## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**EXP**} & \multicolumn{4}{c}{**CON**} \\ \cline{2-10}  & \multicolumn{2}{c}{**Pre**} & \multicolumn{2}{c}{**Post**} & \multicolumn{2}{c}{**Pre**} & \multicolumn{2}{c}{**Post**} \\ \cline{2-10}  & **Firm** & **Foam** & **Firm** & **Foam** & **Firm** & **Foam** & **Firm** & **Foam** \\ \hline Amplitude M/L (mm) &
\begin{tabular}{c} 5.18 \\ (0.85) \\ \end{tabular} & 6.03 (1.23) & 4.98 (0.78) & 5.62 (0.97) & 5.42 (1.20) & 6.12 (1.05) & 5.33 (0.82) & 6.35 (1.93) \\ Amplitude A/P (mm) & 6.61 (2.41) & 8.55 (2.86) & 6.95 (2.41) & 7.86 (2.54) & 7.22 (2.38) & 7.81 (1.71) & 8.55 (2.90) & 9.22 (3.25) \\ Mean Speed M/L (mm/s) & 26.8 (5.8) & 33.5 (10.8) & 24.7 (4.9) & 29.4 (6.7) & 28.1 (8.3) & 31.4 (9.2) & 26.7 (8.9) & 29.6 (11.9) \\ Mean Speed A/P (mm/s) & 25.9 (5.4) & 29.4 (8.3) & 24.5 (5.6) & 28.2 (6.6) & 27.4 (8.6) & 31.5 (8.3) & 24.5 (7.1) & 28.9 (12.0) \\ Frequency M/L (Hz) & 1.03 (0.16) & 0.97 & 0.94 & 0.92 & 0.95 & 0.89 & 0.98 & 0.85 \\  & (0.22) & (0.17) & (0.28) & (0.19) & (0.21) & (0.18) & (0.22) \\ Frequency A/P (Hz) & 0.81 & 0.72 & 0.77 & 0.70 & 0.82 & 0.74 & **0.66 * ** & 0.69 \\  & (0.18) & (0.16) & (0.17) & (0.11) & (0.19) & (0.16) & **(0.17)** & (0.13) \\ Entropy M/L ( ) & 0.61 & 0.62 & 0.61 & 0.62 & 0.59 & 0.61 & 0.61 & 0.60 \\  & (0.07) & 0 (0.09) & (0.06) & (0.09) & (0.08) & (0.09) & (0.09) & (0.09) \\ Entropy A/P ( ) & 0.78 & 0.67 & 0.71 & 0.67 & 0.73 & 0.70 & **0.63 * ** & 0.61 \\  & (0.16) & (0.13) & (0.15) & (0.12) & (0.19) & (0.13) & **(0.20)** & (0.13) \\ Fractal Dimension M/L ( ) & 1.58 (0.04) & 1.58 (0.06) & 1.56 (0.04) & 1.57 (0.07) & 1.57 (0.05) & 1.56 (0.06) & 1.57 (0.05) & 1.54 (0.06) \\ Fractal Dimension A/P ( ) & 1.53 (0.06) & 1.49 (0.07) & 1.50 (0.06) & 1.49 (0.05) & 1.52 (0.07) & 1.51 (0.06) & **(0.08)** & 1.48 (0.06) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mean values (SD) of the COP parameters for two groups (EXP and CON) standing on firm or a foam surface before (Pre) and after (Post) a 12-week exercise period in the frontal (M/L) and sagittal (A/P) planes. nor affect their postural strategies. This result is not unexpected, being in accord with other authors who found neither an association between leg strength and balance [13] nor an effect of strength training on balance [22]. The latter authors used 8-week training, which resulted in a 12-17% increase in leg strength without any noticeable progress in postural control. Second, CON showed a significant decline in postural strategies measured over time in the A/P plane on a firm surface. This means that there must have been a factor between the two tests that, acting differently on the two groups, resulted in significant differences in their final postural strategies. However, these changes do not relate to steadiness but to postural strategies, which so far have not been taken into account in similar research. This study is the first to present such results. As the first test was carried out in November and the second one in March, a possible seasonal balance variability seems a fairly likely candidate here. It has been shown, especially in men, that physical activity in the winter is the lowest [23]. Incidentally, very similar decreases in non-linear parameters and frequency of sway were caused by the transition from hard to foam surface, i.e., when the test conditions were changed from easier to more difficult by imposing additional constraints on postural control in both groups [24]. This may indicate that the lower values of non-linear parameters that CON used on a firm surface during the second test were more suited to standing on foam. Thus, it seems plausible that CON modified its strategies as if expecting greater difficulties in performing the same two tests as at baseline. It is likely that the CNS in CON became aware of the gradual formation of a sensorimotor deficit over time, which led to the observed changes in postural strategies towards their better adaptation to these deficits.