The Science Behind the Crack

The Physiological Effects of a Chiropractic Adjustment

It’s a sound many are familiar with, the sharp, satisfying “crack” that echoes during a chiropractic adjustment. For some, it brings instant relief; for others, curiosity. But what actually causes this noise, and more importantly, what’s happening in the body after that adjustment?

The “crack” is caused by a process known as cavitation. Within our joints is synovial fluid, which helps reduce friction. During a chiropractic adjustment, a quick, controlled force is applied to a joint. This changes the pressure inside the joint capsule, causing gas bubbles (primarily nitrogen) to form and collapse, resulting in the audible pop (Evans and Breen, 2006). Contrary to popular belief, no bones are breaking or grinding, it’s simply a natural physiological response.

But beyond the sound lies a cascade of effects on the body. Spinal manipulative therapy (SMT), the core technique in chiropractic care, has been widely studied for its impact on musculoskeletal pain. A systematic review by Coulter et al. (2018) found that SMT offers comparable pain relief and functional improvement to standard treatments for chronic low back pain. This suggests that chiropractic care may be a valid alternative or adjunct to conventional pain management.

The benefits, however, appear to extend beyond the spine. Research by Holt et al. (2021) demonstrated that SMT, when used alongside rehabilitation in patients recovering from stroke, significantly improved motor function compared to rehabilitation alone. This implies that spinal adjustments may influence the central nervous system in ways that enhance muscle control and movement efficiency. 

This link between the spine and the nervous system becomes even more compelling when we consider brain activity. Haavik et al. (2019) used electroencephalogram (EEG) imaging to observe that chiropractic adjustments altered activity in the prefrontal cortex, an area of the brain involved in pain perception and executive function. These findings support the theory that SMT may influence how the brain processes pain, potentially leading to broader benefits such as improved concentration or reduced anxiety.

In terms of performance, there is growing evidence that spinal adjustments may enhance neuromuscular function. Haavik et al. (2021) found that chiropractic care increased cortical drive, the brain’s ability to activate muscles, especially in individuals with impaired motor control. Meanwhile, Kelly et al. (2006) showed that spinal manipulation improved reaction times, a potential benefit for both athletes and older adults at risk of falls.

Outside of neuromuscular health, chiropractic care is being studied for its role in managing chronic health issues. For example, patients who accessed chiropractic services for spinal pain were significantly less likely to be prescribed opioids, according to a 2020 meta-analysis by Corcoran et al. This raises the possibility of chiropractic care serving as part of a broader strategy to reduce reliance on prescription painkillers, particularly in the UK’s ongoing efforts to manage medication dependency.

The immune system is another area of interest. While no high-quality studies confirm that spinal adjustments directly improve immunity or prevent illness, preliminary findings suggest SMT may induce short-term changes in immune biomarkers. A review by Teodorczyk-Injeyan et al. (2021) found alterations in markers such as interleukins following adjustments, although the clinical relevance is still unclear. Pasquier et al. (2023) further observed changes in neuroimmune responses, including shifts in cytokines like IL-1β and TNF-α—immediately after SMT in patients with neck pain.

Taken together, this growing body of research supports the idea that the spine is not just a structural system but a critical hub of communication between the body and brain. The “crack” may be the audible symbol of a deeper neurological reset. Whether the goal is pain relief, enhanced performance, reduced medication reliance, or simply better movement, chiropractic adjustments may offer more than just momentary satisfaction—they might contribute to longer-term health outcomes.

References

• Coulter, I.D., Crawford, C., Hurwitz, E.L., Vernon, H., Khorsan, R. and Booth, M.S., 2018. Manipulation and mobilisation for treating chronic low back pain: a systematic review and meta-analysis. Spine Journal, 18(5), pp.866–879.

• Evans, D.W. and Breen, A.C., 2006. A biomechanical model for cavitation during spinal manipulation: implications for clinical theory. Manual Therapy, 11(3), pp.214–220.

• Haavik, H., Niazi, I.K., Holt, K. et al., 2019. The effects of chiropractic spinal manipulation on central processing of tonic pain: A pilot study using sLORETA. Scientific Reports, 9, p.103.

• Haavik, H., Niazi, I.K., Holt, K. et al., 2021. Chiropractic spinal adjustment increases the cortical drive to the lower limb muscle in chronic stroke patients. Frontiers in Neurology, 12, p.747261.

• Holt, K., Haavik, H., Murphy, B. et al., 2021. The effects of four weeks of chiropractic spinal adjustments on motor function in people with stroke: A randomised controlled trial. Brain Sciences, 11(6), p.676.

• Kelly, D.D., Murphy, B.A. and Backhouse, D.P., 2006. The effect of spinal manipulation on reaction time. Journal of Manipulative and Physiological Therapeutics, 29(7), pp.511–515.

• Corcoran, K.L., Bastian, L.A., Krause, D.A. and Noorbaloochi, S., 2020. Association between chiropractic use and opioid receipt among patients with spinal pain: asystematic review and meta-analysis. Pain Medicine, 21(2), pp.e139–e145.

• Teodorczyk-Injeyan, J.A., Injeyan, H.S., Ruegg, R. and McGregor, M., 2021. Spinal manipulative therapy and its influence on the immune system: a systematic review of relevant literature. Brain, Behavior, & Immunity – Health, 13, p.100237.

• Pasquier, M., Yousry, M., Descarreaux, M., Ferland, F. and Léonard, G., 2023. Immediate neuroimmune response to spinal manipulative therapy in non-specific neck pain: a randomised placebo-controlled trial. Scientific Reports, 13, Article 11739.