A Little Bit about HIIT and How It Kept Our Ancestors Strong and Lean

There are many exercise “buzzwords” peppering the fitness landscape these days. But there’s one that you might have heard more often than others: HIIT, or high intensity interval training.  Chances are you’ve heard the term from your trainer, gym buddy, or maybe you read about it. According to a survey conducted by the American College of Sports Medicine, HIIT is one of the two top fitness trends for 2014, along with bodyweight training.

HIIT is characterized by short bursts of intense exercise in which the aim is to give a 100%, all-out effort. The intervals are followed by short and sometimes active rest periods. HIIT is extremely effective and versatile. There are many benefits to high intensity interval training, including: a higher basal metabolic rate (rate of oxygen consumption while awake but at rest); more efficient metabolism; it’s quick and convenient, and no equipment is required to do it if you can’t make it to the gym or are traveling.

Nearly any form of exercise can take the form of HIIT. For example, by pairing exercises that work opposing muscle groups (called supersets) and performing them back-to-back with little rest, you can achieve the HIIT effect. Running sprints on the treadmill interspersed with short periods of walking for recovery achieve the same end, too. Creating a circuit of 4-5 bodyweight exercises performed in rapid succession with minimal rest is also an effective way to incorporate HIIT in your training regimen.

So given all these factors, why hasn’t HIIT caught on beyond the fitness community? Why is traditional cardiorespiratory exercise still the crowning glory of the mainstream fitness world? For one, it’s hard to retrain people about exercise habits when popular wisdom of the past 40-odd years dictates that sustained aerobic exercise is the key to a healthy ticker and weight loss. Marathoners, cyclists, and other athletes are exalted for their endurance and mental fortitude. An endurance race such as an Ironman bestows permanent bragging rights to its competitors. It is a point of pride for people to log the miles run and cycled. Time spent slogging away on the elliptical has value, or “financial currency,” one might say. But do cardio adherents ever cash in? What’s the return?

Let’s look at some statistics. Today, just over one-third (1/3) of American adults are obese and over sixty-eight (68%) percent are overweight. Simply put, we are the fattest and the unhealthiest we’ve ever been as a nation, a nation that loves its cardio.

Now, I know what you’re thinking: “Those statistics are a result of the exceedingly sedentary nature of our lives. Most folks who do cardio exercise regularly are not the ones contributing to those statistics.” While that’s mostly true, there are people who “do cardio” and are overweight and unhealthy. They hit the gym or the pavement with the best of intentions, but they’re probably not seeing the results they want. Why is that? Why might our bodies, from a biological standpoint, respond better to short bursts of intense exercise? What explains the disparity in body composition of a sprinter v. a marathoner? Could the answer lie in our DNA blueprint?

Mark Sisson, author of The Primal Blueprint and several other books about the Paleo lifestyle, certainly thinks so. A self-proclaimed recovering cardio enthusiast, Sisson argues that as a species, we have not evolved to “aerobicize” at the “chronic and sustained high intensities” that many people choose to do these days to optimize their health and ward off disease. He argues that HIIT is one of the key elements to recapture, in modern times, the lifestyle that kept our ancestors lean and healthy. Sisson successfully cured himself of several debilitating autoimmune diseases by trading in the endurance cardio for a program characterized by short sprinting workouts interspersed with long walks, hikes, and easy bike rides.  Coupled with altering his diet, Sisson’s workouts helped him increase his aerobic capacity and build muscle by working out less, but smarter.

In order to understand why his methods were successful, you have to look back to how we evolved as a species. Humans evolved two primary energy systems that make physical activity possible. The first energy system uses fat as fuel for metabolic activity. This system sustains us through periods of rest, and provides continuous fuel for low levels of aerobic activity. When in the presence of lots of oxygen, fats are efficient and burn easily, allowing us to take those long walks, hikes, and bike rides without too much difficulty. The reason this system evolved is because it allowed our hunter-gatherer ancestors to cover long distances on foot, foraging for food, and kept them from starving when food was scarce.

The second energy system, or ATP-PC system, enables us to perform short bouts of intense work for brief intervals. This is called the ATP-PC system. ATP (adenosine triphosphate) provides for a quick burst of energy, while PC (phosocreatine) replenishes ATP when depleted. Both molecules work together to push us through grueling sprints and other HIIT-based workouts, but they can only sustain such levels of intensity for 10-20 seconds. This is why we can’t sprint or do other high intensity activities for prolonged periods of time.

The interesting fact about this ATP-PC energy system is that these brief bursts of high intensity exercise force a small “growth spurt” in the muscle, a beneficial adaptation for both prehistoric and modern man. In other words, when you engage in high intensity interval training, you encourage muscle growth and strength. Your body responds in the way evolution designed it to!

HIIT is an incredibly effective and efficient way to burn fat, build muscle, and get on with your life which, let’s face it, is most people’s goal. Most of us don’t want to spend hours in the gym, and HIIT makes it possible to both cut down the time spent exercising and up the fun factor. As previously mentioned, nearly any physical pursuit can be modified into a HIIT workout, so do what you enjoy: just do it faster!  Take a cue from prehistoric man and adapt your exercise plan to make those evolutionary adaptations work for you! No doubt you’ll have more fun, more time, and a more lean and sculpted physique to show for it!

For more information about Mark Sisson, visit his website: www.marksdailyapple.com.