The rundown on HIIT and LISS
I´m back with my second article for BTN and today I will cover a really interesting and debatable topic – HIIT & LISS.
Questions that I cover for you today are
- What is HIIT?
- What is LISS?
- What are the benefits and drawbacks of HIIT and LISS?
- Does timing for HIIT matter?
- Does timing for LISS matter?
- Practical implications
What is HIIT?
HIIT stands for High Intensity Interval Training. It consists of short intervals where you go all out for 10-30 seconds followed by 1-3 minutes of rest or really low intensity work (i.e. slow walking, cycling at minimal resistance, etc.).
A typical HIIT session could look like 5 minutes of warm up, 5x30s all out spin bikes sprints, deadmill sprints or regular sprints for example, followed by 2.5 minutes of rest/really low intensity and then 3 minutes of cooldown. Go to the gym, get shit done and walk out in 23 minutes – perfect when you are on a tight schedule.
What is LISS?
LISS stands for Low Intensity Steady State. It consists of low intensity work (i.e. slow cycling, walking, cross-trainer, etc.) where your heart rate should be around 50-65 % VO2 peak.
"Research has shown that LISS around 50-65 % VO2 peak elicited the highest rate of fat oxidation ".
If our heart rate is higher than this, your body will need to use more energy from carbohydrates as the breakdown from fat to energy is too slow.
A typical LISS is 30-75 minutes of cycling, walking or cross-trainer for example.
*MISS stands for Moderate Intensity Steady State and is around 65-75 % VO2 peak but is only briefly mentioned here.
What are the benefits and drawbacks of HIIT and LISS?
To not make this article way too long and complex, I have decided to summarize the key differences below.
- Time efficiency: Typical HIIT 15-25 minutes vs. typical LISS 30-75 minutes
- Difficulty: True HIIT, where you push your body to the point it has got absolutely nothing left to give, is both physically and mentally taxing. LISS, on the other hand, is super simple: Keep your heart rate at a comfortably level (between 50-65 % VO2 peak) and just keep going
- Risk of injury: HIIT training has obviously a higher risk of physical injury than LISS and different types of HIIT also has different injury risks
Therefore I have included some strategies to use to reduce the risk of injury when performing HIIT:
Lastly, HIIT has a higher coronary disease risk than LISS and HIIT is more suitable for active and healthy people .
Frequency: HIIT training is very taxing so if you have never done HIIT before, the recommendation is that you only do it once a week and after a while increase the frequency to two times per week . LISS on the other hand can easily be done every day without worrying about overtraining/ under recovery.
Enjoyable: Personal preference!
- If you are easily restless = HIIT
- Like physical challenges = HIIT
- Short of time = HIIT 
- Prefer listening to podcasts or watching television/series = LISS
- Easily stressed/anxious = LISS 
Total calories burned: HIIT burns more calories than LISS during the same period of time but LISS can be done for a longer period of time, without worrying about overtraining, and therefor can LISS burn more calories per session? (see table below).
HIIT also burns more calories compared to LISS post training. This is called EPOC (excess post-exercise oxygen consumption) and it compromises of 6-15% of net total oxygen cost of the exercise .
Calories burned during HIIT and LISS are estimated numbers taken from .
Effects on muscle growth: A really old study (1980) by Hickson showed that strength development was reduced when strength training and LISS were compared to only strength training but these differences were first seen after 9 weeks . This research was also supported by a meta-analysis (study of studies) by Wilson and colleagues in 2012 .
A recent study by Kikuchi and colleagues (2016) also showed that HIIT interfered with muscle hypertrophy and 1RM strength .
Effects on cardiovascular fitness and insulin levels: Trapp and colleagues (2008) studied whether 15 weeks of HIIT or LISS had any effects on cardiovascular fitness and fasting plasma insulin levels. They found that both HIIT and LISS significantly improved cardiovascular fitness but only HIIT significantly lowered plasma fasting levels .
