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.