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THE LAST WORD On a high A number of athletics and cycling world records have been set at high-altitude venues, for example during the 1968 Olympic games in Mexico City. Presumably the air is thinner so there is less resistance, enabling them to run or cycle faster. But surely oxygen uptake at altitude is more difficult, so there must be a point at which altitude no longer favours athletes. What is this point and why? And which tracks or velodromes come nearest to it?
■ Mexico City is about 2250 metres
In the short term, athletes will breathe harder, leading to respiratory alkalaemia (increased blood pH), and heart output will increase to circulate the blood faster in an attempt to compensate. After several weeks acclimatisation, the density of blood vessels in muscle and the number of red blood cells both increase, carrying more oxygen to the working muscle. In addition, the kidneys excrete extra bicarbonate to compensate for the alkalaemia caused by rapid respiration and consequent reduction in carbon dioxide levels. These effects will not confer any advantages to the exerciser while they remain at
above sea level so as the questioner correctly points out, air is less dense here because of the “Above about 2500 metres reduced atmospheric pressure – heart rate and oxygen 580 millimetres of mercury delivery are stretched (mmHg) compared with to the utmost” 760 mmHg at sea level – so you can’t make a decent cup of tea because the water boils at 92 °C altitude, though they would as opposed to 100 °C. briefly be of benefit if the athlete This reduced density of the air were to return to sea level. undoubtedly reduces the work At yet higher altitudes, above that needs to be done by a cyclist, about 2500 metres, heart rate and who must cut a path through it, oxygen delivery are stretched to but it poses problems in terms of the utmost, beyond the ability of oxygen availability. Although the body to compensate for them, oxygen always makes up 21 per and work output and athletic cent of the atmosphere, the performance decrease. fractional pressure it exerts in It would appear that reduced Mexico City is only 120 mmHg, air density is the only explanation compared with 160 mmHg at for the performances at the 1968 sea level. This means there is Olympics, though doubtless a noticeable reduction in oxygen athletes undertook extensive pressure at the interface between altitude training. air and blood in the lungs’ alveoli, Ian Jeffcoate leading to mild hypoxia and a Department of Veterinary Cell reduction in the amount of Sciences oxygen delivered to body tissue. University of Glasgow, UK
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
■ Altitude affects both running and cycling in two opposing ways. The power needed to overcome air resistance varies approximately with the velocity cubed and in direct proportion to the density of the air. The important consequences of this are that air resistance is far more significant at high speeds, and that it can be reduced by going to altitude, where the air is less dense. The other effect of thin air is that the athlete receives less oxygen. In a race lasting less than 20 seconds, most of the energy comes from oxygen-independent glycolysis, in which the muscles break down carbohydrates without requiring large amounts of oxygen. This, combined with the sprinters’ high speed, means that sprint race times will be quicker at high altitude. Competitors in longer events depend more on aerobic respiration, so for any running race taking more than about a minute the benefits of altitude are lost. In cycling, the equation differs, because the higher velocity means that up to 90 per cent of the energy expended by a cyclist is used to counter air resistance, so almost all world record times would be faster at altitude. The 400 metres athletics event sits somewhere between a flat-out sprint and an aerobic distance race. A 1991 study in the Journal of Applied Physiology (vol 70, p 399) suggests that the ideal altitude for this event would be between 2400 and 2500 metres, close to that of Mexico City.
Do Polar Bears Get Lonely? A brand new collection ight serious enquiry, brilliant insight and the hilariously unexpected cted Available from booksellers m/ and at www.newscientist.com/ polarbears
Indeed, one of the more enduring records set at the 1968 Olympics was achieved by Lee Evans in the 400 metres. Sam Baylis Malvern, Worcestershire, UK
This week’s questions NET LOSS
What would be the consequences for society if the internet was switched off permanently and without warning? Mike McCullough Preston, UK WHISPERING TREES
Different kinds of tree make different sounds when rustling in a summer breeze. What is the physics behind this? Robin Trew London, UK REPULSIVE ADVERTISING
I have a friend who is so irritated by advertisements breaking into his TV sports viewing that he has vowed to boycott those advertisers’ products. Has anyone studied negative responses to advertising like this, or the possible negative effect of sports-shirt sponsorship? Certain soccer clubs – Real Madrid and Manchester United, for example – are intensely disliked by more people than actually support them. Has sponsoring such a team ever damaged sales or the popularity of the firm whose name appears on its shirts? Alan King Liverpool, UK
THE LAST WORD On a high A number of athletics and cycling world records have been set at high-altitude venues, for example during the 1968 Olympic games in Mexico City. Presumably the air is thinner so there is less resistance, enabling them to run or cycle faster. But surely oxygen uptake at altitude is more difficult, so there must be a point at which altitude no longer favours athletes. What is this point and why? And which tracks or velodromes come nearest to it?
