LAUSR

We welcome the opportunity to respond to Armstrong and Welsman’s comment [1] on our recent paper ‘Developing a New Curvilinear Allometric Model to Improve the Fit and Validity of the 20-m Shuttle Run Test as a Predictor of Cardiorespiratory Fitness in Adults and Youth’ [2]. All sport, exercise, and health-related scientists/researchers agree that cardiorespiratory fitness (CRF) is a wellestablished and robust indicator of cardiovascular health, as well as a valuable predictor of all-cause mortality. They also agree that CRF can be accurately assessed by the direct measurement of maximal oxygen uptake ( V̇O2peak) in youth or ( V̇O2max) in adults. V̇O2peak and V̇O2max are commonly regarded as the “gold standard” criterion measure of CRF recorded in the units (mL.kg−1.min−1), recognising that V̇ O2peak (or V̇O2max) must be divided by the entire body mass to best reflect CRF [2–4]. Recently, Welsman and Armstrong [5] have attempted to allometrically scale or adjust V̇O2peak for differences in body mass (M) using some undisclosed function of M to explore the relationship between V̇O2peak and 20-m shuttle run test (20mSRT) speed. They found that the relationship between V̇O2peak and 20mSRT speed was not significant, except for when the entire body-mass related V̇ O2peak (mL.kg−1.min−1) was adopted as the criterion measure, in which case the association between 20mSRT speed and V ̇O2peak became significant [5], a fact that makes the rationale for Welsman and Armstrong’s paper [5] and current letter redundant. Despite its importance, direct measurements of V̇O2max in epidemiological or population studies are rare—primarily due to feasibility issues related to the time to administer the test and the lack of having V̇O2max routinely measured in clinical practice. Therefore, estimating or predicting CRF (i.e., V̇O2max recorded in mL.kg−1.min−1) has emerged as an This is a reply to a letter, which is available at https:// doi. org/ 10. 1007/ s4027902101462-5.