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Effects of different forces on the lumbar spine: How do we influence this through exercise?

The movements in the spine are flexion, extension, rotation and lateral flexion.

These movements occur as a combination of rotation and translation in the following 3 planes of motion: sagittal, frontal and horizontal.

Image 1: Shows the 3 planes of motion

These movements result in various forces acting on the lumbar spine and sacrum: compressive force, tensile force, shear force, bending moment and torsional moment.

Eg: with lumbar flexion, a compressive force is applied to the anterior aspect of the disc and a distractive force is applied to the posterior aspect of the disc. The opposite forces occur with lumbar extension.

Tensile stress occurs when two forces pull on an object in opposite directions so as to stretch it and make it longer and thinner. An example of tension is when you hang from a pullup bar. Gravity pulls down on your body which causes tension in the spine.

Compression pushes or presses an object so as to make it shorter and thicker. Right now, whether you are sitting or standing, certain structures in your body are experiencing a compressive load. When you stand, gravity is “pushing down” on your body while the reaction force of the floor is “pushing up”. So, your intervertebral discs and your sacroiliac joints are experiencing a compressive stress.

Torsional loading is when forces acting on a structure cause a twist. This is what happens on the spine when you twist the body from side to side, for instance. When you bend laterally to pick up an object in one hand there is a bit of torsion going on in the spine. Likewise, when you carry something heavy in one hand.

Shear stress is two forces acting parallel to each other but in opposite directions so that one part of the object is moved or displaced relative to another part. The best way to visualize shear is to think of how scissors work. Shear causes two objects to slide over one another. This results, of course, in friction. If one vertebra is being caused to slide relative to another then there is a shear stress between them. You undergo shear stress all the time when you walk. Every time you take a step, for example. As one leg leaves the ground and the other leg takes all your weight this creates a shear stress in the pelvis because the ground is pushing up on one side of the body through the supporting leg while gravity is pushing down on the unsupported side.

Image 2: Shows forces placed on the lumbar spine and sacrum

Those forces are inevitable during any sport activities and the athlete need to deal with it. The physiotherapist goal is to find out a strategy to reduce any possible dysfunction associated with the Lumbar Column to having a good absorption of the forces through the spine, and to educate the people about exercises technique and movement pattern, which is essential to optimize those forces.

The treatment plan is going to be selected in regards of the goal to achieve. For example:

- Improve ROM (range of motion) of structures related to L5-S1: Hip ROM on all the movement planes, Thoracic ROM on Rotation, Lumbar ROM on all the movement planes, Ankle Dorsiflexion;

Image 3: Shows example exercises to improve ROM related to L5-S1

- Improve Lumbar stabilisation: good activation of Abdominal Oblique External, Abdominal Oblique Internal, Multifidus, Psoas, Glutes Max and Medius muscles;

Image 4: Shows example exercises to improve lumbar stabilisation

- Work Capacity: synonymous of local muscular endurance. This can be defined as the ability to produce or tolerate variable intensities and durations of work and contributes to the ability of an athlete to perform efficiently in a given sport. This adaptation increases the ability of the system to produce more work during repeated efforts, allows the local musculature to tolerate or demonstrate resilience to a larger training volume of work, and supports the performance of work closer to the intensity and duration required for sporting performance.

Image 5: Shows example exercises to improve work capacity

- Motor Control: Maintenance of spinal integrity during skilled movement tasks depends not only on muscular capacity but also on the ability to process sensory input, interpret the status of stability and motion, and establish strategies to overcome predictable and unexpected movement challenges.

Image 6: Shows example exercises to improve motor control

By Andrea Cutrupi

April 2022

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