If sit-ups have always felt a little brutal, you are not imagining things. According to Will Harlow, a physiotherapist who specializes in over-50s fitness, sit-ups are actually a poor choice once you pass 60.

The reason is simple. Sit-ups repeatedly flex your spine. They mainly work the rectus abdominis, that’s the outermost stomach muscle, rather than the deeper muscles that stabilize and protect your spine. Those deeper muscles are the ones that really matter as we get older.

The good news is that there is a better way. Harlow outlines three floor exercises that train the deep core without putting your spine through the wringer. You can do all of them lying on your back.

Start Here: Activate Before You Move

Before any of the exercises, Harlow recommends a quick activation step. Gently flatten your lower back toward the bed. Then lightly draw your navel inward. That is your deep core switching on. Keep it engaged throughout everything that follows.

The Three Exercises

Tabletops. Lie on your back with your knees bent. Activate your core, then lift one leg to a tabletop position, thigh vertical, knee at a right angle. Lift the other leg to match. Pause briefly, then lower one leg at a time. Keep your core engaged and your spine stable the whole time.

Core leg extensions. Hold that tabletop position with your core active. Slowly extend one leg straight out in front of you, then bring it back. Alternate sides. The key is keeping your lower back pressed down throughout.

Advanced tabletop leg raises. Hold one leg in the tabletop position and straighten the other. Slowly lower the straight leg toward the floor, then raise it back up. Maintain core activation and keep your lower back in contact with the bed at all times.

Work through them in order. The first two build the foundation. The third adds a real challenge once you are comfortable.

A good exercise mat and a few minutes on the floor a few times a week is all this takes. Your back will thank you for making the switch.