Tracking core body temperature

I’ve recently seen online articles about women being advised to take their rectal temperature on a daily basis, in order to track their circadian rhythm, to determine their sleep patterns. They use the term core and rectal synonymously. So, apparently, there is still a need for an accurate measurement. Is anyone else aware of this?

True core body temperature nowadays is generally tracked using central venous catheters with a temperature probe installed and inserted into a central vein. I would argue that rectal thermometers are pretty darned close accuracy wise and way more fun!

I believe that’s what a basal thermometer is used for.

I don't know about Circadian rhythym or sleep cycles, but rectal temps QAM, before getting out of bed, with a Basal Body Thermometer (which has the normal scale expanded) is still the recommended way to track ovulation. BBT goes up about 1 degree on ovulation, and stays there until the next menstruation occurs.

The circadian rhythm makes the body temperature fluctuate during the day. Lowest during the night and highest late afternoon. Wake up or basal temperature should normally be the lowest you can measure when awake and can be used as an indication for hormonal balance (also for men) and to track the cycle. In order to evaluate the circadian rhythm you need more measurements during the day to see how the temperature rises and falls again. E.g. by taking the temperature every 2 hours and plotting this in a graph. This can show how the body responses to stress and how the circadian / biorhythm functions. Rectal measurement gives the most stable reading for this purpose. Although women can also do it vaginally. Oral and axillary might work for the morning measurement since the body is still in rest and no others factors will influence the reading. But only use one method for such a graph, you can’t mix them. This is what I know about the circadian rhythm.

Theres also a pill athletes swallow allowing the coach to track body temps of players to avoid heat stroke