Complex sentence: It is used not only to replenish low glutamine levels after intensive exercise but it also promotes muscle production and maintenance, preventing your body from entering a catabolic state (muscle breakdown) and hastens the recovery of micro-torn muscle fibres.
Split into simpler sentences: It is used not only to replenish low glutamine levels after intensive exercise but it also promotes muscle production and maintenance. It also prevents your body from entering a catabolic state (muscle breakdown) and hastens the recovery of micro-torn muscle fibres.