocol in which there is an all-out vigorous intensity exercise involving 350% of VO_2peak. They go beyond the aerobic capacity and hence the name anaerobic HIIT, meaning that the body has an oxygen debt which is taken care of by extra breathing during the recovery period. As expected, SIT is interspersed with longer periods of complete rest. SIT may not be ideal for older persons and those with heart disease and other related medical ailments, because of the abrupt changes in heart rate and blood pressure.

High intensity protocols are quite demanding for the persons, though the intensity is adapted to the aerobic capacity of the individual. The risks of these high intensity protocols are a concern and certainly more studies are needed. Supervised workout is mandatory initially in the case of HIIT till the participants are accustomed to the intensity. Heart rate is measured with a wearable heart rate monitor during the exercise to make sure that the permitted limits are not exceeded. In aerobic HIIT, the recommended peak heart rate is 85-90% of the age predicted maximal heart rate. Age predicted maximal heart rate is calculated as 220-age of the person in years. Medical opinion from the regular physician is mandatory before starting supervised HIIT programs in those with existing heart disease or any other significant medical problem. Home based HIIT programs are possible if sufficient support is provided by experienced centers.