Interpreting Aerobic Fitness in Youth: The Fallacy of Ratio Scaling

Abstract

In this paper, we draw on cross-sectional, treadmill-determined, peak oxygen uptake data, collected in our laboratory over a 20-year period, to examine whether traditional per body mass (ratio) scaling appropriately controls for body size differences in youth. From an examination of the work of pioneering scientists and the earliest studies of peak oxygen uptake, we show how ratio scaling appears to have no sound scientific or statistical rationale. Using simple methods based on correlation and regression, we demonstrate that the statistical relationships, which are assumed in ratio scaling, are not met in groups of similar aged young people. We also demonstrate how sample size and composition can influence relationships between body mass and peak oxygen uptake and show that mass exponents derived from log-linear regression effectively remove the effect of body mass. Indiscriminate use of ratio scaling to interpret young people's fitness, to raise "Clinical Red Flags", and to assess clinical populations concerns us greatly, as recommendations and conclusions based upon this method are likely to be spurious. We urge those involved with investigating youth fitness to reconsider how data are routinely scaled for body size.

Sex-Specific Longitudinal Modeling of Youth Peak Oxygen Uptake

“…Ratio scaling is "convenient and traditional" (13), but it does not have a rigorous scientific rationale, is often not statistically justified, favors lighter individuals, and penalizes heavier (overweight or more mature) youth (45,46,50). Allometric scaling has challenged the "convenient and traditional" interpretation of youth aerobic fitness and indicated that, with body mass appropriately controlled for, there is a progressive increase in peakVO 2 with age in both sexes (48).…”

Associations of cardiorespiratory fitness, adiposity, and arterial stiffness with cognition in youth

“…CRF, estimated by 20-meter shuttle run test (Huang et al, 2015;Westfall et al, 2018) and peak oxygen uptake (VȮ 2peak ) scaled, that is, divided, by body mass (BM) have been positively associated with cognition in some Chaddock, Hillman, Buck, & Cohen, 2011;Chaddock, Hillman, et al, 2012;Davis et al, 2011;Voss et al, 2011), but not all studies (Chaddock, Erickson, Prakash, Kim, et al, 2010;Ruiz et al, 2010) in children and adolescents. However, scaling the measures of CRF by BM has no clear physiological rationale because it may not remove the effect of body size and composition on CRF (Tanner, 1949;Welsman & Armstrong, 2019). VȮ 2peak scaled by lean mass (LM) has been considered the most appropriate method to express CRF (Loftin, Sothern, Takashi, & Bonis, 2016).…”

Expert’s Choice: 2018’s Most Exciting Research in the Field of Pediatric Exercise Science

“…The 20mSRT has been proposed as a suitable and feasible health indicator for international surveillance in children and adolescents (90) and as a means of evaluating physical activity interventions (89). Others have argued that estimating/ predicting peakVO 2 from 20mSRT performance scores is untenable (10), the use of per-body mass ratio scaling is fallacious (10,168), the establishment of thresholds for cardiometabolic risk in children using current criteria is indefensible (9,10), and the use of field test performance estimates of peakVO 2 to evaluate physical activity interventions is specious (12). In this lively debate, Mintjens and colleagues' (107) thoughtful systematic review of longitudinal studies of the influence of CRF in childhood and adolescence on future cardiovascular risk factors is timely.…”

“…Unfortunately, the majority of papers that directly determined peakVO 2 only reported it in ratio with body mass. It has been demonstrated theoretically (169,170) and empirically (9,168) that ratio scaling has neither a sound scientific rationale nor statistical justification. Moreover it is age-and maturity-status-driven fat free mass, not body mass, which is the most powerful morphological influence on peakVO 2 (9).…”