Kinesiology of Exercise

Side Bend

Side bends involve not only the abdominal and lower back muscles, but also the quadratus lumborum. A key low back muscle, the quadratus lumborum is very important in lateral stability of the spine. The only exercise that involves this muscle is the side bend and its several variants. 

Major Muscles and Actions Involved

In side bends the quadratus lumborum, the internal oblique and external oblique, the rectus abdominis, and the erector spinae muscles are involved in lateral flexion of the spine. In this action the trunk is pulled over to one side via contraction of the muscles on the same side of the body midline.

Sports Uses

This exercise is important for all athletes who throw overhead for maximum distance or force (baseball pitchers, outfielders, football quarterbacks, javelin throwers). It is also important for overhead hitting (tennis serve and smash, racquetball ceiling shot, badminton overhead clear and smash) and when you reach up as high as possible (basketball rebounding, volleyball spike, catching fly balls).

Exercise Analysis

  • When executed correctly, the side bend exercise is relatively difficult to execute (except for the standing position variant). The muscles involved in this exercise are often weak for this action because people generally exercise only in the anterior-posterior plane (from back to front), not in the lateral plane.
  • The usual range of motion in this exercise is not great. The maximum appears to be 25-45 degrees on one side. Therefore, if you are not extremely flexible and you find yourself going through a range of motion greater than 45 degrees, you are most likely moving your hips or and rotating the shoulders to increase the range of motion.
  • When you execute the side bend exercise from a standing position, your pelvic girdle must be stabilized by your hip joint muscles. When lateral flexion occurs, your upper body moves down mainly due to gravity; your upper body rises due to the actions of the internal and external obliques, quadratus lumborum, erector spinae and rectus abdominis on the side to which you are moving.
  • When you do the exercise on the Glute-Ham-Back machine or lying on the floor, it involves all the muscles on one side. However, execution on the Glute-Ham- Back machine is more effective because of increased tension and a greater ROM, which gives
    greater over all development to the muscles.
  • It is important to understand that this is the only exercise in which your trunk is pulled from the opposite side (below the horizontal) through to the same side. In this variant the muscles work directly against the pull of gravity.
  • The quadratus lumborum is a major muscle involved in this movement because lateral flexion is its only action. Development of this muscle is needed for lateral stability of the spine and in preventing the spine from curving to the left or right, a condition known as scoliosis. Because the quadratus lumborum is a deep muscle, it cannot be felt or seen, but it is critical for a safe and pain-free lower
  • To help ensure that you have proper isolation of the muscles involved, remain in the lateral plane during exercise execution. Do not rotate your trunk or hips to the right or left prior to or during the action. Doing this brings other muscles into play but, more importantly, it may cause injury.
  • For further analysis check out our premium Kinesiology of Exercise EBooks.