High-intensity exercise is gaining popularity. The terminology is, however, often confusing and misleading. The acronyms are similar, but there are some differences.
HIIT. High-intensity interval training or HIIT is the most common term. Although it is rather broadly applied, HIIT specifically refers to cardiorespiratory exercise. While there are no specific protocols, per se, they all involve the manipulation of training intensities between high- or ultra-high-intensity intervals and low-intensity recovery intervals. Generally, the high-intensity intervals are greater than 85-95% (depending on fitness level) of maximum intensity. Maximum is usually determine as maximal oxygen uptake (VO2max), which requires a maximal graded exercise test, or heart rate maximum (HRmax; 220-age—not this is a very rough estimate). Recovery intensities are usually <50% of maximum. The interval:recovery ratios vary from protocol to protocol, but it is not as important as the total work done.
The beauty of HIIT is that a lot of work can be performed in a rather short period of time (some protocols, e.g., the Tabata IE1 protocol*, are as short as 8-12 minutes. HIIT workouts can also be as long as 30-45 minutes (or longer).
I consider the three bioenergy systems (ATP-PC, glycolytic, and oxidative) when determining the interval durations. The ATP-PC system is our ultra-intensity, short-duration energy system that utilized the stored adenosine triphosphate and phosphocreatine for muscle contraction. There is usually enough ATP and PC in the cell to sustain maximal effort for up to 15 seconds. The glycolytic energy system involves the breakdown of glucose or glycogen to pyruvate (or lactate). Because lactate is produced, it is also often referred to as the “lactic acid system”. One is in this energy system between 30 s to 2 minutes of intense exercise (at least 70-85% of maximum). The oxidative energy system (or aerobic energy system) involves low-to-moderate-intensities for a duration of greater than 3 minutes. Depending on goals, the interval durations vary accordingly.
The famed Tabata IE1 protocol involves 8 cycles of ultra-intense cycling (yes, cycling, not burbees) at about 170% VO2max (extremely intense!) for 20 seconds followed by 10-s recovery intervals. Given that 170% VO2max is virtually impossible (the study involved Olympic speedskaters, some of whom could not complete the study), I tend to use quotation marks around Tabata (e.g., “Tabata”) for similar workouts that might approach the necessary intensities. While the likely effect will be less than in the Tabata et al. study*, it is a great intense workout that can be performed in as few as 8 minutes. I would suggest a somewhat longer duration (e.g., 12 or 20 minutes including warm-up and cool-down and, perhaps, more cycles). “Tabata” is great for a quick stimulus to the cardiorespiratory system, though the immediate calorie expenditure may less than longer workouts (there is a possibility, however, of a more sustained post-exercise energy expenditure).
Longer HIIT workouts allow for a greater calorie burn and a more effective stimulus to the cardiorespiratory system. Again, there is no ideal protocol. My suggestion would be to work from the allotted time and caloric goals. I have a favorites protocol scheme I have adapted from an (I believe it was) old Men’s Health magazine. I warm up with a moderate-intensity for 3 minutes, followed by a slightly more intense 4 minutes, 1 minute high-intensity, 3 minutes recovery, 5 cycles of 1:1 (minutes) high-intensity to recovery (last recovery for 2 minutes), and 2 cycles of 1:3 (minutes) high-intensity to recovery. This is a mice 30-minute workout that can be performed on any aerobic exercise.
Fartleks, or tempo-training, is a variation of interval training. Interval training utilizes more uniform intervals (e.g., 1:1, 1:1, 2:1, etc.), whereas, Fartleks (Swedish for “speed play”) are a be more random. An example might involve randomly picking up the pace (“tempo”) between landmarks—e.g., telephone poles or street corners. Another is a “fun” group exercise involves a line of runners, say 10. The rear runner sprints to the front, then the next, and so on. Like intervals, the durations and intensities are determined by the desired energy system(s).
HIIT is an effective change or pace from regular steady-state exercise. As long as one considers the energy systems, anything goes be creative, but be safe (HIIT may not be for one with certain health conditions).
Interval training need, also, not be only high-intensity. Moderate-, or even low-, intensity intervals can be effective ways of increasing the amount of exercise that can be performed in an allotted period of time.
HIIT is (at least in my opinion) limited to cardiorespiratory training and not the same as HIIRT and HIRT. These will be discussed in the upcoming Part 2 and Part 3.
Be your best today; be better tomorrow.
Carpe momento!