Machine Trunk Rotations
Exercise machines provide a much better way to perform twists than a broomstick (see broomstick twist) because they offer lateral resistance. Unfortunately, machines that are made for twisting are relatively rare. Your obliques have to contract powerfully to oppose that resistance. Without a machine there is practically no resistance even if you perform hundreds of reps. If no machine is available, a simple elastic band can provide proper resistance.
1. Standing Machine Twists
Stand on the twist disc with your feet apart and your knees slightly bent. Grasp the grips with your hands. Firmly contract your abdominal muscles and rotate the pelvis from one side to the other using your abs to control the range of movement (keep your shoulders fixed). Twist through an arc of around 90º. Breathe naturally in short intervals. This exercise mainly works the external and internal obliques and, to a lesser degree, the rectus abdominis. Best results are obtained with very long sets. Standing machine twist can be dangerous if performed without adequate abdominal control. It is easy to let the momentum of the twist take over, with the ligaments and smaller muscles of the spine restraining the movement. This must be avoided. It is also unnecessary, and the exercise is a quick route to knee and back injuries. Moreover, it is completely useless if your aim is to reduce fat around your waist or increase the size of the muscles in this area.
2. Rotary Torso Machine (Machine Kneeling Twist)
This machine may be seated or kneeling in your gym. They work in similar ways to train your abdominals. Adjust the seat height so that the hips and knees are at 90-degree angles. Adjust the back pad so that the head is directly under the machine’s axis of rotation. Select the appropriate resistance on the weight stack. Adjust the starting point so that the weight stack is slightly elevated from the bottom position upon starting the exercise. Position the body in an upright posture with the chest up, the back fiat, and the abdominal muscles tight. Grasp the handles and rotate the hips to the side in a slow, controlled motion until they are facing the direction opposite the starting position. Slowly return to the starting position without letting the resistance rest on the weight stack between repetitions. Repeat the motion while maintaining proper body positioning. Concentrate on maintaining neutral spine throughout the exercise, not allowing your pelvis to tilt to the front or back.
3. Seated Machine Trunk Rotations
Adjust seat height so that pads are positioned across upper chest. Select desired full left or right rotation start position. Grasp handles and pull chest firmly against pads. Squeeze thigh pads firmly. Rotate your upper body completely to opposite side and return. Repeat for opposite side. Make sure you control the movement in each direction; do not allow the machine to “run away with you”. The dual angled foot pegs and thigh pads provide for multiple stabilization opportunities to ensure it is the torso that is moving and not the hips and legs. It also ensures that spinal alignment is maintained throughout the movement. The rotary torso action is important as it works the oblique abdominal muscles which are essential to maintain a controlled movement of the spine. However, the range of motion limiter must be set correctly to avoid the risk of the machine twisting you too far. For this reason, set the limiter to stop the machine movement just short of your full degree of spinal twist (full range motion). In this way you will avoid the possibility of overstretching.
Muscles Involved in Machine Torso Rotations
Main muscles: internal and external obliques
Secondary muscles: rectus abdominis, transverse abdominal, quadratus lumborum
Antagonists: the same muscles on the other side of the body
Instead of twisting your torso using all kinds of twisting machines, you can lie on the floor and twist using your legs. Your legs can be either bent or straight (the most difficult version of this exercise).