6.5. Cardiorespiratory fitness of young adults (V)

6.5.1. Measurement of cardiorespiratory fitness

The traditional Åstrand-Ryhming step test (Åstrand & Ryhming 1954) was chosen for this study as an objective exercise test because stepping is a familiar exercise mode to most people, and the method is inexpensive, portable and requires little calibration. The shortening of the original test from five minutes to four minutes was done to save the total time of 100 hours in the testing of 6,000 subjects. In our study, a relatively high mean heart rate after the stepping and a small heart rate difference between the third and the fourth minutes indicated that this step test was long enough, and the intensity was high enough for most of the subjects to result in a steady state at the suggested heart rate level of 125–170 beats/min (Åstrand & Ryhming 1954).

Model 4 was the most accurate of the four models tested and was therefore used to calculate VO_2peak for those who participated in medical examination. The non-exercise Model 3 was used to calculate VO_2peak for those who did not participate in step test in medical examination but provided data on their physical activity and body dimensions by postal inquiry. Model 3 seemed to be as accurate as the objective Model 2 in predicting VO_2peak. Non-exercise models have been reported to be as accurate as submaximal exercise testing (Jackson et al. 1990) and seem to be a reasonable alternative when objective exercise testing is not possible, but an estimation of VO_2peak is needed. In epidemiological studies of this kind, non-exercise models provide a method for replacing missing data for those who did not participate in the exercise test, but filled out the questionnaire with data about their physical activity level and anthropometrics.

Model 2 was formed by adding BMI into Model 1, which increased the accuracy of the estimation. Model 2 is suggested to be used when there is a need to calculate VO_2peak objectively for the whole cohort population, for instance when an independent effect of both physical activity and cardiorespiratory fitness on certain outcome is evaluated.

VO_2max was also calculated by the traditional Åstrand nomogram (Åstrand 1960, Åstrand & Ryhming 1954) based on body weight and heart rate after four minutes’ stepping, with a correction factor of 0.935 for age (Åstrand 1960). The Åstrand nomogram overestimated the VO_2max notably, 5 ml·kg^–1·min^–1 in males and 10 ml·kg^–1·min^–1 in females. Therefore the development of more accurate prediction models for the present study population was necessary.

6.5.2. Reference values of cardiorespiratory fitness

Reference values for cardiorespiratory fitness have usually been formed on the basis of relatively small (Shvartz & Reibold 1990) and, most probably, selected samples. Subjects who agree to participate in a maximal exercise test may be selected by their relatively high level of physical activity and fitness. In such cases, the reference values may be too high when compared with actual fitness of the population. In the present study, the subjects in the laboratory sample which performed the maximal exercise test had slightly higher levels of fitness and physical activity than the whole cohort population. By projecting the model-predicted values to a highly representative population of 4,073 males and 4,368 females, we assumed to have more representative reference values compared with the slightly selected laboratory sample.

The present mean values of VO_2peak for 31-year-old males and females were very similar (± 1 ml·kg^–1·min^–1) compared with the norm values presented by Shvartz & Reibold (1990) which are generally used in Finland. A low level of cardiorespiratory fitness is associated with an increased risk of cardiovascular diseases and mortality (Blair et al. 1989, Laukkanen et al. 2001, Talbot et al. 2002). Especially the least fit 20% of males and the least fit 40% of females had a higher mortality risk than more fit males and females in the follow-up study of about 10,000 males and 3,000 females (Blair et al. 1989). The present reference values were also very similar to the 20^th percentiles of VO_2max provided by Institute of Aerobics Research in USA for males and females aged 20–29 years and 30–39 years (Franklin et al. 2000), with the exception that the limit for the least fit 20% was at about 2–3 ml·kg^–1·min^–1 higher in our data, which suggests that the present population of Finnish males and females includes fewer persons with a very low fitness level.

6.5.3. Participation in brisk exercise and cardiorespiratory fitness

Our result showed a linear dose-response relationship between the frequency of participation in brisk exercise and cardiorespiratory fitness. A similar dose-response relationship was also observed among overweight and obese males and females, although the level of VO_2peak related to body weight was naturally lower in persons with increased BMI. At age 31, very low levels of VO_2peak were associated with a combination of infrequent participation in brisk exercise and increased BMI. On the other hand, obese persons may have a relatively high level of cardiorespiratory fitness if they are physically active. Persons with BMI equal to or greater than 30.0 had generally VO_2peak very close to the average, if they participated in brisk exercise four times a week or more.

Regular participation in brisk exercise is important in terms of maintaining and enhancing cardiorespiratory fitness. Gathering a large total amount of both light and brisk physical activity is valuable in terms of weight management, and therefore indirectly enhances cardiorespiratory fitness as well. Regular physical activity, a high level of cardiorespiratory fitness and maintaining normal weight are all important in terms of overall health.

These reference values can be used in fitness testing and physical activity counseling. Figure 9 demonstrates how the levels of physical activity and obesity are both strongly associated with cardiorespiratory fitness. By comparing the fitness test results to these reference values one can deepen the interpretation of the results and evaluate the level of physical activity generally needed to achieve the wanted level of fitness.