Because the 20 pound leg weights are so expensive, I only purchased one. Also, I have found I can save a little time (very important with three young kids) if I do all three leg exercises on one leg, then switch the weights to the other leg and do both sets on that leg. Is this reducing the effectiveness of the exercises?

Though it's more convenient to do the Strong Women Stay Young leg exercises with two ankle weights, many women follow the program successfully with just one weight. Instead of alternating legs as they do the leg exercises, they do two sets of each exercise on one leg, then move the weight to the other leg and do another two sets, as you're doing. This is fine - but for those exercises done standing, it does put additional strain on the supporting leg. Here are a couple of suggestions if you're working with a single ankle weight: