I recently purchased an exercise machine and am beginning to work out. It has a heart rate calculator. What target heart rate am I seeking? T. M.

Dear T. M.: It is generally possible to work our effectively and safely by observing three simple rules:

• Move at a pace that you can maintain for 20 to 30 minutes. If you are huffing, puffing, and need to stop 5 or 10 minutes in to the activity lower your pace.

• Do not press so hard that you cannot carry on a conversation or count out loud to 10 without feeling completely out of breath.

• If you wake up the next day feeling like a rusty tin man who’s been left out in the rain, back off your pace.

To answer your question specifically, the formula to use is 220 minus your age times 65 %. For example a 45 year-old would optimally exercise at a heart rate of 220 – 45 X .65 = 114 beats per minute. -Dr. Peterson