What does the cryptic crossword clue "After massage on back go for physical exercise (6)" mean?

The wordplay uses a reversal. RUB (reversal="”massage” reversed/”back”") + PEE (synonym="”go”") = BURPEE The answer is BURPEE.

After massage on back go for physical exercise (6)

Guardian Cryptic #29399 | 17 Across | 2024-06-03 flower