High Intensity Interval Training vs Low Intensity Steady State
There have been common misconceptions in the fitness industry around which type of cardiovascular exercise is actually the better one.
In this article we compare the efficiency of High Intensity Interval Training against that of Low Intensity Steady State cardiovascular exercise.
When you want nothing but weight loss, endurance or maximum cardiovascular improvement, that’s one thing, but when you want to burn fat while retaining muscle and strength, and when time efficiency is important to you, your choice of a cardiovascular program is more important.
We take a closer look at the effects of both types of training on an individual’s metabolism, fat loss and impacts on strength training.
There are two schools of thought:
Aerobics and the “fat burn zone”: The argument is that fat can only be burned in an aerobic environment. According to this logic, less intense exercise is actually superior for fat loss.
Interval training and the “after burn”: Advocates of interval training have argued it causes you to burn calories at an accelerated rate even after you have finished exercising. This, they argue, makes it superior to steady state aerobics.
So, which is better?
People tend to take one side and defend it because it’s part of their preference, their ideology or even part of a commercial program they are promoting. As a result, many people end up confused or following a plan that’s right for someone else, and wrong for themselves.
The quick answer to this question is “it depends.” It depends on an individual and his/her goals and preferences. For that reason, the ideal cardio program can vary widely from person to person, and prescriptions have to be flexible.
What is HIIT Cardio?
HIIT or high intensity interval training involves short bursts of high-intensity exercise working at over 90% of your maximum heart rate (henceforth MHR), combined with rest periods, or lower intensity exercise, in order to allow heart rate to drop. This can be done with virtually any type of cardio exercise, for example; a 30 second sprint followed by a 2 minute cooling down period, this would then be repeated a number of times. HIIT is favoured by many athletes due to the fact that it is far more time efficient, can increase lean muscle tissue and boost metabolism. However, it is worth being aware of the functions of HIIT in order to avoid catabolism and overtraining.
Much like weight training, HIIT places pressure on the Central Nervous System (CNS) as it causes micro trauma to both fast twitch and slow twitch muscle fibers. HIIT also creates a much higher level of lactic acid in the muscle; this is a by-product where insufficient oxygen is available in the muscle, resulting in glycogen being used for energy via a process known as glycolysis – this is known as the anaerobic threshold.
HIIT Calorie Expenditure
Working at a higher intensity will obviously result in higher calorie expenditure. Although, the higher the intensity, the shorter the intervals tend to be. Depending on a person’s fitness level, weight and body composition, working at 85% of your MHR will burn upwards of 15 kcals per minute. However during the rest periods; in which heart rate tends to level out between 65-75% of your MHR, calorie expenditure drops to 8-10 kcals per minute.
As mentioned, HIIT can increase metabolism whilst resting, due to the body using calories to repair damaged tissue. Although boosting your metabolism may seem favourable, this tissue damage can interfere with recovery from weight training.
Taking the above figures into consideration, 30 minutes of HIIT can burn upwards of 350kcal (also taking into consideration the increase in post-workout metabolism).
HIIT also offers these benefits over low intensity steady state cardio:
- preserves muscle mass
- increased Excess Post-Exercise Oxygen Consumption (burn more calories after the fact)
- significantly increased aerobic and anaerobic fitness
- decreased fasting insulin and increased insulin sensitivity
- reduced abdominal and subcutaneous fat
- stimulates hormones to increase metabolic rate
HIIT & Carbohydrates
Working at 85% and over of your MHR requires glucose and glycogen to be used as a primary energy source, in the absence of glucose & glycogen, muscle tissue is broken down into amino acids to be used as a secondary energy source. This is bad news for athletes and bodybuilders trying to maintain lean mass whilst dieting. Therefore HIIT during times of severe calorie restriction, and especially carbohydrate restriction, is not advisable. There isn’t currently any conclusive evidence regarding the effect of fasted HIIT, although the studies could suggest that fasted HIIT cardio may increase the levels of the anabolic enzyme; p70s6k.
What is LISS Cardio?
Low intensity, steady-state cardio means exactly that; working for prolonged periods of time at 60-75% of your MHR. This is known as the aerobic training threshold; where sufficient oxygen is available for a muscle to function without using glucose as an energy source.
In the aerobic threshold, fat is oxidised and used as a primary energy source. This makes fasted LISS cardio favourable with many athletes, as adipose fat stores in the body are used for energy.
Many athletes also choose to use shorter periods of LISS as a form of active recovery; pumping nutrient-rich blood to muscle tissue.
LISS Calorie Expenditure
Calorie expenditure during LISS is significantly lower than during HIIT on a per-minute basis; however, whereas HIIT requires resting periods at a lower heart rate, LISS can be performed at a consistent level with a calorie expenditure of roughly 10 kcal per minute, depending on the person.
Two major issues with LISS are:
- It can become incredibly tedious, especially with low energy levels whilst dieting.
- It takes a significant amount of discipline for athletes to remain within the low intensity training threshold. Increasing intensity and crossing over training thresholds can begin to cause catabolism, especially if muscle and liver stores are depleted of glycogen.
