Saturday, December 1, 2007

XC Endurance Training Theory – Norwegian Style

XC Endurance Training Theory – Norwegian Style
By Stephen Sieler

Borrowing from theoretical physics lingo, I am going to try to present a "Unified Field Theory" if you will of Cross Country ski training, from the standpoint of endurance capacity development. Unified because it represents a conceptual blend of my own experience, understanding of the physiology, translations from the Norwegian training literature, and numerous conversations with a national class coach here whose insights I value and trust. Field fits too, because I am going to try to talk in terms that make sense out in the field, not just in a lab. Unfortunately, a lot of sport scientists can't think beyond the lab and the "8 week study." Theory is also appropriate, because no scientist worth his bodyweight in salt would propose to have the all complexities of physiology and training adaptations nailed down.

I should also point out that this framework does not assume limitations on training time, it is based on the long term development of elite athletes. This is an important point. Much of the research based on untrained or moderately trained individuals doesn't apply to the elite. However, although this material is built up from elite training experience, the basic principles have relevance to us all.

The Big Picture
Below is a training intensity chart, similar perhaps to many you have seen before. It is a closely patterned after the basic intensity classifications for endurance training used by XC skiers and trainers in Norway. When they denote training intensity, this is the language used. I have added another column, lactate concentration. These values are based on several sources including long term studies of elite rowers in Germany. I think rowing and XC are very similar because they are both quadripedal exercise modes.

* Heart rate is based on the average value at the end of an interval bout or on the top of hills in other training forms.
** Explaining the Two Thresholds I need to write another separate article on this issue of blood lactate and exercise intensity. The basic lactate threshold (also called anaerobic threshold) concept is a useful tool but also over-simplistic. The traditional way of viewing the lactate threshold is that it is the exercise intensity at which the working muscle becomes "anaerobic" and lactic acid production commences. This is wrong, but the idea persists in the popular literature because it is an easy concept to get across.

The reality is this. Even at rest we are producing lactic acid in small quantities. Blood concentrations stay low because this lactic acid that is being produced one place can be taken up and used by another tissue. At low exercise intensities, no or only a very small increase in blood lactate concentration occurs. In fact, we sometimes see blood lactate drop a little from resting values at low exercise intensities, depending on what the athlete just ate. However, if we increase the exercise intensity enough, but not too much, we see blood lactate concentration increase to a new stable concentration. Now we are crossing the Low Intensity Threshold (LIT). At this intensity(s), the blood lactate is not out of control. Lactate removal or clearance can also increase so that a new steady state is achieved. The highest blood lactate concentration that can be maintained during a 30 minute exercise bout corresponds to what we call the Maximal Lactate Steady State or MLSS. This lactate concentration varies with the sport. It is higher in activities that have a smaller active muscle mass like speed skating and cycling (4-6 mM). It is lower in rowing and XC which employ more active muscle mass simultaneosly (3-4 mM). There are also inter-athlete differences, of course. The intensity at which it occurs varies with training status. When the intensity climbs above the MLSS workload, then we have exceeded the High Intensity Threshold (HIT) on the chart. At these intensities, lactic acid concentration would continue to climb over time until the concentration becomes high enough to inhibit muscle contraction and causes fatigue. The rate of accumulation will depend on how high above this threshold the intensity is and how effective the body is at clearing blood lactate. We have growing evidence to indicate that the best endurance athletes have higher lactate clearance rates. They get rid of lactic acid faster. So LIT represents an intensity at which blood lactate begins to rise. Between LIT and FIT we are working in a range where the increased production is accomodated for by increased clearance by non-working muscles, the heart (a lactic acid lover), the liver etc. HIT is the traditional red line, the exercise intensity above which fatigue is just a matter of minutes! How much time can be the difference between winning and losing.

