You can perform side bends with weights to develop muscle strength or as a body weight exercise to develop spinal mobility. Whichever type of side bend you perform, it is important that you only lean sideways and do not allow your body to twist. Another important factor is to avoid bending too far. An excessive range of movement may place your spine in a potentially injurious position. Side bends involve numerous muscles.
Erector spinae is the collective term used to describe the eight muscles that run and overlap the length of your spine. Forming two columns on either side of your spine from the base of your skull to your pelvis, when both sides contract at once, these muscles cause spinal extension. When you perform side bends, one side of your erector spinae works, while the other side relaxes. The anatomical term used to describe bending to the side is lateral flexion.
Your obliques wrap around your midsection like a corset and are essentially your waist muscles. There are three oblique muscles: external, internal and transverse. In addition to supporting your internal organs and being involved in the action of spinal rotation, the obliques are heavily involved in side bends.
The rectus abdominus is the muscle located on the front of your abdomen and is commonly referred to as your abs. Your abs are separated down the middle by a strip of connective tissue called your linea alba. This means that you can use your abs one side at a time. Whereas crunches and other more traditional ab exercises use your entire rectus abdominus, side bends work one side at a time.
Quadratus lumborum, or QL for short, is a small muscle that runs from your iliac crest at the top of your pelvis to your lower ribs and lumbar spine. Located on both sides of your body, when they work together these muscles help keep your lumbar spine aligned and stable, but side bends recruit one side at a time.
Side Bend Exercise
Kundalini yoga offers a version of a side bend that will work all of the key muscles; give you length through your torso and greater flexibility. Standing with your feet two to three feet apart, bring your arms up to shoulder height and out to the sides. Exhale and raise your right arm over your head as you bend at your waist to the left. Let your left hand slide down your left leg as far as it will go without overly-pulling the muscles on your right side. Inhale and return to your start position and then repeat the side bend to the right. Carry on, gently bending from side to side, in time with your inhalations and exhalations for up to one minute.