Exercising within your target heart rate range will not only ensure an effective workout in terms of a fat and glucose burn, but also will provide an important aspect of exercise safety.

Key Phrases:

Resting heart rate: the heart rate at which you are at resting metabolic function. As in your heart rate upon waking luxuriously on a Saturday morning, and before moving much.

Pre-exercise heart rate: the heart rate immediately prior to initiating an exercise session. This heart rate will be faster than the resting heart rate.

Target heart rate range: the heart rate range between which you will gain a safe and effective exercise workout.

To calculate your individualized target heart rate range, you will need to find your pulse to determine your pre-exercise heart rate. Start with your index and middle fingers and place them gently on either your radial or carotid artery; either the artery that lies 3 inches below your thumb (radial), or on the neck, 1 ½ inches from your Adam’s apple (carotid). Find and feel your heartbeat, look at a second hand watch, then count how many heartbeats you feel in 15 seconds; multiply that number times 4, to know your one-minute heart rate. Example: 17 heartbeats felt in 15 seconds equates to a heart rate of 68.

My preference to calculate target heart rate range is to use the Karvonen Formula. As opposed to the standard 220 – your age formula, the Karvonen takes into account your pre-exercise heart rate, affording you the opportunity to dial in a specific and individualized target heart rate range for your exercise session.  The formula is as follows:

220 – age – pre-exercise heart rate x 65%, x 85% + pre-exercise heart rate

For a 50-year-old woman with a pre-exercise heart rate of 68, it looks like this:

220 – 50 = 170 (max heart rate)

– 68 = 102

x 65% = 66;              x 85% = 87

+ 68 = 134;               + 68 = 155

target heart rate range = 134 – 155

Several external factors may affect heart rate: hydration status, level of fitness, adrenaline (stress) response, certain medications, and caffeine to name a few. Someone who is new to exercise and therefore may be “deconditioned” (less than optimal fitness level), will likely note that their resting, pre-exercise, and exercise heart rate is higher than what is age predicted.

When writing an exercise prescription for this 50-year-old woman beginning an exercise program, we would start at the 65% level of exercise intensity, so that her exercise heart rate stays around 134 beats per minute. As she works up to 5 – 6 exercise sessions per week over the course of 6 – 8 weeks, her exercise prescription will be modified, allowing her to increase her exercise intensity to work at higher heart rate response, at 155 beats per minute.

As the heart muscle becomes more conditioned, each contraction becomes more efficient, so that ultimately fewer heartbeats per minute are required to pump the same volume of blood. In the real world this translates as a lowered resting and pre-exercise heart rate, as well as a lowered exercise heart rate response, ultimately allowing the exercising person to increase their workout to achieve a higher heart rate response.  Conditioning takes several months to achieve.

Another valuable aspect of determining the effectiveness and safety of your exercise program is to assess your Rate of Perceived Exertion (RPE).  This is a subjective response, and it basically allows you to assign a numerical value to your exercise intensity. I use a modified scale of 1 – 10, with 1 being the amount of energy required to sit up in a chair, and 10 being a marathon effort. An RPE of 3 is moderate, 4 is somewhat hard, and 5 is hard. 3 – 5 is the range of perceived exertion that I include in an exercise prescription.  (6 is very hard, 7 is very, very hard, and so on). An RPE of 6 and above is correlated with an anaerobic level of exercise; anaerobic means “without oxygen”—oxygen feeds the muscles and aids in fat burning, thus the presence of oxygen is favorable while exercising (and most other times as well!).

As a side note, athletes who are conditioned to train for competition are often at their anaerobic threshold; for most of us who exercise to stay in shape and optimize our health, maintaining an aerobic exercise program is suggested.

Future articles will address additional exercise considerations: frequency, type, duration, and how to mix it all up.

Have at it!