Begin in a high plank position with your hands directly under your shoulders, feet hip-width apart, and body forming a straight line from head to heels. Engage your core, glutes, and quads to maintain stability. Without shifting your hips or letting your torso rotate, slowly reach one arm straight out in front of you, hold briefly, then return it to the ground. Alternate arms with each rep, focusing on minimising any movement through your spine or lower body. Keep your neck neutral and breathing steady throughout the exercise.