Introduction to maximal oxygen uptake (VO2 max)

Because cross country skiing engages about all of the major muscle groups in the body, cross country skiing is an excellent method of training for physical fitness and dynamic muscular endurance. For the same reason, top cross country skiers generally have exceedingly high maximal oxygen uptakes (VO2 max). Maximal Oxygen Uptake (units are liters per minute) is predominately a function of cardiac output, or how much blood the heart can pump. Therefore, maximal oxygen uptake has a "central limitation". Cardiac output is a function of stroke volume, the amount of blood the heart pumps in one beat. The stroke volume is determined by the end diastolic volume (how much blood your heart can accommodate) and end systolic volume (how completely it can empty). Both the end diastolic and end systolic volumes are a result of the number, size, and the strength of the muscle fibers (left ventricular mass and maximal contractility), how large the blood volume (preload) is, how much the arteries can dilate, (afterload) and the size of the pericardium. The pericardium is a non-elastic sack around the heart that may limit maximum filling. The lungs could also be a limiting factor in cases of disease, altitude, or possibly at very high work loads.

Maximal Oxygen Uptake

Oxygen consumption is considered the standard for measuring the physiological intensity of exercise. If heart rate is the tachometer, then oxygen consumption is how much gas per mile you're burning to achieve a certain speed. In cross-country skiing, success is largely dependent on the body's oxygen uptake ability. The more oxygen that can be delivered to the working muscles, the greater the energy supply, and the faster the body can travel over distance.

Elite cross-country skiers are considered the most powerful in oxygen uptake capacity. This is partly due to genetics, but those genes are the foundation on which the athlete builds an aerobic powerhouse over many years of training in a sport that demands the highest aerobic output.

Exercise science has determined that you achieve specific training adaptations by exercising at various intensities or percent-ages of VO2 max. Oxygen uptake capacity is measured directly, however, only in the sports physiology laboratory with expensive equipment by qualified professionals to which few of us have ready access. Fortunately, research has shown a reliable relationship between oxygen consumption and heart rate (beats per minute) for monitoring intensity during training. The methods for calculating intensity levels by heart rate, described later in this chapter, produce results that accurately correspond with relative percentages of VO 2 max.

Remember that in each stage of the training plan, the amount and type of exercise you do will determine how fit and race ready your body will become. The physiological effects of each training intensity will dictate the amount of each training component scheduled during a given training cycle. For example, low-intensity over distance training sessions are most effective if the intensity is between 55 and 65 percent of VO2 max. This develops aerobic energy pathways and improves capillary density in muscle tissue, proliferation of muscle cell mitochondria, oxidative enzyme activity, and fat substrate mobilization and utilization in the muscle cells. Concurrently, intervals and race/pace sessions, when planned appropriately, are best accomplished at an intensity at or slightly below the anaerobic threshold (AT).

Cross-country skiing and VO2 max

Since more muscle groups generally are engaged in skiing than in walking (the use of the arms to pull and push on the ski-poles), the overall energy expenditure involved in transporting the body on skis from one place to another may be as high as, or higher than, the energy expenditure when moving the body the same distance on foot.

Liters/minute is the absolute value of maximal oxygen uptake (example: 6.2 liters). Milliliters (ml) per kilogram (kg) per minute (min) is the relative value (example: 6.2 liters = 6200 ml/75 kg = 82 ml/kg/min).

A maximal oxygen uptake of 7.4 liters/minute has been reported in a Finnish cross-country skier, Mieto. Also reported is 94 ml oxygen uptake kg/min for a male Olympic champion; 75 ml/kg/min for a female skier.

The efficiency of skiing is illustrated by the following examples:

It is thus clear that skiing, even at submaximal speeds, requires a high aerobic work capacity. Accordingly, most elite cross-country skiers have maximal oxygen uptakes of 5.5 liters/min or more (in excess of 80 ml/ kg/ min), with a maximum of 94 ml obtained in an Olympic Champion (15 km race), an extremely high aerobic power. The corresponding figures for the top Swedish female cross-country skiers are 3.5 to 4.4 liters/ min or 70 to 75 ml/ kg/ min. This is shown in the graph.

Look at swimming and compare it with cross country skiing. For swimming, men (68%) and women (60%) have a much lower VO2 max than cross country skiers, men (90%) and women (70%).

