Related Clues:

• Muscles toned by crunches
• Planks strengthen them
• Six-pack in a gym
• Crunches can make them shredded
• Stopping tech
• Like swallowing first of beers in six-pack?
• Workout goal, perhaps
• Parts of a six-pack
• Sailor's muscles?
• Some are rock-hard
• Inhalation assistants
• Core part, informally
• Plank targets
• Internal stabilizers
• Planking targets them