Before exploring the difference between High Intensity Interval Training (HIIT) and Low Intensity Steady State (LISS) cardio, it should be said that cardio isn’t the answer to your fat loss prayers. Fat loss is determined by calories in vs calories out in which nutrition carries the bulk of the responsibility in driving the result. Cardio is merely an accessory to your plan, additional movement, additional activity, additional calories; but you want the most bang for your buck right? So we’re going to look into HIIT vs LISS to work out which one is best for you..
What is HIIT and LISS?
High Intensity Interval Training (HIIT) is a training technique which couples high intensity increments of exercise with maximum effort rapidly raising your heart rate, together with moderate intensity, short, active recovery periods. Usual HIIT sessions can be between 5-30 minutes and burn from 150 calories to 600 calories. An example of this would be a 20-45 second sprint followed by a 45 second-2 minute steady pace walk to cool down and bring your heart rate back to normal and then repeating it. On the other hand, Low Intensity Steady State (LISS) cardio is cardio consisting of low-moderate intensity work usually over a longer period of time. This would include moderate pace on the elliptical or bike between 30 minutes to an hour.
There are two ways that muscle can burn blood sugars (glucose):
1. Aerobic work - with air such as LISS
2. Anaerobic work - without air such as HIIT and weight training
The lactate threshold and anaerobic threshold are two good indicators of performance of cardio as it shows which produces Adenosine Triphosphate (ATP- which is the biochemical way to store and use energy). To test this simplicity, when doing LISS the fact that you can still hold a conversation shows you’re below the lactate threshold and anaerobic threshold, as opposed to an inability to speak during HIIT showing a state above the anaerobic and lactate thresholds. During low intensity exercise, blood lactate remains at or near resting levels. As exercise intensity increases there comes a break point where blood lactate levels rise sharply which occurs in more HIIT style training. As the exercise intensity increases requiring more oxygen consumption, this rise in the lactate threshold is normally expressed as a percentage of your VO2 max. For example, if VO2 max occurs at 24 km/h on a treadmill and a sharp rise in blood lactate concentration above resting levels is seen at 12 km/h then the lactate threshold is said to be 50% VO2 max.
What does it all mean for fat loss and burning calories?
HIIT is said to increase EPOC (excess post-exercise oxygen consumption) resulting in an elevated fat loss state for up to 24 hours after you finish your workout. That is why many conceptions rely on the ‘after burn’ theory in saying why HIIT is more effective. Long, slow, low-intensity cardio will produce a small EPOC effect that will at best, last only a couple of hours after the workout. Basically the 400 calories you burn during the workout will be all that is burnt, because the EPOC effect afterwards is negligible. However, studies have shown that after HIIT workouts, the EPOC effect can still be found up to 38 hours after the workout - basically your body is burning fat to fuel the restorative processes for 38 hours AFTER your workout. So, even though you may have only burned 250 calories during your HIIT workout, the total calories burned after will add up. Those calories, plus the 250 burned during the HIIT workout surpasses the 400 burned during the slow, steady-state workout but see how the difference is fairly minimal and also dependant on a number of variables?
In short, intensity is not a switch that is set on either on high or low - it's more like a dial. Cardio can be prescribed through a range of intensities and durations. A higher intensity over a greater period of time will always be your better answer in regards to the superior of HIIT vs LISS. The longer answer is, it depends on your needs and on the type, intensity, frequency, and duration variables you are comparing. Some may classify 45 minutes of jogging as LISS as well as 45 minutes walking - the two have varying calories burnt in each session with jogging HIIT usually wins for effectiveness, and always for efficiency.
Lowering intensity hoping to get into the mythical ‘fat burning zone’ is misguided and without conclusive scientific support. That will only burn less calories. To maximize fat loss, the opposite is essential. Whatever your time frame, 4 minutes, 15 minutes 30 minutes, 45 minutes - whatever, the more intensely you work in that time, the more calories you'll burn and the more body fat you'll lose.
The bottom line
Cardio is a little extra push when it comes to fat loss. It shouldn’t be the only tool you rely on and instead shouldn’t take priority away from your nutrition which for fat loss should be geared in a calorie deficit ensuring you’re hitting your macronutrient intake for maximised results. Resistance (weight) training should also be done more frequently as it has a greater EPOC and muscle retention. So when you’re doing cardio you just want the most for that time you have dedicated to burning those few extra calories. So here’s some tips in helping you decide:
If you’ve worked a full work day have already done your weight training and have minimal time to slot in cardio than you need to consider burning the most amount of calories in the little time you have. So in this instance, HIIT would be more preferred in that it burns a similar amount of calories between the instant and the afterburn as say a 45 minute LISS session.
Consider your ability and fitness level which will ultimately determine what is more ‘intense’ for you. If you’re relatively fit or of an elite athlete level you might need a higher intensity style of training to reach your VO2 max so doing a very light almost walk pace on the elliptical might not be effective for your fitness level in raising your heart rate and burning the calories you have the potential to burn in that session. In this instance HIIT may be more challenging or a higher intensity LISS proportionate to your fitness level.
3. What is practical and carries less risk
Think about what condition your body is in before embarking on any sort of cardio venture. If you’re significantly overweight, have an underlying injury, or if you're susceptible to orthopedic stress or joint problems, or if you are accustomed to being sedentary high intensity exercise could be dangerous. There’s no use pulling a hamstring leaping into sprints after reading an article about HIIT and doing it before you’re physically ready. For many people who fit the above criteria, combining resistance training with LISS exercise such as walking is an ideal choice (and diet will be the real fat burning workhorse).
Personal preference is another factor to consider. If someone hates a certain type of training, the odds are against good compliance. So you should always consider what you enjoy doing so you’re not resenting every minute of it.
5. Muscle preservation for athletes
As an athlete it is favourable to optimize your training and reach your goals as efficiently as possible. Studies have shown that when comparing low-intensity, long-duration cardio of 60 minutes with 4-10 sets of 10-30-second all-out sprints it was found that long duration cardio decreased muscle size. In this case, research says that high-intensity activity such as sprinting leads to greater fat loss over muscle loss than low-intensity training.
Conclusively, adding cardio either through a few higher-intensity sessions and/or LISS each week can burn off 900-1,500 calories, which allows you to eat an extra 130 to 200 calories per day or essentially accelerate fat loss without adding more food. As well as this cardio assists with bettering your health and increasing your fitness levels which in turn can increase the performance of day to day tasks and weight session through a greater work capacity and less rests.
There's no single best type of cardio for everyone. Low, moderate and high intensity exercise can ALL help you burn fat. When intensity is low, it simply takes much more time and volume to get the same results. Be mindful of frequency, duration and mode and choose carefully as if you’re overdoing your cardio regime falling way below the optimal deficit you could also compromise strength and muscle gains and just be losing muscle and water weight on the scale. Be smart with your cardio.
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7. Naimo, M.A., et al., High Intensity Interval Training Has Positive Effects on Skeletal Muscle Hypertrophy, Power, and On-Ice Performance. Journal of Strength and Conditioning Research, Conference Proceedings, 2013.
Yours in Health & Fitness,
The Equalution Team