The “core” remains a somewhat nebulous concept; but most researchers consider it the corset of muscles and connective tissue that encircle and hold the spine in place. If your core is stable, your spine remains upright while your body swivels around it.

But, McGill says, if you concentrate on strengthening only one set of muscles in the core, you can pull your spine out of alignment.

Instead, he suggests, a core exercise programme should emphasise all the major muscles that girdle the spine, including but not concentrating on the abs. Side plank — lie on your side and raise your upper body — and the “bird dog” — in which, from all fours, you raise an alternate arm and leg.

As for the abdominals, no sit-ups, McGill said. They place devastating loads on the disks.

An approved crunch begins with you lying down, one knee bent, and hands positioned beneath your lower back for support. “Do not hollow your stomach or press your back against the floor,” McGill says. Gently lift your head and shoulders, hold briefly and relax back down.

These three exercises, done regularly, McGill said, can provide well-rounded, thorough core stability. “I see too many people,” McGill said, “who have six-pack abs and a ruined back.”