Here is a thought experiment: Imagine spending less time working out and getting more fit. How would that make you feel? Of course this would be great, right? Unless, you're one of those rare humans who enjoy spending hours toiling away in the gym reading gossip magazines as you go through your daily calisthenics. I, on the other hand, want more bang for my buck wasting no time in the gym. In two well done scientific studies published in the 2013 February issue of TheJournal of Physiology, the researchers describe their recent discoveries "that three sessions of sprint interval training (SIT), taking just 90 min per week, are as effective as five sessions of traditional endurance exercise, taking five hours per week, in increasing whole body insulin sensitivity via two independent mechanisms". Sprint interval training has also been shown to produce superior cardiovascular and weight loss effects when compared to long steady state cardio training (SST). The really amazing thing is SIT provokes these advantages in less half the time. Additionally, sprinting, not jogging, has shown to decrease belly fat faster and utilizes glucose more efficiently preventing it from being stored as fat.
"A growing body of evidence demonstrates that high-intensity interval training (HIIT) can serve as an effective alternate to traditional endurance-based training, inducing similar or even superior physiological adaptations in healthy individuals and diseased populations, at least when compared on a matched-work basis."- The Journal of Physiology
We are the end products of thousands of years of successful evolution and you can bet your ass that our ancestors didn't do steady state cardio training. For one, they had no access to treadmills and/or spin classes. And if you can believe it our hunter gatherer brethren moved a lot more than you do...some estimates have them walking up to 10 miles per day. Their walks were nothing like our Sunday strolls and no steady state pace either. If current hunter gatherer societies are any indication, they climbed, hopped, jumped, sprinted, dug, lunged, crawled and ran during the course of the day, everyday. Humans have evolved to engage and be proficient in burst like activities. Our bodies are really well designed and super energy efficient for bipedal perambulation (upright walking), long distance running and short sprinting. Some scientists believe that we evolved to be long distance runners and persistence hunters (chasing an animal down until it literally drops from fatigue, sometimes for up to 20 hours!).
Dr. Dan Lieberman of Harvard theorizes early man evolved to be long distance runners. This is evidenced by many factors including our ability to dissipate body heat faster than any other large animal, our spring like tendons especially that of the Achilles, and our capacity to run longer (not faster) than any other living animal. While this may be true, I do not believe its not the whole story. Many of us are built for speed not marathon like endurance. Don't believe me? Take a look at the differing body types of top marathoners vs. sprinters. Each are uniquely equipped with certain muscle fibers, body types and hormone levels in order to perform well in their respective activity. Yet, both types have the ability to sprint well (not really the case the other way around) and you can be sure that our hunter gatherer ancestors were required to do it on a daily basis or they'd be dead.
Notice the body type difference between the marathoner and sprinter
It is commonly known that regular bouts of long steady state cardio is catabolic (tearing down) in nature and will lower one's testosterone levels. Where as sprint interval training stimulates your anabolic (building) response with increases in both testosterone and human growth hormone. That being said, I am not completely against steady state cardio training. For many people its the best option. The evidence based research is becoming less murky and for certain populations it looks like SIT also called (high intensity interval training or HIIT) may be a more efficient training method than SST.
Pros of Sprint Interval Training
Greater fat loss, although not during the session but during EPOC (excess post exercise oxygen consumption) which is higher after a bout of SIT than SST: meaning it increases your metabolic rate more.
Sprint interval training may improve the muscle's ability to use fat for fuel more effectively than aerobic steady state training.
It takes a lot less time! A minimum of 6 minutes to a max of 30 minutes.
SIT has been shown to burn more of the harmful abdominal fat than SST.
Subjectively people report that SIT is more enjoyable.
Research shows that SIT may inhibit your appetite whereas SST may increase it.
Sprint interval training is not for beginners or people suffering from injuries. Due to the nature of the intense forces and high level exertion required to complete a SIT session it is not for everyone and needs to be initially implemented with a smart micro-progression based program to prevent injury. Talk to your doctor before attempting such a routine and then consult with an athletic coach or trainer to design a proper customized program. Too much SIT can be a huge drain on your body, raise your cortisol levels and white blood cell count especially if you are not getting enough sleep and are stressed out on a daily basis. For many type A personalities who seem to gravitate toward this this type of training, it may be the exact opposite of what they really need. It is easy to over train a already stressed out body, so be careful with your training.
For 60-120 seconds do a moderate (faster than warm up) pace.
Then start sprinting at your all out effort for 30 seconds.
Go back to the moderate pace for 60-120 seconds.
That is one interval. Easy peasy. Repeat for a total of 5 to 10 intervals.
Cool down for a 5 minute walk at a fast pace.
I usually have beginners start at 6 minutes and then depending on their goals I may add up to 30 total minutes of SIT. If you have the time and motivation a blend of both modalities might be the best solution.