The hollow body hold: lower back down, shoulders and legs hovering

From the side, a good hollow hold looks like a shallow dish: lower back flat on the floor, ribs drawn down, pelvis tucked under, and head, shoulders and legs lifted a few inches. Gravity pulls your arms and legs towards the floor, and because they sit at the ends of a long lever, that pull tries to tip your pelvis forwards and arch your lower back. The rectus abdominis, the deep abdominal wall and the obliques resist it, while the hip flexors hold the legs up and the front of the shoulders holds the arms.

It belongs to the same anti-extension family as the plank and the dead bug, but the shape is a curve with the lower back flattened, not a straight line. Gymnastics coaches see it as a basic body position that many skills build on, from swings on a bar to the start of a V-up, which is why it turns up in bodyweight and conditioning programmes.

If your back lifts even in the dead bug's start position, build that first: the hollow asks for the same flat back with your shoulders off the floor. The core training guide shows where it fits with carries, other holds and the big lifts. If you are pregnant or postnatal, ask your doctor or midwife which core exercises suit you.

1. Lie on your back on a mat, knees bent, feet flat and arms by your sides.
2. Breathe out fully and tilt your pelvis so your lower back presses into the mat. Slide a hand underneath: you should feel firm pressure, not a gap.
3. Keeping that pressure, curl your head and shoulder blades a little off the floor, chin slightly tucked, eyes on your knees.
4. Lift your feet so your knees are over your hips and your shins level with the floor, hands reaching towards your feet. This is the tuck hollow, the first rung of the ladder below.
5. Breathe in short, quiet breaths behind a firm stomach, and lengthen a lever only when the tuck feels steady.

The whole exercise depends on one point of contact that you cannot see while you hold it. Check it these ways, the most reliable first.

• A hand test. A partner or coach tries to slide fingers under your lower back during the hold; if they get through, the back is up.
• A sheet of paper. Lie on a thin sheet and have someone tug it: if it slides out easily, the contact has gone.
• Where you feel it. Effort low in the stomach is right. If the work moves to the front of your hips or into your lower back, the pelvis has probably tipped.
• Ribs and stomach. Ribs flaring up or the stomach doming outwards usually comes just before the back lifts.
• A side-on video. Ten seconds filmed at hip height shows a lifted back as daylight under it.

When the back lifts, shorten a lever rather than finishing the time: bend the knees, raise the legs or bring the arms forwards. If you feel pain in your lower back, end the hold and speak to a doctor or physiotherapist.

Your arms and legs are the levers: the further they reach from your middle, and the closer to the floor, the harder your trunk works. Move up a rung when you can hold three sets of about thirty seconds with the back down throughout.

Arms by your sides keep their weight close to your middle. Overhead, they add a long lever and pull on the ribs: if the ribs flare, stop the arms level with your ears or slightly forwards rather than reaching for the floor. Stiff shoulders often make this end the harder one.

A hollow rock keeps the full hollow shape and rocks it, like the runner of a rocking chair, between your upper back and your tailbone. Start them when three thirty-second full holds are comfortable. Nothing bends: the rigid shape tips as one piece.

1. Set the full hollow with your back pressed down.
2. Start with a small nod of the head and arms, and roll back towards your shoulder blades.
3. Roll forwards onto your lower back and tailbone, legs still low and the shape unchanged.
4. Keep the rocks small, then build a steady rhythm of about one a second.

If your hips fold on each rock, it has turned into half a V-up; if the arms and legs swing on their own, the rock stalls. Shorten the levers until the shape holds. Beyond rocks, a light dumbbell held overhead makes the static hold harder, and the hollow is the start and finish of each V-up.

Both are anti-extension holds. They differ in shape, in where the load goes and in who else joins in.

Neither wins on every count. The plank is easier to start and trains the straight line of a push-up. The hollow is the shape gymnastics and many bodyweight skills ask for, and it suits people whose elbows or wrists dislike planks. Feeling one more in your stomach does not make it the better exercise; plenty of people use both in a week.

It has two good places in a session. In a warm-up, one or two holds of ten to twenty seconds before overhead pressing, pull-ups or gymnastics work rehearse the ribs-down brace. In a core block after your main lifts, do three sets two or three times a week, alongside an exercise for another job such as a Pallof press. Keep long, hard sets for after heavy squats or deadlifts, not before. Progress the rung before the time: once thirty seconds is comfortable, the next rung does more than chasing a minute.

The hold needs only a mat and room to lie at full length. RPM's floor photos show a turf lane in the functional area and a dumbbell rack for the weighted hold; on a free guided tour, ask whether mats are available and where floor work fits at your hour. You cannot see your own lower back here, so a personal training session is a quick way to have it checked, and you can ask for a female personal trainer.