Cross-Country Skiers Who Crank Up Intensity Achieve Higher VO2max!

Adaptation to high-intensity vs. low-intensity training - exercise science research is not very supportive of the high-volume paradigm.

Top-level cross-country skiers and their coaches tend to embrace a high-volume, low-intensity training paradigm.

Training programs unveiled at international cross-country skiing coaches' seminars reveal that elite and very good skiers usually spend less than 20 percent - and sometimes as little as 10 percent - of training time at an intensity below lactate threshold during a year of training and competition.

Training volumes tend to be fairly high. Some elite-level skiers average about 725 hours of workouts per year (about 14 hours per week). Of those 725 hours, it is not uncommon for 90 percent to be spent below lactate-threshold intensity.1

What Is The Lactate Threshold?

Lactate Threshold (LT) is the highest steady-state exercising intensity an athlete can maintain for prolonged periods of time (>30 minutes). It relates to the muscle fatigue and loss of performance that endurance athletes like cyclists, rowers, runners, swimmers and cross-country skiers experience by doing sustained high-intensity exercise.

Lactate is a by-product of anaerobic metabolism that is produced during exercise, when lactate acid is produced. During light and moderate-intensity exercise, blood concentration of lactate remains low. The body is, therefore, able to remove (absorb) lactate faster than your muscles produce it.

When intensity is high, there's a point when lactate absorption fails to keep up with the rate of production. This is the Lactate Threshold. Excessive blood lactate and hydrogen ion concentrations combine to interfere with efficient muscle contraction, and as a result, power output drops, suffering increases, and you're forced to back off.

Is that the right way to do it? Exercise science research is not supportive of the high-volume paradigm, but the answer given to this question by elite-level cross-country ski coaches is usually "yes." The coaches often support their contention by pointing out that Olympic and World Championship medalists tend to use this high-volume, low-intensity approach to training.

Note, though, that since high-volume, low-quality training is almost universally accepted in the cross-country ski world (as with many other endurance sports), high-volume athletes usually end up competing against other high-volume athletes at major events like the Olympics and World Championships.

Thus it's no surprise that the winners' circles are primarily reserved for high-volume athletes, since they make up the vast majority of competitors. The most naturally-gifted athletes also tend to gravitate toward high-volume training, since they usually link up with successful coaches who have traditionally favored low-intensity approaches.

There is certainly no reliable scientific evidence to support the value of high-volume, low-intensity training. In fact recent research suggests the opposite.

Recent Research

For example, in a study carried out with top-quality American cross-country skiers, athletes who dramatically increased their quantity of high-quality training achieved impressive improvements in performance, while those who stepped up their volume of training in a traditional way failed to improve at all (ibid).

In this study, 14 cross-country skiers (eight women and six men of comparable ability) were followed carefully over a 2-year period. During the first year, all the athletes trained in a similar way, using the currently popular high-volume, low-intensity program.

Over the course of the year, they averaged 660 hours of training (about 12.7 hours per week), of which a paltry 16 percent were spent at lactate-threshold intensity or higher (Regular readers of PP will recall that our recommended goal is at least 25 percent).

The average age of the skiers was 23-years old; the women had been training seriously for eight years, boasted 16 percent body fat and an average VO2 max of 60, while the men had been working for 11 years, had 6 percent fat and VO2 max of 70. All used the same strength-training schedules, and the overall periodization of training was similar.

What Does VO2max Mean?

VO2 max is defined as the maximum amount of oxygen that your body can take in, deliver and use in one minute.

It is limited both by the amount of oxygenated blood the lungs and circulatory system can process, and by the amount of oxygen the muscles can extract from the blood. It is estimated that VO2 max goes down about 1 percent per year. The fall in marathon performance is known to be about 13 percent per decade.

In fact, this periodization plan was simple and traditional. For 23 weeks, from May through October, they worked on developing an 'aerobic base'. During this 'basic endurance period' they completed about 17 hours of training per week, with just 4-5 percent of total work classified as 'quality' - i.e. above lactate threshold. In other words, almost half the year was taken up with lots of low-quality skiing.

Maintaining Volume & Boosting Intensity

The basic endurance period led on to the 10-week 'pre-competition period', which lasted from November to mid-January. This period included the early season preliminary competitions, and the overall training philosophy involved maintenance of high volume (17 hours per week) with an increased quantity of intense work.

There was an emphasis on intervals carried out at about lactate-threshold intensity, as well as some racing simulations. Training at about lactate threshold or above added up to around 4.5 hours - about 25 percent of the total training load.