LISS & Carbohydrates
LISS cardio results in fat being used as a primary energy source, making it an incredibly effective tool whilst implementing low-carbohydrate diets such as the Atkins diet and other ketosis-based diets.
In terms of LISS, the effects come about from different means. LISS revolves around the body’s multiple mechanisms for creating energy. The body will use the highest percentage of fat for energy while at complete rest. The body will use the lowest percentage of fat for energy while at complete work.
LISS attempts to maximize fat loss during the actual workout by avoiding a complete work environment. When performing LISS, you will perform enough work to bring your heart rate to 60-70% of your MHR. This keeps things simple and attempts to burn a fair percentage of fat for energy to perform the workout.
LISS is straight forward. Perform work, but perform it in a manner that is low intensity in order to keep fat burning at play.
LISS is also less demanding on the nervous system, allowing you to perform it frequently without mental burnout, which can be detrimental to one’s resistance training workouts.
Your goals and cardiovascular exercise
The choice of cardio really depends on what your goal is. If you’re on a low carbohydrate, low calorie diet, realistically you’re going to be low on energy and glycogen.
HIIT cardio will decrease glycogen almost immediately and in conjunction with weight training its going to take a lot out of your system and will strain your CNS. If you train with a lot of volume, it wont help out with your recovery.
However, if you’re on a moderate to high carbohydrate diet for gaining muscle, HIIT can be very beneficial. Not only may it actually help build muscle over time, it also boosts the metabolism in a way that LISS can’t. HIIT is also very easy to fit into your training schedule at 15-20 minute duration compared to 30-60 minutes of LISS. .
Cardio can be prescribed through a range of intensities and durations. Here’s the quick and simple answer: Want more fat loss? Push yourself. Turn up the intensity dial regardless of the type or mode. High intensity cardio that burns more calories will produce more fat loss.
Most people only associate steady state with low intensity. But what if you do approximately 30-45 minutes steady at the highest intensity you can tolerate? High Intensity Steady State cardio acknowledges that there’s an intensity dial and that the total amount of calories burned is a product of intensity times duration. .
Lowering intensity hoping to get into the mythical “fat burning zone” is misguided. That will burn less calories! To maximise fat loss, do the opposite: However much time you have – 4 minutes, 15 minutes 30 minutes, 45 minutes – the more intensely you work in that time, the more calories you’ll burn and the more body fat you’ll lose.
Although HIIT wins for efficiency, very brief HIIT (such as 4 minutes of sprints), will not burn more calories and get you leaner than 30-45 minutes of HISS.
It is possible that you could burn twice the calories in half the time (for example, 15 minutes of high intensity will easily burn more than 30 minutes of low intensity walking). Keep in mind that no matter how intensely you train, you can only burn so many calories per minute. Maximum fat loss is achieved when you hit the sweet spot in the middle where intensity multiplied by duration equals the highest accumulated calorie burn, inclusive of EPOC.
While performing HIIT, you’re essentially spiking your heart rate to a near max rate and following that spike with a recovery period, which serves the purpose of preparing you for your next spike. You’re literally working your heart, as it is a muscle, and it should be exercised beyond its normal daily drone, the resting heart beat.
Working your heart beyond average workload is one benefit of a solid HIIT session. Working = strengthening, and this shows over time as you’ll find that your heart will become more efficient at handling larger cardio workloads.
Walking can contribute nicely to weight loss and maintenance over time. The problem is that very low intensity, long duration exercise is inefficient. It doesn’t burn many calories per unit of time. When you’re physically able to do so, including some high intensity cardio in your plan is very important to maximise fat loss. Otherwise you’ll need hours of LISS exercise every week and it’s going to be a longer haul to get to your goal.
There’s some irony in that the average overweight or unfit person probably can’t duplicate “the best” high intensity protocols. It’s one thing to identify what’s optimal, it’s another to identify what’s practical for each individual. There’s also personal preference to consider. If someone dislikes a certain type of training, the odds are against good compliance.
It is wiser to do the type of cardio that you have a personal preference for. Whichever one fires you up the most, because you will most likely work harder at it. HIIT is quicker, proves to be more effective for fat loss, creates metabolic changes, and helps with muscle retention, but not everybody can do HIIT. LISS is safer, but takes twice as long to accomplish similar gains and it still has its place for fat loss in moderate amounts, from a pure calorie burning standpoint (meaning only to burn calories & not make changes to your metabolism).
High intensity exercise could be dangerous if you’ve been sedentary for life, if you don’t have your doctor’s approval for vigorous exercise, if you’re obese, or if you’re susceptible to orthopedic stress or joint problems. For many people who are overweight, combining resistance training with LISS exercise such as walking is an ideal choice, and diet will be the real fat burning workhorse.
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. If the type, frequency, duration and mode aren’t carefully chosen, you could also compromise strength and muscle gains.
It is therefore recommended to do regular rotation of HIIT and LISS, depending on your goals. Everyone is different, and your current goal will dictate just how you should rotate the to.
Eat smart, train hard and let the results come!
By Letitia Kleynhans