The Basic Recipe
Here are the basic philosophies of the Norwegian system with some explanation and comments along the way:

1. Build the program around weekly high intensity training/intervals!
XC country skiing races are won by athletes with VERY high maximal aerobic capacity. This capacity requires both genetics and hard training. The athlete should build the program around TWO hard/interval sessions per week. In general, the emphasis is on long intervals in the 3 to 8 minute range. This 2 hard session/week rule of thumb is a consistent feature from the junior level all the way up to the international class. For example, here is some actual training data for three elite Norwegian skiers when they were juniors (18-19 years old), during the competitive season.
Vegard Ulvang: 1.9 interval/hard training sessions pr week (including competitions)
Anders Eide: 1.6 " "
Anita Moen: 1.9 " "

All three were averaging 8.5 hours/week volume during the racing season at that age (a volume which is significantly reduced from what they do during the preparation period). Interval/hard sessions are part of the training program beginning in August and through the competitive season, which concludes in early April. The only period where we see a deemphasis on high intensity work is during May, June, and July. So, when I get asked the question, "when should I start doing intervals?," I usually reply "two months ago." Hard training bouts at high physiological intensity are an important part of the training program most of the time. What will change is the absolute intensity (and duration in some cases) of these bouts as the athlete approaches competitive form.

Similarly, international medal winning athletes like Marit Mikkelsplass and Kristen Skjeldal, who are 10 years older or more and competing at the international level, are still averaging 2 hard sessions per week, according to their coach. So, the number of high intensity sessions/week does not increase over the development of the athlete. However, with the improved basic endurance that they develop over years of increasing training volume, the quality of these hard training sessions does improve. This is a fundamental concept of the preparation of XC skiers. High volume, low-intensity work builds the basis for extending the athlete's performance capacity with the hard sessions. The two are complementary. At the elite levels, both are necessary for success.

The interval/hard sessions have the primary effect of stressing the cardiovascular system. We think this is very important for increasing/maintaining a high maximal oxygen consumption. These sessions also are important for stressing the lactate clearance and buffering systems which are stressed during competitions. High intensity interval training IS NOT an ideal method for inducing muscular adaptations such as mitochondrial proliferation and increased capillary density. The adaptations induced by high intensity sessions occur relatively quickly, but are also more quickly lost with inadequate volume of high intensity training.

2. Do (most of) the remainder of the endurance training volume each week at LOW (below the LIT) intensities.
The volume of this work does change and can be quite high, depending on where the skier is in their development. At the extreme, these sessions can be 4-5 hours long in elite athletes who are accumulating 25 hours a week of training volume. The key concept is that the long distance training is also critical but should not diminish the quality of the interval sessions. If something has to be reduced, it is the low intensity volume, not the interval volume or quality. The operative Norwegian word here is "overskudd" or overshoot. We want the athlete to feel psychologically ready and be physically rested to perform those hard, high quality sessions. The low intensity training is vital because it builds the muscular endurance foundation necessary to allow the cardiovascular system and lactate removal systems to be stretched to their limits during the intervals without overstressing the recovery capacity of the athlete.

This "hard core" philosophy is a departure from thinking and practice 10-15 years ago, when the training volume was considered the key element.

The primary adaptation acheived with a high volume of low-moderate intensity training is at the muscular level. Mitochondrial density increases, capillary density increases, and cyctosolic enzymes involved in fat metabolism are enhanced. It appears that these adaptations can take years to be fully realized. It is important to point out a few points here. First, despite the fact that the very best junior skiers have VO2 max values that are similar to the best senior skiers, no junior skier has ever won a world title. The increasing training volume that is adapted to over several years of high level training seems to be important, even after VO2 max has plateaued. Second, an alarming trend that has occurred over the last several years is that top skiers are reaching their peaks later in life. And, junior skiers who take the step up to the World cup level are taking longer to achieve good results. In Norway, it has been suggested that one of the problems is that junior skiers do not put in the training volume they used to. Too many cars and busses. This is a distraction that Kenyan children have avoided so far, to the demise of the western distance running establishment who chases them from a widening distance.

The Progressive Overload Principle In Action
Total training volume increases progressively over the developmental cycle of a cross country skier. Here are some guidelines for yearly training volume (hours of actual training), in relation to age. These numbers come from material presented by current Norwegian men's national team coach Eric Røste.
Annual Training Volume in Relation to Age:

Keep in mind that this is a progression based on long term development. The late starting athlete is not going to be able to automatically handle those high training loads, just because they are older! When the training is broken down into percentages of hard and "easy" training, it comes out to around 15 to 20% hard and 75-80% "easy" or "steady." Coach Røste also points out that there is some hidden intensive training that occurs during the long steady state bouts (big terrain changes). I hesitate to use the term "easy" this describe this low intensity form of training. The actual Norwegian term used is "langkjøring" or long running. Distance, not time is of the essence here. A 3 hour trail run in the woods, kayak session, or climbing-intensive hike with back pack in the mountains is not "easy" if have only been doing "60 minutes and out" training!

