Keep It Simple

In a recent study, Australian researchers found that using a Swiss ball instead of a bench forces core musculature to contract up to 54 percent harder. What’s more, single-arm, or unilateral, exercises increase core activation even further.

Try a chest press (on a bench first) with a dumbbell in one hand and your other hand at your waist. Start with extremely light weight—the unbalanced movement causes your trunk muscles to contract without much resistance.