Clue: Chap's working out trips for guardians of apples (10)
Answer: HESPERIDES
Explanation: Definition: guardians of apples
**HE'S** ("chap's") + **PE** (physical exercise, so "working out") + **RIDES** ("trips") 
*The Hesperides were Greek nymphs who guarded a grove of golden apples, which appear in the stories of Aphrodite and Hercules