I had a further thought though drifting from the idea of purely measuring to see what’s there. I wondered about the sources of EM fields in people, the naturally occurring ones, and their patterns and sources.
The main components seemed to be the nervous system itself and the muscular system locally or regionally or where the two overlapped more or less. Of the nervous system we might think of the brain but the brain is far removed from the body and somewhat speaking less connected to the body in general - think of the EM field in the knee or foot that would result from the EM activity of the brain (vs say the entrainment discussion where certainly the brain is its own source of the most EM field at least at first order but see next.) The heart seems to be the most commented on source of the strongest EM fields of the body on average at least. And the brain while it has waves of activity actually the strongest waves cause mis-behaviors of the organ (thinking of epilepsy here.) So maybe the pattern of heart activity is a key source of EM field activity relative to the body - and a pulse rate of various levels associated with various kinds of activity and rest and in the low hertz range and of a signal shape that isn’t regular sinusoidal or square waves. There is the double beat of the heart but also there is heart rate variability that is considered a good sign of health (that is to say an overly steady heart rate is a sign of disease.) So maybe a signal rate in the range of heart beats and of a shape of the double beat of the heart, one beat stronger than the other, and with healthy heart rate variability would be a good source of the pattern of signals to consider. There is a third active major component of the nervous system - the digestive system. People have called it a second brain. While the heart is a powerhouse of EM activity the stomach and intestines have strong patterns of engagement and nave been credited with the overall neural activity on par with a cat or dog and this system is much closer to the mass of the body - and also far more variable it seems to me. There is when one is initially digesting vs later phases of things moving through the intestines with contractions. Maybe some patterns there are useful to consider if less mentioned? I mean a sign for the body to begin growing and healing might be when the digestive system is signaling the availability of nutrients. So heart rate and details there of, and the activity of the digestive system are ideas to consider.
Then i had the though that a pulse meter might be something that could pick up signals of heart rate activity and could be a source of signal. Maybe PEMF in sync with the heart rate would matter. Or not. Maybe the heart rate and pattern of a healthy/healing person would be a good source of a signal. Or whatever it is that the digestive signals could be (stomach activity for one phase and intestinal activity for another phase on the scale of hrs.)
The other side of my thinking, on the muscular side, would be of the patterns of walking or jogging and the EM activity of those. Again in the low hertz rate but probably with shapes of activity and release. Maybe those would be an interesting source of signals - just to tell the body there is activity and perhaps arrange resources and activity as if one were active. Kind of like taking a vitamin d3 pill instead of being outdoors for hours doing things.
But this is all speculation. Just thinking outloud.