If you are across the latest fitness lingo then you would have heard those two buzzwords being spoken about

Especially HIIT or high-intensity interval training. It has grown in popularity in recent years to the point where it’s seen by many fitness pros and enthusiasts as the only way to “get results”.

LISS or low-intensity steady state is where you exercise for an extended period of time, 5mins+. It’s that feeling where your heart rate “levels off” or reaches a steady state and you feel like you could keep going and going.

The main difference between the two training styles begins with the energy systems

HIIT resides fully in the phosphagen system, think 0-10 seconds, like sprinting a short distance and the lactic acid system which lasts 30secs-3mins and ends with legs like lead.
Both systems are anaerobic, meaning they do not rely on oxygen for energy but chemical reactions in the muscles which provide massive energy hence, you can give 100% effort but only for short bursts before you can’t continue.
Most HIIT happens in the lactic acid system lasting from around 30 secs to 3mins

The reason for its popularity is that because you can really amp up your intensity, which in turn means metabolism gets a big boost along with a host of physiological adaptations including improved VO2max, improved insulin sensitivity, reduced visceral and subcutaneous fat, reduction in systolic and diastolic blood pressure when elevated and improving HDL cholesterol. Kravitz, L.

LISS resides in the aerobic energy system and as the name suggests relies on oxygen for energy. It is lower intensity exercise and you can sustain it for much longer periods of time without having to stop. It is an interesting one because whilst you burn more fat using this system as a fuel source than HIIT it has lost popularity in the industry, because especially as the body adapts to the current intensity you don’t get the same metabolic impact post exercise as you do with HIIT. In other words, if you only have a short period of time to exercise, which in today’s busy lifestyles is pretty common you get more bang for your buck performing HIIT.

That being said LISS is often a perfect place to begin training if you are de-conditioned.


Because of the reduced intensity, you don’t load the joints as much. Think walking, rather than sprinting and you reduce the likelihood of injury whilst beginning a training regime.

If a client presents at max results de-conditioned and overweight we will usually start with 30min LISS sessions and look to progress to our 60min HIIT sessions as they lose weight, improve fitness and start moving a bit better.

A research study done in 2015 in relatively untrained but healthy young adults, suggested no particular advantage for HIIT in terms of improved VO2 Max over an 8-week training regime compared to LISS. Carl Foster 2015.

The key word again being “untrained”

It should always be the aim of a fitness professional to help the client get results, as safely as possible and you 100% can still get results with LISS. The key is to make sure the client is training at the right intensity for their current weight, fitness, age, injury and experience levels.

Once fitness and confidence improves we believe it’s imperative to include some HIIT training for all the benefits previously mentioned

  • Kravitz, L. (2014).Metabolic effects of HIIT, IDEA fitness journal, Vol.11, No.5, 16-18
  • J Sports Sci Med 2015 Dec 14(4):747-755 The effects of High-Intensity Interval Training vs Steady State Training on Aerobic and Anaerobic Capacity; Carl Foster

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