Cross-country skiing is seen as one of the most physically demanding sports.
Aerobic metabolism is dependent on oxygen and utilized during distance trainings, taking up a lot more energy from the skier, as compared to anaerobic metabolism, by breaking down body fats instead of glucose. Anaerobic metabolism is triggered when the pace or intensity of the activity increases, and essentially means that the body’s oxygen demand is greater than its supply, as the body finds it hard to cope with such demand.
The Science Behind It
As part of any exercise, the body uses both the mechanisms, aerobic and anaerobic, to extract energy, at low and high intensities, respectively.
Aerobic metabolism is relatively slow and activated due to the amount of time available to the body to break down and utilize fats, while in the case of anaerobic metabolism, it only kicks in along with the production of lactic acid, when the body is put under stress for optimum performance; this can be taxing on the body, and needs to be utilized in smaller stints.
The purpose of distance training is to enhance the efficiency and time frame within which the aerobic metabolism stays dominant; otherwise, the body is bound to be fatigued quickly with long term side effects. There is a long list of benefits associated with appropriate endurance training. These include increased blood, stroke and heart volume, oxygen uptake, enhanced optimum cardiac output, increased capillary density, increased mitochondria density, increased activity of citric acid cycle enzymes, and a lowered resting heart rate.
Scientists have come up with identified ‘training zones’ to optimize the above mentioned benefits of distance training and minimize the fatigue that can be a natural by-product of incorrectly executed endurance training. They have identified five physiological training zones, and it is important to note that all distance training ought to be kept within zones one and two only.
Zone one (or level one) is the easiest for aerobic endurance purposes and requires 60 percent of a person’s maximum heart rate, 50 percent of his maximum oxygen uptake (VO2 max), or a blood lactate level at 2.0 mmol or lower. This zone signifies that the body is on aerobic energy mode almost fully, with oxygen being readily available. As you will appreciate, this zone is generally used for low-intensity training, recovery periods and over-distance training. This can be a difficult zone to maintain for skiers who are used to the fast paced skiing, however, this is meant to be the most productive zone if you are looking for longer duration workouts.
Zone two (or level two) is defined as the general endurance zone as the anaerobic energy consumption is increased gradually. Having said that, the aerobic energy mode is still dominant and this should also feel fairly easy on the body. Zone two can be seen as athlete’s 75 percent of maximum heart rate, 70 percent maximum VO2, or a blood lactate level between 2 and 3 mmol. Level 2 can be maintained for longer durations before fatigue kicks in. A good example is when a person cannot easily converse during the workout, then he is most likely going over the speed for his body’s energy requirements.
There is fine balance between the zones and what your body needs to do in order to train safely and longer within these zones. Recreational or professional athletes require proper coaching and guidance on the science behind these zones to avoid a performance slump due to over training and eventually becoming fatigued even during low intensity workouts.
Zones three, four and five are meant to cater to the anaerobic metabolism and are utilized specifically for interval training. 80% of the total yearly volume focuses on endurance training, whereas the remaining 20% is attributable to intervals and strength training. It is important to understand that if you do not execute the endurance training aspect correctly, then the 80 percent of the total yearly training goes wrong too! Training excessively or hardly during distance workouts can be counterproductive in a more profound manner than training very slowly during interval sessions. The athletes and professionals need to comprehend the heart rate values in relation to their personal physiological training zones to avoid this pitfall.
For an uphill terrain, a skier can workout at 120-160% of VO2max for short intervals, and subsequently at periods of lower VO2max, for recovery purposes. VO2max is the highest amount of oxygen the body utilizes during exercise and signifies that anaerobic (non-oxidative) metabolism is assisting with the pace of the skier during the workout, depending on the terrain and other external conditions. If the speed gets faster and workload exceeds the VO2max, then the anaerobic metabolism kicks in to provide the additional demand of energy, leading to an oxygen deficit – difficult to measure or express as a number. Having said that, this oxygen deficit leads to the production of lactate, and the measure of this lactate in the blood may be an indicator of some sort for this oxygen deficit, i.e. higher the blood lactate levels means greater the oxygen deficit.
It can be safely assumed that pole contact time (time period during which the poles are in contact with the ground) can have the ultimate impact on the energy input and hence the speed of the skier, as far as flat terrains are concerned. Bearing this in mind, one can train at greater speeds to reduce pole contact time and extract efficiency overall.
XC skiing places high demands on the skier’s aerobic and anaerobic systems combined, as part of competitive racing and distance skiing. Also, the optimum ΣO2-deficit along with higher body mass can be a vital component in the variance between specialized sprint skiers and distance skiers. Both these forms of skiing require the skier to create oxygen within and then recover from the oxygen deficit during the sprint or between heats in sprint skiing. The ability to achieve high-intensity periods and correspondingly high rates of recovery are important aspects or requirements for any flat terrain skiing. The high rate of recovery from oxygen deficit also assist in producing a changing pacing pattern.
These changing sub-techniques require varying results from the upper and lower body muscles, and these requirements keep fluctuating with the increase in intensity.
You will appreciate that the power exerted is higher during an uphill ski as compared to flat skiing; similarly, the variations in power output and metabolic demand is also higher during an uphill sprint as compared to a flat terrain.
A skier should naturally expect repetitive intensity fluctuations during intermittent downhill moves, as he recovers during such period too. It is this combination of high and long term aerobic energy requirements and repetitive work rates over the VO2peak, along with short bursts of recovery, distinguishes XC skiing from a lot of other endurance based sports.
The sprint skier’s performance is impacted by downhill terrain, either directly (by means of speed or tactics) or indirectly (through economy and/or recovery).
A good majority of sprint races involve one third of the distance on uphill, flat and downhill terrains. The physiological aspects of cross-country sprint skiing allows skiers to recover drastically during the downhill period of the races, and between the heats, as the skier glides for a good part of the journey by staying in a deep stance.
The recovery during the downhill terrain is also associated with the lower metabolic rate, as the terrain varies during cross-country skiing. This, in turn, allows the skier to generate higher anaerobic power when the skier needs to up the gear and move uphill afterwards.
A comprehensive conditioning of the body can be attributed to various factors such as cardiovascular endurance, strength and power of muscles, body coordination, speed or flexibility. For performance optimization during cross country skiing, it is imperative to train all the metabolic systems with the right balance and technique. Cross country skiers spend around 80% of their yearly training on distance training, and for that reason alone, they need to ensure that it is done correctly, to achieve the best results.
One of the basic and most important components of cross country skiing is distance training, and despite the fact that it seems simple, countless athletes try to train excessively and miss the point completely, in respect of the physiological benefits that they should be deriving from it. The best suggestion, particularly for novice skiers, is to slow down and focus on the right technique, along with a complete understanding of the science behind these trainings – particularly, the two metabolisms and staying within the appropriate training zones.
Having said that, aerobic and anaerobic systems may have a profound impact on cross-country skiing, but they are not the only considerations that a successful skier needs to consider. Some other key considerations that skiers need to consider as part of their preparation and competition training includes strength enhancement, right and balanced nutrition, recovery process, psychological aspects et al. These factors need to be instilled in every skier, regardless of his skill level, and this is the joint responsibility of the coach (if there is one) and the athlete himself.