Laurie's Blogs.

I came across another interesting paper recently.

Farrell G, Reily-Bell M, Chapple C, et al. Autonomic nervous system and endocrine system response to upper and lower cervical spine mobilization in healthy male adults: a randomized crossover trial. J Man Manip Ther. 2023 Dec;31(6):421-434. 

The study took 20 healthy young adult males, and performed mobilization techniques on each of them with the following guidelines:

“These techniques consisted of low frequency, mid-range, bilateral, and alternating oscillations of either the upper cervical spine (C0–1 and C1–2) or lower cervical spine (C6–7 and C7-T1). Low frequencies have been associated with ANS processing and mobilizations can be performed within this frequency range. Therefore, a frequency of 3 Hz was selected for each mobilization. Each level was mobilized for three sets of two-minutes, separated by a 30-s rest period. All interventions were performed by the same operator, a certified musculoskeletal physiotherapist specialist with over 30 years clinical experience.”

Participants were randomly assigned to group 1 (upper then lower cervical mobilization, n = 10) or group 2 (lower then upper cervical mobilization, n = 10), separated by a one-week washout period.  The primary outcome measure was salivary cortisol (sCOR) concentration.  Salivary cortisol (sCOR) measures represent a noninvasive, convenient, and reliable way to measure the hypothalamic pituitary adrenal-axis (HPA-axis) activity.

Rationale:

Despite demonstrating clinical efficacy and effectiveness, the underlying mechanisms of spinal manual therapy are not fully understood. One hypothesis is that manual therapy may exert effects on the ‘stress axis’ or ‘stress response’.

Results:

There was a statistically significant downregulation of cortisol secretion from the HPA-axis 30 minutes following lower cervical mobilization. However, there was an upward trending in sCOR levels the night following the lower cervical mobilizations.

Why might lower cervical mobilizations have this effect?

A previous study showed the same trend in cortisol fluctuation following a thoracic manipulation, where there was an initial decrease in salivary cortisol, followed by a reciprocal increase 6 h later.  The thoracic spine has a close anatomical relationship with the sympathetic nervous system (SNS), as does the lower cervical spine with the stellate ganglion of the SNS.  

What are the benefits of reducing cortisol?

1. Improved Mental Health:  Reducing anxiety and depression as well as enhancing focus and memory.

2. Better Sleep Quality: Lower cortisol in the evening promotes relaxation, and helps maintain a health sleep-wake cycle

3. Enhanced Immune Function:  Chronically high cortisol suppresses the immune system, making the body more susceptible to infections. 

4. Balanced Blood Sugar Levels:  Lower levels of cortisol help regulate blood sugar.

5. Healthy Weight Management: High cortisol can lead to fat accumulation, particularly around the abdomen. 

6. Improved Cardiovascular Health:  Chronic cortisol elevation can increase blood pressure and heart disease risk. 

7. Reduced Inflammation:  While cortisol has anti-inflammatory effects in the short term, chronically high levels can cause immune dysregulation and chronic inflammation. 

8. Better Digestive Health:  Lower cortisol supports normal digestive function, as high levels can cause issues like bloating, stomach cramps, and irritable bowel syndrome (IBS).

9. Enhanced Muscle and Bone Health:  Chronically high cortisol can lead to muscle breakdown and reduced bone density. 

10. Increased Energy Levels: Lower cortisol supports a steady energy supply throughout the day, reducing feelings of fatigue and improving overall vitality.

My thoughts:

I like that this study adds a wee bit of knowledge and a novel reasoning for why manual therapy works.  It also brings forth a new rationale for why you would use it.  To this point, I think you could add caudal cervical mobilizations to your senior dog maintenance therapies, to a dog in an early post-operative state, to dogs with digestive issues…  It would take 2 minutes to do, and potentially have a positive benefit.  In regards to the rebound of the cortisol, I’m not sure what to make of that.  However, given that it is a short term rise in sCOR, and cortisol is a natural anti-inflammatory hormone, there could be a role in inflammation control at night (e.g., injury, infection, or immune response).  That being said, this study was done on healthy individuals.  It would be interesting to see the results in different patient populations as a follow up (both human and animal)!