By David Wallace, PT, DPT
The diaphragm is a thin pancake-shaped muscle that sits between the thoracic and abdominal cavities. Its main function is its ability to contract, thereby expanding the lungs and enabling us to draw in a breath. However, in more recent years, other secondary roles of the diaphragm have begun to present themselves in clinical practice and research. This has opened up new avenues for intervention and improvement of low back pain.
The Diaphragm as a postural stabilizer
One 2010 study examined muscle activity of the diaphragm during upper and lower extremity isometric tasks. The muscle activity was visualized using an MRI to assess the position of the diaphragm while resting, as well with isometric activity with upper and lower extremities. Both the upper and lower extremity isometric tasks resulted in a larger diaphragm excursion, indicating its potential role as a postural stabilizer while using the extremities to complete various tasks.
Another study from 1997 established a correlation between increased electrical activity of the diaphragm during sudden postural perturbations, which were initiated by sudden flexion of the shoulder, reinforcing a potential connection between the diaphragm and postural stability.
From the opposite end of the spectrum, there have been a handful of studies also examining diaphragm function in those with low back pain. A 2015 systematic review investigated the potential relationship between those with respiratory disease such as asthma, dyspnea, various forms of allergies, COPD, respiratory tract infections, with the presence of low back pain. A positive correlation was found between the presence of low back pain and most of the investigated respiratory ailments, except for COPD.
A smaller study examined the effects of inspiratory muscle fatigue on two groups: one group of 12 healthy controls and one with 16 subjects who reported a history of low back pain. The subjects’ proprioceptive postural control strategies were measured on a center of force plate both pre- and post-exercise designed targeted to create inspiratory muscle fatigue. After inspiratory muscle fatigue, both groups demonstrated an increased reliance on proprioception from the ankles; however, it was only the group with a history of low back pain that utilized this strategy even in a well rested state. This suggests that there may be a reduced proprioception in the trunk to help deal with postural stability requirements in those with low back pain, and an over-reliance on proprioception from the ankles.
Inspiratory Muscle Training and low back pain
Our greater understanding of diaphragmatic involvement in postural stability has created a new interest in the use of Inspiratory Muscle Strength Training (IMST) to improve posture and low back pain. IMST involves the use of a small cigar-shaped device that provides resistance against inhalation. As the levels are increased, the difficulty is also increased, akin to adding weight to a machine at the gym.
IMST has been shown to affect postural sway and low back pain in various populations. Athletes who reported a history of chronic low back pain underwent an 8 week trial of inspiratory muscle training, which led to both a reduction in postural sway at the ankle as well as a reduction in low back pain. A similar study examined people with a history of low back pain, and showed improved multifidus and core musculature EMG activity after an 8 week intervention of IMST.
As more research continues to accumulate, IMST remains a promising new avenue with potential to improve low back pain for many individuals.