Methods
Neck disability, Pain, ’, pain, neck muscle endurance, depressive, chronic headache, neck disability, headache, endurance of neck extensors, Depression
REGRESSION, RECRUITMENT, CHRONIC HEADACHE, SECONDARY
We conducted a 6-month randomized controlled trial at two centers (UKK Institute, Tampere, Finland, and Metropolia University of Applied Sciences, Helsinki, Finland) from October 2012 to June 2013. The trial design has been published elsewhere.We recruited women aged 18–60 years with chronic headache by using newspaper advertising. The flowchart of the study is presented in Flowchart of the trial.The randomization schedule was generated by a statistician who was not involved in the recruitment of the participants. Block randomization with block sizes of 2, 4, 6, and 8 was used. The randomization sequence involved stratification according to the two study centers. The group assignments were placed in consecutively numbered, sealed, opaque envelopes. After a woman met the eligibility criteria during the baseline-assessment visit to the physical therapist, she opened the next available envelope of her stratum.A sample size of 49 women in each group was calculated to detect a decrease of 20 mm or more on the Visual Analogue Scale (pain intensity), over 6 months, with 90% power and an alpha of 0.05.The 6-month progressive therapeutic exercise program in the exercise group consisted of six modules; the first three included low-load exercises for the neck–shoulder region, and the remaining three specific strengthening exercises for the neck and upper body. Three stretching exercises were included from the third module onward.The control group underwent six individual 45-min sessions consisting of placebo-dosed treatment with 20 min of transcutaneous electrical nerve stimulation (less than 10 mA, phase width 150 ms, and 100 Hz constant frequency [Chattanooga Intelect Advanced device 2765CS, Chattanooga Group Inc., Hixson, Tennessee, US]) once a month for 6 months, rather than weekly as suggested.Pain intensity (primary outcome), and frequency and duration (secondary outcomes) of headache episodes were captured using weekly diaries. The participants reported the intensity of each headache episode by using a segmented Numeric Pain Rating Scale (0–10 integers) which is a validated version of the Visual Analogue Scale,At baseline and at 6 months, neck disability was assessed with the Neck Disability IndexParticipants’ age, education, and occupation were enquired at baseline. At baseline and at 6 months, they were asked about medication, menstruation status, sleep, depressive symptoms (using the Beck Depression InventoryBetween-group differences in the intensity, frequency, and duration of headache episodes based on diaries were analyzed according to the intention-to-treat principle. Data were analyzed in 4-week periods at three time points (baseline, 3 months, and 6 months) with generalized linear mixed models with confounding variables as covariates (age, type of work, smoking, use of headache medication, Work Ability Index score, type of headache, hormonal medication, menstruation status). In the case of count data (e.g., frequency of headache) Poisson or negative binomial regression was used. Prior to analyses, covariates and time were decided as random effects. The potential effect of the study center as a covariate was checked afterward (intra-class correlation coefficient 0.07% for the Numeric Pain Rating Scale), and the study center was excluded from the final models. Neck disability, neck muscle endurance, and neck range of motion were analyzed by analysis of covariance. Odds ratio was used in the analysis of endurance of neck extensors. Effect size was calculated by using Cohen's Before the group assignment was revealed, statistical analyses were conducted with masked identifiers and the statistician was blinded to the group assignment. Complete analyses and blinded interpretation