I started a weight lifting program at the gym. The trainer told me to exhale when lifting the weight and inhale when returning it to the starting position. Is this right? A book I have on lifting weights says just the opposite.

So for example, if you are doing arm curls with dumbbells, breathe out as you lift the weight up. Then as you straighten your arms to return the weight to the starting position, breath in. A good way to remember this is to breathe out whenever you are doing
the most work or a difficult movement.

The worst thing you can do is to hold your breath while lifting weights or when returning weights to the starting position. It's commonly believed that NOT breathing at all during the activity puts increased pressure on your back, chest, and stomach.

A recent study of breath patterns reports natural breathing, inhaling-exhaling, and exhaling-holding all increase pressure in the abdomen about the same. Breathing in and
holding your breath puts the most amount of pressure in the abdomen. Try to avoid this last pattern when lifting.