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HIIT Cardio or LISS: Maximising Fat Loss and Preserving Muscle

February 22, 2016 | 0 Comments
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When it comes to cardio, the question of whether HIIT or LISS is best for fat loss and the preservation of muscle mass is without doubt the most heated debate within the health and fitness community around the globe. 

It appears that every year there is a surge in both the growth and implementation of high intensity interval training (HIIT) for performance athletes, general fitness populations, and most notably, physique basd athletes looking to achieve shredded levels of body fat.

For physique based athletes, cardio is one of the proven tools to help with fat loss alongside nutrition and weight training. However, cardio is also a double edged sword that can potentially hinder the maintenance and growth of muscle mass.

Too little cardio has the potential to greatly undermine the ‘look’ of a physique based athlete on stage; rather than appearing lean and defined a competitor will be unable to show the full potential of their impressive muscular physique, costing them valuable placings. While too much cardio will most certainly hinder the amount of muscle mass a competitor is able to maintain throughout a contest prep, will negatively affect energy and recovery, and may cause a competitor to appear ‘stringy’ and depleted on stage.

In this article, we dissect the two most frequently used forms of cardio performed by bodybuilders and physique based athletes, LISS (Low Intensity Steady State) and HIIT (High Intensity Interval Training). By providing background information on the general benefits of cardiovascular exercise and the pros & cons of these two main types of cardio, we will determine once and for all which form of cardio is most effective for those looking to preserve as much muscle mass as possible whilst reducing body fat.

Benefits of Cardiovascular Training

Typically cardiovascular exercise is most closely associated with continuous aerobic training; that is performing monostructural exercises such as running, cycling, swimming or elliptical training at a steady pace or intensity for 30-60 minutes. This type of cardio termed Low Intensity Steady State (LISS), or sometimes Moderate Intensity Steady State (MISS), has long been the favoured choice of performance athletes, general populations and bodybuilders for increasing cardiovascular health and losing body fat.

Current interest in the benefits of shorter more intense work intervals known as High Intensity Interval Training (HIIT) has sparked numerous studies to demonstrate its ability to increase performance, improve fat loss and maintain muscle tissue. Recent studies have shown that HIIT cardio is able to produce the same, if not superior, adaptations to cardiovascular exercise in comparison to continuous aerobic training such as LISS and MISS.

During both forms of aerobic exercise there is a number of short term (acute) and long-term (chronic) cardiovascular responses and adaptations that occur in the circulatory, respiratory and muscular systems.

Such short-term (acute) responses are known to:

  • Increase Heart Rate
  • Increase the Rate of Respiration (Breathing)
  • Increase Cardiac Output
  • Increase Fat Oxidation
  • Increase Acute Energy Expenditure

Such long-term (chronic) responses are known to:

  • Decrease Resting Heart Rate
  • Increase Cardiac Hypertrophy
  • Increase Blood Volume
  • Decrease Recovery Times
  • Increase Resting Metabolic Rate
  • Increase Chronic Energy Expenditure
  • Increase Strength of Respiratory Muscles

Both HIIT and LISS have proven benefits for improving aerobic capacity, but the biggest question on every bodybuilder’s mind is “Which is the best type of cardio for fat loss?”.

The truth is both forms of cardio have merit when it comes to losing body fat and getting in the best shape possible for a bodybuilding or physique based competition. The type of cardio used will be very dependant on various individual differences, so to help us make an informed decision, let’s look a little deeper at these two forms of cardio.

LISS (Low Intensity Steady State)

Low Intensity Steady State cardio has long been the preferred form of cardio for fat loss within the bodybuilding community; visions of greats such as Ronnie Coleman and Kai Greene pounding away on the pavement or stairmaster immediately spring to mind.

LISS is performed at a constant steady pace for between 30-60min, often within a target heart rate zone (intensity) of between 50-65% of maximum heart rate. Advocates of LISS training will often reference the known fact that a greater percentage of stored body fat as opposed to muscle glycogen (stored glucose) is used for energy when performing cardio at lower intensities.

