## 4 Discussion  
The aim of this study was to investigate if a neck muscle endurance test and/or morphological characteristics of DN muscles were correlated to pain intensity, neck disability and headache impact in patients with neck pain. The muscle endurance test reported a weak to moderate negative correlation to NDI and HIT-6, but not to pain intensity. No ultrasound measurements were correlated to pain intensity, NDI or HIT-6, but DN flexor muscles' CSA showed a weak negative correlation with NDI. In women with neck pain and low levels of disability, the endurance tests for neck flexor and extensor muscles have demonstrated a negative correlation with neck disability and the impact of headaches. This suggests that patients with mild neck disability and weakness in the neck flexor and extensor muscles experience higher levels of neck disability, and headaches have a greater impact on their daily life. [PERSON] et al. also reported similar findings, showing a negative correlation between the neck extensor endurance test and the Neck Disability Index (NDI) in patients with chronic pain [17]. Additionally, this study found that patients with chronic neck pain exhibited higher overall muscle fatigability and a smaller size of the deep neck extensor muscles. The results of this study can be added to those presented by [PERSON] et al. [17] in patients with chronic neck pain. These results could be important in the prevention of neck pain. The endurance of the neck flexor and extensor muscles is affected and correlated with the perception of neck disability and headache. In this sense, these patients rarely attend health services, given that cervical pain does not have a significant impact on quality of life [13]. However, it is crucial to consider that this pain could potentially become chronic, making it essential to train the cervical musculature to prevent self-perceived cervical disability. Further research is needed to confirm these findings and explore effective preventive measures. The results of CSA showed a weak negative association only for DN flexor muscle and neck disability. Concerning ultrasonography measurements, only DN flexor muscles' CSA showed a weak negative correlation with NDI [60], and therefore subjects with mild disability who have a higher CSA present a lower NDI. In this sense, patients with neck pain for less than 3 months and low levels of disability may present decreased endurance of the neck flexor and extensor muscles, but the CSA may not be affected yet. It has been described that the reduction in DN endurance may lead to a decrease in the CSA when this situation is maintained over time [26]. A clear example in the literature is patients with chronic neck pain. This type of patient presents a decreased activation of the DN flexor and extensor muscles, and a reduced CSA [17; 28]. This fact is also described in women; [PERSON] et al. showed a reduction in the CSA of multifidus muscles in chronic neck pain in comparation with a healthy control [28]. Therefore, compared to what happens with patients with chronic neck pain, patients with low neck disability in the acute or subacute period do not present correlations between the DN extensor muscle CSA and the self-perceived symptoms, but there is a correlation between the DN flexor CSA and NDI. [PERSON] et al. [27] conducted a systematic review with a meta-analysis that compared the morphological characteristics of the muscles between healthy controls and patients with chronic neck pain, showing that the size of longus coli was slightly smaller in patients with chronic neck pain, but the size of the multifidus was equal between groups. Although more