transitive verb
1 : to torture on the rack : inflict pain or punishment by pulling or straining
2 a : to afflict with torture, pain, or anguish comparable to that suffered on a rack *her heart went out to this racked girl— Adria Langley* *racked with jealousy* b : to afflict and agitate very much with or as if with trouble, stress, anxiety, doubt, unpleasant emotion, or illness *the Greco-Roman world had been racked by revolutions— A.J.Toynbee* *was obviously racking his brains as his answer T disclosed— Robert Grant *1940*
3 a : to stretch, strain, or extend violently b : to twist the meaning of : pervert the sense of c : to raise (rents) oppressively d : to harass or oppress with high rents, exactions, or extortions
4 chiefly Britain a : to supply a rack with feed for (as a horse) — used with up b : to fasten (an animal) in place at the rack
5 : to work, stretch, or treat (material) on a rack *rack leather* *rack rubber* *rack ore*
6 : to work by a rack and pinion or worm so as to extend or contract *rack a camera*
7 : to seize (as parallel ropes of a tackle) together so as to prevent running through the block
8 : to place (as pool balls) in a rack — often used with up
intransitive verb
1 a : to become forced out of shape or out of plumb b : to sway together from side to side of their proper position relative to the keel — used of a ship's sides
2 Scotland : to undergo straining or stretching : lengthen or give under tension
synonyms see AFFLICT

Seems like a bad choice of words on the author's part, as it has all sorts of meanings, but nothing really explicit.