Introduction

Dysphagia or swallowing difficulties can be present in a wide array of neurological conditions (such as ALS and Parkinson’s) often encountered in physiotherapy practice. Mostly, these swallowing problems are treated by someone specialized in speech therapy, but as these patients are also consulting physiotherapy practice for related comorbidities, it would be interesting to know if our profession could be of value in supporting swallowing rehabilitation by any means. This article aimed to examine the effect of craniocervical flexor exercises on the activation of the suprahyoid muscles during swallowing.

Methods

Eighty healthy participants aged 17-29 years were included in this randomized controlled trial. They scored less than 3 points on the Eating Assessment Tool 10, which is a self-administered, symptom-specific outcome instrument for dysphagia. A score of more than 3 points indicates a disturbance in swallowing function. The score below 3 confirmed that the swallowing function of these participants was normal.

The intervention consisted of a 4-week craniocervical flexion exercises training. This training was performed for 5 days per week and for 20 to 30 minutes of duration. Meanwhile, the control group did not receive any intervention. The training required the participant to nod to perform a flexion movement of the upper cervical spine and hold it for 10 seconds. This was repeated 10 times with a 3- to 5-second break in between each repetition. If the participant was able to hold the contraction correctly for 10 repetitions of 10 seconds, progression to the next level was made. The pressure of the stabilizer was progressively increased from 20-30 mmHg, by increments of 2 mmHg each. As such, progressions could be made from 20 mmHg to 22 mmHg, to 24 mmHg, .. etc, until the level of 30 mmHg was achieved.

The outcome measures included:

• The Craniocervical Flexion test (CCFT): The CCFT is performed to evaluate the control and endurance of the deep cervical muscles: the M. Longus Capitis and the M. Longus Colli. A pressure sensor (the Stabiliser) was placed under the neck of the participant between the earlobe and the chin, with the participant in supine. The pressure sensor was positioned and inflated to an initial pressure of 20mmHg. The participant was asked to perform a nodding movement and the movement was controlled by the examiner to ensure a correct performance, without activation of the superficial muscles.
• The tragus-to-wall distance: This test measures the extent to which the participant has a forward head posture. The subject is placed with the back, scapulae, and buttocks against the wall with the heels 10 centimeters from the wall. From this position, the chin is drawn in as much as possible. The distance between the tragus and the wall is measured.
• Using a goniometer, cervical range of motion was measured for flexion, extension, lateral flexion, and rotation.
• Cervical muscle strength was assessed using the Kendall manual muscle strength assessment. Strength was rated from 0-5 using the Kendall method, which is comparable to the Medical Research Counsil (MRC) method.

• The Activation of the suprahyoid muscles (M. Digastricus, M.Mylohyoideus, M. Stylohyoideus, M. Geniohyoideus) was assessed with surface EMG.
  • A maximal voluntary isometric contraction (MVIC) of these muscles was assessed by asking the participants to open their jaw as strongly as possible against a constant resistance applied by the assessor for 6 seconds.
  • Next, the activation of the suprahyoid muscles was assessed during a swallowing task. The participants were asked to swallow 10 mL of water in a single swallow, as is often done in dysphagia screening. The EMG signals during this task were recorded.

From the CCFT, the activation score and the performance index were calculated. The activation score is the number of repetitions of 10 seconds that are performed correctly. The performance index is calculated by multiplying the pressure increase by the number of correct repetitions performed. For example, when a participant reaches the level of 24 mmHg and can hold it correctly for 10 seconds for 6 times, the performance index is 4×6=24. When the pressure level of 30 mmHg is achieved for 10 correct 10-second repetitions, the performance index reaches its maximum of 10×10=100.

Results

Let’s look at the results, can craniocervical flexion exercises improve swallowing function? Eighty healthy individuals were included. The participants in the intervention and control groups were equal at baseline.

The activation score at the start of the study was 2.15 in the control group and 2.54 in the intervention group. The between-group difference in the activation score was 3.41 after the four weeks.

Looking at the calculated performance index revealed that the between-group difference favored the intervention group with an increase of 23.7 (95% CI 18.93-28.47) from baseline until the 4th week.

