Strengthening your obliques doesn't require any exercise machines. They are part of your core, which stabilizes your torso and hips and produces a variety of movements. The external obliques rotate and flex the trunk, while the internal obliques assist the external obliques in the same movement patterns and provide some trunk stability. These muscles don't work in isolation. With a set of free weights, you can train them to function better with other muscles in your body.
Any overhead lifting will automatically engage your core, which braces your trunk and back to prevent injury and maintain your balance. A study published in the May 2012 issue of "European Journal of Applied Physiology" showed that the core, including the rectus abdominis and external obliques, had a higher activity when the dumbbell shoulder press is performed in a standing position rather than in a seated position. Doing overhead lifts with one weight also had a higher activity than performing with two weights. Therefore, you can strengthen your obliques by doing a barbell overhead press, Olympic lifting and a single-arm kettlebell press.
Squats and Swings
Although you may not feel your obliques and other ab muscles working, they are constantly engaged when you perform lower-body exercises, such as squats and kettlebell swings. Abdominal muscles stabilize your body to maintain normal spine alignment to handle heavier loads during a back squat or front squat or when you're standing on an unstable surface. Researchers at the Memorial University of Newfoundland, Canada, showed that abdominal stabilizers have higher activity when squats are performed on an unstable surface instead of a stable surface. In a kettlebell swing, your core stabilizes your trunk to help control the rate and direction of the downward phase of the swing. The core prevents your torso from flexing and your body to lose your balance.
Twists and Throws
Medicine ball throws provide abdominal power to excel in most sports, such as baseball and lacrosse. To properly generate throwing power without throwing your back out, a strong lower body and a stable core are needed. A study published in the February 2012 issue of "Journal of Strength and Conditioning Research" showed that the one-rep max squat test is the best predictor of throwing power among other tests, such as the bench press test and 40-yard dash. Researchers concluded that core strength can affect how much force your extremities produce. Sample throwing exercises include medicine ball twists, overhead tosses, chest passes and ground slams.
Your body weight can be used as its own resistance to condition your obliques, especially in lower-body plyometrics. This involves explosive and repetitive contractions of your muscles over a short period of time. To minimize the amount of shock that your lower back, hips and knees receive in plyometrics, your abdominal muscles work like shock absorbers to cushion your joints and internal organs. Researchers at the University of Tokyo in Japan found that your external obliques and rectus abdominis activate within 100 milliseconds before the feet land on the ground from a height of 35 centimeters. All plyometric exercises that involve ground contact will work your obliques, including box jumps, depth jumps, lateral bounding, jump-rope exercises and stair bounding.