For good balance you need to be able to maintain your stability when you shift your weight as you move. When you lean to one side (keeping your spine straight) you are shifting your body weight to just short of where you lose your balance and we call this moving to the limits of stability.
If you can smoothly and safely shift your weight in either a sideways or forwards and backwards direction then you will be less likely to lose your balance.
Try it out!
Demonstrate by leaning and reaching so that you are moving to the limit of stability.
Shifting your weight from foot to foot becomes more difficult as you decrease your base of support. You can make moving to the limits of stability more difficult by decreasing your base of support or by holding at the limit for a longer time.
Try this out in front of the mirror – did you move to your limits without bending your trunk? Can you feel the weight moving in your leg/feet?\
Remember, it’s a shift of weight using your leg muscles, not bending at the torso/waist/hips. This is a common error.
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Source for the image: https://myhealth.alberta.ca/Health/pages/conditions.aspx?hwid=zm2302