Dr. Norman (a Canadian biomechanist), based on film data collected during the 1988 Olympics in Canmore, Calgary estimated that:

These estimates imply that energy must come from sources other than aerobic metabolism, since no athlete has a sufficiently high oxygen uptake and that recovery (restoration of homeostasis) must take place during high levels of work. This requires the highest values for maximal oxygen uptake, a tremendous ability to buffer the byproducts of the anaerobic metabolism quickly, and large glycogen stores. We should design training fully to develop these qualities in each athlete. Said another way, not only must peak energy production be extremely high, but beyond any recorded level of aerobic power for humans.

The debt must be repaid while sustaining near maximal levels of oxidative metabolism. You can see in the graph, that during the first twenty minutes of cross country skiing, the maximal oxygen uptake is as high as 130%. After two hours, cross country skiers utilized 80% of their VO2 max during a 50 km race!

U.S. Olympic cross country skiers compared to Swedish cross country skiers

It is clear that a high maximal oxygen uptake is critical for high level cross country skiing.. Cross country skiers need a big engine (aerobic power). Once an athlete has this basic ability other parameters become much more important. The minimum VO2 max range we believe necessary to achieve for international success is 5.5 liters per minute for men, and 3.5 liters per minute for women.

Swedish studies indicate that male athletes who never progressed beyond National Team nomination were in the 5-5.3 liter per minute range. Those qualifying for Olympic and World Championship Teams were in-the 5.6-5.8 liter per minute range, and medalists were in the 6-6.2 liter per minute range.

In general, Olympic Gold Medal winners have a V02 max no lower than 6 liters per minute for men, and 4 liters per minute for women.

The graph above shows maximal oxygen uptake values for top American and Swedish men and women from the 1970's, while the values for the U.S. cross country skiers are in a very high range, our average values were 6-9% lower than our Swedish competitors. In an individual it is unlikely that this difference would be significant, but as average values for a large group, it shows us that we were slightly behind in this area at that time.

Among elite male long distance runners and cross country skiers, the highest VO2 max value recorded for a male is from a champion Norwegian cross country skier who had a VO2 max of 94 ml/kg/min. The highest value recorded for a female is 74 ml/kg/min in a Russian cross country skier. In contrast, poorly conditioned adults may have values below 20ml/kg/min!

U.S. Cross Country Ski Team Field Method

The method used by the U.S. Cross Country Ski Team can be done completely in the field, and is specific to each training activity. The test is used to determine the intensity needed for the U.S. cross country ski team members to improve maximum oxygen uptake.

What you need to conduct the field test while roller skiing:

  1. An accurately measured constant grade of 1 kilometer, approximately 3-4 minutes, and at a grade of 5-1 0%.
  2. A heart rate monitor with a memory.

To run a thorough test, 10-12 steady runs up the hill will be necessary (minimum of 6-8). The first run should start at an intensity corresponding to Low Intensity 1. During each run the skiers should try to maintain the pace as steadily as possible. The pace is increased each run by 5-10 heart beats, and subsequent runs are done until the skier reaches maximum pace and intensity.

The coach times each run, and later calculates speed for each run. The heart rates for the last minute of each run are averaged and graphed according to speed. When graphed, the heart rate will go up linearly relative to speed. The Conconi Point, or maximal steady state, is determined by the inflection point in the graph. The inflection point in the graph is caused by a decrease in the rate of increase in the heart rate or a break in the linear slope of the curve.

Other methods for systematic increases in speed during the test can be done, such as pacing on a bike with a computer pacer.

It is recommended that testing on foot be done on 5-10% grade. By the nature of ski training most skiers cannot run fast enough on the flat to complete the test and still be taxed cardiovascularly. By doing it uphill, the test eliminates the need to be a particularly good foot runner.

Initial testing with this method should be carried out for foot running, roller skiing-classical and free-style, to determined if there is a significant difference. Once this is determined, one test every two to three weeks is all that is necessary.

To determine training intensities based upon Conconi Test.

Zone Bottom Top
Conconi Point Hr -50 -30
Conconi Point Hr -30 -10
Conconi Point Hr - 5 +5
Average Race Hr 30-50k race 5-8k race

Sample Training Zones for an athlete with a Conconi Point of 175.

175 - 50/30 125-145
175 - 30/10 145-170
175 - +5/-5 170-180
175 or Long Race Average 175+10
185 or Short Race Average  

Estimate your maximal oxygen uptake (VO2 max). You'll find various formulas and calculators on the following pages:

When you are finished with the above pages, close the window to return to the Olympics Sport and Science Site.

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© April, 1998, Montana State University-Bozeman