Nearly 80 million US adults have cardiovascular disease (CVD), resulting in a 314 billion dollar price tag. So it is no wonder that those in the fitness industry are on a constant mission to improve those statistics. Unfortunately, not much has changed since I entered this industry over 20 years ago. When I was lecturing at Colorado State University, I remember sharing the message that CVD was responsible for one death every 34 seconds. Today, the American Heart Association (AHA) reports that number is now one death every 36 seconds, which is nearly 2,400 deaths per day. With only a two-second change over the past decade, we have room for improvement!


Stop the Cardio

Stopping the �cardio� is a message I have been arguing and lecturing about since I finished my doctorate over 10 years ago. Now, I certainly am not advocating removing exercise modalities that improve the cardiovascular condition � quite the opposite. Instead, I want health care professionals to get better educated on this topic and, in turn, help the population to become more effective in improving their cardiovascular condition, losing their excess fat and improving their overall health.

Unfortunately, in the fitness industry, �cardio� exercise is synonymous with low- to moderate-intensity continuous exercise (LMICT), which is the mundane, repetitive, television watching, book reading, 20 to 60 minute workouts everyone has been indoctrinated into thinking is necessary to be cardiovascularly healthy as well as to lose weight. The education of personal trainers has improved considerably from when I was first espousing this message at fitness conventions in the mid-1990s; however, there is still a long way to go in educating the general public, medical community and many in the fitness industry.

I still consistently overhear personal trainers telling their clients that they also have to �do their cardio� following a personal training session, which typically involves lifting weights, often while sitting, using a compartmentalized muscle-group approach. Even more experienced trainers who recognize the cardiovascular benefits of multi-joint resistance exercise are often still unable to resist prescribing a �cardio� regimen to their clients. One would think that, after experiencing a few sets of 60-second Turkish Get-ups, common sense would prevent any trainer feeling the need for such a prescription, but it typically takes more than common sense to break the dogma they have been hearing for so long.

The �cardio� message that you have been hearing is not necessarily incorrect; rather, it is not the most effective at its goal and, most importantly, is not very time efficient. Moreover, there are actually some negatives along with the positives of LMICT. The early guidelines of the American College of Sports Medicine (ACSM) still ring load today: engage in �aerobic� rhythmical activities, such as walking, running, biking and swimming, for 20 to 60 minutes at an intensity of 50 to 85% of one�s maximal aerobic capacity, three to five times per week. Of course, it was the research coming from the universities that influenced these recommendations, and there is no doubt that, in the early sports science era, more research focused on LMICT than high-intensity interval training (HIIT) or sprint interval training (SIT).

Part of the bias towards this mode of exercise came from the fact that it was easier to examine oxygen consumption from LMICT than HIIT and � trust me when I tell you from first hand experience � that all graduate students in the early days of sport science research wanted to use the metabolic equipment to measure oxygen consumption. I also do not think it is a coincidence that the subjects for many of these early exercise studies were students, who had classes three to five times per week that were of a sufficient duration to collect data for 20 to 60 minutes. The recommended 50 to 85% intensity is merely a default of the selected duration; anyone exercising for that length of time will maintain that level of intensity, plain and simple.


Focus on HIIT

Research on LMICT simply demonstrates that it can induce a training effect. It is rather ironic, however, that one of the pioneers of exercise physiology, Per-Olof �strand, who presented the method of how to measure maximal aerobic capacity at the 1967 Proceedings of the International Symposium on Physical Activity and Cardiovascular Health, warned that �too often bold conclusions about the individual�s physical fitness and maximal performance are drawn from knowledge of [their] maximal oxygen uptake.� 

There is a significant body of research that demonstrates the superior benefits of HIIT over LMICT. Whenever researchers have compared these two types of training regimes side-by-side, HIIT has always matched LMICT and usually produced more favorable results along with a much lower time investment. Now, an article of this length obviously cannot cover the vast array of data on this topic, but there are a few pioneering articles that are worthy of mention (go to, and click on downloads to read more research on HIIT).


Research Supports HIIT and SIT

In 1996, a Japanese researcher by the name of Tabata published a study demonstrating that a SIT protocol, lasting less than four minutes, had a comparable improvement in aerobic capacity to an endurance protocol that lasted 60 minutes at a time. Further, the SIT protocol improved the subject�s anaerobic capacity, while the LMICT protocol did not.  

