So for a 50-year-old, maximum heart rate is 220 minus 50, or 170 beats per minute.At a 50 percent exertion level, your target would be 50 percent of that maximum, or 85 beats per minute.
A “normal” RHR falls between 60 and 100 beats per minute. An RHR under 60 can indicate that you're more physically fit and may be associated with better heart function. An RHR that is above 100 beats per minute can reflect exposure to stress, excessive caffeine consumption or an illness
