TRAINING
Orienteering Fitness (Part 2) Steve Bird In Part 1 (AO Dec’04) we looked at some of the factors which affect our physical performance in Orienteering events. In particular we saw how VO2max changes with age and gender, but that by maintaining reasonable levels of fitness, older competitors do not suffer the same reduction in VO2max as does the general population. VO2 and VO2max – The amount (volume) of oxygen we use each minute is our
VO2 and the maximum amount that we are able to use each minute is our VO2max. Both of these are commonly expressed as the amount of oxygen being utilized, divided by the person’s body weight in kilograms, they are therefore given in units of millilitres of oxygen / kg body weight / minute (ml/kg/min).
S
O if we ignore the confounding factor of ageing by comparing individuals of the same age, fitter orienteers will have a higher VO2max than unfit orienteers. This means that fit orienteers can utilize oxygen at the high rates required to sustain relatively fast running speeds, whereas a less fit orienteer with a lower VO2max can only utilize oxygen at a rate sufficient to sustain a slower speed. If a person attempts to run at a speed that requires more oxygen than they are capable of using, then their muscles will need to use supplementary sources of energy which are gained from anaerobic metabolism. The problem with these is that they result in the formation of lactic acid which, if it accumulates, causes fatigue and forces you to slow down or stop. If two individuals were to run at the same speed, the fit individual may be well within their aerobic capacity (VO2max) and therefore find the pace comfortable, whilst the unfit individual may be exceeding their aerobic capacity, in which case they would start to accumulate lactic acid, feel fatigued and have to stop. Running speed versus VO2 80.0
Oxygen utilisation (ml/kg/min)
70.0 60.0 50.0 40.0 Elite
30.0
Non-elite
20.0 10.0 0.0
11
13
15
17
19
21
23
Speed (km/h)
Responses at VO2max – Typical figures for a fit elite orienteer working at VO2
max would be a heart rate of 180-190 bpm, a stroke volume of 120-140 ml per beat, a cardiac output of 21.6-26.6 litres per minute, 75-80% of the cardiac output being directed to the exercising muscles and a ventilation of 140-160 litres of air per minute.
2. Lactate threshold
In reality a certain amount of lactic acid is produced at speeds which are somewhat slower than that needed to reach VO2max. However, because the amount produced at these speeds is small, it can be easily removed from the muscle by the blood flowing through it. So it does not accumulate to a level that causes fatigue. When you increase your running speed there is an increase in the amount of lactic acid produced by the muscle, in which case it has to be removed at a more rapid rate if it is not going to accumulate. 30 THE AUSTRALIAN ORIENTEER MARCH 2005
However if you continue to increase your speed you will eventually reach a speed at which the lactic acid cannot be removed fast enough and its production will exceed its removal, causing it to accumulate quite rapidly. This is the speed at which you feel that burning sensation in the muscles or when running uphill and fatigue rapidly sets in. The maximum running speed that you can sustain for a prolonged period of time is just below this speed and is known as your Maximum Lactate Steady State (MLSS). In untrained individuals this maximum lactate steady state tends to occur at running speeds corresponding to around 65% of their VO2max, but it is trainable and in highly trained individuals it may not occur until running at speeds that require in excess of to 80% VO2max. So not only can you increase your VO2max with training, but you can also increase the % of it that you can run at without accumulating lactic acid. Both of these adaptations on their own would mean that you could sustain a faster running speed, and together you get a cumulative improvement in your sustainable running speed. So to illustrate the implications of this, imagine the scenario where there are two orienteers running along together at a speed of 14 km/h. This running speed will require an oxygen consumption of about 40 ml/kg/min. If one of them has a VO2max of 67 ml/kg/min this means that they will be at 60% of their VO2max, which will feel like a comfortable, steady running speed to them. However, if the other orienteer has a lower VO2max of 50 ml/kg/min, this means that their rate of oxygen consumption will be close to their maximum (90% VO2max), and at this speed they will be above their maximum lactate steady state and consequently accumulating lactic acid in their muscles. They will be finding the speed hard and will soon tire, whereas the fitter orienteer could run quite a bit faster and still not experience excessive fatigue. In an event, we tend to find our maximum sustainable running speed ourselves on the basis of our perceptions of fatigue. Ideally this will be around our maximum lactate steady state, although in reality we will tend to fluctuate around it as we will accumulate lactic acid when running uphill and then have to slow down to recover. If we try to run faster than our MLSS we will tire and have to slow down, if we run slower than this, we will feel comfortable but won’t complete the course as quickly as we could have.
3. Running Economy
From the above it can be seen that the fitness requirements for orienteering are similar to other endurance running events but it’s worth remembering, that bush orienteering presents a unique challenge with its underfoot conditions and obstacles. Consequently being able to run smoothly and efficiently in terrain is another important fitness attribute. It would appear that orienteers who train in typical terrain can develop the running technique and biomechanical movement patterns that enable them to run more easily over rough terrain. A study 1 showed that when a group of orienteers and track runners ran at the same speed on firm tracks they used the same amount of oxygen. But when running at the same speed through orienteering terrain, the track runners used their oxygen inefficiently, probably because of a lesser ability to cope with the uneven underfoot conditions making them ‘stagger’ a bit when running. This suggests that they would tire more rapidly, and indicates that to compete well in bush events, orienteers should spend at least some of their training time in orienteering terrain. Reference: 1. Jensen K, Johansen L and Karkkainen O -P (1999). Economy in track runners and orienteers during path and terrain running. Journal of Sports Sciences, 17, 945 - 950. The numerical values presented in this article are general averages and are included for illustrative purposes. Your own values will vary from these according to your body size, age, gender, fitness and personal metabolism.
Professor Steve Bird is Director, Centre for Population Health, Sunshine Hospital, Melbourne. Steve worked with the Great Britain National Orienteering Squad for over 10 years.
