One-leg pikes are a challenging core exercise that targets the abdominals, hip flexors, and shoulders. Start in a plank position with your hands directly under your shoulders and your body forming a straight line from head to heels. Lift one leg towards the ceiling while simultaneously lifting your hips towards the ceiling, forming an inverted V shape with your body, then return to the plank position and repeat on the other side, alternating legs to engage both sides of the core effectively.