Relation between endurance of deep cervical flexor muscles and physical activity level, perceived stress, sleep quality, and smartphone addiction.

: To determine the reference values of deep cervical flexor muscle endurance and its relationship with associated parameters.: The International Physical Activity Questionnaire, Perceived Stress Scale, Pittsburgh Sleep Quality Index, and Smartphone Addiction Scale-Short Version were used in the study. The craniocervical flexion test was performed to measure the endurance.: Endurance (mmHg) values were determined as 24.23 ± 2.39 (women), 24.15 ± 2.65 (men), and 24.19 ± 2.51 (students). The cumulative endurance (mmHg) scores were determined as 27.50 ± 21.29 (women), 27.65 ± 25.42 (men), and 27.57 ± 23.33 (students). There was no correlation between the endurance of the muscles and age, gender, body mass index, physical activity level (except walking score), perceived stress, sleep quality (except sleep latency component), and smartphone addiction ( ˃ 0.05).: Defining the reference values of Stage 2 and cumulative endurance would be of great value for preventing, diagnosing, and managing cervical area problems.