TRAINING

Warm Up: more than just about feeling warm

Introduction

Warming up before an orienteering event is an important part of your race preparation and failing to do so can put unnecessary strain on your body, which may adversely affect your performance and perhaps increase the risk of injury.

Warming up is not just about feeling warm, although this is one of the consequences and benefits. A warm-up is important because of the considerable physiological adjustments your body has to make when you go from being at rest to running. To illustrate this point I have put some indicative figures in Table 1. These are illustrative, as the exact values will vary from one person to another, as well as being affected by how fast you run, how fit you are and your body size, but nevertheless they do indicate the magnitude of the responses your body has to produce. As with previous articles the text of this piece is worded in the context of Foot Orienteering and running, but the same principles apply to Mountain Bike Orienteering, or indeed any strenuous exercise.

Your body at rest

At rest your body needs relatively small amounts of oxygen, typically in the region of around 0.6 litres a minute, or if we represent this in terms of body weight, about 10 millilitres of oxygen per kilogram of body weight per minute. This is supplied to the muscles and other organs of the body by breathing gently to oxygenate the blood and by maintaining a steady heart rate that delivers the blood around the body. Typical values may be in the region of 12 breaths per minute, each of about 0.5 litres of air, giving a lung ventilation of about 6 litres per minute. At rest the heart will deliver this oxygenated blood with a heart rate of around 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 around 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% is directed towards the muscles, since they are at rest and do not require much oxygen. The remainder is sent to other organs of the body such as the brain and gut.

Your body during exercise

When you exercise your muscles need more oxygen. When you walk the increased demand for oxygen is slight and can be met by small increases in the rate and depth of your breathing, accompanied by a slight increase in your heart rate, perhaps up to 90bpm. If you jog there is a greater demand for oxygen and hence your breathing will increase more dramatically and your heart rate may rise to 120 bpm. In addition to this, the stroke volume of your heart will also increase, causing more blood to be ejected with each beat of your heart and, furthermore, a greater percentage of your cardiac output will be sent to your exercising muscles. This is achieved by the selective dilation of the blood vessels supplying your exercising muscles and a constriction of those supplying other organs such as your gut.

All these of changes are in proportion to the strenuousness of the exercise. So running at a steady pace requires a greater oxygen uptake and hence greater responses by the cardiorespiratory system than gentle jogging. Indeed, when working close to a maximum sustainable running speed, the sort of speed that can be maintained during an event, very large responses are required. Typical figures for a fit elite orienteer may be a heart rate of 165 - 180 bpm, a stroke volume of 120 – 140 ml per beat, a cardiac output of 18 - 25 litres per minute, 75-80% of the cardiac output being directed to their exercising muscles and a ventilation of 130 - 160 litres of air per minute, with a resultant oxygen utilisation of 60 – 70 ml/ kg/min. (Note: the figures given here in the text are for a young, fit, male. The exact values will depend upon the size, age and gender of the individual, as well as their level of fitness.)

Why warm up?

The reason why a warm up is a good idea, is because your body cannot instantaneously go from a resting state to that which is optimal for hard running. It takes time for it to reach a state whereby you can comfortably sustain a good running speed without becoming fatigued. So a warm-up involving a gradual increase in speed from jogging to running will elevate your heart’s cardiac output and your lungs’ ventilation, promote a greater blood flow to your muscles and increase the temperature of your muscles, which along with other biochemical changes will enhance their extraction of oxygen from the blood as it passes through them and promote its effective utilisation. It therefore prepares your body for the hard running you are about to do. Fortunately the benefits of a good warm-up are retained for several minutes after it’s been completed, so you won’t lose any benefits whilst you’re in the start boxes.

The consequence of trying to run hard without a prior warmup is that your body is not prepared for the level of activity being asked of it. For example it’s not able to deliver the amount of oxygen to the muscles and the muscles are not in their optimal physiological state to make use of it. Consequently your body will resort to supplementary processes in order to produce the muscle power needed to run at speed. These are anaerobic processes such as the use of phosphocreatine and the anaerobic metabolism of carbohydrates. The consequences of the latter being an accumulation of lactate and an associated feeling of fatigue. In practical terms what this means is that if you start your event without a prior warm-up you will feel fatigue when running at speeds that you would find relatively easy and comfortable if you had warmed up before hand. It’s also illustrated by a feeling that you may have experienced on occasions when it took you ‘a few controls to get going’. Which was probably at the point when your body’s physiological responses (cardiac output, ventilation, blood flow and oxygen utilisation) finally managed to get to the level you’d been asking of them, as well as having to get rid of any fatiguing chemicals that you’d accumulated during the first few minutes. and effectively adjust each stride as you try to run over uneven terrain and are constantly having to deal with unpredictable foot placements. Finally a warm-up can be used to help you focus and prepare mentally for the event as you gather your thoughts together whilst jogging to the start.

What’s the best warm up?

The specific composition of a warm-up is a matter of individual preference, but it is likely to include a combination of some loosening exercises, steady jogging/running (or cycling in the case of MTBO) and some stretching exercises. It needs to be at an intensity that will gradually elevate your cardiorespiratory responses to the levels they need to reach in the first few minutes of your course as well as ensuring your muscles reach an optimal working temperature. Although you may work quite hard during your warm-up, you should recover from it in the few minutes you have at the start whilst waiting to begin your event, and you should not feel fatigued from it as you set off towards the start triangle. Specific suggestions for what to include in your warm-up will be presented next time.

Conclusions

The benefits of warming up

There is strong research evidence that a warm-up benefits performance, although as Bishop (2003) emphasises in his review, it needs to be of the right duration and intensity to prepare the body, without being so severe that you feel fatigued at the start. So ideally having completed your warm-up and having had a few minutes to recover before the start you should feel ready when you get to your start time. Likewise the preparation needs to attain the balance between warming up the muscles to their optimal level and raising your body temperature by too much. So weather conditions may dictate the length of your warm-up, and if it’s hot you should jog in the shade to try and promote the desired cardiorespiratory responses without unduly raising your temperature by too much.

A warm-up may also reduce the risk of injury and is advocated by the vast majority of coaches and experts. Although it is acknowledged that the research evidence in support of this practice is inevitably largely anecdotal and/or based on logical reasoning, since large randomised controlled trials that involve a perceived risk of injury are clearly unethical. Another possible benefit relating to warming up is the fact that nerve impulses travel more quickly when you are warm, which may help you automatically

System Factor

• There is strong research evidence that a warm-up can benefit your performance. • A warm-up is needed to prepare your cardiorespiratory system and muscles for the demands of running. • It can help to beneficially elevate your muscle temperature on a cold day. • It may reduce the risk of injury. • It can help you to prepare mentally, just before the start.

Reference

Bishop D (2003). Warm Up II. Performance changes following active warm-up and how to structure a warm-up. Sports Medicine, 33(7): 483-498.

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.

Rest Running Change

Ineka Booth (ACT) during the Prologue at Easter. Photo: Bob Mouatt

Heart Heart rate (bpm) 60 - 70 140 - 170 x2.5

Stroke Volume (ml): the amount of blood ejected by the left ventricle of the heart each beat 50 – 70 100 - 140 x2

Cardiac Output (litres): the amount of blood ejected by the left ventricle of the heart each minute 3 - 5 14 - 24 x5

Lungs Breaths per minute ~12 ~30 x2.5

Volume of air each breath (litres) 0.4 – 0.7 3 - 5 x7

Air ventilated by the lungs each minute (litres)

5 - 8 90 - 150 x18

Blood flow % Cardiac output to muscles ~20% ~75% x3.5

Blood flow to muscles (litres) ~1 ~15 x15