One year later showed Babraj and colleagues found that a total working time of 15 minutes (HIIT protocol: 6 total session of 4-6 set x 30 seconds) over a two-week period improved insulin sensitivity by 23% in young healthy males .
HIIT also increases the body’s capacity to oxidize fat .
“15 minutes of HIIT over a two-week period (=67 seconds per day…) improved insulin sensitivity by 23% in young healthy males”
Does timing for HIIT matter?
Gillen and colleagues found no differences in fasted or fed HIIT training (protocol: 10setx60s, 3 days per week, 6 weeks) for body composition, muscle oxidative capacity or insulin sensitivity .
Moberg and colleagues also showed that HIIT prior to resistance training did not influence mTOR signalling nor rate of protein synthesis in trained men .
Does timing for LISS matter?
Brad Schoenfeld and colleagues showed that there were minimal differences between fat loss when LISS were performed fasted or fed. (protocol: 60 minutes, 3 days per week, four weeks) .
Cadore and colleagues (2012) studied whether the sequence of LISS and strength training differently affected acute testosterone and cortisol levels. They found that acute testosterone levels were optimized when LISS was performed before strength training but no differences were found for cortisol .
A recent study by Eklund and colleagues (2016) found that performing LISS and strength training on different days was superior to concurrent training with regards to maximal oxygen consumption and decreased total body fat when training volume was matched .
There is also evidence that if you divide up your MISS into more frequent sessions that you get a small increase in EPOC (you burn more calories) .
Research also shows that when obese women perform LISS, they automatically decrease their NEAT (Non Exercise Activity Thermogenesis) by default .
You want to implement LISS:
- Perform LISS fasted or fed after personal preferences as there is little to no differences in results
- Separate LISS and strength training if possible
- If it is not possible, performing LISS before strength training optimize acute testosterone levels
OBS! If strength training is your primarily goal and you notice a decrease in total volume when doing LISS before your strength training, I suggest you do your LISS after your workout
- Do not perform LISS in expense of your normal daily activities
You want to implement HIIT:
- If you are not active/healthy today, start with LISS and after 4-8 weeks, depending on your fitness level, you can incorporate one HIIT session per week and then increase to twice per week. You can increase it to three times per week if needed but then your rest needs to be spot on
- Perform HIIT fasted or fed after personal preferences as there is little to no differences in results
OBS! Having full muscle glycogen stores during HIIT can theoretically increase output and therefor maximize your results
- Separate HIIT and strength training if possible
- If it is not possible, perform HIIT prior to resistance training as it did not influence mTOR signalling nor rate of protein synthesis
OBS! If strength training is your primarily goal and you notice a decrease in total volume when doing HIIT before your strength training, I suggest you do your HIIT after your workout. Also separate HIIT away from your leg day(s)!
- Do not perform HIIT in expense of your normal daily activities
Always start at the lower end and slowly work your way up (if you need to).
- Stisen AB, Stougaard O, Langfort J, Helge JW, Sahlin K and Madsen K. 2006. Maximal fat oxidation rates in endurance trained and untrained women.
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- Harvard Health Publications. 2016. Calories burned in 30 minutes for people of three different weights. http://www.health.harvard.edu/diet-and-weight-loss/calories-burned-in-30-minutes-of-leisure-and-routine-activities [last accessed 2016-08-10]
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- John A Babraj, Niels BJ Vollaard, Cameron Keast, Fergus M Guppy, Greg Cottrell, and James A Timmons. 2009. Extremely short duration high intensity interval training substantially improves insulin action in young healthy males
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- Moberg, Marcus., Apró, William., Ekblom, Björn and Blomstrand, Eva. 2014. High-intensity cycling performed prior to resistance exercise does not influence mTORC1-signaling and the rate of muscle protein synthesis in the triceps brachii
- Brad Jon Schoenfeld, Alan Albert Aragon, Colin D Wilborn, James W Krieger and Gul T Sonmez. 2014. Body composition changes associated with fasted versus non-fasted aerobic exercise
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Blog originally by Viktor Ström