The spine is the foundation of the human body. It is made up of multiple bones stacked together called vertebrae, which are divided into 5 areas:
- Cervical (7 vertebrae)
- Thoracic (12 vertebrae)
- Lumbar (5 vertebrae)
The areas of the spine are curved in either a lordosis (concave) or kyphosis (convex) position. The cervical and lumbar vertebrae should all be in a position of lordosis. The thoracic vertebrae, sacrum and coccyx are in a positions of kyphosis. These are the normal curves of the spine, and problems can arise when these curves are not present or are excessive.
In between each vertebrae is a jelly-like substance called an intervertebral disc, which helps to absorb the shock of our body weight throughout the day. The discs can also be affected by posture, lifting techniques and muscle imbalances because the disc can become stressed in ways that push it out from between the vertebrae.
The spinal cord runs in a vertical path within the vertebrae, behind the vertebral discs. Nerves branch out from the spinal cord at each vertebral level, where they head out to help our bodies function. When the discs get injured and push the jelly-like substance out of place, the surrounding nerves can be pinched and irritated.
The back can be divided into 2 areas:
- Upper back (thoracic spine)
- Lower back (lumbar spine)
These areas do move independently of each other, but for the purpose of this reference they will be described together as the back. The muscles of the back do a pretty good job of supporting our daily activities as long as we keep them strong, flexible, and working at the appropriate times. Injury can occur when the back muscles are over used while exercising or moving with bad form.
Example of bad form: during a deadlift or kettle bell swing, when the back is over extended rather than fully extending the hips. Over extension of the back can also come from a rounded back at the start of the movement.
So when a coach tells you to keep your back flat and fully extend your hips it’s because they don’t want you to get injured! This also applies to lifting objects off the floor, so make sure you continue your good form even when you’re not in the gym.
*Click on the images below to view the superficial and deep layers of back muscles.
Fun fact: The important thing to understand with the back is that it requires support from the muscles to function properly (i.e. midline stabilizers). If the muscles are weak or are not working properly, the bones, discs and nerves experience more forces than they are built to endure. It’s the repetitive stress that can eventually lead to injury and also decrease the efficiency of your body to gain strength, power and speed. So do your mobility work and keep practicing your midline stabilization. It will pay off!!
* This video focuses on the movement of the thoracic and lumbar spines together, although they have different characteristics and functions. Please see the neck page for more info on the cervical spine.
Major muscles of the back, categorized by function:
- Flexion: abdominals.
- Extension: erector spinae (iliocostalis, longissimus & spinalis) and quadratus lumborum.
- Sidebend/lateral flexion: quadratus lumborum, external oblique and internal oblique.
- Rotation: external oblique and internal oblique.
Created by: Missy Albrecht DPT, CSCS, FMS
Reference: Dutton, Mark. Orthopaedic Examination, Evaluation, and Intervention. Second edition. The McGraw-Hill Companies, Inc, 2008 :1427-1608.