Much of the history of physical fitness involved the utilization of long slow distance training(LSD) as the keystone of performance. Want to drop a weight class or outlast an opponent? Then you better put on your running shoes, hit the road, and don't come back for at least an hour. 10 mile runs were the norm, from runners, to wrestlers, to football and soccer players.
It is obvious that any sedentary person who undertook such a task would surely see drastic physical changes in a short period of time. But what about high level athletes who needed to meet specific performance metrics? Could such a method of training improve a fighters ability to throw a flying head kick in the fifth round or a basketball players ability to get down the court in overtime? It is a relatively recent revelation that the long slow distance mode of training is incomplete and sometimes counterproductive in improving performance at more elite levels.
Interval Training Definition
Interval training (High Intensity Interval Training or HIIT) is the counterpoint of long slow distance training: efforts are done with near maximal effort, just as any display of speed or strength is, and are punctuated by set rest periods. This method is a means of effectively conditioning the body's aerobic and anaerobic pathways simultaneously, thus providing improvement in the relevant attributes governing fitness and athletic ability in a reduced period of time.
Endurance gained from long slow distance training is exclusively aerobic, meaning the LSD trained athlete can carry on for an indefinite period of time so long as the physical demands are low; not ideal considering most sports demand intense efforts to be produced continuously. Intervals, on the other hand, develop strength and power capacities in the context of fatigue: not only is the athlete able to endure into later rounds, but maintain important speed and strength qualities as well.
Does HIIT Work?
Studies have shown that the physiological improvements of frequent high intensity interval training improve these anaerobic (strength and speed) capacities and improve general aerobic fitness similar to long slow distance training. HIIT neophytes not only see anaerobic improvements(which are non-existent in LSD), but enjoy better improvements in aerobic capacity than the long distance runners! Gains are better and these workouts take about 1/4 of the time. An hour long run is now reduced to 15 minutes of intervals, and that includes warmups, rest periods, and cool down. One study showed that the effects of 10.5 hours of LSD in a week could be reproduced by 2.5 hours of intervals. This is the epitome of time leverage; your time is valuable and this makes the most of it.
Benefits of HIIT
High intensity intervals have also changed the way we see fat loss. Typically, the maintenance of a 'target heart rate' for an extended period of time (which amounts to LSD) was the prescribed remedy for excess fat tissue (i.e. fupa). Since your body utilizes fat for energy most efficiently at this range, burning off more body fat simply meant burning off more calories at this 'target heart rate'. But there is a catch: this lipid utilization doesn't occur until most of the glycogen (sugar used for immediate energy) in your body has been burnt through. This means that working at the target heart rate for fat loss won't optimize the percentage of calories burned from fat unless you have already worked out or have fasted prior to workout.
Also, your metabolism drops to normal in a relatively short amount of time after finishing the routine. One of the benefits of HIIT is that it jacks your metabolism through the roof for up to 24 hours post workout, burning extra calories at rest as the body works to spare, if not outright build, muscle tissue.
Long Slow Distance is not without its merits: a higher percentage of calories are used from fat during LSD training and more total calories are burned in a single LSD session than the elevated metabolic activity from HIIT can make up for. For those with no vested interest in building muscle or maintaining strength through weight loss, this may tip the scales in favor of LSD. However, from a performance standpoint, HIIT results in more spared muscle tissue while actively improving sport specific endurance qualities. Also, HIIT results in increased fat oxidation in skeletal muscle and glucose tolerance, while lowering insulin resistance, all of which are critical factors in maintaining a low body fat percentage.
It is now common wisdom that HIIT is the way to go if you want to be the contender. So why do so many people still jog away on their hamster wheels for hours on end? The answer to this cuts to the core of why so many people fail to see results from their diet and exercise routine: laziness and complacency.
The fact is that high intensity interval training is rough. Physiological adaptations are made as a result of systemic stress, and HIIT is a superior method of training because it effectively stresses multiple systems at once. While muscular gain, fat loss, and physical performance all benefit from these strained systems, improvements come at the cost of extreme physical discomfort. The average Joe looking to drop a few is simply not willing to suffer for his goals. When the typical trainee is aware that pain is going to be the immediate result of each successive training session, the likelihood of said trainee returning to the gym diminishes with each workout. It is much easier to sit on a recumbent cycle with a copy of the wall street journal and pretend to work as you actually catch up on what the stock market is doing. This is common and easy. Too bad easy never works.
True champions have all shared the quality of tenacity. Stories circulate like legend of vicious workouts that were punctuated by dry heaves into a trash can, only to be continued once the heaving stopped. 100s of successful free throws were made in a single workout session, dozens of suicides completed after hours of skill drills, tens of miles crossed in the scorching heat. Suffering forces progress by continuously elevating the stress on the body, and this is the mechanism by which change is made.
I do not recommend this protocol for amateur athletes or generic trainees; the ability to push your body to its limits is a skill resulting from years of training. Instead, the common or beginner trainee can benefit from these intense workouts by throttling the effort in the beginning. At the start of a routine work with lower intensity levels. Keep track of your times, leave a little in the tank, and come back hungry next time to beat your previous performance. This allows progress to made continuously, regardless of good days or bad, and will build momentum. Momentum and motivation are one and the same, and both are vital to progress.