High-intensity interval training (HIIT) is characterized by 30-60 second bouts of high-intensity output followed by a very low-intensity exercise (like walking or slow pedaling) which allows one's heart rate and breathing to recover before the next high-intensity segment.
Studies have shown HIIT can produce similar results as low-intensity aerobic exercise, but with significant differences in intensity, duration, and energy output. HIIT participants can experience improved maximal rate of oxygen uptake (VO2max), improved skeletal muscle capillarization, increased enzymes of fat metabolism, and improved insulin sensitivity—all of which result in better overall health-status and physical performance.
Three separate studies report that HIIT can reduce one's body fat percentage using durations of only nine total minutes high-intensity activity per week—without controlling food intake! A 2016 study looked at even shorter weekly time durations and included both male and female participants to see what differences exist between the sexes.
The study involved 24 men (average age 38) and 17 women (average age 41) who performed HIIT three mornings a week using a cycle ergometer followed by a blood sample draw over the course of twelve weeks. Their routine consisted of a two-minute warm-up (moderate intensity) followed by four bouts of 20 seconds at maximum effort (set at 175% of the workload attained in the VO2max test) separated by two-minute recovery bouts using very low-intensity cycling (~20% VO2max).
After the three-month study, the participants experienced a lower body fat percentage (average 1%), higher rates of fatty acid oxidation (average 13%), and a greater VO2max (average 9%). Women had greater gains in their VO2max than men, while men lost more fat than the women. Keep in mind the participants only engaged in high-intensity activity a total of 240 seconds per week!
The “TAKE HOME” message is that if you don't enjoy spending 30-60 minutes per day doing aerobic exercises, then HIIT may be something to consider, as it can produce similar (sometimes even better) results in less time.
