Never Do These

Three movements. Not "be careful with." Not for twelve weeks, not in week fifty. If a class cues one of them, you sit that bit out.

1. Curling your spine forward under load

Weighted crunches. Sit-ups. The finish of a rowing machine stroke where your back rounds over. Picking a box off the floor with a bent back.

When your spine curls forward, the front edge of each vertebra squeezes together and the back edge pulls apart, so pressure stops spreading across the whole bone and lands on the front third of it. The front third is exactly where osteoporotic vertebrae collapse, which is why the failure is called an anterior wedge fracture. Stack two or three of those and you have the rounded upper back you have seen on older women.

Do the hip hinge instead. It gives you every useful thing about bending forward and none of this.

2. Twisting under load, or fast

Cable wood chops. Weighted Russian twists. Throwing a medicine ball sideways into a wall.

A loaded twist puts shear across the discs and the small joints at the back of each vertebra, a sideways sliding force rather than a straight push down, and spines handle straight compression far better than they handle shear.

Turning to look behind you in the car is fine. Reaching for the salt is fine. It is twist plus weight plus speed that comes off the table, and that combination basically only happens in a gym.

3. Standing toe touch

Straight legs, reach for your toes. The seated one counts. So does the forward fold most yoga classes open with.

Everybody assumes this is safe because your hands are empty. Your head, arms and trunk come to roughly half your body weight, and hanging all of that in front of you on a curled spine is the load.

Want the hamstring stretch? Lie on your back, one leg up, towel around the foot. Same stretch. Spine stays flat. If you do not get down on the floor, sit tall on a chair, straighten one leg out with the heel on the ground, and lean forward from the hips with your back straight until you feel it. The rule is the same either way: the bend comes from the hips, never from the spine.

That is the whole list

Everything else in the program is on the table.

One rule underneath all three: your spine's job under load is to hold still. Not to bend, not to twist. Hold still.