Fitness '97, February 1997
If you're recovering from a major illness or taking medication regularly, subtract ten.
If you don't currently exercise, either by choice or because of injury, or if you're prone to catching colds, subtract five.
If you've been exercising consistently for two years or less, or for a longer period but not as regularly, stick with 180 minus your age.
If you've been putting your body through regular paces without injury for more than two years, add five.
Allen figures his maximum aerobic heart rate this way: 180 - 39 + 5 = 146. Oops, there's another factor we forgot to mention: If you've won the Hawaii Ironman six times or more, you add four ticks-making Allen's aerobic maximum an even 150 beats per minute.