How could a beautiful young virgin keep David warm physically?

1 Kings 1:

1 When King David was very old, he could not keep warm even when they put covers over him. 2So his attendants said to him, “Let us look for a young virgin to serve the king and take care of him. She can lie beside him so that our lord the king may keep warm.”

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She was probably a chubby woman

3 Then they searched throughout Israel for a beautiful young woman and found Abishag, a Shunammite, and brought her to the king. 4The woman was very beautiful; she took care of the king and waited on him, but the king had no sexual relations with her.

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Matthew Poole explained:

whose beauty might engage his affections, and refresh his spirits, and invite him to those embraces which might communicate some of her natural heat to him, as was designed.

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Cambridge Bible for Schools and Colleges:

a young virgin] This device, whereby it was thought to communicate vital heat from a young frame to an old one, was adopted by the advice of physicians long after David’s time

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She warmed him up physically and psychologically

BPPLEE said:

If I remember right, didn't one of Solomon's brothers request to marry this woman

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Right.
13 Then Adonijah the son of Haggith came to Bathsheba the mother of Solomon. And she said, "Do you come peacefully?" He said, "Peacefully."
14 Then he said, "I have something to say to you." She said, "Speak."
15 He said, "You know that the kingdom was mine, and that all Israel fully expected me to reign. However, the kingdom has turned about and become my brother's, for it was his from the Lord.
16 And now I have one request to make of you; do not refuse me." She said to him, "Speak."
17 And he said, "Please ask King Solomon—he will not refuse you—to give me Abishag the Shunammite as my wife."
18 Bathsheba said, "Very well; I will speak for you to the king."

BPPLEE said:

and Solomon had him put to death?

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Right.
22 King Solomon answered his mother, "And why do you ask Abishag the Shunammite for Adonijah? Ask for him the kingdom also, for he is my older brother, and on his side are Abiathar the priest and Joab the son of Zeruiah."
23 Then King Solomon swore by the Lord, saying, "God do so to me and more also if this word does not cost Adonijah his life!
24 Now therefore as the Lord lives, who has established me and placed me on the throne of David my father, and who has made me a house, as he promised, Adonijah shall be put to death today."
25 So King Solomon sent Benaiah the son of Jehoiada, and he struck him down, and he died.

BPPLEE said:

And I remember some claiming that this woman is the same one in Song of Solomon

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Right.

1 Kings 1:3-4 (ESV)
3 So they sought for a beautiful young woman throughout all the territory of Israel, and found Abishag the Shunammite, and brought her to the king.
4 The young woman was very beautiful, and she was of service to the king and attended to him, but the king knew her not.

The Shulamite in Song of Solomon 6:13 (ESV)
13 Return, return, O Shulammite,
return, return, that we may look upon you.
Why should you look upon the Shulammite,
as upon a dance before two armies?

But I doubt she was the same woman. It seemed that Shulam was famous for having beautiful women.