Conversation so far:
When was Martina Hingis's first retirement from tennis?
In February 2003, at the age of 22, Hingis announced her retirement from tennis.
How long did Martina Hingis stay in her first retirement?
Martina Hingis was retired for approximately 2-3 years.
Why did Martina Hingis decide to retire in 2001?
Martina Hingis decided to retire due to her injuries and being in pain.

Question: What injuries did she have?
Self-contained rewrite: What injuries did Martina Hingis have when she retired in 2001?