■ Mexico City is about 2250 metres
In the short term, athletes will breathe harder, leading to respiratory alkalaemia (increased blood pH), and heart output will increase to circulate the blood faster in an attempt to compensate. After several weeks acclimatisation, the density of blood vessels in muscle and the number of red blood cells both increase, carrying more oxygen to the working muscle. In addition, the kidneys excrete extra bicarbonate to compensate for the alkalaemia caused by rapid respiration and consequent reduction in carbon dioxide levels. These effects will not confer any advantages to the exerciser while they remain at
above sea level so as the questioner correctly points out, air is less dense here because of the “Above about 2500 metres reduced atmospheric pressure – heart rate and oxygen 580 millimetres of mercury delivery are stretched (mmHg) compared with to the utmost” 760 mmHg at sea level – so you can’t make a decent cup of tea because the water boils at 92 °C altitude, though they would as opposed to 100 °C. briefly be of benefit if the athlete This reduced density of the air were to return to sea level. undoubtedly reduces the work At yet higher altitudes, above that needs to be done by a cyclist, about 2500 metres, heart rate and who must cut a path through it, oxygen delivery are stretched to but it poses problems in terms of the utmost, beyond the ability of oxygen availability. Although the body to compensate for them, oxygen always makes up 21 per and work output and athletic cent of the atmosphere, the performance decrease. fractional pressure it exerts in It would appear that reduced Mexico City is only 120 mmHg, air density is the only explanation compared with 160 mmHg at for the performances at the 1968 sea level. This means there is Olympics, though doubtless a noticeable reduction in oxygen athletes undertook extensive pressure at the interface between altitude training. air and blood in the lungs’ alveoli, Ian Jeffcoate leading to mild hypoxia and a Department of Veterinary Cell reduction in the amount of Sciences oxygen delivered to body tissue. University of Glasgow, UK
Questions and answers should be concise. We reserve the right to edit items for clarity and style. Include a daytime telephone number and email address if you have one. Restrict questions to scientific enquiries about everyday phenomena. The writers of published answers will receive a cheque for £25 (or US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by readers in any medium or format.
New Scientist retains total editorial control over the content of The Last Word. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK, by email to [email protected] or visit www.last-word.com (please include a postal address in order to receive payment for answers). For a list of all unanswered questions send an SAE to LWQlist at the above address.
■ Altitude affects both running and cycling in two opposing ways. The power needed to overcome air resistance varies approximately with the velocity cubed and in direct proportion to the density of the air. The important consequences of this are that air resistance is far more significant at high speeds, and that it can be reduced by going to altitude, where the air is less dense. The other effect of thin air is that the athlete receives less oxygen. In a race lasting less than 20 seconds, most of the energy comes from oxygen-independent glycolysis, in which the muscles break down carbohydrates without requiring large amounts of oxygen. This, combined with the sprinters’ high speed, means that sprint race times will be quicker at high altitude. Competitors in longer events depend more on aerobic respiration, so for any running race taking more than about a minute the benefits of altitude are lost. In cycling, the equation differs, because the higher velocity means that up to 90 per cent of the energy expended by a cyclist is used to counter air resistance, so almost all world record times would be faster at altitude. The 400 metres athletics event sits somewhere between a flat-out sprint and an aerobic distance race. A 1991 study in the Journal of Applied Physiology (vol 70, p 399) suggests that the ideal altitude for this event would be between 2400 and 2500 metres, close to that of Mexico City.
Do Polar Bears Get Lonely? A brand new collection ight serious enquiry, brilliant insight and the hilariously unexpected cted Available from booksellers m/ and at www.newscientist.com/ polarbears
Indeed, one of the more enduring records set at the 1968 Olympics was achieved by Lee Evans in the 400 metres. Sam Baylis Malvern, Worcestershire, UK
This week’s questions NET LOSS
What would be the consequences for society if the internet was switched off permanently and without warning? Mike McCullough Preston, UK WHISPERING TREES
Different kinds of tree make different sounds when rustling in a summer breeze. What is the physics behind this? Robin Trew London, UK REPULSIVE ADVERTISING
I have a friend who is so irritated by advertisements breaking into his TV sports viewing that he has vowed to boycott those advertisers’ products. Has anyone studied negative responses to advertising like this, or the possible negative effect of sports-shirt sponsorship? Certain soccer clubs – Real Madrid and Manchester United, for example – are intensely disliked by more people than actually support them. Has sponsoring such a team ever damaged sales or the popularity of the firm whose name appears on its shirts? Alan King Liverpool, UK