## 1 Introduction
In the scientific literature, several studies evaluated and created indicative values or norms for cervical isometric strength using a large variety of devices (fixed frame dynamometers, computerized dynamometers, or handheld dynamometers), testing positions (standing, sitting, supine, prone, or quadruped) and protocols in different populations, such as workers, athletes and non-athletes, younger and older individuals, and males and females [14; 21; 22; 32; 33; 34; 32; 35; 36; 37; 38; 39; 40; 41; 42; 43]. It should be mentioned that most of the aforementioned studies have mainly focused on absolute cervical isometric strength values, reporting conflicting results concerning age- and sex-related effects [33; 38; 42; 43]. However, there is limited information regarding (a) the relative cervical isometric strength values, (b) the cervical strength asymmetries between left and right sides, and (c) the cervical flexion-to-extension ratios. However, the evaluation and calculation of all the above strength parameters may provide a more complete picture of the proper function, stability, and balance of the cervical spine. There is a notion that the muscular imbalance between the strength of cervical extensor and flexor muscles can be negatively correlated with the stabilization of the cervical spine [24; 36]. It has also been reported that low levels of cervical strength and cervical flexor-to-extension ratio values less than 60% are associated with an increased prevalence and incidence of sport-related concussion in adolescents and adults [36; 44; 45; 46], where other studies have reported no significant relationship between cervical strength and concussion [47]. The measurement and evaluation of the range of motion constitute a basic component of the physical examination of the cervical joint. Numerous studies have evaluated and created indicative values or norms for cervical range of motion using multiple radiological (functional X-rays) or non-radiological devices (goniometers and inclinometers, and electromagnetic, ultrasonic, and optoelectronic systems), testing positions, and protocols in different populations, showing wide variations in the measured values [48; 49; 50]. Age and sex are two of the most important factors that could affect the cervical range of motion; however, previous studies that examined the age- and sex-related effects on cervical range of motion demonstrated controversial results [48; 51; 52]. Several studies stated that (a) females have greater cervical ROM than males and (b) cervical ROM is reduced with increasing age, whereas other studies reported no significant differences between malesand females, or between different ages [48; 51; 52]. Therefore, the influence of sex or age on cervical ROM still merits discussion to draw safer conclusions [48]. Taking all the above into consideration, the main objective of this study was to evaluate and create a comprehensive strength (absolute and relative values, flexion/extension ratio, strength asymmetries), range of motion (ROM), and musculoskeletal pain profile of the cervical spine, using simple, handy, and portable equipment (handheld dynamometer and digital goniometer), in young physically active adults (19-24 years old), while simultaneously examining the possible sex-related differences (males vs. females). It has been hypothesized that males would demonstrate greater cervical strength values than females in all directions of movement, as well as greater cervical flexion/extension ratio values than females, while females would exhibit greater cervical ROM values than males. It was also hypothesized that basic anthropometric characteristics (body height and body mass) would influence cervical absolute strength values, therefore eliminating the differences in relative strength values between males and females. Furthermore, it was hypothesized that males and females would produce similar strength and ROM values in both sides (right and left).