Calculating Maximum Heart Rates by AgeDate: 08/08/2005 at 17:46:05 From: Alex Subject: Heart Rate Find the heart rate of a 15 year old at 85% intensity. I'm not sure if I am supposed to add or multiply. Date: 08/08/2005 at 22:51:44 From: Doctor Wilko Subject: Re: Heart Rate Hi Alex, Thanks for writing to Dr. Math! While the true way of measuring maximum heart rate (MHR) probably involves stress tests done by cardiologists/exercise physiologists, there are formulas we can use as rules of thumb to estimate our maximum heart rates, which in turn will allow us to calculate our target/training heart rates (in this case, 85%). A well-known formula that I've seen used for determining maximum heart rate is A) 220 - (age) = MHR (in beats per minute) The true maximum heart rates of individuals probably aren't linear as this formula suggests. This formula may overestimate the MHR of younger people and underestimate the MHR of older people. The author of this website, Maximum Heart Rate http://www.brianmac.demon.co.uk/maxhr.htm also references these formulas: B) 206.3 - (0.711 * Age) = MHR C) 217 - (0.85 * Age) = MHR While formula A above will probably give you the answer you're looking for, let's calculate the 85% intensity (of MHR) from all three formulas to see how they compare. To do this, we'll calculate 1. The MHR using each of the three formulas above, and then 2. Take 85% of each MHR Formula A: 220 - 15 = 205 (MHR) 205 * 0.85 = 174.25 (85% of MHR) ====== Formula B: 206.3 - (0.711 * 15) = 195.64 (MHR) 195.64 * 0.85 = 166.29 (85% of MHR) ====== Formula C: 217 - (0.85 * 15) = 204.25 (MHR) 204.25 * 0.85 = 173.61 (85% of MHR) ====== Using these three formulas as an estimate of an average 15-year-old's maximum heart rate, you can say that his/her 85% intensity level is somewhere between 166 and 175 beats per minute. Notice that in each case we found 85% by multiplying the MHR by 0.85, which is the easiest way to find a percent of a number. Another useful and probably more accurate formula for determining one's training heart rate is the Karvonen Formula, which is based on an individual's resting heart rate. For more on this, check out this link, Understanding Your Training Heart Rate http://www.primusweb.com/fitnesspartner/library/activity/thr.htm And here are a couple more links you might find interesting: The Walking Site http://www.thewalkingsite.com/thr.html Measuring Exercise Intensity http://www.ginmiller.com/gmf04/artinfo/targetheart1.htm Does this help? Please write back if you have further questions. - Doctor Wilko, The Math Forum http://mathforum.org/dr.math/ |
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