Sacroiliac Joint (SI Joint) Stimulation and Muscle Response

Insights from Indahl et al. (1999)

The sacroiliac (SI) joint is often discussed as a source of low back pain — but does it also play an active role in neuromuscular control?

A pivotal animal study by Indahl, Kaigle, Reikeras, and Holm, published in the Journal of Spinal Disorders, investigated whether stimulation of the sacroiliac joint could trigger muscular activation in the trunk and hip.

Their findings suggest the SI joint is not just a passive structure — it may be part of an integrated reflex system that stabilizes the lumbar spine and pelvis.

Using a porcine (pig) model, researchers stimulated the sacroiliac joint and recorded muscular responses. They found activation in:

• Gluteus maximus

• Quadratus lumborum

• Multifidus

These muscles are central to:

• Lumbar stability

• Pelvic control

• Postural support

• Locomotion

(Indahl et al., 1999)

Why This Matters

The results demonstrated that sacroiliac joint stimulation produces reflexogenic muscular activation.

In other words:

• The SI joint contains nociceptive (pain-sensitive) afferents.

• These afferents can trigger motor responses.

• The activated muscles help stabilize both the SI joint and lumbar spine.

This aligns with modern concepts of spinal stability, where deep muscles like the multifidus provide segmental control, and larger muscles like the gluteus maximus contribute to force closure across the pelvis (Vleeming et al., 1995).

SI Joint Pain and Reflex Inhibition

The authors proposed that sensitization of sacroiliac joint nociceptive afferents could:

• Contribute to mechanical low back pain

• Alter normal muscle activation patterns

• Influence pelvic biomechanics

This is consistent with research showing that pain can disrupt normal motor control and alter muscular recruitment (Hodges & Moseley, 2003).

Thus, SI joint dysfunction may create a feedback loop:

1. Joint irritation

2. Abnormal muscle activation

3. Altered stability

4. Persistent or recurrent pain

Clinical Implications

These findings suggest that evaluating and addressing SI joint dysfunction may influence:

• Gluteal activation

• Multifidus recruitment

• Postural control

• Functional movement patterns

It also opens the door to studying whether manual therapies directed at the SI joint could normalize muscle activation patterns.

Future clinical research could evaluate muscle strength or activation patterns before and after targeted SI joint interventions to determine whether similar reflex changes occur in humans.

A Balanced Perspective

It is important to note:

• This was an animal study (porcine model).

• Reflex responses in animals do not automatically translate to human clinical outcomes.

• More controlled human trials are needed to confirm applicability.

However, the study provides strong anatomical and neurophysiological support for the idea that the SI joint participates in active motor control — not merely structural load transfer.

Conclusion

Indahl et al. (1999) demonstrated that stimulation of the sacroiliac joint activates key spinal and gluteal muscles involved in locomotion and posture. These findings support the concept that the SI joint is integrated into reflex pathways that contribute to pelvic and lumbar stability.

For clinicians, the takeaway is clear:

The sacroiliac joint is not just a joint — it is a neuromuscular control center influencing posture and movement.

Understanding this relationship may enhance assessment and treatment strategies in patients with mechanical low back pain.

References

Hodges PW, Moseley GL. Pain and motor control of the lumbopelvic region: Effect and possible mechanisms. J Electromyogr Kinesiol. 2003;13(4):361–370.

Indahl A, Kaigle A, Reikeras O, Holm SH. Sacroiliac joint involvement in activation of the porcine spinal and gluteal musculature. J Spinal Disord. 1999;12:325–330.

Vleeming A, Pool-Goudzwaard AL, Stoeckart R, van Wingerden JP, Snijders CJ. The posterior layer of the thoracolumbar fascia: Its function in load transfer from spine to legs. Spine (Phila Pa 1976). 1995;20(7):753–758.

Sacroiliac joint involvement in activation of the porcine spinal and gluteal musculature, Indahl, A., Kaigle, A., Reikeras, O., Holm, S.H.

J Spinal Disord, 1999;12:325-30

This experiment involved stimulation of the sacroiliac joint that was found to cause neuromuscular responses in the gluteus maximus, quadratus lumborum, and multifidus muscles. This muscular activation was found to assist in the control of locomotion and body posture and to provide stability to the sacroiliac joint and lumbar spine. Thus, sensitization of sacroiliac joint nociceptive afferents were suggested to not only contribute to mechanical low back pain, but plays a role also in sacroiliac joint biomechanics via reflexogenic activation of the trunk and gluteal muscles. Given the results of this study, a larger double-blind study evaluating sacroiliac joint biomechanics in relationship applied kinesiology diagnostic procedures for the sacroiliac joint could be done, wherein back muscles strength tests are measured before and after a course of chiropractic care for the sacroiliac joints.