Study design

This was a parallel randomised controlled trial that aimed to compare the effects of a 12-week pool exercise programme in temperate water with a 12-week resistance exercise programme in men with CWP. Initially, the study plan was to recruit 20 patients to each group. Due to difficulties in recruitment, only 17 patients were recruited to each group. The authors therefore decided to continue the study as a pilot study.

The primary outcome was fatigue, which was assessed in multiple dimensions with the Multidimensional Fatigue Inventory (MFI-20). The secondary outcomes were symptoms of anxiety and depression and isometric forces of shoulder abduction, knee extension, knee flexion and hand grip. The exploratory outcomes were pain intensity, the number of pain localisations and health-related quality of life. The outcomes were assessed at the study start and after 12 weeks.

Study population

The inclusion criteria were male patients, aged 18 to 60 years, with CWP according to the American College of Rheumatology (ACR) criteria [1]. Patients who had experienced widespread pain for at least three months were classified as having CWP. The exclusion criteria were the inability to understand Swedish; severe psychiatric or somatic disorders, such as other rheumatic diseases, neurologic conditions, cancer, clinically confirmed depression or panic disorder; or having participated in resistance exercise or pool exercise at a physical therapy clinic during the preceding six months.

Recruitment

The patients were recruited in a municipality of approximately 50 000 inhabitants in western Sweden from five primary health care centres that covered the whole municipality. Men with the diagnoses of unspecific pain or FM between 2005 and 2007 were identified by searching all patient records in the five primary health care centres and were consecutively recruited in 2008.

A total of 493 subjects in the patient records had a diagnosis of unspecific pain or FM and were thus contacted by mail with information about the randomised trial. Seventy-four of these patients replied by telephone or e-mail. Further telephone screening resulted in the exclusion of 37 patients because they did not meet the inclusion criteria (n = 33) or refrained from participating (n = 4).

The remaining 37 patients and two additional patients with FM who were recruited consecutively were invited to the examination for the study. Five of these 39 patients were excluded because they did not meet the inclusion criteria or refrained from participating (Fig. 1).

Thirty-four patients were allocated by block randomisation to one of the two intervention group programmes. A statistician prepared sequentially numbered sealed envelopes and created the allocation sequence [30]. A person who was not involved in the examinations opened the envelopes and informed the patient about the treatment group to which he had been randomised. The final number of patients included in the randomised trial was 34, with 17 in the pool exercise group and 17 in the resistance exercise group (Fig. 1). The socio-demographic data for the two groups are given in Table 1.

Table 1 Demographic data of the two exercise groups Full size table

Procedure

Examinations

The examiners were trained physiotherapists who were blinded to the patients’ group assignments in the randomised trial. The patients were examined according to the ACR criteria for CWP, which included a pain localisation sheet [5] and a standardised interview. The patients completed a battery of questionnaires and performance-based tests at baseline and 12 weeks after baseline. All of the patients were instructed not to change their baseline medical treatment throughout the 12-week study period.

Intervention

The pool exercise programme comprised 50-min sessions in groups of six to eight patients twice a week for a period of 12 weeks in 33 °C water, supervised by a physiotherapist. The session included aerobic exercise for endurance, strength, flexibility, coordination and relaxation.

The patients were instructed to exercise at their own rhythm and to modify the exercises individually with respect to thresholds of pain and fatigue. During the 12-week study period, they were encouraged to increase intensity and resistance with or without water equipment. The intensity during the pool exercise session was assessed with the rate of perceived exertion (RPE, 6–20) on the Borg’s scale [31] on two occasions at intervention weeks 8 and 11.

The resistance exercise programme was performed twice a week for 12 weeks with free weights and resistance machines in groups of approximately eight to ten patients, supervised by a physiotherapist.

The session lasted approximately one hour and included exercise for all four limbs and the back and trunk using dynamic exercises with eccentric, concentric and isometric muscle actions [32].

A standardised protocol for resistance progress was applied [32–34]. During the 12-week study period, the load was planned to be increased individually from approximately 40 % to 80 % of one repetition maximum (RM) established at baseline. One RM is defined as “the heaviest resistance that can be used for one complete repetition of an exercise” [35]. At week one, the patients performed three sets with 15–20 repetitions of each exercise. When the load increased, they still performed three sets but with fewer repetitions. All of the sessions started with ten minutes of warm-up on an ergometer bicycle.

