According to the American Heart Association, heart rate is affected by factors both inside and outside the body. Body size, body position, personal emotions and use of certain medications can affect heart rate, although in some cases to a minimal extent. Air temperature also has a small effect on heart rate. Although exercise changes heart rate during the time of the activity, it does not affect resting heart rate much.
A person's resting heart rate is the rate at which the heart beats when the person is sitting or lying down in a calm or relaxed state of mind. The American Heart Association explains that most adults have a resting heart rate between 60 to 100 beats per minute. A lower resting heart rate is sometimes seen in individuals who are in top physical shape.
The resting heart rate is affected by several factors, according to the American Heart Association. When a person shifts position from resting to standing, the pulse generally speeds up a bit. Body size may also have a small effect on the resting heart rate, with the very obese tending to have a slightly faster pulse. The ambient air temperature can affect heart rate as well, with warm weather and humidity causing an increase of five to 10 beats per minute.
Emotional upset or stress can have a more significant effect on the resting heart rate, typically raising it. In addition, medications can also affect resting heart rate, as the American Heart Association points out. Beta blockers, which block adrenaline in the body, slow the pulse, while thyroid medication can raise it.