Firming the four ab muscles doesn't create the tightest stomachs. "Look back to those athletes' bodies during the Olympics," says University of Texas at Austin kinesiology.
"It suggests your neck muscles—specifically the sternocleidomastoid and scalene—are trying to power your abs," explains movement specialist Perry Nickelston, D.C.
Nickelston argues that shallow chest breathing limits strength and power in squats, dead lifts, and plyometrics.
Stanforth believes the fingerlike muscles along your ribcage support your shoulder blades. If your shoulder blades "wing" when planking, they're not firing.
Most people's hip-flexor muscles are tight and weak. Tight psoas can switch off other muscles, including abs and butt, reducing workout efficiency.
Inner thigh adductors. They create a powerful center by working with your abs, especially the obliques. "Since the abs are weak and underworked, the adductors are overworked," Nickelston explains.