## 3 Results
### Maximal Isometric Lower Back Extensor Strength  
Table 2 shows the values obtained for maximal isometric lower back extensor strength (from the 2 nd to the 5 th attempt) in all three postural positions measured in the first session for all subjects and for individual categories. The highest values of maximal isometric lower back extensor strength were measured in a sitting position, followed by values measured standing. The lowest values were measured in the prone position.  
A significant difference in the values measured appeared between the 1 st and 2 nd attempts made by men \(\geq\)50 years (data not shown). To avoid any potential distortion arising out of the learning effect or fatigue (even though neither of these were demonstrated), values measured at the first and the last attempts in all measurements were excluded.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Variable** & **Sex** & **Total** & **18–29 Years** & **30–49 Years** & \(\geq\)**50 Years** \\ \hline \multirow{2}{*}{Sex (_n_)} & Male & 30 & 10 & 15 & 5 \\  & Female & 30 & 10 & 15 & 5 \\ \hline \multirow{2}{*}{Age (years)} & Male & 35.8 \(\pm\) 11.7 & 26.9 \(\pm\) 1.4 & 34.4 \(\pm\) 3.7 & 57.6 \(\pm\) 11.5 \\  & Female & 38.4 \(\pm\) 11.1 & 26.6 \(\pm\) 1.4 & 40.2 \(\pm\) 4.6 & 56.6 \(\pm\) 6.4 \\ \hline \multirow{2}{*}{Height (cm)} & Male & 182.9 \(\pm\) 8.3 & 183.8 \(\pm\) 7.2 & 183.0 \(\pm\) 8.5 & 180.8 \(\pm\) 10.9 \\  & Female & 167.7 \(\pm\) 6.3 & 170.4 \(\pm\) 5.8 & 166.4 \(\pm\) 6.3 & 166.0 \(\pm\) 6.5 \\ \hline \multirow{2}{*}{Weight (kg)} & Male & 81.9 \(\pm\) 8.8 & 82.0 \(\pm\) 8.0 & 82.8 \(\pm\) 10.1 & 79.0 \(\pm\) 6.8 \\  & Female & 62.2 \(\pm\) 6.8 & 61.1 \(\pm\) 5.7 & 62.3 \(\pm\) 7.4 & 64.0 \(\pm\) 8.2 \\ \hline \multirow{2}{*}{BMI (kg/m\({}^{2}\))} & Male & 24.5 \(\pm\) 2.4 & 24.4 \(\pm\) 2.8 & 24.7 \(\pm\) 2.6 & 24.2 \(\pm\) 1.4 \\  & Female & 22.1 \(\pm\) 2.0 & 21.0 \(\pm\) 1.5 & 22.5 \(\pm\) 2.2 & 23.2 \(\pm\) 1.7 \\ \hline \multirow{2}{*}{Education} & Primary education (_n_ (\%)) & Male & 0 (0) & 0 (0) & 0 (0) \\  & Female & 1 (3.3) & 0 (0) & 0 (0) & 1 (20.0) \\ \cline{2-6}  & Secondary education (_n_ (\%)) & Male & 1 (3.3) & 1 (10.0) & 0 (0) & 0 (0) \\  & Female & 10 (33.3) & 1 (10.0) & 7 (46.7) & 2 (40.0) \\ \cline{2-6}  & Tertiary education (_n_ (\%)) & Male & 29 (96.7) & 9 (90.0) & 15 (100.0) & 5 (100.0) \\  & Female & 19 (63.3) & 9 (90.0) & 8 (53.3) & 2 (40.0) \\ \hline \hline \end{tabular} Data are expressed as mean \(\pm\) standard deviation. _n_: number of individuals; BMI: body mass index; (%) percentage of individuals from a certain category men/women; Primary education: graduated from elementary school; Secondary education: graduated from secondary school with state exam; Tertiary education: graduated from university.  
\end{table}
Table 1: Characteristics of subjects in all subgroups.  
The consistency of the data, expressed as the repeatability of measurements in one session, was excellent (ICC 0.975-0.996) for all six successive attempts and the 2 nd to 5 th attempts in all three postural positions (Table 3).  
Both short-term and long-term test-retest reliability emerged as excellent in all three techniques measuring maximal isometric lower back extensor strength: ICC varied from 0.937 to 0.992 (Table 4). The difference between values measured at the first and the second visit was not clinically significant.  
The strength of lower back extensors was significantly lower in the age category \(\geq\)50 years in the prone position. The same tendency was evident in the standing and sitting positions. However, the difference was not statistically significant. The lower back extensor strength in sitting and standing positions was significantly higher in men than in women (Table 2).