Comment on: Beck ON, Kipp S, Byrnes WC, Kram R. Viewpoint: Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance. J Appl Physiol, in press 2017. Title: Quantification of exercise intensity as energy expenditure: reliability and units of measurement. Richard C Blagrove 1,2 Glyn Howatson 2,3 Philip R Hayes 2 1 Faculty of Health, Education and Life Sciences, Birmingham City University, Birmingham, United Kingdom. 2 Department of Sport, Exercise and Rehabilitation, Northumbria University, Newcastle-upon-Tyne, United Kingdom. 3 Water Research Group, Northwest University, Potchefstroom, South Africa. Corresponding author: Richard Blagrove Email: richard.blagrove@bcu.ac.uk Address: Department of Sport and Exercise Science, Faculty of Health, Education and Life Sciences, School of Health Sciences, Birmingham City University, City South Campus, Westbourne Road, Edgbaston, Birmingham, B15 3TN, United Kingdom Word count: 246 words