## 1 Introduction  
Non-specific neck pain is an increasing health concern among the working-age population [1]. Almost two-thirds of the global population experience neck pain at least once in their lifetime [2], making it the third most burdensome condition among musculoskeletal disorders [3]. Neck pain imposes a significant social and economic burden [4], increasing societal costs and reducing work productivity [5; 6]. In most cases, the cause of the pain cannot be pinpointed, thus defining the condition as non-specific neck pain [7]. The pain localization is in the posterior neck region, between the superior nuchal line and the spinous process of the first thoracic verteba [8].  
Many modern professions and occupations require workers to maintain constant sitting or standing positions, affecting their health [9], especially when occupational activities involve a forward-tilted neck [10]. Sitting at work for more than 95% of the working time is considered a risk factor for developing neck pain [11]. Moreover, long working hours with few breaks limit workers' physical activity [6].  
Various treatment protocols are utilized for work-related neck pain [12]. Evidence-based physiotherapy recommends combining manual therapy, exercise, and education [13].  
Although a systematic review analyzing 40 articles concluded that there is no single superior type of physical exercise for people with chronic non-specific neck pain [14], different interventions such as manual therapy techniques [15], TENS [16], massage or laser treatments [17], cervical traction [18], as well as stretching, strengthening, endurance training, aerobic conditioning, and cognitive-affective elements [19] may be included in treatment protocols. Additionally, there is strong evidence that for chronic neck pain, mobilization does not need to be applied at the symptomatic level for improvement [8]. Although home-based programs are low-cost and feasible, training adherence is often low [20]. A statistically significant decrease in pain was shown after the self-stretching interventions [21]. Furthermore, it is seen that a stretching exercise program performed regularly for four weeks may decrease neck and shoulder pain and improve neck function and quality of life in office workers suffering from chronic neck pain [22]. Performing stretching exercises can help increase muscle flexibility and endurance [23]. Some studies show that patients with non-specific neck pain can benefit from muscle energy techniques, such as post-isometric relaxation [24]. It is suggested to include post-isometric relaxation in the treatment of non-specific chronic neck pain in individuals with a forward head posture [25].  
TENS is a therapeutic strategy that can be proposed to alleviate chronic neck pain [26]. The mechanism of pain relief mediated by low-frequency TENS includes promoting endorphin release, leading to vasodilation in the injured tissue [27]. The use of TENS in combination with other therapies allows patients to increase their activity levels and improve function [27]. However, the clinical efficacy of post-isometric relaxation (PIR) and self-stretching (SS) in addition to TENS remains unclear. This study was conducted to explore the effect of post-isometric relaxation combined with TENS compared to self-stretching combined with TENS for working-age patients complaining of chronic non-specific neck pain.