ResearchEffect of neck strength training on health-related quality of life in females with chronic neck pain : a randomized controlled 1-year follow-up study

Background: Chronic neck pain is a common condition associated not only with a decrease in neck muscle strength, but also with decrease in health-related quality of life (HRQoL). While neck strength training has been shown to be effective in improving neck muscle strength and reducing neck pain, HRQoL among patients with neck pain has been reported as an outcome in only two short-term exercise intervention studies. Thus, reports on the influence of a longterm neck strength training intervention on HRQoL among patients with chronic neck pain have been lacking. This study reports the effect of one-year neck strength training on HRQoL in females with chronic neck pain. Methods: One hundred eighty female office workers, 25 to 53 years of age, with chronic neck pain were randomized to a strength training group (STG, n = 60), endurance training group (ETG, n = 60) or control group (CG, n = 60). The STG performed high-intensity isometric neck strengthening exercises with an elastic band while the ETG performed lighter dynamic neck muscle training. The CG received a single session of guidance on stretching exercises. HRQoL was assessed using the generic 15D questionnaire at baseline and after 12 months. Statistical comparisons among the groups were performed using bootstrap-type analysis of covariance (ANCOVA) with baseline values as covariates. Effect sizes were calculated using the Cohen method for paired samples. Results: Training led to statistically significant improvement in the 15D total scores for both training groups, whereas no changes occurred for the control group (P = 0.012, between groups). The STG improved significantly in five of 15 dimensions, while the ETG improved significantly in two dimensions. Effect size (and 95% confidence intervals) for the 15D total score was 0.39 (0.13 to 0.72) for the STG, 0.37 (0.08 to 0.67) for the ETG, and -0.06 (-0.25 to 0.15) for the CG. Conclusions: One year of either strength or endurance training seemed to moderately enhance the HRQoL. Neck and upper body training can be recommended to improve HRQoL of females with neck pain if they are motivated for longterm regular exercise. Trial Registration: ClinicalTrials.gov NCT01057836 Background Neck pain is one of the most common musculoskeletal disorders in Western societies [1-4]. Along with considerable costs for the individual and the society, neck pain is a frequent source of disability causing humane suffering and affecting the well-being of individuals. Just as health is a state of complete physical, mental, and social wellbeing and not merely the absence of disease or infirmity [5], the outcome measures of an intervention ought to be multidimensional and include the subjective experience of the patient. This can be achieved using a health-related quality of life (HRQoL) measurement tool [6]. Neck pain has been shown to be associated with a decrease in HRQoL in several studies [1,7-12]. While no gold standard exists for assessing HRQoL among patients with neck pain, several different measurement instruments have been used, such as the Short Form-36 Health Survey (SF-36) [13] or subscales of the SF-36, 15 Dimensional HRQoL instrument (15D) [6], EuroQoL Group 5 * Correspondence: petri.k. salo@jyu.fi 1 Department of Physical and Rehabilitation Medicine, Central Finland Health Care District, Keskussairaalantie 19, FI-40620 Jyväskylä, Finland Full list of author information is available at the end of the article BioMed Central © 2010 Salo et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Salo et al. Health and Quality of Life Outcomes 2010, 8:48 http://www.hqlo. com/content/8/1/48 Page 2 of 7 dimensional instrument (EQ-5D) [14], and the Healthy Days Measures [15]. Since neck pain is associated with a decrease in neck muscle strength, [16-21] neck strength training has been one means in seeking cure for neck pain. In addition to gaining neck muscle strength, neck strength training has been shown to be effective in reducing neck pain and the disability associated with it [22-24]. In a recent best-evidence synthesis [25] and Cochrane review [26] it was concluded that interventions that involved exercise combined with manual therapy were more effective in treating patients with neck pain than were alternative strategies. Although strength training seems to be an efficient way of treating patients with neck pain, its effect on HRQoL has not been shown. The authors found only two studies where the influence of strength exercises on neck pain was assessed with HRQoL measurements [22,27]. In those short-term exercise studies no significant gains in HRQoL were observed [22,27]. Because short-term training have been shown to produce only temporary improvements in various outcome measures, intensive resistance training for at least one year is recommended to gain sustainable results [28]. Thus, the purpose of the present study was to evaluate whether 12 months of neck strength or endurance training could improve HRQoL in females with chronic neck pain. This study was a secondary analysis of the randomized, controlled study conducted by Ylinen et al. [23]. Methods Subjects 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 [23]. 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. Measurements 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 [6]. 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 [12]. 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 [32].