As such, many bodybuilders and physique based athletes will deliberately perform low intensity cardio first thing in the morning in a fasted or semi-fasted state in conjunction with supplemental protein or branch chain amino acids (BCAAs). Overnight glycogen stores are used by the body for a number of regenerative processes during sleep resulting in lower glycogen levels first thing in the morning upon waking, therefore the reasoning behind early morning fasted LISS is to make use of these depleted glycogen levels and tap into fat stores for energy.

However the reason why LISS is so popular amongst bodybuilders and physique based athletes is the very same reason it has come under scrutiny. Whenever cardio is performed the body undergoes a variety of metabolic processes including the breakdown of amino acids for energy; this is known as proteolysis and puts the body in a catabolic (muscle breakdown) state. The effect of this process is worsened in an un-fed (fasted) state and magnified as both the frequency and duration of cardio increases.

In fact in a recent study by Lemon et al, the impact of fasted state cardio on the breakdown of muscle tissue (proteolysis) was measured. The study found that training in a fasted state (glycogen depleted) increased leucine oxidation, a key marker that amino acids are being broken down for fuel by being converted into glucose. Fasted cardio also produced more than double the nitrogen loss as compared to fed-state cardio.

This study gives merit to performing cardio in a ‘semi-fasted’ state by consuming a small amount of free form branch chain amino acids or pure whey protein isolate prior to cardio to ensure there are sufficient amino acids to help preserve nitrogen balance.

Individuals who wish to perform early morning cardio, would therefore be best off consuming a small pre-cardio cocktail prior to their cardio workout. This should contain approximately 5-10g of supplemental BCAA ideally with 3-4g of leucine to promote protein synthesis and decrease total protein breakdown, without dramatically impacting on the fat loss benefits of low intensity steady state cardio in a glycogen depleted state.

Below outlines a number of pros & cons of LISS:

Pros

  • Shown to directly use a greater percentage of calories from fat rather than glycogen
  • Provides active recovery to help recovery from resistance training
  • Less taxing on the CNS and muscular system
  • Easier on joints, ligaments and tendons
  • Is not psychologically taxing
  • Is more easily programmed into a bodybuilding pre-contest regime
  • Much easier to prescribe for sedentary and overweight populations

Cons

  • Sessions are often frequent, long and tiresome (particularly during contest prep)
  • Few calories are expended after the exercise session
  • The body adapts quickly to LISS reducing its metabolic benefits and total calories expended
  • Fasted-state LISS cardio has greatest risk of muscle protein breakdown (proteolysis)

HIIT (High Intensity Interval Training)

High Intensity Interval Training is a form of cardio that uses a mixture of short intense sprints, typically in the range of between 10-60 seconds, alternated with complete rest periods or periods of low intensity active recovery in an interval fashion.

The popularity of HIIT amongst bodybuilders and physique based athletes has grown exponentially in recent times thanks to the shift towards balancing both performance goals and aesthetics. Many competitors are moving away from long burdensome cardio sessions in favour of short high-intensity efforts. A lot of the anecdotal reasoning behind HIIT training for physique based athletes is that it more similarly resembles the demands of resistance training and as such may help promote similar adaptive processes such as greater muscle retention.

On the opposite side of the spectrum HIIT cardio is criticised by LISS advocates who claim that the majority of calories required to fuel HIIT cardio workouts are expended from glucose stored in muscle tissue as opposed to fatty acids. This may be true, however studies have shown that performing HIIT cardio compared to LISS cardio stimulates the nervous system and various metabolic processes that can help to burn more calories and increase metabolic rate long after the workout itself is completed.

These benefits of HIIT are in-part due to the phenomenon called EPOC (Excess Post-Exercise Oxygen Consumption) which essentially is the amount of oxygen required to restore the body to homeostasis; it is this physiological effect that explains why the body continues to burn calories long after a HIIT workout is complete.

In addition, HIIT places a greater demand on the anaerobic (oxygen lacking) pathway to produce ATP, the energy currency of the body. Because of this, during the post-exercise recovery period the body will take in more oxygen for regenerative processes including the re-synthesis of muscle glycogen, production of ATP, and to help the body repair muscle tissue damage.

Research continues to show that HIIT is far more effective at maximising fat loss and creating desirable metabolic changes than LISS cardio performed in typical ‘fat-burning zones’. Overall HIIT cardio can help to burn a lot of fat, sculpt and retain muscle mass, whilst also building anaerobic threshold and lactic threshold capacity. Interestingly, high-level performance and Crossfit athletes often train in this exact fashion, combining strength programs with high-intensity metabolic conditioning, and they undoubtedly have some of the most muscular and well conditioned physiques year-round.