The forward head posture decreased in both groups and the between-group difference was -0.89 (95% CI -1.11 to -0.66).

No differences were observed between the groups for neck range of motion, except for left rotation. Muscle strength was significantly higher in the intervention group for the extensors.

Considering the EMG analyses, the study showed that the peak amplitude of the suprahyoid muscles decreased by -8.54 (95% CI -15.17 to -1.91). The mean suprahyoid amplitude decreased by -6.09 (95% CI -10.01 to -2.17), both results favoring the intervention group.

Questions and thoughts

When is the craniocervical flexion movement not performed correctly? The authors described it clearly in their paper. The authors rated the test as performed incorrectly when:

• The pressure increases initially with more than 2 mmHg
• The movement is performed too quickly
• The superficial muscles contract
• The pressure does not return to the starting point when the participant relaxes
• The lordotic angle is lost or the individual raises his head

You could control for these incorrect ways when you give the craniocervical flexion exercises to your patients.

The paper found significant differences in favor of the intervention group for improvements in the execution of the craniocervical flexion exercises (activation and performance scores), the tragus-to-wall distance, left rotation and muscle strength of the extensors. The EMG analysis revealed that less activation of the suprahyoid muscles was required during the swallowing task. It appears that craniocervical flexion exercises improve swallowing function.

No improvements were observed in the cervical spine range of motion, except for left rotation, but as this was the only result improving here, it was possibly a type I error.

A slight improvement in forward head posture was observed in the intervention group. As far as we know, the minimally clinically important difference (MCID) for the tragus-to-wall measurement is not determined for healthy populations. Most of the research focuses on people with ankylosing spondylitis, and in this sample, 1-2 centimeters of improvement is generally considered the MCID.

An increase in the strength of the cervical extensors was observed, however, the fact that this had not been evaluated using dynamometry makes the interpretation somewhat unsure. However, the relationship between upper cervical spine flexion and lower cervical spine extension is well established. The fact that the people learned to use the deep cervical flexors of the upper cervical spine, could have led to more efficient use of the extensors in the lower cervical spine contributing to extension. On the other hand, it could be a finding indicating that people did not always truly perform the deep upper cervical flexion well, but instead performed a cervical extension and hence improved their strength in the cervical extensors as well. It was not mentioned if the intervention was supervised, so it could be the reflection of an incorrect way of performing the deep cervical flexion exercise.

A decrease in the activation of the suprahyoid muscles means that fewer motor units are necessary to perform the same swallowing task. This is an important finding for people with neurological disorders.

Talk nerdy to me

The control group did not receive any intervention. Did they know the purpose of the study and the procedures before randomization? If they knew, they would possibly expect no benefits when randomized to the doing-nothing group. In this case, it would be logical for the intervention group to expect that craniocervical flexion exercises improve swallowing function.

It was not mentioned in the article whether the intervention was supervised or performed at home. As such, we can not confidently state that the exercises were performed correctly or corrected by the investigators.

No objective strength measurements were obtained, which may bias the results. The same investigator conducted the treatments and assessments and hence there was no blinding of the assessor, which may have also induced bias in the results. Not many details are given about the randomization procedure at all.

Take home messages

The suprahyoid muscles’ effectiveness, which aid in swallowing, can be increased by performing deep cervical flexion training. This intervention can help in people with swallowing disorders such as those often seen in neurological disorders. The performance of the deep cervical flexor muscles increased and this reflects a better stabilization of the upper cervical spine during the swallowing task, which lowers the activation needed from the suprahyoid muscles. In fact, earlier studies also showed that swallowing in a chin-down position is more effective and reduces the risk of aspiration. Thus, craniocervical flexion exercises improve swallowing function in this healthy population.

Reference

Toksal Uçar A, Yalçın AI, Cetin H, Bostan G, Bilgin S. The effect of craniocervical flexors endurance training on suprahyoid muscle activation in healthy adults: A randomised controlled trial. J Oral Rehabil. 2024 Apr 25. doi: 10.1111/joor.13703. Epub ahead of print. PMID: 38661347.