All experimental protocols were approved. authors obtained the consent to conduct the study from the Senate Ethics Committee for Scientific Research (SKE 01-45/2016) and confirmed conducting research to the standards set by the Declaration of Helsinki [25]. The study involved 61 subjects. The study population consisted of 31 Brazilian jiu-jitsu athletes, recruited from sports clubs. The control group were 30 subjects who had never done martial arts. The participants constituted a convenience sample. Each participant was informed about the purpose and procedure of the research, as well as the of possibility of withdrawing at any time during the study. All participants gave their informed consent to participate in the project.
The criteria for subject inclusion in the study population were: age between 18 and 45 years, having trained BJJ for a minimum of 6 months with the intensity of a minimum of 1.5 hours per week, having trained BJJ non-professionally (without participation in contests). The criteria for subject inclusion in the control group were: age between 18 and 45 years, being physically active except for training BJJ or any other sports professionally. The exclusion criteria for the study were: subjects below 18 years of age, with congenital disorders, chronic diseases or disability, as well as subjects with ongoing injuries or pain disorders in the locomotor system.
The subjects’ age was between 24 and 43 years (in the study population it was 31.7±5.2 years, and in the control group it was 29.7±4.36 years). We did not find statistically significant differences between body mass or body height between the two groups. Table 1. presents the biometric data of the study population subjects. The mean time of training BJJ in the study population was 3.89±4.13 years. The athletes trained a mean of 4.06±2.8 times per week, and the training sessions were 1.5 hours long.
Table 1. Subjects’ biometric data
Descriptive statistics
|
Age (years)
|
Body mass (kg)
|
Body height (cm)
|
BMI (kg/m)
|
|
SD
|
|
SD
|
|
SD
|
|
SD
|
Study population (n=31)
|
37.74
|
5.22
|
81.16
|
10.44
|
179.06
|
7.73
|
25.3
|
2.83
|
Control group
(n=30)
|
29.67
|
4.36
|
77.53
|
14.93
|
180.2
|
9.15
|
23.74
|
3.24
|
Total
(n=61)
|
30.72
|
4.89
|
79.38
|
12.87
|
179.62
|
8.41
|
24.53
|
3.11
|
Statistical significance (p)
|
Z=1.52 p=0.126
|
Z=1.31 p=0.191
|
Z=-0.62 p=0.535
|
Z=2.19 p=0.029
|
Z-result of the U Mann-Whitney test; p-level of significance;
Postural stability assessment was conducted with the use of the photogrammetric method based on the projection of the moiré method. The equipment for the computer-based body posture assessment system Mora 4th Generation was used. This method is non-invasive, easy to use, easily available, and it is easy to analyse the obtained results. Moreover, the photogrammetric method allows for comparison of results, as it is increasingly often used in postural assessment studies. All the measurements were taken by the same researcher, a physiotherapist (K.S.), trained to operate the equipment while maintaining the constant conditions and procedure of the tests. Before the measurements were conducted a suitable room was adapted for the tests. The tests need to be conducted in a darkened room, so the windows were curtained, and the space in the room was organized properly so as to ensure safe and non-embarrassing conditions for conducting the measurements (the subjects needed to undress for the tests). To calibrate the Mora4G correctly, before each measurement session the device was adjusted using the spirit levels on the front and the side of the device. The researcher measured subjects’ body mass and body height, and then, with the subject standing, marked palpated bony landmarks with a marker pen (spinous processes C7-S1, cervico-thoracic junction, thoracolumbar junction, scapula inferior angles, spina iliaca posterior superior, kyphosis peak, lordosis peak). To ensure comfortable and non-embarrassing conditions, female subjects could use a specially prepared cloth to cover the chest, attached to the body with adhesive tape. Subjects stood with their back to the projector-receiver device at a constant distance of 2.6 m, with their feet placed under their hips and hands along the body, eyes looking forward. Then, the measurement was taken. According to the producer, the measurement error with the MORA 4G system is 1cm at a maximum. Subjects’ body posture was analysed in the sagittal, coronal and transversal planes, presented in Figure 1.
To analyse the photogrammetric measurements, we used the following parameters:
DCK (%) Spinal height from C1 to S1
ALFA (º) Lumbosacral region inclination
BETA (º) Thoracolumbar region inclination
GAMMA (º) Upper thoracic region inclination
DKP (mm) The length of kyphosis between C7 and peak of kyphosis
KKP (º) Thoracic kyphosis angle
RKP (mm) The length of kyphosis between C7 and thoracolumbar junction
GKP (mm) The depth of thoracic kyphosis
DLL (mm) The length between S1 and peak of lordosis
KLL (º) Lumbar lordosis angle
RLL (mm) The length of lordosis between S1 and thoracolumbar junction
GLL (mm) The depth of lumbar lordosis
KLB (º) Shoulder line inclination difference
UB (º) The difference in the depth of scapula inferior angles inclination
OL (%) The difference between the distance of the scapula inferior angles from the spine
TT (%) Difference in the height of the waist triangles
TS (%) Difference in the width of the waist triangles
KNM (º) Angle of pelvis inclination
KSM (º) Angle of pelvis rotation
For the purpose of this study, the Polish validated version of the Oswestry Disability Index (ODI) was used. The ODI is used for the functional state assessment of patients with low back pain and it is the golden standard for the functional assessment in this group of patients. The questionnaire is accessible, patients can complete it on their own and it can be done in minutes. The subjects also filled out the author’s original questionnaire consisting of 8 questions which comprised of the following: the biometric data (age, body mass, sex), data on the subjects’ physical activity (duration, intensity, type), and injuries subjects sustained as well as spinal pain (location, symptoms, causes, pain intensity etc.).
Statistical analysis
Statistical analysis of the collected data was conducted with the STATISTICA 13 programme (TIBCO Software Inc., Palo Alto, CA, USA). Quantitative data was presented in the form of descriptive statistics using such measurements as arithmetic mean and standard deviation. The relationships between qualitative data were assessed with the chi-squared test, and the differences in two groups in quantitative data were assessed with the Mann-Whitney U-test. The non-parametric test was chosen as there was lack of normal distribution in the analysed variables. Normal distribution was verified with the Shapiro-Wilk test. Statistical significance was set at p<0.05.