The Great Debate
The number one question most people have about cardio is, “What type of cardio is best for fat loss?” There are those that say low intensity cardio performed for longer periods of time is better for fat loss, while others claim that short duration, high intensity cardio sessions will give the best results. This is the part that tends to confuse people the most. Advocates on both sides of the argument are usually pretty passionate in their beliefs. To know which style of cardio to perform, it helps to know how each one helps you burn fat.
Low Intensity, Long Duration Cardio
For many years this has been a staple in many bodybuilders fat loss arsenal. Generally, this type of cardio is performed at a constant pace for 60 minutes or more. It is commonly referred to as Low Intensity Steady State Cardio (LISS). The main argument for this type of cardio is that, of the calories burned, most of it comes from fat.
During any type of exercise, the level of intensity is very important. It is well known that the lower the intensity of any exercise, the greater the percentage of energy derived from fat oxidation. (1) As the intensity of exercise rises more of the calories being burned come from muscle glycogen and muscle tissue. This is why advocates of LISS usually prefer to walk on a treadmill or stair stepper for long periods of time. They feel that by doing this they are burning more fat and less muscle.
The only problem is that during the entire time any type of cardio is being performed your body is in a catabolic state and it is breaking down muscle tissue for energy. Switching from a low intensity pace to a more moderate pace and lowering the duration a little may be a better option.
Moderate intensity steady state cardio has been proven to lead to the greatest amount of fat oxidation. Research has shown that fat oxidation is highest when training at about 65% Vo2 max. (2) At this intensity level, not only is the greatest amount of fat being burned, but this rate of exercise can be continued for somewhat longer durations as well.
When dieting for a contest body fat levels will become minimal at some point. At this point muscle tissue breakdown becomes more likely. Limiting the amount of time that your body is catabolic is of utmost importance if you wish to hold onto all the muscle you worked so hard for. So for maximum fat loss and muscle retention, moderate intensity cardio for a rather moderate duration is the best choice.
High Intensity, Short Duration Cardio
High intensity, short duration cardio has become more popular in recent years. The most effective form of high intensity cardio has been proven to High Intensity Interval Training (HIIT). HIIT allows for very high intensities to be used and alternated with short periods of recuperation. Many people shy away from high intensity cardio claiming that nearly all of the calories that are expended come from stored muscle glycogen and not from fatty acids.
This is very true, but those people are forgetting one very important thing. Fat loss occurs through a process called lypolysis. Lypolysis occurs during periods when energy expenditure exceeds caloric intake. (3) The most important thing during cardio is burning enough calories to create a deficit. This can be accomplished in much less time with high intensities.
Even though stored carbohydrates in the form of muscle glycogen are the primary fuel source at higher intensities, fat loss will be greater with the use of HIIT. Studies show a greater loss of subcutaneous fat with HIIT as compared to those that performed standard LISS endurance training. The reason for this is because post exercise lipid utilization is greatly enhanced with HIIT. (4) This means that even after activity has ended your body will keep burning fat. So not only can you burn calories during training, but your metabolism will also get a boost. This is definitely a nice bonus if you ask me.
Another concern that a lot of people have about HIIT is that at higher intensities a greater amount of amino acidsare broken down and used as energy. This is true, but many people will be shocked to find out that if HIIT sessions are kept short then they can actually help retain and even build muscle. You read that right, cardio can help you build muscle. Any type of intense cardio will cause your body to release growth hormone (GH).
The growth hormone response to aerobic activity is determined by the % of Vo2 max. (5) Therefore, the more you push yourself, the higher growth hormone levels will go. I know many of you are thinking, “So what? If I am supposed to keep my sessions short I will only get 15-20 minutes of highergrowth hormone levels.” The good news is that, not only will these brief, high intensity sessions cause an immediate GH increase, but GH levels can keep increasing even after training has ceased. (6)
GH is not the only hormone affected by HIIT. Testosterone levels can also be optimizing through strategic use of HIIT. During and following high intensity aerobic exercise, testosterone levels become elevated and remain elevated for a couple of hours into recovery. This only holds true with short durations though. Prolonged high intensity exercise results in an initial increase in testosterone followed by a decrease to below baseline levels. (7)
This is yet another reason why it is important to keep these sessions as intense as possible, but very brief. There is one problem with HIIT though; there are limits as to how many sessions can be performed before it becomes counterproductive. If high intensity sessions are performed too often, then baseline testosterone levels will decrease, and will lead to an increase in amino acid breakdown. This is why it is best to keep these sessions to only a few per week.
Anabolic hormones, such as testosterone and GH, are the key to building and keeping muscle. HIIT training can produce sharp increases in both of these hormones, which will go a long way to help retain muscle when calories are low. HIIT training can also increase fat burning by boosting the metabolism. This is why HIIT cardio is also a great choice for getting shredded while maintaining or even gaining muscle along the way.
So, which type of cardio should you use to help you get to that next level of conditioning? The answer is…both. HIIT cardio can only be performed a few times a week for it to be effective, but not many people can get into contest shape doing only a few cardio sessions per week. LISS sessions will need to be added to make sure enough cardio is being performed every week.
This is not the only reason to use both types of cardio. Both approaches shed fat effectively, but thru different pathways. HIIT cardio will increase lypolysis primarily by speeding up the metabolic rate, whereas LISS will burn more fat and calories during the actual workout. As I stated earlier, I can’t give an exact number of sessions you need to perform each week since the differences in individual metabolism’s can vary greatly. A good place to start would be with 2 to 3 HIIT sessions per week and add in some LISS sessions as needed.
Even though some people love cardio and others hate it, I think it is safe to say everyone loves winning. Applying sound strategies in your cardio routine will help put you one step closer to first place.
By Neale Cranwell