A Canadian research group headed by Dr. Martin Gibala also focuses much of their research on SIT. In a 2005 study by Burgomaster et al., it was shown that just 16 minutes of SIT over two weeks doubled the endurance capacity of the subjects. Upon hearing this information, a common response from health care professionals is that they appreciate this mode of training has its place for athletes, but it has no place for the de-conditioned individual. Again, the research does not support this position; rather, HIIT is not only appropriate for all populations, the results are often more beneficial in de-conditioned subjects.

In the June 2007 issue of the AHA journal, Circulation, Wisl�ff et al. showed some dramatic benefits of HIIT, as compared to LMICT, in 27 heart failure patients with an average age of 75.5 years. The difference in the increase in VO2 max as a result of the two training protocols was striking: 14% for the LMICT group and 46% for the HIIT group. Anaerobic threshold, from an absolute perspective, also increased more in the HIIT group, as compared to the LMICT group. HIIT also had dramatic improvements in heart morphology and performance, essential factors for individuals with heart failure. Of particular interest were increases in left ventricular ejection fraction (35%) and stroke volume (17%), while LMICT elicited no improvements. It was also shown that HIIT, but not LMICT, reduced the plasma levels of oxidized LDL by nine percent and increased the patient�s antioxidant status by 15%. Furthermore, the patients� quality of life, established via a questionnaire, increased more with HIIT than LMICT. It is also interesting to note that informal comments from the patients found the varied procedure of HIIT motivating, whereas LMICT was described as �quite boring.�

At the end of the day, in patients with post-infarction heart failure, HIIT was superior to LMICT in improving LV remodeling, aerobic and anaerobic capacity and quality of life. These are just a small selection of studies comparing HIIT to LMICT with respect to cardiovascular health and conditioning; the same superior benefits of HIIT apply to fat metabolism when compared to LMICT � without getting into the research, have you ever seen a fat sprinter?


Look at this issue from a few common sense perspectives:


1.       Throughout humankind�s development, short duration, high-intensity exercise has been a prerequisite for both survival and human progression. Research on hunter-gatherer tribes has always shown them to have excellent cardiovascular capacities and lean physiques without engaging in a significant amount of LMICT.

2.       Athletes in the early days of sports simply attained their fitness from engaging in their respective sport. Well, the vast majority of sports are high-intensity interval-based.

3.       Have your clients imagine or even experience sprinting up a flight of stairs for just 60 seconds and then ask them what they think would happen to their overall fitness if they repeated this activity just a few times a day � intuition would tell them that they would improve their conditioning quickly. The reason is based on a basic physiological principle: we adapt to stress, and SIT will quickly stress our physiology. LMICT is actually not that stressful to our physiology, and so you will need to do a ton of LMICT in order to induce a change for the better. You can begin SIT at lower intensity levels that still challenge your clients, but, as changes occur, the key principle to remember is to increase the intensity, not the duration. It is about quality � not quantity.


Research has shown that just eight to 12 minutes of HIIT per week can have dramatic physiological benefits. So, if you are working with a client on a corrective exercise program or basic strength program, you can include three to four minutes of HIIT within two to three workouts per week for a very time-efficient approach. Short intervals with an equal work/recovery ratio adding up to 60 seconds work well. For example, do three 20-second �sprints� with 20 seconds recovery between each interval or two 30-second intervals with a 30-second recovery. Do not use an interval longer than 60 seconds. The intensity takes an exponential dive when you do, and you will lose the training affect on both the aerobic and anaerobic metabolism attained with SIT. A number of exercise modes can be utilized. Self-paced equipment such as a stationary bike, sprint treadmill or sprint stepper work best; one can also sprint up hills and staircases or, when appropriate, use whole body exercises such as Turkish get-ups to obtain the desired effect.

Dr. Mark J. Smith received his masters degree in exercise science and a doctorate in physiology from Colorado State University, with his doctoral research focusing on cardiovascular disease. Dr. Smith is considered a leading authority on the health benefits of high-intensity interval training and has developed innovative and time-efficient protocols that are effective for both weight loss and cardiovascular health. He has been lecturing to health care professionals on this topic for over 10 years. Dr. Smith also collaborates with Dr. Loren Cordain, the renowned author of The Paleo Diet. In addition to his research and consultancy work, he has a clinical practice in Rancho Mirage, California. For more information, email Mark at