Three hundred forty-seven female office workers from different workplaces in southern and eastern Finland were referred to the study through their occupational health care systems. Potential subjects were identified through the local offices of the Social Insurance Institution, which provides state-financed rehabilitation in Finland. A questionnaire was mailed to these prospective participants to confirm their status regarding the inclusion and exclusion criteria. At this stage 121 candidates were excluded because of not meeting the eligibility criteria. Finally a total of 180 females met the inclusion criteria and also entered the study. Inclusion criteria were: female, aged 25 to 53 years, office worker, permanently employed, motivated to continue working, motivated for rehabilitation, and constant or frequently occurring neck pain for more than 6 months. Exclusion criteria were severe disorders of the cervical spine, such as disk prolapse, spinal stenosis, postoperative conditions in the neck and shoulder areas, history of severe trauma, instability, spasmodic torticollis, frequent migraine, peripheral nerve entrapment, fibromyalgia, shoulder diseases (tendonitis, bursitis, capsulitis), inflammatory rheumatic diseases, severe psychiatric illness and other diseases that prevent physical loading, and pregnancy. A detailed flowchart depicting the step-by-step enrolment process was published in an earlier report . The subjects were randomized into two training groups and into a control group. A randomization into three groups of ten persons was performed blind before inviting the subjects to the rehabilitation centre. After obtaining 30 subjects, 10 in each group, they were ranked by the neck and shoulder pain and disability index and divided into 10 blocks of three groups. From each block, one subject was randomized to one of the training groups or to the control group according to a computer generated list. This stratification was used to ensure that subjects with equal severity of neck symptoms were present in each group. The trial was conducted between February 2000 and March 2002.
All of the participants provided written informed consent before entering the study. The study design was approved by the ethics committee of the Punkaharju Rehabilitation Centre, Punkaharju, Finland.
All measurements were performed blind by the same physical therapist at baseline and after the 12-month intervention period. HRQoL was measured using the generic self-administered questionnaire 15D, which includes the dimensions mobility, vision, hearing, breathing, sleeping, eating, speech, elimination, usual activities, mental function, discomfort and symptoms, depression, distress, vitality, and sexual activity . Each dimension has five grades of severity. The 15D can be used both to obtain a profile across the 15 dimensions and a single index score ranging from 0 (being dead) to 1 (full health). The 15D has proven to be reliable and valid instrument for measuring HRQoL [6, 29–31]. It has also been used to describe the impact of different chronic conditions on HRQoL, including neck problems .
A neck strength measurement system (Kuntoväline Ltd, Helsinki, Finland) was used to test the isometric neck muscle strength with patients seated in a standard position, and the methodology followed the same method used in the reliability study reported earlier .
The subjects were randomized into three groups: a strength training group (STG, n = 60), an endurance training group (ETG, n = 60), and a control group (CG, n = 60). Both of the training groups participated in a 12-day rehabilitation program in a rehabilitation centre; the program was then performed as a home training program for one year.
The STG used a rubber band to train the neck muscles in a single series of 15 repetitions, each repetition reaching resistance level of 80% of the patient's maximum isometric strength as recorded at baseline. The patient sat in an upright position and the other end of the rubber band was attached to the patients head and the other end to a sturdy stand. The patient then bent from hips directly forwards, obliquely toward right and left and directly backwards. The erect posture of the spine was maintained throughout the exercise. The subject's ability to reach the 80% resistance level was checked with a handheld isometric strength testing device (Force-Five, Wagner Instruments, Greenwich, CT) attached to the rubber band, at the baseline and at 2- and 6-month follow-up visits for controlling the progress of the training. In addition, a single adjustable dumbbell was used to perform upper body exercises: dumbbell shrugs, presses, curls, bent-over rows, flies, and pullovers. For each exercise, one set of 15 repetitions at the highest load possible was performed. Training was progressive such that if a patient could do 20 or more repetitions, weight was added.
The ETG trained their neck muscles by lifting the head up from supine position in three sets of 20 repetitions. The patients used a pair of dumbbells each weighing 2 kg to perform three sets of 20 repetitions of the same upper body exercises the STG was performing. Both training groups exercised three times per week and also performed a single series of squats, sit-ups, and back extension exercises in addition to 20 minutes of stretching exercises for the muscles trained.
The CG received written information and a single guidance session concerning the same stretching exercises that the training groups were performing. In addition, all the three groups were encouraged to perform aerobic exercise three times a week for 30 minutes.
Compliance with the specific training programs was collected via a training diary throughout the 12-month intervention. The training diaries were checked at 2-, 6-, and 12-month visits for the two training groups and at 12-month for the control group.
The results are expressed as means and standard deviations (SD). Statistical comparisons between the groups in baseline characteristics were performed using analysis of variance. The differences between groups in 15D dimensions and total score were tested by using bootstrap techniques due to the skewed distributions. Bootstrapping is a re-sampling method, in which you make no assumptions on distribution . A bootstrap-type analysis of variance was used to test differences at baseline. Changes between the groups were tested by bootstrap-type analysis of covariance (ANCOVA) with baseline values as covariates. Effect sizes were calculated using the Cohen method for paired samples . An effect size of 0.20 was considered as small, 0.50 as medium, and 0.80 as large. Confidence intervals (95% CIs) for the effect sizes were obtained by bias-corrected bootstrapping (5,000 replications) . Post hoc (observed) power calculation was done based on Monte Carlo simulation of ANOVA designs. The α-level was set at 0.05. All statistical analyses were performed using STATA (for Windows), version 10 (Stata Corp, College Station, TX, USA).