In my exercise class, we are often on hands and knees trying to balance on one leg and one arm. I find if very hard to keep my back straight when doing this exercise. Is this true for everyone or do I have some specific weakness?

A recent study at McGill University in Canada confirmed your suspicions. Finding a neutral position for the spine is more difficult on hands and knees than in sitting or standing.

This is likely because of gravity and the position of the hips and knees. Lifting an arm and the opposite leg is a difficult exercise for everyone. It requires strength, balance, and coordination. The spine has a harder time returning to a neutral position when on hands and knees. The easiest position to return to neutral is in standing.

This exercise is an excellent one for many reasons. When done properly, it builds strength, helps prevent bone loss, and promotes good balance. These are important for anyone, but especially for aging adults.