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The Interval Epidemic

Fri, Nov  3, 2006 - By Zachary Caldwell

For a long time the conventional wisdom in endurance athletics was that a focus on easy aerobic training was the key to success. People muttered about the evils of lactic acid which was rumored to be the cause of everything bad in sports. The advent and availability of heart-rate monitors saw lots of skiers out tiptoeing around the woods in fear of setting-off the alarm signifying that they might be in danger of going beyond a “level 1” effort. Too much training at HR levels above that magic level 1 might result in the only thing worse than lactic acid: the dreaded condition of overtraining. It’s not quite clear how so many athletes going so slowly could end-up overtrained, but it happened (really!).
 
Not Training Hard Enough

During my ongoing formative years one of the strongest influences in my life has been my uncle John. Uncle John never went in for all this easy training crap. He would go off on scathing diatribes about what a bunch of whimps all these so-called “athletes” were. Naturally I adopted many of Uncle John’s viewpoints, and joined him in the opinion that, on the whole, our skiers weren’t training hard enough.

And there was scientific evidence that Uncle John had a point. As early as the mid-seventies George Brooks (do a google-search – it’s worthwhile) was doing research which established the model of an intracellular lactate shuttle which opened the door to the idea that lactic acid might be more than just an end-point waste metabolite. In the years since it has become increasingly clear that lactic acid is a great mechanism for the mobilization of fuel, and can be metabolized aerobically by skeletal muscle. Maybe lactate isn’t as evil as we were all indoctrinated to believe!

The Body Adapts to Stress
 
The one piece of training theory that seems unassailable is that of adaptation. That is; the body will respond to a stress with an adaptation that allows it to tolerate that stress. Ski racing puts some pretty extreme demands on the body, and the principle of adaptation seems to dictate that some demanding training is in order. And perhaps, if lactate isn’t all bad, we should be training to tolerate and utilize lactate as fuel. Well, in the past couple of years we’ve finally started to see a shift in the conventional wisdom. All the talk now is about intensity and intervals. We’ve seen the introduction of intensity blocks throughout the off-season where athletes are doing intervals every day for up to two weeks. You might expect that I’d be happy with all this hard training, but you’d be wrong. The situation is worse than ever before. So what gives?

Interval training first crept into the training theory jargon sometime during the sixties. Uncle John remembers conducting a coaching seminar in Hanover (sometime after he coached the 1966 FIS team) where one of the coaches asked him if he ever did any interval training. He’d never heard of it. By his recollection the idea first came out of central Europe – maybe Germany – and the Swedes quickly responded that they’d been doing effectively the same thing for years in the form of fartlek training. The basic premise of interval training is simple – by doing short bouts of intensity with recovery periods in between you can sustain an overall higher workload than you could sustain continuously. If you go really hard for five minutes then take five minutes rest, and repeat that three times, you’re likely to cover more ground than if you just go for fifteen minutes straight.

But intervals also seem to offer another enticement; they’re kind of technical and you get to pay attention to a wrist watch, and often a heart rate monitor. The attraction of coaches and athletes to structured thinking and planning is as strong as the attraction of moths to a porch-light. In the years since interval training first showed up the use of intervals has become so prevalent that “intervals” and “intensity” have become almost synonymous. Many athletes will only encounter high intensity training in the form of races or intervals.

And intervals have migrated into easier training too. It’s commonplace for athletes to do level 3 or “threshold” intervals, even though threshold is by definition sustainable (which renders the whole point of the interval structure somewhat moot). I’ve even heard of people doing “level 2 intervals”, which has to be one of the most inane ideas I’ve encountered.

The current proliferation of interval-heavy training plans seems to have originated with research and subsequent training recommendations by Jan Helgerud. Many of Helgerud’s ideas were adopted and popularized for use by cross country skiers by the Norwegian women’s national team coach Svein Tore Samdal. I admit to a certain amount of ignorance on the specifics of Helgerud’s work having never read his original research. So I apologize if I mis-represent any of his work – but my target here is the type of training that has trickled down into the US scene.

