New research was published recently that uses Total Human Model for Safety (THUMS) to investigate what muscles are involved in upright posture and imbalances like forward head posture (FHP) or dropped head syndrome (DHS).
 Forward Head Posture |  Visual of the thoracic and cervical spine with forward head posture |
What is THUMS?
THUMS, developed by Toyota Motor Corporation and Toyota Central R&D Labs., Inc, is an advanced computerized model of the human body that has been used for crash testing along side regular physical crash test dummies. THUMS can simulate many different human aspects of human form from skin to bone to muscle to internal organs, allowing researchers to understand the extend of injuries people might suffer from any type of accident.
Why this research was done
The researchers wanted to figure out a way to measure what muscles are responsible for maintaining good upright posture and what muscles are not working correcting that cause certain posture imbalances. In the introduction to the study they discuss the challenge of this:
Although muscle activity can be measured using electromyography (EMG), this method is limited to a small number of muscles on the body surface. Muscles involved in spinal movements, such as the flexion and extension of the head and neck are located deep within the body, making it challenging to measure their activity and placing a significant burden on study participants during experiments.
They go on to say:
Conversely, predicting muscle activity through simulation using a human body model is useful for understanding the mechanisms underlying the development of DHS and the effects of rehabilitation. Recent advances in the construction of human body models using computer simulations and finite element (FE) analysis have enabled a detailed analysis of the complex dynamics of the musculoskeletal system. This study aimed to determine the effect of individual muscle activities on the maintenance of an upright posture using a human body FE model to elucidate the mechanism underlying the onset of symptoms related to spinal asymmetry.
How advanced is THUMS?
To give you an idea of how advanced this THUMS modeling is, they imputed the characteristics of 320 skeletal muscles, bone, tendon, ligament, and intervertebral stiffness etc. To get as good a picture of how each spinal erector muscle impacts posture, they split the erector spinae muscle into 17 individual multifidus muscles on each side, longissimus thoracis, iliocostalis thoracis, and iliocostalis lumborum muscles. The total number of elements in the model was approximately 210,000 with approximately 120,000 nodes (in other words highly detailed!).
Their model also looked at muscular compensation in the human body and posture.
When any muscle in the human musculoskeletal system is damaged, other muscles and ligaments often compensate by exerting extra effort. Understanding how the roles of the damaged muscles are compensated by other parts of the musculoskeletal system is valuable from a clinical and rehabilitation perspective.
What did the research find?
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They then modeled what happened when each spinal erector muscle group was shut off and what muscles then had to increase activity to maintain upright posture. The results of these tests showed that when multifidus (L1-S) and longissimus thoracis was inhibited it caused the largest compensatory activity of the other spinal erectors. This highlights the importance of the lumbar multifidus and longissimus thoracis muscles in maintaining upright posture.
The paper also goes on to describe the importance of the hip flexors especially the psoas major and iliacus muscles in maintaining good upper body posture. The research shows when the psoas major and iliacus muscles are inhibited it causes a decrease in trunk and hip extensor activity which "suggests the importance of the PM (psoas major) and Ili (iliacus) muscles in maintaining upright posture."
In the discussion section of the paper, the authors explain:
When the multifidus (L1-S) or the longissimus thoracis muscles was inactive, a pronounced forward tilt of the neck, trunk, and pelvis was observed. The multifidus (L1-S) is an extensor muscle in the lumbar region, whereas the longissimus thoracis is an extensor muscle in the trunk, including the lumbar region.
The psoas major and iliacus muscles are hip flexors. Therefore, in this condition, where the area below the femur is fixed, a decrease in the strength of the hip flexor muscles may lead to easier hip extension, causing a posterior tilt of the pelvis and subsequent posterior tilt of the neck, trunk, and pelvis.
How does the research change or reinforce posture alignment therapy?
This research reinforces what I have been teaching clients for over 24 years - the importance of proper psoas and ilicus strength and function to maintain pelvic alignment which is key to supporting the lumbar spine. This also reinforces the importance of the lumbar and thoracic extensor (especially the multifidus and longissimus thoracis) strength and function to maintain lumbar and thoracic spinal alignment and how the cervical spine and head are responding to what the pelvis, lumbar and thoracic spine are doing. These are all essential components to how I, as a posture alignment therapist, look at the human body. Any therapy that does not look the entire body when helping a client address forward head posture or dropped head syndrome is missing the most important piece of the therapy equation.
How can I find help for my posture issue?
If you or anyone you know is dealing with forward head posture, dropped head syndrome, or any other posture imbalance and related pain, contact me today for a free posture evaluation.
Links:
Nakahira, Y., Iwamoto, M., Igawa, T. et al. Effect of individual spinal muscle activities on upright posture using a human body finite element model. Sci Rep 15, 3430 (2025). doi.org/10.1038/s41598-025-86788-0
THUMS https://www.toyota.co.jp/thums/about/
Nakahira, Y., Iwamoto, M., Igawa, T. et al. Effect of individual spinal muscle activities on upright posture using a human body finite element model. Sci Rep 15, 3430 (2025). doi.org/10.1038/s41598-025-86788-0
THUMS https://www.toyota.co.jp/thums/about/
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