Come into an all fours position on an exercise mat with your hands directly under your shoulders and your knees directly under your hips. This is your start position. Keeping your core braced and a neutral spine slowly extend your right leg up and out behind you until it's fully extended with your hip, knee and ankle all in alignment. As you do this, simultaneously extend your left arm out in front of you until you shoulder, elbows and wrist as all in alignment. Hold this position for a count of one before gently reversing the movement, returning to the start position. Repeat the same sequence using the opposite leg and arm. Keep alternating sides for the required number of reps (or time).