Interval Training - NOT a magic bullet

Chances are if you've ever been wandering through your local sports shop, browsing the latest bonded-seam bun-hugging compression shorts, you've overheard a couple endurance enthusiasts whispering conspiratorially about intervals. Perhaps it was their last session together, when they pushed to complete exhaustion in a 6x4min L4 workout up Mad Turtle Hill or some other notorious local proving ground. Point being, intervals are forefront on the mind of aspiring and experienced endurance athletes alike. But does the substance live up to the hype? 
 

Your typical endurance athlete

Interval training has a long and storied history in endurance athletics. Generally regarded as the "bible" of running training, author Tim Noakes' Lore of Running describes the origin of interval training in England, where in the early 1950s, Austrian Franz Stampfl coached many of the great British milers (notably, Roger Bannister and Chris Chataway) using alternating periods of short, high intensity and rest. As Noakes writes, "this training method replaced the outdated notion of simply trying to improve your time for the total distance. Stampfl believed that interval training taught athletes to be mentally tough and to believe in their ability to extend themselves in a way they had never done before." (Noakes, Lore of Running, 4th ed, pg 384) The British-born renowned cross-country coach Peter John L. Thompson, currently residing and coaching out of Eugene, argues an even earlier beginning:

"To find the origins of the special form of repetition training known as Interval Training we must go back in history, over 70 years to the late 1930s. At that time a German coach, Dr. Woldemar Gerschler...carried out experiments in the form of repetition training where an athlete would run over a relatively short distance, such as 200m, at a relatively fast pace, a number of times. The name of the system, 'Interval Training', was because the rest or recovery period between the faster runs was considered the most important and vital part of the training. It is during the interval that the heart adapts, growing larger and stronger. " (Thompson, http://www.newintervaltraining.com/old-interval-training.php) 

 

And even earlier, we can turn to the Swedes, who invented "fartlek" ("speed play") training, which involves a more liberated approach to intensity, allowing the athlete to modulate the speed and effort during on-times, and also adjusting them to fit terrain, especially in locales lacking a track facility with measured distances. 

 

Gosta Holmer, innovator of "fartleks"

OK, enough history. Taking all of the above we can safely conclude that intensity training through interval work has a proven background in endurance athlete success. But the point of this essay is not to justify that fact; rather, the most important aspect of interval training is knowing when and how to use intervals. Metabolically speaking, your aerobic base (that crucial physiological component which allows you to run long distances, ski 30km without stopping, and be a generally fit person) is tied inextricably to the production of mitochondria (we won't conduct the bio lesson now, so for background on mitochondria, check out Lore of Running or your old high school bio textbook). Simply put, mitochondria are your cellular energy factories. They take glycogen (the body's storage form of carbohydrate) and turn it into ATP and other byproducts - the fuel for your muscles. Without these factories you simply could not function. The problem is, high intensity training actually can damage your aerobic system by destroying mitochondria. It's the same situation as over-racing. When you repeatedly put your body into a state of high fatigue, especially by exceeding your aerobic threshold and producing lactate, the pH in your system sways into an acidic realm. Cellular components like mitochondria cannot live in an acidic environment, and they start to die. So you can imagine, if you're performing intervals only, without adequate base training (sub-70% of max HR) and recovery sessions in between, you will be destroying your crucial energy factories (mitochondria) without simultaneously rebuilding them through aerobic training.

While nothing feels quite as satisfying as finishing a hard workout, it must be couched upon a firm aerobic foundation

Understandably, high intensity is imperative, both for training purposes and of course in racing. But there's a reason why athletes structure a "training season" and a "racing season"; you must rebuild your aerobic base (your mitochondrial facilities) in between racing seasons, otherwise you wouldn't have anything left in your body to provide energy after several months of mitochondria-killing efforts.
 
All of the above is meant purely to emphasize the role of intervals in a comprehensive training protocol. Intervals are not the sole means of producing endurance success. They may be more sexy than a boring two hour run at 120bpm, and pro athletes tend to get their visibility during their hard training sessions than the slow ones, but that should not justify a diet of intensity alone. Think of it as the frosting on the cake - if there's no cake, you can frost the cake plate, but even a child could then recognize that there ain't much substance.

Stay tuned to Methow Endurance for more detailed background and explanation on structuring intervals into your training plan. They are irreplaceable, but they cannot stand alone.