An exercise that primarily focuses on building strength in the core muscles is the plank. This isometric exercise involves maintaining a stable position while engaging the abdominal muscles, lower back, and glutes. Variations include side planks and planks on different surfaces to challenge stability further. Planks improve core strength, which is essential for overall stability, balance, and athletic performance. Strong core muscles are vital for almost all physical activities and can reduce the risk of injuries during exercises and daily routines by improving posture and alignment.