The study was approved by the Ethics Committee of the Saarland University, application number 16-12 and was registered at the Deutsches Register Klinischer Studien (DRKS), registration number DRKS00012265.
Sample of persons
The patients were recruited through medical practices, clinics, rehabilitation facilities, and self-help groups in Saarland and Rhineland-Palatinate, from January to April 2018. The study took place in the respective rooms of these organizations and at the Saarland University. Inclusion criteria, person suffering from PD, confirmed by a physician were included. Exclusion criteria, patients with the already described contraindications (e.g., fresh bone fracture/joint replacement, severe coronary heart disease, untreated high blood pressure, acute thrombosis, inflammations, hernias, discopathies, rheumatoid arthritis, cardiac arrhythmia, cardiac pacemaker, deep brain stimulator, aortic aneurism, or migraine) were not included according to the recommendations [12,13,14]. The sample consists of 36 persons, 50% male and 50% female. The average age is 69.29 ± 11.52 years, the average stage of disease according to Hoehn and Yahr is 2.11 ± .79, the subjects have been affected for an average of 7.36 ± 4.63 years, and the hip width is 33.25 ± 1.53 cm. There are 11 of the test persons suffer from freezing. Table 1 shows the characteristics of the sample sorted by test groups.
Table 1 Characteristics of the sample, sorted by test groups, means ± standard deviations When comparing the groups, only a significant age difference between group 3 and groups 2 and 4 can be observed.
Variable sample
Freezing is examined with the 360° turn test, in which the patient rotates once to the right and once to the left around the body’s longitudinal axis. The number of steps required is measured [27]. In the 360° turn test, there is a trial in each direction. The number of steps per direction (360° turn left, 360° turn right) and the common mean value of both turn directions (360° turn combined) are evaluated. Flexibility is measured by the Sit and Reach test (S&R) [28]. The range is measured in centimeters while sitting (negative values above, positive values below the sole of the foot). The test person has one probation test and three main tests. The best value (best of 3) and the mean value of the three passes (mean of 3) are evaluated. Both test procedures were carried out directly before and directly after the treatment.
Treatment sample
A side-alternating vibration platform (Galileo med Advanced) from Novotec Medical was used as the treatment. Three different vibration frequencies (6, 12, and 18 Hz) were used, and a placebo condition (control group, standing on the switched-off vibration plate) was created. The test persons were instructed to stand as upright and relaxed as possible with slightly bent knees (26–30°) without holding on to the platform, as recommended [9,10,11]. The stand width was set at 33 cm (average hip width of the sample) using adhesive tape on the panel. This corresponds to an amplitude of 4 mm. The test persons were not informed of which group they belonged to. For this reason, the display was concealed. The examiners were also blinded. Five sets of 60 s each were used with a 60 s pause between the sets with the corresponding frequency. The assignment to the different vibration frequencies was randomized by drawing lots showing only the group number, sorted by sex, so that the ratio within the groups should be balanced. Recruitment and assignment were done by A.D. and P.B..
Compared to multiple sessions, a single session of WBV leads to higher effects on motor symptoms. In addition, compared to randomized WBV, harmonic WBV leads to higher effects. Most of analyzed studies use a 5 × 60-s protocol that seems to lead to the highest effects [23], so all these parameters were chosen for this study.
Figure 1 shows the course of the examination.
Hypothesis
There is a difference in performance between pre- and posttest freezing and mobility depending on the vibration frequency.
Statistics
A K-S test was performed to verify a normal distribution of the data. In the case of a normal distribution, an ANOVA with measurement repetition is calculated; in the case of a non-normal distribution, a Kruskall-Wallis-ANOVA is calculated if the data do not suggest a normal distribution even after logarithms. The effects time (within, pre- to posttest), frequency (between, different application frequencies), and the interaction time*frequency are determined. Effect sizes are specified using standardized mean differences (SMD) and their 95% confidence interval (CI). The following categorization is performed: small effect SMD < .30, medium effect SMD > .50, large effect SMD > .80 [29].
Statistica 8 is used to calculate the differences and RevMan 5.3 is used to determine the effect sizes.
The significance level is set to p < .05.