In reference to:
A Biomechanical Review of the Squat Exercise: Implications for Clinical Practice
Straub RK, Powers CM. A Biomechanical Review of the Squat Exercise: Implications for Clinical Practice. Int J Sports Phys Ther. 2024;19(4):490-501. doi: 10.26603/001c.94600. PMID: 38576836; PMCID: PMC10987311.
Dear Editor,
Sometimes scientific knowledge seems to run in circles. At some point one finds oneself in old discussions that were assumed to be settled a long time ago.
This is what I experienced when reading ‘A Biomechanical Review of the Squat Exercise: Implications for Clinical Practice’ by Straub and Powers. This paper describes and analyzes the squat exercise as an effective exercise with several therapeutic applications, and low back pain is mentioned
With this comment I do not have the intention to argue that the squat exercise is not applicable. There will be some useful application of this exercise for sure. However, some arguments, claims and suggestions in the paper by Straub and Powers are diametrically opposed to current scientific viewpoints. And although the authors refer to a large number of articles that span a considerable number of years, several essential articles are omitted or ignored.
In the paragraph SQUAT DEPTH it is argued that lumbar spine flexion is coupled with an increase of compressive and shear forces at the lumbar spine. This is contradicted by literature.
An increase in shear force and compression is not caused by the shape of the spine, but much more by the inclination of the trunk and the weight that is carried .1–3
Shear forces in the lumbar spine are predominantly counterbalanced by the facet-joints, even with the lumbar spine in flexion. Flexion oriented torques generated by trunk weight and inclination, and the lifted load, are counterbalanced by a combination of passive and active elements in the trunk.4,5 The force distribution between these elements largely depends on the amount of lumbar flexion.2,3 In lordosis the extension force predominantly comes from muscle.5
With increasing flexion, increasing passive support can be addressed, as the well-known flexion-relaxation phenomenon shows.6–8 In (sub-) maximal flexion the extension is mainly supported by passive structures like the thoracolumbar fascia. In this position the erector spinae muscle remain EMG-silent.4–6,9,10
Figure 2 of the paper shows a more flexed spine and a spine with more lordosis. It is stated that the flexed posture (A) has less tolerance to compressive loads. This is in contrast with the findings of Adam and Dolan.2,3 According to their studies, lumbar flexion provides a better distribution of force within the discs, leading to improved compressive resistance.3 Furthermore a flexed posture will allow passive elements like the thoracolumbar fascia to contribute to extension force on the spine and pelvis.11 Since the point of attachment of these structures is more distant from the pivot point, the lever arm is larger than that of lumbar muscles.8 Consequently, to provide an equal extension moment the actual tension force can be smaller when using the fascia predominantly. This leads to the conclusion that that in flexion the spine has an increased tolerance to compressive loads and not decreased as suggested in the commentary
Finally, low back pain patients tend to fix their lumbar spine when bending forward.9,12 This is considered a protective strategy where back muscles contract abundantly to limit motion of the lumbar spine. This deviant, protective behavior is supposed to diminish over time. Application of the squat motion mimics and stimulates the aberrant compensatory behavior. From a therapeutic perspective this is not a desired therapeutic effect.
There are situations where the squat applies. This is clearly not the case in patients with lower back pain. Therefore, it is confusing that Straub and Powers have included this point of reference in their article. The squat increases compression, which puts more strain on the lower back and above all hinders the recovery of normal movement behavior of the lower back. Better advice would therefore be not to use the squat when recovering from lower back pain.
Jan-Paul vanWingerden, Spine and Joint Center, Rotterdam, the Netherlands
References
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