The final 'competition period' also lasted 10 weeks, from mid-January through March. Volume was cut considerably to 10-11 hours per week (a 35-40% reduction) but the amount of quality work (4-4.7 hours) stayed roughly the same as during the pre-competition period.

Since volume was trimmed so drastically, however, the relative amount of quality training rose to 35-48 percent of the total. When the competition period ended, there was a 9-week break before the start of a new training macro cycle.

By the end of the competition period, things had become extremely interesting. By this time, seven of the athletes had met three important improvement criteria: increasing VO2 max by at least 7 percent, boosting lactate threshold by at least 10 percent and raising the number of points they received on the United States Ski Association (USSA) Points List by more than 10 percent.

Since things had gone so well, these athletes were placed on the same training program for the following year ('If it ain't broke why fix it?') except for the fact that their total training volume was increased by 6 percent.

Piling On The Volume

Why 6 percent exactly? Once fairly high levels of VO2 max and lactate threshold are attained, athletes have customarily piled on greater volumes of training in attempts to push these physiological variables even higher. Traditionally, annual increases of 5-10 percent have been perceived as optimal.2

This is true across the full range of endurance sports; swimmers, cyclists and rowers often attempt to increase training volume by such amounts from year to year in an effort to improve. Sometimes this is just because they don't know what else to do, but many athletes and coaches believe that volume swings are a strong stimulus for improvement.

Meanwhile, though, the other seven cross-country skiers in the U.S. study failed to satisfy the improvement criteria during the first year (we'll explore the reasons for that in a moment) and were placed on a different training plan for the following year, which emphasized higher-quality workouts.

The amount of intense training they carried out roughly doubled during the following year, while volume held steady.

Thus, two different training schemes were evaluated: a classic step-up in volume versus a remarkable increase in training quality without any extra volume.

It is important to understand that this research does not constitute a scientific comparison of volume vs. intensity: for that it would have been necessary to divide a group of roughly equivalent athletes into two sub-groups, one following a more-intense program and the other a high-volume slogfest.

The groups in this study could not be considered equivalent, since they had shown differing responses to the first year's high-volume work.

Nonetheless, the study succeeded in examining two key training questions:

  1. What happens when you take a group of successful endurance athletes and attempt to make their training progressive by adding on more volume (in terms of distance or time)?
  2. What happens when you take a group of athletes who have apparently responded less well to traditional training schemes and place them on a regimen of high-quality training?

As mentioned, the second year high-quality work for the 'underachievers' was uniquely intense. During the 23-week basic endurance period training at lactate-threshold intensity or above increased from just 0.7 hours per week in year 1 to 3.8 hours in year 2.

During the pre-competition period, quality training increased from 4.5-8.5 hours per week, so that in year 2 the skiers were performing more than an hour of high-quality work per day! Finally, during the 10-week competitive period the underachievers boosted high-quality effort from 3.9 to 6.4 hours per week.

Over the full 43-week period of the second year, the first-year 'poor performers' amassed a total of 236 hours of high-intensity training (5.5 hours per week), compared with just 100 hours during the first year. Correspondingly, low-intensity training volume plunged from 443 hours (10 hours per week) to just 283 hours (6.6 per week). Their training had truly become red hot!

So how did the two groups compare during the second year of training? Remember that during the first year the high-volume trainers had improved VO2 max from an average of 64.1 to 67.3 - a significant advance - and upgraded lactate threshold by around 7 percent.

By the beginning of year 2, VO2 max and lactate threshold had fallen to pre-first-year values again, and the gains in those variables during the second year were exactly the same as those achieved during the first year. In other words, the 6 percent volume boost did nothing for the skiers physiologically. Second-year competitive results were also equivalent to the first year's achievements.

The Underachievers Blossomed

What of the so-called underachievers? Well, while they didn't do much during their first (traditional high-volume) year, they had truly blossomed - both physiologically and competitively - by the end of their second, high-intensity year. VO2 max, which didn't improve at all during the first year, increased by 5.5 percent (from 67.3 to 71.0) during year 2.

Lactate threshold, which was stagnant during year 1, responded to the high-intensity program by soaring by almost 20 percent! Not surprisingly, the underachievers - now almost overachievers - significantly improved their USSA point totals and individual placings at the U.S. National Championships.


