What exactly are HIIT and LISS?
HIIT stands for ‘’high intensity interval training’’, and consists of short intervals of sprinting coupled with low-moderate intensity work. While not strictly limited to running (cycling and swimming are also alternative methods), a common example of this would be a 30 second sprint followed by a one-minute cool-down walk to bring your heart rate back to normal before repeating 5-10 times. LISS stands for “low intensity steady state” cardio, which consists of purely low-moderate intensity work. Walking or lightly jogging on the treadmill is a common example, as well as riding a stationary bike at a relatively slow pace.
Why do HIIT?
Exercise intensity is discussed in terms of percentage of VO2 max. This is the maximum rate of oxygen consumption during exercise, and plays a major role in determining endurance during longer exercise sessions (such as distance running). In most studies that demonstrate the advantages of HIIT, subjects reached between 80 and 100% of their VO2 max during the high-intensity periods of the exercise routines. This ideal area (known as Vmax) is where breathing becomes labored, and you feel as though you can’t suck in enough air – around 90% of your “all-out” effort.
The most important aspect of HIIT exercises is to repeatedly reach and maintain your Vmax. As you can imagine, this requires a pretty significant amount of anaerobic effort (think sprinting, not fast jogging).
The second-most important thing to know is the total amount of time you exercise at your Vmax determines the effectiveness of the HIIT workout, which is simply a matter of the duration and intensity of both your high and low intensity intervals.
Why HIIT is better than LISS
- Fast and furious – An effective HIIT workout can take as little as 4 minutes if performed with maximum intensity. While there is no “right” amount of time to dedicate to a HIIT workout, somewhere in the 8-15 minute range seems to be the most popular, and is more than adequate for achieving the desired results. Compare this with LISS cardio, which requires an average of 45-90 minutes per session, several times per week, in order to become effective.
- Keep your muscle intact – A HIIT cardio workout places a greater demand on the anaerobic pathway to produce adenosine triphosphate (ATP) — the energy “currency” of the body. This means that during the post-exercise recovery period, the body will take in more oxygen for regenerative purposes, including the re-synthesis of muscle glycogen, which helps to help the body repair muscle tissue damage. Due to LISS’ low-impact nature, a longer time is needed performing each workout, which can lead to raised cortisol (a stress hormone) levels, causing the body to go into a catabolic (muscle-wasting) state.
- Burn fat by doing nothing – Due to a phenomenon known as Excess Post-Exercise Oxygen Consumption (EPOC), which essentially means a greater amount of oxygen is required to return the body to homeostasis (a normal, balanced, pre-exercised state) by restoring muscle glycogen and muscle proteins that are damaged during exercise. It is this increased oxygen consumption that explains why the body continues to burn calories long after a HIIT cardio workout is completed. LISS workouts have been shown to have a significantly shorter recovery period, with little or no EPOC effect taking place, meaning that the majority of calories burned are during the workout itself.
While HIIT workouts have some undeniably fantastic benefits, Part 2 of our series will take a look at the reasons why LISS cardio is preferable in certain training regimens, and how it can outperform HIIT depending on training goals!