Cardiorespiratory fitness To the editor: I am not satisfied that Bailey et al have provided us with the "specific facts and comprehensive data" mentioned in the introduction of their paper "A current view of Canadian cardiorespiratory fitness" (Can Med Assoc 1 111: 25, 1974). The authors might have pointed out how the "Swedish standards" for aerobic power advanced by Irma Astrand in 1960 were calculated. The average range was the mean ± one standard deviation of the measured maximal oxygen uptake values from a group of women aged 20 to 65 years who had actively participated in an organized exercise class since leaving school - hardly average normals! The male values were obtained from a group of draymen and men attending fitness classes, not only in Stockholm but also in Philadelphia! The values for low, average and good in this publication and in the American Heart Association booklet are guidelines for fitness; they are not population norms and they have no proved correlation to health, longevity, presence of coronary disease, or even performance in most sports carried out in middle age. There is no specific information justifying the application of this grading system to a population. In presenting her standards Astrand stated "A person's capacity should be related to his occupation . and degree of physical training". The Toronto values were based on the results of a submaximal step test that has not been compared with the ergometer for values over the necessary range of fitness, age and sex. A comparison of different populations is possible only when subjects are chosen in the same manner and tested in the same manner. The prediction of aerobic

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power by the authors' method is subject to considerable inaccuracy, and Rowell, Taylor and Wong (J Appi Physiol 19: 919, 1964) found values as much as 40% too low. If this degree of error can occur in the controlled environment of a research laboratory, even greater errors are likely in a mass screening program. The prediction of aerobic power is highly dependent on methodology. For example, a group of 55-year-old Winnipeg men had mean predicted values of 23 ml/kg *min by c.rgometer and 34 ml/kg *min with the Bruce treadmill test, a 48% difference. These problems with predictive methods make it essential that identical tests be used when populations are compared. When aerobic power is related to body weight the obese individual usually scores low. The degree of unfitness of a population as measured on an ergometer is therefore correlated to the level of obesity. To get around this, Astrand obtained normal values 'by dividing absolute oxygen uptake by normalized weights of 58 kg for women and 72 kg for men, a process that increases the values in most populations. When measuring cardiorespiratory fitness it may be 'more appropriate to use lean body mass to normalize for body size and to eliminate obesity and a dominant third variable. Even though the metabolic demands of running and walking are related to body weight, aerobic power per kg of body weight can be just an index of obesity. I would agree that many Canadians are less fit than they should be, but the same likely applies to citizens of most countries. Bailey et al have not provided us with any satisfactory evidence that Canadians are less fit than any other population, or less fit than in 1966. The authors' method of presenting their data no doubt serves the needs of Health and Welfare Canada, a department that is currently hoping to reduce the high cost of medical care by promoting personal fitness. This objective is admirable, but the readers of

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CMAJ should expect more objective reporting and more critical and accurate editorial comment. The Participaction television commercials give us more than enough propaganda. There are even a few Canadian 60-year-olds who are just as good as the average 25-year-old Swede. GORDON R. CUMMING, MD

Head, section of cardiology Children's centre Health Sciences Centre winnipeg, Man.

To the editor: It is difficult to dispute many of the "motherhood" issues raised by Dr. Cumming. Neither Dr. Bailey nor I would argue the point that there remains a need for more specific facts and comprehensive data. The testing of what was a close approximation to a random sample of the Saskatoon population provides a rather clear picture of the situation in one part of Canada, but, as Dr. Cumming argues so forcibly, there is a need to apply the same methodology to random samples from other parts of our nation and from other countries such as Sweden. Eventually such an ideal study may be carried out, but in the meantime it is necessary to offer advice both to patients and to government on the basis of existing information. We fully realize the limitations of Irma Astrand's "norms..; nevertheless, as a Swedish expert she considered these appropriate standards to recommend to her people in 1960. Our report merely indicated that the Saskatoon population fell short of these widely known standards and also those the American Heart Association is currently recommending to its patients. We were careful to stress that these were recommendations and that the somewhat lower AHA figures probably provided a more appropriate fitness objective for the Canadian population than would the Astrand tables. We were well aware that there can be difficulties in comparing step test and bicycle ergometer data, and our

Letter: Cardiorespiratory fitness.

Cardiorespiratory fitness To the editor: I am not satisfied that Bailey et al have provided us with the "specific facts and comprehensive data" mentio...
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