I’m having a hard time finding a good answer through Google, so I’m coming to the Dope for help.
I am trying to get pregnant, and I’m charting my basal temperature and using FAM (Fertility Awareness Method) because it seems scientifically sound to me and it’s an easy and cheap way to monitor my fertile phases. Everything I have read about taking my temperature emphasizes the importance of not moving at all before popping the thermometer in. They go so far as to say don’t roll over, and only move one arm to get the thermometer off the nightstand, because you’ll throw the readings off if you do. Really? Sitting up will ruin everything? How does that make any sense? Yes, muscle activity will raise my temperature, but it’s going to take more than a minute, isn’t it?
There’s two issues. One is muscular activity, the other is blood return
In terms of muscular activity, that can raise body temperature within seconds. I was assisting somebody sampling wild lizards once. In that case we had the grab the animal before it moved at all. They had determined that 2 seconds activity was enough to raise the body temperature so much the readings were worthless. So it sure doesn’t take minutes.
The other issue is blood return. Blood is pumped *out *of the heart, but it can only find its was back through the action of the muscles and changes in posture. When you move, especially when you change from reclining to sitting position, you dump a whole lot of blood back into the heart at once. That blood was moving slowly through the extremities, and is now in circulation. The sudden slug of blood from the extremities can have an instantaneous and significant effect on temperature in its own right. In addition to that, it causes an increase in the strength and speed of heart contractions, increased respiratory rate, increased blood pressure and various other physiological effects. Any of those can easily throw out measurements of basal temperature.
Remember that you are only talking about a variation of a degree or so, so something that causes a change of half a degree is significant.
Actually, in looking for ovulation indicators, the change is in tenths of a degree. And yes, any motion is going to affect it. Of course, what you’re looking for is a change from one day to the next, so I suppose (IANAD) that if you did EXACTLY the same thing each morning it might even out.
I’ve been able to get readings accurate enough to chart ovulation when I’ve had to roll over, or feel around on the nightstand for a few seconds to find my thermometer among the clutter on there. Getting up or talking is definitely too much activity.