Prof. Kai Savonen
To identify causes of disease, a standard epidemiological study design is to measure a set of variables at baseline and to compare them with health events during a period of follow-up. One modification of this approach is to measure the apparent change in the variable between the first and second baseline visits and then compare the change with health outcomes during the follow-up period. Results from this second design are used to infer that risk factor change is related to changes in health outcomes. Because change is involved, the findings are interpreted as providing stronger evidence of causality than findings from a single measurement although inferences drawn from this kind of study design have also been criticized .
Laukkanen et al. studied a population-based sample of 579 men aged 42 to 60 years at baseline examination and at re-examination 11 years later . Maximal oxygen uptake (VO2max) was measured at both visits using respiratory gas exchange during maximal exercise testing, and the difference (ΔVO2max) between visits was calculated. The mean ΔVO2max was -5.2 mL/min/kg. During median follow-up of 13.3 years after the second examination, 123 deaths (21.2%) were recorded. In a multivariate analysis adjusted for baseline age, VO2max, systolic blood pressure, smoking status, low- and high-density lipoprotein cholesterol and triglyceride levels, C-reactive protein level, body mass index, alcohol consumption, physical activity, socioeconomic status, and history of type 2 diabetes and ischemic heart disease, a 1 mL/min/kg higher ΔVO2max was associated with a 9% relative risk reduction of all-cause mortality (95% confidence interval, 5-13%).
A definite strength of the present study  is that cardiorespiratory fitness was assessed by the gold standard method of measured respiratory gas exchange during exercise. While the findings are in line with previous studies [3,4,5], the present study adds new information, however, by having a longer follow-up as well as a longer interval between repeated exercise tests than in previous studies. The limitation is that changes in other risk factors between examinations were not modelled in survival analysis. The results underline the importance of preventing fitness loss with age for mortality risk reduction. Increased attention needs to be placed on strategies to maintain or improve fitness.
Note: The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology
1. Williams PT. The illusion of improved physical fitness and reduced mortality. Med Sci Sports Exerc 2003;35:736-40.2. Laukkanen JA, Zaccardi F, Khan H, Kurl S, Jae SY, Rauramaa R. Long-term change in cardiorespiratory fitness and all-cause mortality: a population-based follow-up study. Mayo Clin Proc 2016;91:1183-8.3. Erikssen G, Liestøl K, Bjørnholt J, Thaulow E, Sandvik L, Erikssen J. Changes in physical fitness and changes in mortality. Lancet 1998;352:759-62.4. Kokkinos P, Myers J, Faselis C, Panagiotakos DB, Doumas M, Pittaras A, Manolis A, Kokkinos JP, Karasik P, Greenberg M, Papademetriou V, Fletcher R. Exercise capacity and mortality in older men: a 20-year follow-up study. Circulation 2010;122:790-7.5. Lee DC, Sui X, Artero EG, Lee IM, Church TS, McAuley PA, Stanford FC, Kohl HW 3rd, Blair SN. Long-term effects of changes in cardiorespiratory fitness and body mass index on all-cause and cardiovascular disease mortality in men: the Aerobics Center Longitudinal Study. Circulation 2011;124:2483-90.
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