By John Meeks, CSCS, Precor Master Coach, CFL1

Over the last 15 years the words HIIT and Metcon have become as synomous with hard-core, time sensitive, results-based training that is not for the faint of heart. Many times fitness professionals use these words interchangeably. However, while there are many similarities, understanding what they mean and where they came from will better enable you to use these workout methods to exceed any fitness goal.

Let's start off with the term Metcon, which is an abbreviated version of the term metabolic conditioning. This term has been made hugely popular with the growth in CrossFit™ and is the term that CrossFitters use to describe their all out, go as fast as possible, vomit-inducing workout of the day. However, my research indicates that the first person to use this term was Arthur Jones, the inventor of Nautilus, in an October 1975 issue of Athletic Journal magazine. At the time of Jones's article many in the fitness industry divided training and athletic proficiency into two areas: muscular strength and cardio respiratory conditioning. Popular opinion perceived that short high intensity anaerobic bouts of weight training were used to increase muscular strength, which had little effect on cardiovascular conditioning. Similarly, longer low intensity bouts of aerobic training were believed to increase cardiovascular conditioning with little or even negative affect on muscular strength.

Jones believed in another form of training that he coined as "Metabolic Conditioning." Jones defines metabolic conditioning as "the ability to work at a high level of intensity for a prolonged period of time. The ability to work at a level very close to 100 percent of intensity for a period of at least 20 minutes, instead of one minute previously considered possible." This does not mean that any specific muscle is working at 100%, but that the body as a whole is working at its highest intensity for that extended period of time. The key concept with Jones' metabolic conditioning is that the athlete moves from exercise to exercise with minimal rest while maintaining a specific rep scheme and quality of movement.

Most of Jones references with metabolic conditioning were used primarily with circuits of weight training exercises over a period of 20 minutes. Over time this concept has evolved and metabolic conditioning has become the term used to describe almost every high intensity regimen. However, in its simplest form metabolic conditioning can be defined as specific exercises and training aimed at improving certain energy systems. Primarily, the goal is providing adaptation and efficiency in the glycolytic energy system, but most workouts will provide some adaptation in both the anaerobic and aerobic systems.

So what really defines a metabolic conditioning workout?

1. High Intensity: Based on Jones' definition, workouts need to be at a maximum sustained effort.

2. Rest: Rest can be fixed like an interval (such as 30 seconds between rounds) or it can be variable depending on when the athlete feels ready to perform a complete set of the next exercise with proper form and range of motion.

3. Metcon style workouts can be done as a weighted circuit, single modality activity (running, rowing, swimming, biking, etc.), gymnastics movements or a combination of all of these.

HIIT is short for high intensity interval training and is essentially what the name describes: working at a high intensity (such as targeting 90% of max pace or 9 or 10 in perceived effort) followed by a period of rest for a set amount of intervals. HIIT has been around for a long time and can even be referenced back to Roger Bannister (the first person to run a sub 4:00 mile) and his 400 meter repeats with specific rest between each run. However, it has really become popular in the last 20 years by some research done in 1996 by Izumi Tabata. For those unfamiliar with the origin of the Tabata Regimen, Izumi Tabata trained Olympic Speed Skaters on a cycle ergometer and required them to maintain an intensity 170% of their VO2 max for 20 seconds followed by a 10 second break for 7-8 intervals. The skaters would train four times per week like this with an additional day of steady state training. Results showed an increase in

VO2 Max (14%) along with anaerobic capacity (28%), which resulted in Tabata becoming one of the most popular words in the gym.

Tabata is just one of many high intensity interval training regimens. Another example would be the Gibala protocol. Professor Martin Gibala at McMaster University came up with a training protocol made up of 60 seconds of intense exercise (95% of VO2 max) followed by 75 seconds rest for 8-12 cycles three times per week. Just recently, this training was tested at McMasters University for its efficacy compared to moderate intensity continuous training. The research, which was published in April, 2016, compared cardiometabolic health benefits and insulin sensitivity of a 10 minute high intensity workout versus a 50 minute moderate intensity workout over 12 weeks. Both groups showed peak oxygen uptake by 19%, plus comparable increases in insulin sensitivity and skeletal muscle mitochondrial content despite a five-fold lower volume and time commitment.

So what really defines a HIIT workout?

1. High Intensity: >80% of max heart rate or greater than 8 out of 10 on rating of perceived exertion

2. Periods of rest or active recovery: These will be dictated by the protocol you are following or based on a progression to reach a specific goal. For example, decreasing rest times each week between 500 meter repeats on the rower in order to achieve a specific 2k time goal in the future. These are normally fixed periods of rest.

3. Typically these are done with single modality activities: Running, rowing, biking, swimming, etc. However, there are no rules that say that these types of workouts cannot be used with more complex equipment or even weight training exercises.

In summary, HIIT workouts are a form of metabolic conditioning, but not all metabolic conditioning workouts would fall in the HIIT category. Which leaves us with the critical question: how are these workouts going to help you reach your fitness goals?

The primary reason for these workouts is increasing EPOC, or excessive post-exercise oxygen consumption. After high intensity workouts, the body's metabolism is elevated as it is trying to return to homeostasis. During this time the body burns additional calories. The research varies from two hours to 24 hours after your workout and depends on its intensity and duration. Secondly, this type of training is much more efficient, achieving the effectiveness of steady state workouts in a lot less time. Thirdly, according to Tabata's research, certain protocols can simultaneously provide increases in aerobic capacity and anaerobic capacity.

Metcon and HIIT, along with strength training, plyometrics, and steady state aerobic conditioning are all tools in your fitness toolbox. Intentional coordination of these different elements of fitness will provide variety, break through plateaus, and help you reach your fitness goals.

References

1. GIBALA, MARTIN J, ET AL. Physiological Adaptations to Low-Volume, High-Intensity Interval Training in Health and Disease. The Journal of Physiology: 2012.

2. GIBALA, MARTIN J, LITTLE, JP, VAN ESSEN M, ET AL. Short term sprint interval versus traditional endurance training: similar initial adaptations in human skeletal muscle and exercise performance. The Journal of Physiology, 575:901–911, 2006.

3. GILLEN, JB, ET AL. Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five Fold Lower Exercise and Volume and Time Commitment. http://journals.plos.org/plosone/article/asset?id=10.1371%2Fjournal.pone...

4. JONES, ARTHUR. Flexibility and Metabolic Condition. Athletic Journal. http://arthurjonesexercise.com/Athletic/Flexibility1.PDF

5. TABATA, ET AL. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc 28 (10): 1327-30, 1996.