Introduction

As the spine consists of many different joints, many movement strategies can be used throughout functional tasks such as bending or lifting. However, people with low back pain or a history of pain in this region often become very rigid while moving their spine. They generally use a strategy where the pelvis and thoracic spine move in the same direction. Dissociated movements, however, require opposite movements from the pelvis and thorax. At the same time, pelvic-thoracic motion dissociation can help people with movement restrictions to “unlock” other movement strategies, but many people find it difficult to achieve it. This study wanted to examine if people could dissociate pelvic and trunk movements during a repetitive task and if short training could improve this.

Methods

The participants were equipped with retroreflective markers attached to their skin from spine levels T8 to S1. The study used a cross-over design.

Baseline

The participants underwent two tasks of trials before and after a targeted training protocol. The tasks included:

1. Lift/Lower Task: Participants performed 35 continuous lift/lower cycles using a 1.8 kg box, lifting it between two shelves at knee and shoulder height, at a speed from 0.5 Hz following a metronome. After this task, 10 minutes of rest was allowed.
2. Pelvic Tilt Task: Participants performed 35 continuous standing anterior to posterior pelvic tilt motions, aiming to isolate pelvic movement while minimizing torso and limb movements. This repetitive task followed a metronome of 1Hz so that each tilting motion was performed over 2 seconds.

Training

After these two measurements were obtained, all participants received a 20-minute pelvic-thoracic motion dissociation training. The training was designed to improve pelvic motion control and its dissociation from trunk movement. The progression included:

• Cat-Cow Motions: Performed in a quadruped position, first freely and then with an object placed to limit trunk movement, promoting pelvic-thoracic motion dissociation.
• Guided Pelvic Tilts: Initially done in a kneeling position with physical guidance, then in a standing position, and finally with only verbal cues at a set pace.

Follow-up

After this training, the participants performed the repetitive lifting and pelvic tilting tasks again.

The movements of the thorax and pelvis were objectified from the kinematic data obtained through the retroreflective markers. A local coordinate system was constructed from which 3D angles could be calculated. The movements of the thorax and pelvis were however only analyzed for flexion and extension motion.

From this information, six coordination patterns between pelvic and thorax motion were determined. These patterns refer to the different ways the thorax and pelvis can move relative to each other during motion

• In-Phase: The pelvis and thorax move in the same direction and with similar magnitudes. They are effectively synchronized in their movement. For example: Anterior tilt of the pelvis and Flexion of the thorax.
• In-Phase Pelvis Dominant: The pelvis and thorax move in the same direction during the motion. However, the pelvis moves significantly more than the thorax.
• In-Phase Thorax Dominant: Similar to the in-phase pelvis dominant pattern, both the pelvis and thorax move in the same direction, but here, the thorax moves more than the pelvis.
• Anti-Phase: The pelvis and thorax move in opposite directions with similar magnitudes of movement. For example: Anterior tilt of the pelvis and extension of the thorax.
• Anti-Phase Pelvis Dominant: The pelvis and thorax move in opposite directions, but the pelvis moves more than the thorax.
• Anti-Phase Thorax Dominant: In this pattern, the pelvis and thorax move in opposite directions, but the thorax movement is more pronounced.

The Anti-Phase movements represent dissociated movements between the pelvis and thorax. The Anti-Phase pelvic dominant coordination pattern was the pelvic tilting task and training objective. The Anti-Phase and Anti-Phase Thorax dominant were also desirable, but the authors were mainly interested in the Anti-Phase pelvic dominant coordination pattern.

Local dynamic stability during the lifting/lowering and the pelvic tilting trials was analyzed by sampling lumbar spine flexion and extension angular motions.

Results

Seventeen healthy people participated. They were free from any history of low back or pelvic pain. Their mean age was 25.3 years and they were on average 173.7 cm tall and weighed 71.7 kilograms.

Ten participants were classified as high skill and seven were classified as low skill, based on a visual observation of their ability to perform the pelvic tilting movement competency during the repetitive pelvic tilting trial.

Continuous Pelvic Tilt trials

At baseline, there was a large and significant difference in the coordination patterns between people from the high- and low-skill groups observed during the continuous pelvic tilt trials.

• Before the training, people classified as a low-skill group used In-Phase movements and to a lesser extent In-Phase and Anti-Phase pelvic dominant coordination patterns during repetitive pelvic tilt trials.
• The participants with high movement skills used more Anti-Phase and Anti-Phase pelvis dominant patterns before the training protocol. This means that they use a dissociated movement pattern during the repetitive tilt trials. When they tilt their pelvis anteriorly, they couple this with thorax extension.

In brief, the low-skilled participants used more In-Phase movements and the high-skilled participants used more Anti-Phase movements.

After the training phase:

• In the low-skill group, the use of In-Phase pelvis dominant and Anti-Phase pelvis dominant was significantly increased. In contrast, the use of In-Phase movements was reduced, although not significantly.
• After completing the training phase, no differences were observed in the high-skill group.

