Fitness and Fatness as Health Markers through the Lifespan: An Overview of Current Knowledge

Abstract

There is an increasing body of evidence supporting that both fitness and fatness levels relate to current and future individuals' health status. In this article, we discuss the meaning of fitness and fatness/obesity, and make an overview of what is currently known about fitness and fatness as potentially modifiable risk factors related to health and disease from preschool children to older adults. We describe the methods available for fitness assessment in each age group, providing reference/criterion values when available. Most of the existing previous reviews are focused on specific age groups with the advantage of allowing more in-depth analysis of the evidence, but the disadvantage of losing the overall understanding of the fitness and fatness binomial through the human lifespan, which is the ultimate goal of the present article.

Keywords: Physical fitness; adolescents; adults; cardiorespiratory fitness; children; fatness; health; obesity; older adults; preschool.

Fig 1.

Graphical illustration of the key concepts and focus of the present article.

Fig 2.

Graphical illustration of physical activity- and fitness-related concepts. PA = physical activity; METs = metabolic equivalents.

Fig 3.

Graphical illustration of the associations of BMI, BF%, FMI, and FFMI with CVD mortality and physiological explanation. Reproduced with permission from Ortega et al.^[5] BMI = body mass index, BF% = Body fat percent, CVD = cardiovascular disease; HR = Hazard Ratios; LV = left ventricular; RV = right ventricular.

Fig 4.

Evidence-based fitness test batteries to assess fitness in preschoolers, children, and adolescents. Adapted from Ruiz et al.^[12] and Ortega et al.^[7] with permission of the publisher. It is important to note that the fitness tests included in the PREFIT battery have major adaptations so that can be used in preschool children. As an example, the 20 m shuttle run test initial speed was reduced from 8.5 to 6.5 km/h, because the original speed was too difficult for 3–5 year olds. It is important to note that the standing on 1 leg test was selected based on the systematic review, but later testing in preschool children has shown poor reliability, being therefore its usefulness in this age group highly questionable (this is represented in the figure with the symbol “?”). Detailed information on the adaptations, practical consideration, and reliability of the tests included in the PREFIT battery has been published elsewhere.^[8] The standing on 1 leg test has shown a poor reliability in this population, being therefore highly questionable its usefulness in this age group. ALPHA = Assessing Levels of PHysical Activity and fitness; BMI = body mass index; PREFIT = assessing FITness in PREschoolers.

Fig 5.

Hazard ratios (95% CI) of incident CVD risk factors by combined categories of changes in CRF and percentage body fat. Reproduced with permission from Lee et al.^[23] CI = confidence interval.

Fig 6.

Illustration of the Fat but Fit paradox in relation with CVD mortality and all-cause mortality in men and women. Reproduced from Ortega et al.,^[19,25] with permission of the publishers. Unfit-fit was categorized as below-above the age- and sex-specific percentile 20th within each original study. BMI = body mass index; CVD = cardiovascular disease.

Fig 7.

Illustration of the Fat but Fit paradox in older adults. Figure based on the data shown in Table 7 of the article published by Sui et al.^[29] Obesity was defined based on BMI using the standard cut-points (BMI ≥ 35 kg/m² to define severe obesity) (A), based on BF% using the cut-point of ≥ 25% and ≥ 30% for men and women, respectively (B), and based on waist circumference ≥ 102 cm and ≥ 88 cm for men and women respectively (C). Unfit-fit was categorized as below-above the age- and sex-specific percentile 20th within each original study. BMI = body mass index; BF% = body fat percent.