Engage your core and pull your knees towards your chest. Flex your abs at the peak, then lower the carriage with control, avoiding a sudden drop.
To maximize engagement, round your spine slightly as you draw your knees towards your chest, which will help target your abdominal muscles more effectively. Maintain control throughout the entire movement, resisting the urge to let gravity pull the carriage down quickly, as this can compromise your form and reduce muscle activation. Concentrate on squeezing your abdominal muscles throughout the exercise, feeling them contract as you pull your knees in and release as you lower, to ensure you're working the intended muscle group. A slow, deliberate descent will also help you maintain proper spinal alignment and prevent lower back strain.