Related Clues:

• Washboard from working out
• Possible focus for a CrossFit session
• Flat 'six-pack'
• Apple part in a compost heap
• Part of the big apple?
• Core components
• Core muscle group, briefly
• Crunch target
• The pack in a six-pack
• 'Rock-hard' muscles
• Many admire ripped ones
• Nuclear reactor area
• Muscles worked in sit-ups
• Eight-pack makeup
• Task abandoned by husband -- one needs heart