A plank hold is an isometric exercise that strengthens the core muscles, including the abdominals, obliques, and lower back. To perform a plank, start in a push-up position, resting on your forearms and toes. Keep your body in a straight line from head to heels, engaging your core and avoiding sagging or arching your back. Plank holds can be modified for different fitness levels. Beginners may start on their knees or perform a forearm plank, while advanced practitioners can try side planks or add leg lifts. Holding the position for 20 to 60 seconds is common, gradually increasing the duration as strength improves.