TRAINING

Orienteering Fitness (Part 1)

Steve Bird

The numerical values presented in this article are general averages. Your own values will vary from these according to your body size, age, gender, fitness and personal metabolism.

TO perform well in any sport you need to have the required fitness, technical skills and mental attributes. All of these are vital and the exact requirements will differ between sports, making it necessary for you to apply sport specificity to your training. So whilst doing a varied mixture of activities will have some health and fitness benefits, if your main objective is to be fit for Orienteering you must focus your training to meet the specific demands of our sport. This series of articles will review some of the physical and fitness demands of Orienteering, with the aim of providing an insight into the physiological requirements of our sport and consequently how we should train for it. The series is written from the perspective of foot Orienteering, but the physiology and basic principles also apply to mountain bike Orienteering (MTB-O), for which the assessments and training would be undertaken on a bike rather than running. In order to target our training appropriately it helps to know what we are trying to achieve. The most obvious of these is being able to sustain a fast running speed, over variable terrain for prolonged periods of time. The key physiological and biomechanical attributes required to do this, are:

1. A high capacity to utilize oxygen (VO2 max) 2. An ability to run at relatively fast speeds without accumulating high concentrations of lactic acid in the muscles 3. An ability to run fluently and economically over orienteering terrain.

Other factors of acknowledged importance are muscle strength and flexibility, but these will not be discussed here in detail.

1. Maximum capacity to utilize oxygen (VO2-max)

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 are commonly expressed as the amount of oxygen being utilized, divided by the person’s body weight in kg. The values expressed in units of millilitres of oxygen / kg body weight /

Our muscles require energy in order to function. We get this energy from the carbohydrates and fat rich foods we eat. Our digestive and biochemical pathways breakdown carbohydrate into glucose, which is then stored as glycogen in the muscles and liver. The fats contained within our food are stored at various sites around the body, including within the muscles and under the skin (subcutaneous). The stores of fats and glycogen contained within the muscles are then used to provide the muscles with energy. The liver glycogen and other fat stores are kept as reserves that can be used if the levels of glycogen and fat within the muscles become depleted. Oxygen is needed to release the energy contained within the fats and carbohydrates stored within the muscles. This oxygen is delivered to the muscles via blood that is sent around the body by the pumping action of the heart. At rest our muscles use relatively small amounts of energy, and consequently only require small amounts of oxygen, typically around 7 ml/kg/min. This is why we have relatively slow breathing and heart rates at rest. These may be in the region of 12 breaths per minute, each of about 0.5 litres of air, giving a ventilation of about 6 litres per minute. This is air going in and out of the lungs, not the actual amount of oxygen getting into the body and being used by the body. Resting heart rates are often in the region of 72 beats per minute, with each beat ejecting about 70ml of blood (a factor known as the stroke volume). This means that at rest, the heart will eject 72 x 70ml of blood a minute, approximately 5 litres. The amount of blood ejected each minute is known as the cardiac output. Of this cardiac output, only about 20% (1 litre) is directed towards the muscles with the remainder being sent to other organs of the body such as the brain and gut. Training causes an increase in the volume of the heart and a concomitant increase in its stoke volume. So in order to achieve the same cardiac output the heart has to beat less often. This is why fit people often have a much lower than average resting heart rate. When we exercise our muscles need more oxygen, with amount being proportional to the intensity of the exercise. So when walking steadily the demand for oxygen may be double that required at rest (~15 ml/ kg/min) and can be met by moderate increases in the rate and depth of breathing, and a moderate increase in heart rate, perhaps up to 90bpm. If we jog our muscles require oxygen at a faster rate (perhaps ~ 25 ml/kg/min) and breathing will increase more dramatically. In order to deliver the additional oxygen, heart rate may increase to 120 bpm and the stroke volume of the heart will increase, causing more blood to be ejected with each beat. A greater percentage of the cardiac output will be sent to the exercising muscles. This is achieved by the selective dilation of the blood vessels supplying the exercising muscles and a constriction of those supplying other organs such as the gut. These changes are in proportion to the strenuousness of the exercise and as we try to run faster our VO2, heart rate and lung ventilation will all increase. Unfortunately these increases cannot go on indefinitely as there is a maximum rate at which our heart can beat and at which we can breath. This means there is a maximum rate at which oxygen can be delivered to the muscles. This is our VO2max. The good news is that our VO2max can be increased by appropriate training, thereby enabling us to sustain faster running speeds, but it will also decline if we stop training for more than a week or two. Male international orienteers usually record VO2max values in excess of 70 ml/kg/min, while female international orienteers tend to have slightly lower values in the region of 60 - 70 ml/kg/min (the reasons for this will be left for another article). These high values will have been achieved through hard training and to some extent fortunate genetics, which have provided them with some natural predisposition towards a high VO2max and hence being a good endurance athlete. Average VO2max values for the general population are much lower, approximately 47 ml/kg/min for males and 40 ml/kg/min for females in the 21 - 34 age group. For active, but non-elite orienteers their VO2max values are likely to be somewhere between those of the general population and the elites. There is a slight decline in VO2max with age, due to a loss of cardiovascular function as part of the ageing process. This goes some way towards explaining why the fastest and fittest orienteers tend to be in the 21 - 34 age group. However, there is also some evidence to suggest that remaining active in sports (such as Orienteering) ameliorates the declines in the agerelated loss in physical capacity commonly seen in the general population. Indeed our fit older competitors will not only have a superior VO2max to their sedentary counterparts of the same age, but are also likely to be superior to sedentary individuals some 20 years their junior. The manifestations of this can be seen through some of our best 50+ orienteers giving some 20 – 30 year olds a run for their money. In the next edition we will look at how VO2max can be related to ability and performance in Orienteering. Professor Steve Bird is Director, Centre for Population Health, Sunshine Hospital, Melbourne. Steve also worked with the GB National Orienteering Squad for over 10 years.