Design and randomization
Patients were recruited from the osteoporosis outpatient clinics of Klinikum Südstadt hospital and the University hospital of Rostock. All study participants had proven osteoporosis (T-score ≤ −2.5). Patients who were unable to complete the entire training program during the period of the investigation were excluded from analysis.
Patients were randomized on a 1:1 basis. The permuted block design was used for randomization [18]. The block size was randomly selected. The randomization envelopes were numbered in ascending order. A proband to be randomized opened the envelope with the lowest number among all sealed envelopes.
Intervention
Over a period of 3 months, 44 patients with osteoporosis completed a twice-weekly 30-minute intensive exercise program designed to stabilize the trunk. Both groups completed a training program that consisted of 5 phases. Exemplified in Figure 1 are the 4 main phases of the Sling training represented. Phase 2 had in the course of the intervention no longer be practiced explicitly. The PT group completed similar exercises without slings (eg chair-rising exercises pelvic lift, step-ups).
Phase 1: Systematic cardiovascular and neuromuscular warm-up (PT group: general keep-fit exercises; ST group: step aerobics)
Phase 2: PT and ST groups: functional strength exercises focusing on correct posture
Phase 3: PT and ST groups: functional strength exercises for global surface muscles of the torso; ST group: dynamic sling exercise
Phase 4: Segmental stabilization (SST), both static and dynamic (PT group: exercise/medical ball; ST group: sling)
Phase 5: Stretching and relaxation
Each exercise session included all of the five phases.
Measurement of quality of life using the Qualeffo-41 questionnaire
Qualeffo-41, the questionnaire of the International Osteoporosis Foundation, was used to assess quality of life. This questionaire is intended for use in clinical trials. The questionaire was validated in a multicentre study in seven countries involving patients with stable osteoporosis and control subjects. The domains it covers are pain, physical function, social function, general health perception, and mental function (mood) [19, 20]. Total scores and individual scores of each domain were standardized to a percentage using the following formulae:
(1)
(2)
Domain scores are calculated by averaging the answers of one domain and transforming the scores to a score from 0 to 100. The total score is calculated by summing all answers of questions 1–41. The raw total score ranges from 41 to 205 and this is transformed to scores from 0 to 100. All answers are standardized so that 1 represents the best and 5 (or 3, or 4) represents the worst quality of life.
All patients completed the questionnaire before the start of intervention, after 3 months of exercise, and at the 3-month follow-up investigation after cessation of the exercise program.
Ethics committee approval
Informed written consent was obtained from all patients. The study was approved by the regional ethics committee for medical research.
Statistical analysis
All data were stored and analyzed using the SPSS statistical package 19.0 (SPSS Inc. Chicago, Illinois). Descriptive statistics were computed for variables of interest. The computed statistics included means and standard deviations of continuous variables, and are presented as mean ± SD, frequencies, and relative frequencies of categorical factors.
Testing for differences in continuous variables between the two study groups was achieved by the two-sample t-test for independent samples or the Mann–Whitney U-test by ranks as appropriate. Selection of the test was based on evaluation of variables for normal distribution, employing the Kolmogorov-Smirnov test. Fisher's exact test was used for between-group comparisons of categorical variables.
Comparisons within groups between the time points of evaluation were performed with regard to percentage changes versus baseline by one-sample t-tests against 0, and for percentage change between the time points named “follow-up” and “after training” by a paired t-test. Adjustments of alpha levels were carried out using the Bonferroni correction, i.e. the level of significance was lowered to 0.05/3 = 0.017.
All p-values resulted from two-sided statistical tests; the level of significance was set to p≤0.05 when no Bonferroni correction was required.