Possible Clues:

• Working in stone is a strain
• The effect of force exerted in or on something
• XXX is enough to make the North tight
• Sounds as if one is taught that XX + X gets to the North
• Nervous strain apparent in notes played
• Mental or emotional strain
• At a stretch this makes it XX X to the North
• XX, X on the end
• One isn't (anag.)
• Strained state of numbers at home without love