Introduction to maximal oxygen uptake (VO2 max)

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.
A good skier covered 30 km on a snow-covered lake in 1 hr 20 min (speed 6.25 m/s). The 1996 time in the Swedish Vasa race, 86 km (with some 30,000 participants), was 3 hrs 49 min (average speed 6.23 m/s). The terrain is relatively flat. In the Olympic Games in 1994 the 50 km winner finished after 1hr 50 min 55 sec (average speed 7.51 m/s). For comparison, the best time in track running 10,000 m gives a speed of 6.34 m/s, and for marathon about 42.2 km, 5.65 m/s.
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.
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:
For a man, skiing on flat terrain at a pace to win an Olympic medal required 75 milliliters of oxygen per kilogram of body weight, per minute. Uphill skiing, during the first 20 minutes, required 110 milliliters per kilogram of body weight per minute of energy output.
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!

credit and deepening: btc.montana.edu