Background data

Information about socio-demographic data, the duration of widespread pain and pharmacological treatment was gathered in a standardised interview.

Marital status referred to whether the patient lived with another adult.

Employment referred to the percentage of full time work divided into 4 range categories. Full time work was defined as 40 h per week.

Sick leave and disability pension were divided into 3 categories: none, part time or full time sick leave or disability pension.

Medication

The uses of analgesics, non-steroidal anti-inflammatory drugs (NSAID) and psychotropics were considered positive if the patient used the medication regularly or as needed.

Self-administered questionnaires

The MFI-20 (4-20)

The questionnaire assesses 5 subscales of fatigue: general fatigue, physical fatigue, mental fatigue, reduced motivation and reduced activity. The MFI-20 contains 20 statements that refer to aspects of fatigue experienced during the recent days. The sum score of each subscale ranges from 4 to 20 and a higher score indicates a higher degree of fatigue [36, 37]. The MFI-20 has shown satisfactory construct and content validity [38, 39] and test-retest reliability for CWP [39]. The MFI-20 has been shown to be sensitive to changes in previous exercise studies in populations with FM and CWP [27, 28, 40]; however, there is no established minimal clinically important difference for the instrument.

The hospital anxiety and depression scale (HADS) (0–21)

The HADS contains 14 statements, with a rating scale from zero to three, in which a higher score indicates a higher degree of distress. The scores build two subscales for anxiety (HADS-A) and depression (HADS-D), ranging from 0 to 21. A cut-off score of eight is suggested to indicate possible anxiety and depression [41]. The HADS is regarded as a valid and reliable instrument for assessing anxiety and depression in medical patients [42, 43] and has also been applied in research on CWP [27, 44].

FIQ pain

The subscale for pain intensity (0–100 mm) included in the Fibromyalgia Impact Questionnaire (FIQ) was applied in the study [45, 46]. The FIQ has shown good sensitivity in demonstrating therapeutic change [47], and the Swedish version of the FIQ has shown satisfactory validity and test-retest reliability for patients with FM [45].

Pain localisation

The localisation and distribution of pain were reported in a self-administered pain drawing with 18 predefined body regions, ranging from zero to 18, which referred to the number of body regions in pain [5].

Short form-36 (SF-36)

A generic instrument assessing health-related quality of life, comprising eight subscales. The subscales build two composite scores, the physical component summary (PCS) and the mental component summary (MCS) (0–100), which were both included in the study. A higher score indicates better health-related quality of life [48]. The Swedish version of the SF-36 has been validated in a general Swedish population [49].

Performance-based tests

Shoulder abduction

The isometric force of shoulder abduction was measured with Isobex 3.0 (Medical Device Solution AG, Burgdorf, Switzerland) in the plane of the scapula at 45° and a shoulder elevation of 90° while in a standardised position. The subjects were seated on a chair with their feet supported by the floor. The dynamometer was placed on the floor, and the band from the dynamometer was placed proximal to the styloid process of the ulna [50].

Knee extension and flexion

Muscle strength of the knee extensors and flexors was measured with a pressure transducer with an amplifier (Steve Strong, Stig Starke HB, Goteborg, Sweden). The patients were seated with back support and a seat belt around the waist. Both legs hung freely with a 90° knee angle. A non-elastic strap was attached between the ankle and the pressure transducer. The subjects were instructed to pull the ankle strap in either knee extension or flexion maximally for 3 s. The best of three efforts was reported as the maximal isometric quadriceps/hamstrings force [51].

Hand grip

Hand grip force was measured as the sustained maximum voluntary contraction during ten seconds, measured using an electronic instrument, the Grippit [52].

Statistics

The descriptive data are presented as the mean and standard deviation (SD) or by number and percentage. For comparisons between the exercise groups, the Mann–Whitney U test was used for continuous variables, and the Mantel-Haenszel chi-square test for ordinal categorical variables. For comparisons within groups, Wilcoxon’s signed rank test was used for continuous variables. To control for possible type 1 errors, the upper limit of the expected number of false significant results was calculated for the secondary and exploratory outcomes by the following formula: α/1 – α × (Number of tests – Number of significant tests), where α is the significance level. The patients who completed the 12-week examination were compared with the patients who did not complete the 12-week examination for differences in socio-demographic data, the MFI-20 subscales and the FIQ subscale for pain intensity at baseline, using the Mann–Whitney U test for continuous variables and the Mantel- Haenszel chi-square test for ordinal categorical variables.