Intervals and Recovery
 
The training plans that have grown out of the ideas of Helgerud and Samdal have included a lot of what I would consider to be short intervals – in the four-minute range. The basic premise behind all of this is that central system capacity, and cardiac output specifically, is the greatest limiting factor for elite level aerobic athletes. A program of lots of intervals has been shown to increase the maxVO2 of soccer players. And indeed, any physiologist will confirm that hard (high intensity) training is the only way to quickly increase maxVO2. The problem is that repeated bouts of high lactate concentrations can cause real problems with recovery and will almost certainly lead to an over-training effect when experienced at the frequency that has been prescribed. So there has been an emphasis on controlling the intensity and duration of the efforts to minimize the accumulation of lactic acid, but still tax the heart significantly enough to trigger the maxVO2 improvements.

In my opinion there is a major flaw in this approach. While the capacity of the heart to move blood is without question of utmost importance, we still have to live with results of our training in the periphery –our muscles have to be able to sustain the workload. The cellular environment in a working muscle is a balance between lactate production and clearance. Lactic acid is always being produced, and it’s always being “cleared” (utilized, buffered, burned, etc). If we set-out at a pace at which the rate of lactate production slightly exceeds the capacity for lactate clearance we will experience an increasingly acid environment as time passes, until the workload can no longer be sustained. Bottom-line: it takes a while for a steady-state environment to be achieved. When we do short intervals we’re very seldom reaching a sustained equilibrium. We’re producing lactate more quickly than it can be cleared or used. And we’re ceasing the effort before the increasing lactate levels put us into difficulty.

When an athlete does a lot of short intervals the result is that he’ll become very comfortable setting out at a pace that can be easily sustained for four minutes. But what happens when the effort has to last more than four minutes? Recall the concept of the lactate shuttle and the idea that lactic acid can be metabolized as fuel? Well, all this must be trained as well. A program that trains only the metabolic pathways for lactate production while ignoring the capacity to tolerate high concentrations and utilize lactate as a fuel source has a predictable outcome. The type of effort that has been trained so extensively will not be sustainable. We’re conditioning athletes to blow up after a K and a half!

A Solution

So what is the solution? First I’m calling for more hard training and now I’m saying that people are doing too many intervals! In my mind the solution is to take another look at the events that we’re asking athletes to train for. Leaving aside the sprints (where we seem to be doing pretty well) ski races have to be considered sustained efforts. I’m generally in favor of more sustained intensity efforts in training. It has to be understood that these efforts will result in sustained high lactate concentrations. That is a good thing because it will prompt the necessary adaptations allowing improved tolerance for and utilization of lactate. But these efforts also have to be respected – they demand more recovery than a set of short intervals resulting in relatively low lactate concentrations.

Intervals do have a place in training for ski racing, without question. When they’re done hard they can help to quickly sharpen a racer’s form for peak efforts. Intervals can be configured to generate higher peak lactates than can be sustained for a long effort, which can help to raise the tolerance for high lactate concentrations in competition. At lower than peak lactate efforts intervals give us an opportunity to train at higher levels of output than could be sustained for a race. And race-pace intervals can be used to mitigate the recovery demands of a true race effort.

One of the greatest fears of ski racers is “peaking too early”. This typically means being the strongest guy in September (when there are few races scheduled). A heavy dose of interval training through the Summer is a really good way to peak too early. Some coaches will point out that tight control of the efforts and patience in execution will help avoid an early peak, but even top level athletes are susceptible to misjudgment. Kris Freeman will readily acknowledge that he was in peak form during September of 2005, and that he didn’t have that form again during the race season. Different athletes react differently to a given training load. I’ve worked with skiers who need lots of tolerance intervals and about ten race starts before they can race fast, and others who can come off an easy-distance training regime and race at near peak levels. But the beauty of sustained efforts is that they are self-regulating. Because the effort is sustained, the type of energy systems that are trained are by definition sustainable. It would be very hard to peak too early by doing only sustained intensity training. The main concern is recovery and avoiding a chronic overtraining effect.

Still Need to Train Hard

Uncle John was right – skiers DO have to train hard. There are great gains to be made by forming an alliance with lactic acid. And there is a time and place for intervals as well. But if you find yourself doing four minute intervals in May it’s worth remembering that nobody is handing out medals for the best maxVO2 test in June. Don’t be afraid to train hard year-around. Don’t hide from competition or race efforts. Knock yourself out with sustained efforts. But save your structured interval training for when you have specific tolerance gains to make.