Ok, now I am going to be lazy and just fool around a bit........partly because I was on the IDT for 45min at 100% of max theoretical HR (174bpm) ( (and a bit more ). Interesting (again): THE SURPRISING HISTORY OF THE “HRmax=220-age” EQUATION. Robert A. Robergs, Roberto Landwehr. JEPonline. 2002;5(2):1-10. The estimation of maximal heart rate (HRmax) has been a feature of exercise physiology and related applied sciences since the late 1930’s. The estimation of HRmax has been largely based on the formula; HRmax=220-age. This equation is often presented in textbooks without explanation or citation to original research. In addition, the formula and related concepts are included in most certification exams within sports medicine, exercise physiology, and fitness. Despite the acceptance of this formula, research spanning more than two decades reveals the large error inherent in the estimation of HRmax (Sxy=7-11 b/min). Ironically, inquiry into the history of this formula reveals that it was not developed from original research, but resulted from observation based on data from approximately 11 references consisting of published research or unpublished scientific compilations. Consequently, the formula HRmax=220-age has no scientific merit for use in exercise physiology and related fields. A brief review of alternate HRmax prediction formula reveals that the majority of age-based univariate prediction equations also have large prediction errors (>10 b/min). Clearly, more research of HRmax needs to be done using a multivariate model, and equations may need to be developed that are population (fitness, health status, age, exercise mode) specific. Robergs2.pdf Interesting that so much focus is also placed of training heart rate, and not on rate of HR recovery or even resting HR dynamics over a period......which is utilized to indicate training status. But then also, say you become fitter and your bone and muscle density increases while for fat percentage decrease.................but wait, your BMI increase to severely obese values.......of brother, you are a high risk for the insurance company and you need a premium adjustment. Oh....the IDT session for this unfit, overweight, abrasive, obnoxious buffel......interval work for 45min.....no warm-up or cool-down.......just balls to the wall while listening to ACDC and Def Lepard. Sorry for the stone age electronics and display.......I am old school and it is my birthday one of these days. As you were, carry on......