Below outlines a number of pros & cons of HIIT:

Pros

  • Quick workouts that do not require much time to complete
  • Burns a lot of calories in short periods of time during exercise
  • High amount of calories burnt after exercise
  • Greater impact on metabolic pathways
  • Can encourage the preservation of lean muscle mass
  • Promotes both aerobic and anaerobic work capacity

Cons

  • Workouts are often physically and psychologically demanding
  • Taxing on the CNS and muscular system
  • Greater risk of injury
  • Greater impact on recovery and must be programmed accordingly
  • Not suitable for all populations

Putting It Together

Before we begin the discussion on the use of either HIIT or LISS for optimal fat loss and muscle retention; it needs to be stated that the number one fundamental principle to losing body fat is creating a total daily caloric deficit through a sound nutritional strategy.

In bodybuilding and physique based sports the name of the game is maintaining as much muscle as possible whilst also pushing the envelope towards extremely low body fat levels. Therefore for most competitive physique based athletes it is completely possible, and even desireable, to see substantial fat loss during the first stages of a contest prep diet without the introduction of either form of cardio. At the start of a weight-loss program priority should always be placed on engaging in regular high-intensity resistance training and reducing caloric intake, whilst maintain sustainable macronutrient quantities and ratios.

Those who are able to see steady fat loss throughout their entire pre-contest diet without the introduction of either steady-state or high-intensity cardio are truly blessed; they dramatically increase the likelihood of maintaining all of their hard earned muscle mass. Unfortunately for most athletes, cardio is a necessary evil in order to achieve the extreme level of conditioning required for competition.

Generally speaking, both HIIT and LISS have their place when it comes to fat loss and muscle retention.

The research is clear that HIIT leads to better improvements in fat loss and physiological adaptations in a shorter period of time; incorporating 2-3 HIIT sessions per week will alter muscular metabolism, increase oxidative capacity and have a profound effect on boosting metabolic rate correlating to more fat loss.

Unfortunately, HIIT cardio also follows the law of diminishing returns, especially for the overtrained, underfed and highly stressed competitive physique based athlete. For most people more than 3-4 HIIT sessions per week becomes extremely taxing, making it difficult to recover, and can negatively affect the performance of their resistance/weight training workouts. At this point HIIT cardio becomes counter-productive to the primary stimulus for maintaining lean muscle mass.

For these reasons LISS can be used to fill in the gaps by providing a less obtrusive form of cardio that can actively improve recovery between resistance training sessions whilst helping to create a daily caloric deficit by burning calories during the cardio workout. The downside for using LISS is that it is often very time consuming, particularly as the body becomes adapted to its aerobic demands. It is not uncommon to hear competitors spending more time on cardio machines than lifting weights, which is perhaps the fastest way to lose valuable muscle mass.

As a general recommendation most individuals can obtain great results at the beginning of a weight-loss program by performing as little as 10-15 high intensity intervals 2-3 times per week in combination with their resistance training program. Using HIIT cardio in the beginning helps to save time whilst maximising the metabolic and fat loss benefits of this style of cardio.

As an individual finds themselves deeper into a contest-prep diet, motivation can drop and individual recovery abilities come into play, so adding more HIIT sessions is often not the most optimal approach. At this point adding LISS cardio throughout the week can help to create a caloric deficit to keep fat loss moving along steadily without impacting on recovery. For many it is not feasible to be performing split cardio and weight sessions, so adding 20-30 minutes of LISS after a workout 2-3 times per week can be a sound strategy for the competitive physique based athlete.

Final Thoughts

The frequency and duration of each form of cardio will be very dependant on an individual’s metabolic capabilities as well as the amount of total weight loss and rate of loss required. The ultimate goals is to obtain a steady rate of fat loss by using the most minimal dose of cardio possible.

In conclusion, a combination of both HIIT at the start of a pre-contest diet, and LISS toward the end, appears to be the best approach when looking to maximise fat loss and maintain workout intensity to preserve lean muscle tissue.

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