Question of the Day 4 June: Target Heart Rates

From Cyndie in Kentucky this week –

…A friend working with a trainer has been telling me that walking isn’t enough of a workout to help me drop some weight. Her trainer says that you have to get your heart rate up really high to make fat burn, and told her to take my age (42) from 220 to get my target heart rate. That sounds really high and is hard for me to do walking, this doesn’t sound right to me…

Cyndie, appreciate the opportunity today to answer your question, and you’re right, the information passed on from your friend’s trainer is actually not correct.

The rule of thumb the trainer appears to have suggested you use, the 220 – your age calculation, is a commonly used rule of thumb (for example, used here by the Mayo Clinic) to estimate an individual’s Maximum Heart Rate target. There are of course potential flaws in using a rule of thumb calculation here, as there are of course other issue that may modify the results, such as medications you’re taking (i.e. beta blockers), your overall health, your overall fitness level, your fitness history (how long have you been working out and what types of exercise have you done), your injury history, and more.

Using the rule of thumb above, your target maximal heart rate would be 178. But that’s not really the number you need to be thinking about…

You Really Want to Your Use Your Heart Rate Guides to Work Aerobically to Burn Fat

When you go through your day completing most of your routine tasks (clinically called activities of daily living), you’re not exercising anywhere near your maximal heart rate; your body is working aerobically to burn fuels efficiently using oxygen. In the right setting metabolically, that includes burning fat as fuel, which from your question is what you’re trying to do.

If you significantly up the intensity of your effort (exercise or really aggressive ADLs), there is a point at which your body is forced to change over to another fuel processing system – anaerobic work – think of this like the maximal effort you might make when doing repetitive sprints as part of a training program. That’s stressful, inducing the production of stress hormones (which among other things slows down fat burning), and can lead to overtraining, excessive inflammation, and injury.

So you really want to know your maximal aerobic training heart rate.

Thankfully, a host of smart men and women have done the hard work and derived some fairly easy calculations to discover that number. My favorite is Dr. Maffetone’s 180 Formula.

Simply put, you subtract your age from 180, and modify that number using the four criteria he’s listed at the link above. From what you’ve shared, it appears your calculations would be 180 – 42 = 138, with another 5 subtracted as you’re just getting back into training (Dr. Maffetone’s modifier [b]), making your maximal aerobic training target a heart rate of 133.

Note that’s the maximal suggested target rate, and brisk walking, or walking hills should readily get you in the range of 85% to 90% of your maximal aerobic target, and will very likely aid in burning fat, which you’ve stated is your primary goal.

These numbers are of course rule of thumb guidelines, and must be modified specifically to match your own unique and specific health and fitness. Keep up the good work and get out there walking – I’m a huuuuuge fan of walking as a fitness and weight loss tool.