HIIT vs LISS: Is It Really a Debate?

With most articles put emphasis on which is better, people are pitting these two styles of cardiovascular training against each other, like many things in the fitness industry people seem intent on making this an either or when in reality both are extremely beneficial training modalities for different reasons and both should be used at appropriate times depending on an individuals needs.

8 min read
Sean Klein
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Sean Klein
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In This Resource
  • What is Cardiovascular Training
  • What is LISS
  • What is HIIT
  • So Which Should I Use? HIIT vs LISS
  • How Much LISS vs How Much HIIT
  • Which Modality Can I Use
  • HIIT For Muscle Groups
  • HIIT is Not For Muscle Gain
  • Reach Out
  • References

What is Cardiovascular Training

Before we start to define different types of cardiovascular training, it is important to define the base term. Cardiovascular training is the intentional increase in work/output (various modalities) that results in increased energy expenditure and the physiological response which is associated with this increased work. When we run, when we cycle, do Crossfit or any number of other activities we are intentionally increase output and creating physiological stress. This physiological stress allows the body to create adaptations to the type of demands placed on the body.

What is LISS

LISS is an acronym for low intensity steady state and involves a sustained period of low intensity (low heart rate and perceived exertion). These sessions typically last between 30-90 minutes depending on factors like training age, genetics, time available etc.

Using heart rate zones for LISS can be difficult, the easiest and simplest way for you or for your clients to work with is perceived exertion. The goal during a LISS workout is to be able to maintain a conversion while performing the workout, this is often known as conversational pace.

LISS is an extremely effective way to improve your cardiovascular systems through improving:

  • Mitochondria Content
  • Increased Stroke Volume
  • Improved Cognition and Brain Health
  • Improved VO2 Max
  • What is HIIT

    HIIT is an acronym for high intensity interval training and involves repeated bouts of near maximal output. This create a great deal more fatigue and requires much higher percentage of heart rate to perform, it also requires much less time as these intensities cannot be sustained for long periods of time.

    Using perceived exertion is again very beneficial for HIIT training, especially as these sessions will often be so intense that they will not allow you to be continuously looking at a heart rate monitor throughout.

    HIIT, like LISS, creates a variety of adaptations that are beneficial to the cardiovascular system:

  • Improved VO2 Max
  • Increased mitochondrial content
  • Reduced inflammation
  • So Which Should I Use? HIIT vs LISS

    The answer to this is HIIT + LISS, you should be using both of these training modalities to train optimally for health and performance.

    HIIT is far more time effective than LISS to achieve similar results, so on days when you are struggling for time and need to get a quick workout in then HIIT may be your best option.

    Whereas LISS is much easier to recover from as the intensity is much lower, meaning that it has little impact on the rest of the day. Personally going back to work after performing an intense HIIT workout is difficult, my heart rate takes a long time to come back down to baseline and I have much more lingering fatigue compared to performing a LISS workout. This needs to be factored into making decisions about what type of cardiovascular training you are going to be doing in the week and when, if you programme assault bike sprints during your lunch break before a big meeting you will likely regret it.

    How Much LISS vs How Much HIIT

    It is impossible to prescribe accurate exercise frequencies without discussing it with an individual without having a detailed conversation with them about a variety of topics. However I can provide some minimums that will allow you to get a feel for how you should be designing your week of exercises.

    Weekly Minimums

    LISS x 90’ per week

    HIIT x 1 per week*

    Resistance Training x 2 (30-60’)

    *HIIT is very intense and beginners who are just starting exercise will be much better off building towards HIIT over a period of a couple of weeks by performing medium intensity steady state, which will allow them to become comfortable with a certain level of fatigue and high heart rate. This is especially important for those who have been sedentary for a long time as you will not be conditioned to perform high output sessions.

    Breaking the LISS into two or even three sessions can be a great way to make this amount much more approachable. If you are sedentary individual and you adopt this training programme successfully for six months you will transform your physical health.