3. In General, Avoid "Middle of The Chart" Intensities.
This should not be taken too dogmatically. Sometimes the intensity climbs during a steady state workout as a function of the terrain, or getting chased by a dog! And even the top skiers say that sometimes it is a nice variation to pick up the pace just a bit on the long tours. However, the main point is important:

"Train too hard on the easy days, and soon you will be training too easy on the hard days!"
Ok, after reading so far, two questions might be swirling about in your brain:

1. "If interval training is so important, why not do more?"


2. "Why not do more of the low intensity distance training at higher intensity, or in other words, what is wrong with the "pretty tough" medium intensity workout?" Whatever happened to "No Pain, No Gain?"

I think answering both requires not only a knowledge of muscle and heart physiology, but an understanding of the "whole athlete". Historically, many people have made the mistake of thinking of training one-dimensionally. By this I mean they only think of training as a means to induce the positive physiological changes that result in better performance. This type of thinking rapidly leads to the "more intensity is better" or, more precisely, "more intervals are better" mentality. In the lab, numerous sport scientists have designed short training studies with untrained subjects and demonstrated that those who train at higher intensity improve more in the short run. I have done it myself, having made rats run hard intervals 5 days a week before! Clearly, intensity is a critical determinant of the training response. BUT, pushing intensity too far, too often leads to big problems when we try to extrapolate to the long term development of the elite endurance athlete.

Training must be thought of "two-dimensionally." The first dimension is training as inducer of positive change. The second dimension is training as a stress that does cellular damage, alters brain chemistry, and disturbs hormone levels, negative consequences all in all. When we realize that the training sword cuts both ways, then the "magic" of ensuring the long term progress of the elite athlete can be understood as an exercise in maximizing the "Benefits to Risk ratio," both from week to week and over the long haul.

The answer to both "why not more interval sessions?" and "why so much low intensity steady state work?" is similar I think. I call it avoiding regression towards the mean. If we try to do hard/interval training (read: high lactate accumulation over many minutes) too frequently, we either break down completely or we end up performing many of the interval sessions at inadequate intensity. It can be either the head or the body that cracks, but the result is the same. If we instead try to turn up the intensity on those "long tour sessions," they become too stressful and too limited by glycogen availability, and we shorten them.

As a related point, one of the best ways to end up overtraining is to have too little variation in training intensity (coined "training monotony" in some nice research on speedskaters and cyclists by Dr. Carl Foster). Athletes can eventually handle high workloads if they successfully avoid letting all the workouts drift towards a middle of the road intensity.

Is this training structure unique to XC skiing?
I would have to say YES and NO right now. In general terms, I would say no. This philosophy of training is generally consistent with observations in rowing, cycling and running (though perhaps less so with running as it relates to the Kenyans). It looks very similar to the current pattern in international rowing. However, some might argue that the high volume of low intensity work is particularly evident in rowing and XC skiing. If that is true, I propose that these sports ARE unique in an important way. They require the simultaneous work of all four limbs. This is an exercise situation that humans have evolved away from. The human cardiovascular system was not designed to support the energy demands of quadrapedal movement. We just don't have the big pumps like sled dogs and race-horses. So, when the upper limbs are added to the mix, the sympathetic stress load is higher at any given absolute work load. This may mean that higher volumes of low intensity work are a better way to train the upper limbs and lower limbs simultaneously while avoiding overtraining. Another approach is to spend more time isolating the upper-body during endurance training. This is an issue I will discuss more in other articles!

A SUMMARY of the "UNIFIED FIELD THEORY" for XC ski endurance training.
1. Build the the typical training week around 2 hard/high intensity training sessions.
2. Increase the total volume of training with primarily low intensity work at not more than 70-75% % or so of HR max. Don't view these long, low intensity sessions as valueless, and don't adopt a "harder must be better" approach!
3. Avoid a training condition in which each session begins to take on the same medium intensity.

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