You contain the information you need within.  Listen to your body, trust your body. 

As a baby you instinctively knew when you were hungry and full.  You still have that capacity.  Discover more in the book Intuitive Eating.

As a toddler you knew when and how to move your body, and you did it joyfully.  You didn't need a heart rate monitor, Fit Bit, stopwatch, smartphone app, or any other piece of technology to tell you what to do. 

In the words of Dr. George Sheehan:

    By the time we reach adulthood, we should be able to read the messages our body sends us.      Technology is not only unnecessary; it is inadequate.  The body has information that is     technologically inaccessable.  We are the sole recipients of this otherwise unavailable data.