The 'control' group of cross-country skiers spent 16-17 percent of total training time working at high intensities during both years of the study. They made good physiological and performance gains during the first year, but they did not respond in an enhanced way when training volume was increased by 6 percent in the second year.

As we have pointed out many times in these pages, advances in training volume are a poor stimulus to fitness improvement in athletes who already train fairly extensively.

Meanwhile, the 'treatment group' (the initial underachievers), whose members increased high-intensity training by 136 percent and reduced low-intensity volume by 36 percent in the second year, achieved remarkable gains in both fitness and performance.

This Research Carries An Important Message

Once they have reached a fairly high level of performance, endurance athletes tend to plateau and stagnate from year to year. A key reason for this stagnation may be that they are simply carrying over their basic training from one year to the next.

Since they already adapted physiologically to the training to the fullest extent possible during the first year, it is unreasonable to expect any further adaptation during subsequent years. As the great Arthur Lydiard once asked: 'Isn't it odd that endurance athletes tend to train in the same way over and over again - yet expect different results?'

As the U.S. study reveals, another reason for stagnation is that experienced athletes tend to rely on increases in volume to make performance improvements. Endurance runners currently logging 50 miles per week want to go to 70, the 70-milers want to go to 100, and the 100-milers entertain thoughts of 120 miles per week or more!

Cross-country skiers, rowers, swimmers and cyclists tend to aim for 5-10 percent upgrades per year, but the strategy is equally unworkable because volume 'tweaks' are fairly weak stimuli to fitness once a substantial level of training has been attained.

By contrast, upgrades in intensity can make a major difference. The U.S. researchers concluded that athletes who don't respond to traditional high-volume training can often benefit greatly by shifting to more intense work. While this may be true, a close look at the data reveals that the problem encountered during the first year by the underachievers was that they simply did even less quality work than the 'controls'.

During year 1, this latter group completed eight more hours of high-intensity training during the competitive period than the underachievers. And while the controls logged 48 hours of strength training during the pre-competition and competition periods of year 1, the underachievers put in just 30 hours of resistance work.

Thus, the underachievers cannot simply be regarded as non-responders: they may simply not have done enough quality (including strength) training during the first year.

Are Much Higher Levels Of Intense Work achievable?

For the future, we certainly need more studies like this one, which is the first to manipulate training protocols over two full competitive seasons in serious endurance athletes. We need more work on the differences in adaptation to high-intensity vs. low-intensity training, and we certainly need more explorations into how much of the total training 'pie' should be devoted to above-lactate-threshold training sessions.

For years, we have been stuck on 25 percent as the ultimate bullseye for quality work, and many serious athletes carry out much less quality work than that. (Many of the world's top cross-country skiers, for example, are known to stick at 11-12 percent as their annual average.) Much higher levels of intense work are achievable - and may well be highly desirable.

Of course, endurance runners are loath to increase quality exertion to 35 percent (or more) of total mileage, partly in the belief that high-intensity training significantly raises the risk of injury. However, there is nothing as injury-provoking as a steady rise in mileage; one study determined that a good predictor of injury in runners is the number of miles completed in the previous month of training - not the intensity with which the work was performed.3

Another investigation revealed a marked rise in injury risk when runners pushed their training beyond 40 miles per week, not when they enhanced intensity.

Indeed, research suggests that the two best predictors of injury in endurance runners - a prior history of injury and the number of consecutive days of training - do not involve speed at all.4

If quality training is introduced to a program gradually and progressively, it should actually be protective against injury because higher speeds place greater forces on muscles and connective tissues than lower speeds, thus producing a strengthening effect. Higher speeds also require greater coordination, which should also help to prevent injury.

It is especially intriguing that the under-achieving skiers in the U.S. study achieved such an amazing gain in lactate threshold (almost 20 percent) during the second year, compared with an approximate 7-8 percent rise in the controls. While this difference between groups was not reported to be statistically significant, the substantial threshold gain is what one would expect in response to very high-quality effort.

Such exertions cause average training blood-lactate levels to increase, putting increased pressure on muscle cells to 'learn' to clear lactate from the blood and process it at high rates for energy. Ultimately, this has a profound effect on lactate threshold, one of the best predictors of endurance performance.


  1. Medicine & Science in Sports and Exercise, vol 31(8), pp 1211-1217, 1999
  2. Medicine and Science in Sports and Exercise, vol 24, pp 1040-1047, 1992
  3. American Journal of Sports Medicine, vol 15(2), pp 168-171, 1987
  4. Running Research News, vol 9-5, pp 8-9, 1993