If the sway in your lower back gets too large then the back starts to buckle and give pain.

Tuck your butt in!

Place your hands on your hips. Tilt your pelvis back and forward (tailbone down, pubes up) until your lower back feels more comfortable or less painful.

Many people experience this good posture balance in other activities:
In sport there is the ‘weight low’ stance;
In sailing there is the ‘sea legs’ stance;
In the military there is the ‘at-ease’ stance;
Also in tai chi, dance, haka, Pilates, ….
Or a confident, ‘I feel good!’ stance.

Keep your lower back balanced when walking, standing, exercising or carrying items.

This posture is with the centre of balance in the pelvis. This is the most efficient use of your body.