Yoga for Osteoporosis: # 1 Way to Reduce the Risk of Vertebral Fragility Fractures: Muscle Strength
A major line of defense against osteoporotic vertebral fractures is the strength of the muscles that attach to the spine. Following Wolff’s law, which governs bone formation, strong muscles exert a stronger pull on the bone, in turn stimulating bone formation and strengthening the bone.
In addition, the muscles that attach to the spine serve a critical role in producing movement and in stabilizing the spine. Muscle strength serves as a protective factor against fracture, with muscle contraction offering a first line of defense against overloading or collapse by dissipating energy and controlling where high stresses on the bone occur. If muscles are fatigued or weak, these important functions are reduced, increasing the likelihood of micro-damage or fracture in the bone.
One important muscle group in this context is the spinal extensor muscles, or erector spinae. These are the muscles that run the full length of the spine from the low back to the neck. This muscle group helps keep the trunk upright by counteracting the forward pull of gravity towards flexion. The erector spinae thus are key postural muscles; they are tonic muscles, which contain a predominance of type I slow twitch muscles fibers linked with endurance and long-term tone.
Also important are the multifidi, the small muscles that go from vertebrae to vertebrae and control the movement of each segment of the spine.
Weak back extensors are linked to poor posture, particularly increased kyphosis in the thoracic spine (i.e. slumped posture). Conversely, researcher believe, strong back extensors may protect against thoracic vertebral fractures in people with osteoporosis.
This protective effect likely results from several factors: People with strong back extensors are less susceptible to developing a kyphotic posture. In addition, strong back extensors may help slow bone loss in the spine and help preserve intersegmental integrity between the vertebrae (see below).
Most people lose strength in the extensor muscles over time. This is due to a combination of lower levels of activity and an age-related decline in the number of motor units in the muscles, i.e. motor neurons and the skeletal muscle fibers they innervate.
With growing weakness, the extensor muscles gradually lose the ability to support an erect posture, setting up a vicious cycle: Once the kyphosis of the thoracic spine increases, the extensor muscles get permanently lengthened. This further reduces their ability to support the spine during movement and to support an erect posture, further increasing kyphosis and pressure on the anterior portion of the vertebral body.
Take Away Lesson: Keep the muscles around the spine strong by engaging in frequent and varied movement that challenges the spine and trunk in all directions, especially extension.
Low back extensor strength also has been linked to lower bone mineral density in the spine. Particularly useful for strengthening the back extensors are yoga poses like Cobra pose and Locust pose, both of which strengthen the spinal extensor muscles.