In my last blog - What is 3D Strength? - I explained why I think 3D muscles at the hip and shoulder may be the root cause behind many of the sore necks, shoulders, backs, hips and knees that I see in clinic. The idea is based on observing patterns in clinic, but to be scientifically proven the theory needs to be supported by scientific research.

The Evidence

2D Hips

Hips People with persistent hip pain have 3D muscle weakness, both on their painful and non-painful side (Harris-Hayes et al., 2014). When comparing people with and without hip osteoarthritis, people with hip osteoarthritis are weaker in all their hip muscles, but the 3D muscles seem to be where the biggest differences are found (Loureiro et al., 2013) People with greater trochanteric pain syndrome have smaller, weaker 3D muscles in the hip (Cowan et al., 2020; Plinsinga, et al., 2019). Lower Backs Research shows people with persistent lower back pain more commonly have weakness in gluteus medius on the side their lower back pain is worse (Cooper et al., 2016) and reduced gluteus medius muscle activation (Yodthee et al., 2026). There is also a correlation between weak gluteus medius (Sadler et al., 2019) and 3D hip muscle weakness more broadly (Pizol et al., 2023; Pizol et al. 2024; de Sousa et al., 2019) and low back pain. Knees

People with knee osteoarthritis tend to have less 3D muscle strength moving the leg sideways away from the body at the hip (Deasy et al., 2016). Being stronger in this 3D movement is associated with 17-20% less risk of cartilage damage worsening in knee osteoarthritis two years down the line (Chang et al., 2019). Like with hip osteoarthritis, people with arthritis on the inside of their knee are weaker in all their hip muscles, but particularly their 3D hip muscles (Hinman et al., 2010). Weaker hip 3D muscles also have a link with ITB syndrome in distance runners (Mucha et al., 2017), predict non-contact ACL injuries in athletes (Khayambashi et al., 2016) and strengthening the 3D hip muscles is more effective in treating patellofemoral pain syndrome than strengthening the quadriceps (Alammari et al., 2023).

2D Shoulders

Shoulders The 3D muscles that rotate the arm out are consistently weaker in people with rotator cuff related shoulder pain (Tyler et al., 2005; Maestroni et al., 2020), and this 3D weakness directly impacts the ability to move the arm (Manoso-Hernando et al., 2025). Reduced 3D muscle strength predisposes overhead athletes to developing shoulder problems, rather than the weakness simply occurring as a consequence of pain (Clarsen et al., 2014; Kwan et al., 2021). During rehab, working the 3D muscles specifically at the shoulder improves pain more than generic shoulder exercise (Chaconas et al., 2017), improves the arm performance more than generic rehab and improves the alignment of the ball in the socket more too (Gamiel et al., 2025). Necks There is a clear, strong link between neck conditions and 3D shoulder muscle weakness and tears (Çetin, 2019; Zhang et al., 2015) & between shoulder pain and neck pain (Libardoni, 2020). There is evidence showing people with 3D shoulder muscle pain have reduced neck motion, particularly turning the head to look over the affected shoulder (Manoso-Hernando et al., 2024; Requejo-Salinas et al., 2025). People with pain related to their 3D shoulder muscles also have lower pain thresholds in their neck (Requejo-Salinas et al., 2025). Perhaps the most convincing evidence that 3D shoulder issues cause many neck issues however, comes from surgical studies. Some classic studies from the 90's on shoulder surgery for people with neck and shoulder conditions showed: operating on only the shoulder resolved the neck complaints (Hawkins, 1990), or substantially improved the neck pain in 66% of cases (Manifold & McCann, 1999). Both studies have significant flaws by modern standards, but recent research adds weight to the idea the shoulder is ultimately responsible for many neck issues. People who had only 3D shoulder muscle tears and those with 3D shoulder muscle tears + pinched nerves in the neck both did similarly well in terms of recovery after their 3D shoulder muscles were repaired (Moorthy, et al., 2021). Another very recent study similarly found shoulder 3D muscle repair clinical outcome improvements (pain interference, physical function and depression) scores were very similar when comparing people going into surgery with only 3D shoulder muscle tears vs 3D shoulder muscle tears + other neck conditions (Shaikh et al., 2025). Outcomes are not so good for people who undergo neck surgery who experience a combination of neck and shoulder pain. In a study of 70 people having neck fusion surgery for prolapsed discs in their neck, 22 (31.4%) did not improve and 18 of those who didn't improve (4 in 5 who didn't improve) had torn a 3D shoulder muscle (the other 4 who didn't improve had different shoulder conditions) (Khan et al., 2021). Taken together, these studies show improving 3D shoulder muscle function surgically has similar benefit for people with with 3D shoulder muscle tears and neck conditions as just 3D shoulder muscle tears; but neck surgery does not appear to help people with neck and 3D shoulder muscle tears. This suggests when someone has a neck and shoulder issue, it is issues with the 3D shoulder muscles that are more often than not the key driver, not the neck condition.

Summary

The existing research shows fairly convincingly people with neck, shoulder, back, hip and knee pain often have 3D muscle issues, and that addressing these issues can help people recover. Some of the existing research hints that 3D muscles may be the cause of many of these aches and pains, but to say the currently available evidence proves this would be an overstatement. The existing research does not definitively prove or disprove the theory, but there is growing evidence based support for the theory.

References

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