    Which Modality Can I Use

    The modality (type) of exercise you chose to perform HIIT and LISS is an important factor for your long term success of building a capable cardiovascular system. As with most topics, the modality of training you use will be highly dependant on a number of individual factors.

    People who have been sedentary for long periods of time should focus on non load-bearing activities like biking and rowing, as these will not lead to repetitive strain injuries in ways that running will. Whereas those who have experice running can also use this modality to perform both styles of cardiovascular training. Personally I like to use a mix of both, this means my running volume never gets to the point where I am getting Achilles tendon issues or knee pain whilst I continuously stress my cardiovascular system through running and biking. If we take into account that resistance training should also be in your week, using at least one non load-bearing activity per week can really help mitigate injury and avoid nagging pain.

    Mix model HIIT is often use in training style like CrossFit, Orange Theory and Bootcamp style training. Mix model is where a variety of movements are used to create a high intensity stimulus. However there is so much variety in both content and quality of these sessions that it’s hard to note on their efficacy. These styles of training often involve high amounts of either strength training and gymnastic training within HIIT circuits and therefore the stimulus becomes hard to track without taking a session to session approach. These are all effective training styles, but for this article I will not discuss mix model styles further as it can be very convoluted.

    HIIT For Muscle Groups

    We have already defined HIIT as a period of high intensity cardiovascular output. Therefore there should be no mistake that this is not putting emphasis on a specific muscle group, it is stressing the cardiovascular system as a whole. So how can I do HIIT for my glutes? The answer is you cannot, these are completely different training styles with completely different adaptations. One involves hypertrophy of the glutes and the other involves increasing VO2 max etc. These sessions simply represent a complete misunderstanding of resistance and cardiovascular training that is pushed by companies like Nike and Apples that have no expertise in the field and will just use buzzwords that people have heard others discussing. Avoid any coach or app that is encouraging you to perform HIIT for your chest or glutes.

    HIIT is Not For Muscle Gain

    Although HIIT has been shown to cause muscle growth in overweight obese men and women, I would highly recommend not using HIIT intervals to gain muscle mass. Muscle gain may result from some mixed model activities like CrossFit, but only to those who are performing very high volumes of specific movement patterns within a high intensity interval training circuit. I suggest that if you are not practicing CrossFit in a CrossFit gym with a coach then you should not use HIIT for muscle growth. This seems extremely intuitive considering the definition of HIIT discussed above.

    HIIT may also be more effective than LISS at preserving muscle mass, but again this feels like a mute point, muscle mass, strength gains etc will come from resistance training. It’s important to point out that these studies were performed on overweight individuals who have little experience resistance training, meaning almost any form of physical exertion might illicite muscle mass gain or maintenance. I think we can all agree that bike intervals are not going to be the modality that builds a muscular physique.

    Reach Out

    We currently do not offer cardiovascular training on our application, but we do plan to add this feature in the future. If you need help or just have any questions, do no hesitate to reach out at sean@programme.app with your questions.


  • MacInnis MJ, Gibala MJ. Physiological adaptations to interval training and the role of exercise intensity. J Physiol. 2017 May 1;595(9):2915-2930. doi: 10.1113/JP273196. Epub 2016 Dec 7. PMID: 27748956; PMCID: PMC5407969.
  • Blue MNM, Smith-Ryan AE, Trexler ET, Hirsch KR. The effects of high intensity interval training on muscle size and quality in overweight and obese adults. J Sci Med Sport. 2018 Feb;21(2):207-212. doi: 10.1016/j.jsams.2017.06.001. Epub 2017 Jun 8. PMID: 28647284; PMCID: PMC7104622.
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    This resource was written by Sean Klein. Sean Richard Klein has thousands of hours of coaching experience and a BSc in Sports Science with Management from Loughborough University. He owns a gym in Bayonne France, CrossFit Essor, which runs group classes and a Personal training studio.

    Sean Klein


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