While nothing changed for the high-skilled participants after the training phase, the low-skill group still used significantly more In-Phase pelvis dominant and In-Phase movements compared to the high-skill group. Still, they increased in doing more Anti-Phase Pelvic dominant and In-Phase Pelvis dominant movements while they reduced In-Phase coordination patterns. This means they learned to use more pelvic movement in the repetitive pelvic tilt trials.

Repetitive lift/lower trials

During repetitive lifting and lowering tasks, both before and after the training, the participants used in-phase coordination patterns around 75% of the time, and in-phase thorax dominant about 20% of the time, irrespective of belonging to the high- or low-skill group.

No difference between the groups emerged at baseline or after the training phase. Likewise, no difference within the groups was observed, apart from a very small, but likely insignificant difference in the high-skill group as seen in the picture below (*).

Questions and thoughts

In summary, the participants who had difficulties dissociating movements of their pelvis and thorax during repetitive continuous anterior and posterior pelvic tilts improved their ability to do so after a brief 20-minute training session. They could use more pelvic motion during the repetitive pelvic tilting trials and were able to better dissociate movements between the pelvis and thorax. Participants who already had high skills for these anterior and posterior pelvic tilt movements before the training did not improve their ability to do so after the training session.

Low back pain patients frequently report movement stiffness and often perform poorly on motor control tests assessing control and pelvic-thoracic motion dissociation. This study showed that brief training can help individuals increase their capacity to control and disassociate their movements, resulting in more movement strategies available to ease their feelings of movement stiffness. This in turn could improve better control over their low back movements and more comfortable mobility. This could be beneficial for persons with acute or chronic back pain, as well as those with mild pain. However, we have to keep in mind that this study examined healthy people free of any low back pain.

No differences were observed during the repeated continuous lifting and lowering trials. Not between high and low-skill participants, nor before or after the training sessions. Thus, the participants in this study did not significantly change the way they coordinated their pelvis and thorax during the continuous lifting/lowering task after training to separate pelvic and thoracic movements.

• The authors stated that this was consistent with their hypothesis, as lifting/lowering is a well-known movement performed in close coordination between the pelvis and thorax. Lifting is usually an in-phase movement, with the thorax and pelvis moving in the same direction. So the pelvis will tilt anteriorly as the thorax moves into flexion and vice versa.
• The authors point out that it is not necessary or intended to separate the movements of the pelvis and thorax during lifting and lowering. This is something I personally liked about this study. The authors did not state that lifting should be done with a straight back to protect the spine, which you often read in “medical advice”. They stated that lifting is mainly done from a flexion of the thorax and an anterior tilt of the pelvis.
• This corresponds to the findings of an earlier earlier research review I wrote, where lifting was compared across three lumbar positions: lifting with a flexed, neutral, or extended spine. In this particular study, more strength and efficiency were found when lifting was done with a flexed spine. When looking at the methods of that particular study, indeed, lifting with a flexed spine was an in-phase flexion movement.
• As such, it appears that there is no superiority in keeping your back straight when lifting an object.

Unfortunately, this study did not investigate whether the participants could have achieved some pelvic-thoracic motion dissociation during the lifting/lowering task if instructed to do so. This could have been interesting since this capacity would give persons more movement variability during functional tasks.

Personally, I liked how this article did not emphasize the use of pelvic-thoracic motion dissociation to create a “correct movement pattern”. Instead, they were interested in creating more movement variability, especially, giving people more ways to perform a lifting task.

Talk nerdy to me

The analysis of local dynamic stability during the pelvic tilting trials revealed that the low-skill group had more stable movements compared to people in the high-skill group. After the training, both groups had significantly less stable movement. This was in contrast with the hypothesis of the study. The authors, however, question the ability of their analysis to provide meaningful results.

Something to bear in mind was the use of skin markers, which may be subject to movement artifacts. This was a cross-over design, which has the advantage that the treatment impact is compared within every subject, as each subject is his or her own control. Thereby, inter-subject variability from group comparisons is reduced, allowing the effect of covariates to be decreased. Second, it is possible to acquire an estimate with the same level of accuracy as a parallel design, even with fewer individuals, which is often a limitation in studies using a small number of participants.

Take home messages

A short 20-minute training session was able to modify movement strategies in people who have difficulties performing pelvic movements. After the training, people were able to use a lot more pelvic movements during a repetitive pelvic tilting motion exercise.

Reference

Shannick J, Armstrong-Harper L, Sheppard E, Larson DJ, Brown SHM. Can training to dissociate trunk and pelvic motion influence thorax-pelvis coordination and lumbar spine dynamic stability? Musculoskelet Sci Pract. 2024 Aug;72:102955. doi: 10.1016/j.msksp.2024.102955. Epub 2024 Apr 13. PMID: 38636346.