Why Cardio Isn't the Devil

Tis the time of year for everybody to renew their promise to be healthier, lose fat, and get in the best shape of their lives. What this really means will depend upon whom you ask. For most people, losing fat is synonymous with improving their health. By far the most popular goal in health and fitness, many trainers can spout 20 ways to help clients burn fat. As a trainer, our job is to provide the most effective, efficient, and healthy way to achieve the goal without harming the client. Studies have shown the diet combined with exercise will result in the greatest fat loss, but nutrition alone far exceeds exercise alone [1]. I’m not the first, and I’m definitely not going to be the last to tell you, nutrition is king, resistance training is essential, and cardio has gone by the wayside for fat loss…but does it still have a place in our training?

Most people starting on a fat loss journey start out the same, with jogging. Why do they start with jogging? Because it’s easy, requires only shoes and a place to jog.

Let’s take Sal as an example. Sal wants to get fit, so Sal does what so many have done before, started eating better and jogging. Sal is losing weight, feeling better, and then the all-knowing internet disparages jogging as not worth the time and convinces Sal to stop jogging and get into the gym and do resistance training and HIIT despite clear indicators that Steady State will benefit Sal. Since everybody wants the biggest return on their investment, Sal jumps ship and joins the HIIT train and continues to make progress; amazing progress with no more mind-numbing cardio.

Despite LISS having been shown to burn significantly more calories than weight training or High Intensity Interval Training during the activity [2], it still gets a bad rap because it takes considerable time when compared to HIIT. Given the data and numerous studies confirming it, HIIT appears to be nominally more effective than LISS for fat loss when looking only at calories burned training times are equalized. In the 24 hours after training, HIIT Training resulted in burning approximately 100 more calories than LISS over the course of the day [3]. Another study showed HIIT resulted in a 10% increase in calories burned in a 24 hour period compared to LISS, despite having the same caloric burn during the activity [4].

Some will use the “efficiency adaptation” argument, that it will take longer to burn the same number of calories after training in a style for a length of time, but they fail to consider the exact same thing happens with strength training or HIIT training. The solution is a simple one, up the intensity or up the volume. If we’re talking running, that means run faster or run further, nullifying the rationale that “it takes longer to burn the same number of calories.” Despite other claims that LISS will slow metabolism, I have only found research that demonstrates lowered metabolic rates DURING exercise which recovers soon after the conclusion of activity [5,6]. Does this mean it isn’t possible? No, it just means I haven’t found any research that demonstrates ONLY LISS will lower metabolism over time.

The problem I have with eliminating LISS is not in the nominal difference in caloric burn between activities, the amount of time, or the boredom, but in the impact on the heart itself. Because the heart is a muscle, it is subject to hypertrophy, just as any other muscle. I may become very unpopular for this, but LISS has its place in fat loss training and definitely in heart health.  Mike Robertson, MS, CSCS, co-owner of IFAST gym in Indianapolis says “One of the biggest misconceptions about HIIT is that it develops the aerobic system and the anaerobic system equally, but aerobic and anaerobic exercise actually place very different demands on your heart and your muscles.” This is where I believe trainers are doing a disservice to their clients by pushing them to avoid LISS altogether. Several studies have shown the positive effects of training on the heart: lower heart rate, decreased blood pressure, improved cholesterol levels, reduced inflammation of the arteries, etc.

There are two common types of hypertrophy in the heart and both occur in the left ventricle. Eccentric hypertrophy, which is the increase of the diameter of the left ventricle resulting in increased volume. The other versions is concentric hypertrophy, which results in increased wall thickness and decreased volume of the left ventricle through the thickening of the walls. In 2002, The Journal of the American College of Cardiology noted the significant increase on the left ventricle mass compared to sedentary individuals [7]. Further, in a study published by the American Heart Association, both endurance trained and strength trained athletes demonstrated increased LV wall thickness, but strength trained only demonstrated the most [8]. In addition, only the endurance trained athlete demonstrated increased LV diameter [8,10]. While the loss of LV volume may not set off alarms, let’s explore the result of lower LV Volume. By having a lower volume, the person is prone to higher blood pressure and higher resting heart rate. By having a thicker wall and lesser diameter, there is greater chance of “skipped beats” as a result of the ventricle not being full when the heart beats [9,10].

Given that most overweight people already have high blood pressure and increased resting heart rate (in excess of 72 bpm) it is risky to remove LISS from their training protocols and prescribe HIIT as a means to lose weight given the likelihood of extreme spikes in blood pressure and heart rate. In general, LISS cardio will effectively improve heart performance and aerobic conditioning better than HIIT or weight training alone while limiting such spikes. Also, while it is very unlikely, there is the possibility of sudden cardiac death caused by having too high of a heart rate in combination with extremely high blood pressure, which is more likely to occur during bouts of HIIT or max effort weight training. Taking an untrained individual, as most beginners are, and removing the gradual process by which they can lower their heart rate and blood pressure while improving aerobic conditioning through steady state cardio is like blocking off everything above third gear and telling someone to drive on the highway. It may work for a while, but eventually, something is going to blow. Even if weight is lost through other methods, the benefit of LISS cardio on the heart cannot be overlooked.

In the era of instant gratification and the greatest return on investment, fitness is not sacred. We are all looking for the “shortcuts” and the fastest way to get fit, but we have to remember, we should be able to stand before we sprint. The long slow road of LISS may be boring and it may not have the best returns on time, but it will safely get you ready to merge on the highway and keep you in shape to stay there.

Sources:

1. Miller, W., Koceja, D., & Hamilton, E. (1997). A meta-analysis of the past 25 years of weight loss research using diet, exercise or diet plus exercise intervention. International Journal of Obesity, 21, 941-947.
2. Trapp, E.G., Boutcher, S.H. Fat loss following 15 weeks of high-intensity, intermittent cycle ergometer training. Obesity Reviews 341, 2006.
3. Treuth, M.S., et al. Effects of exercise intensity on 24-h energy expenditure and substrate oxidation. Medicine & Science in Sports & Exercise 28(9):1,138-1,143, 1996.
4. Meuret, J.R., et al. A comparison of the effects of continuous aerobic, intermittent aerobic, and resistance exercise on resting metabolic rate at 12 and 21 hours post-exercise. Medicine & Science in Sports & Exercise 39(5 suppl):S247, 2007.
5. Sidossis LS, Gastaldelli A, Klein S, Wolfe RR. Regulation of plasma fatty acid oxidation during low- and high-intensity exercise. Am J Physiol. 1997;272:E1065–70.
6. Romijn JA, Coyle EF, Sidossis LS, Zhang XJ, Wolfe RR. Relationship between fatty acid delivery and fatty acid oxidation during strenuous exercise. J Appl Physiol. 1995 Dec;79(6):1939-45.
7. Scharag, Jurgen., et al. Right and left ventricular mass and function in male endurance athletes and untrained individuals determined by magnetic resonance imaging. J American College of Cardiology. 2002 Nov; 40(10).
8. Pluim, B, Zwinderman, A, van der Laarse, A, van der Wall, E., The Athlete’s Heart: A meta-analysis of Cardiac Structure and Function. http://circ.ahajournals.org/content/101/3/336.full
9. Rawlins, J, Bhan, A, Sharma, S., Left Ventricular Hypertrophy in Athletes., European Heart Journal – Cardiovascular Imaging, 2009 Feb; 350-56.
10. Mihl, C, Dassen, W, Kuipers, H., Cardiac Remodeling: concentric versus eccentric hypertrophy in strength and endurance athletes., Netherlands Heart Journal, 2008, Apr; 16(4): 129-33.