## 4 Discussion  
The main aim of this study was to compare dynamic sitting vs. conventional sitting as to trunk posture adaptations on the sagittal plane (thoracic kyphosis and lumbar lordosis) in order to validate a novel (not yet on the market) dynamic stool (called \"EnergyBack\"). Consistent with this aim, our results evidenced on a sample of healthy people a significant difference (\(p<0.001\)) between dynamic vs. conventional sitting posture as to the degrees of thoracic kyphosis and lumbar lordosis. Interestingly similar significant differences were found also between standing posture vs. dynamic sitting posture (\(p<0.001\)) as well as between standing posture vs. conventional sitting posture (\(p<0.001\)). Together with the increase in hours spent in seated postures (e.g., during working or recreational activities), the incidence of musculoskeletal disorders (in particular involving the back) also appears to be rising [15]. Thus, sitting features (e.g., type of chair and its design or seat comfort) have become a main issue in the prevention of back disorders. Even if there is no consensus on \"what is an optimal sitting posture\", those sitting postures that match with the natural shape of the spine are deemed advantageous from a postural point of view [7; 8; 9]. To date, there is evidence about the use of chairs aimed at promoting lordotic lumbar postures, which would be associated with decreased lumbar muscle tension and improved back muscle strength [16]. The reduction in trunk muscle tension and the maintenance of \"optimal\" lumbar lordosis have been reported to decrease loads on the intervertebral discs [17]. Furthermore, dynamic sitting on an unstable base of support has been proposed to facilitate spinal motion during prolonged sitting in order to help prevent back muscle fatigue via alternating motor unit activation [18]. \begin{table}
\begin{tabular}{c c} \hline Age (years) & 29.5 (12.1) \\ mean (SD) & 29.5 (12.1) \\ \hline Sex & 41/59 \\ male/female & 22.0 (2.4) \\ \hline \end{tabular} Abbreviations: SD, standard deviation.  
\end{table} 
Table 1: Information about our sample. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{**Parameters**} & \multicolumn{3}{c}{**Mean Data**} & \multicolumn{3}{c}{**Post-Hoc Comparisons**} \\  & & & & & **(Fisher’s LSD Test)** & \\ \hline \multirow{4}{*}{Dorsal kyphosis (\({}^{\circ}\)) mean (SD)} & \multirow{2}{*}{36.5 (6.6)} & \multirow{2}{*}{52.5 (6.6)} & \multirow{2}{*}{44.5 (5.2)} & \multirow{2}{*}{40.001 (-17.7; -14.2) \({}^{\star}\)} & \multirow{2}{*}{\(<\)0.001 (-9.7; -6.3) \({}^{\star}\)} & \multirow{2}{*}{\(<\)0.001 (6.2; 9.7) \({}^{\star}\)} \\  & & & & & & & \\ \hline \multirow{3}{*}{Lumber lordosis (\({}^{\circ}\)) mean (SD)} & \multirow{3}{*}{22.0 (2.4)} & \multirow{3}{*}{7.0 (28.2)} & \multirow{3}{*}{16.6 (9.2)} & \multirow{3}{*}{\(<\)0.001 (24.1; 29.8) \({}^{\star}\)} & \multirow{3}{*}{\(<\)0.001 (14.5; 20.2) \({}^{\star}\)} & \multirow{3}{*}{\(<\)0.001 (-12.5; -6.8) \({}^{\star}\)} \\  & & & & & & & \\ \hline \hline \end{tabular} Abbreviations: \({}^{\circ}\), degrees; SD, standard deviation; CI, confidence interval. \({}^{\star}\) = statistically significant after Bonferroni correction (\(p<0.016\)).  
\end{table} 
Table 2: Mean data and post-hoc comparisons. Spinal stability is a key factor for trunk posture [19]. It is frequently trained by using stability ball exercises, which may improve trunk endurance and contribute to postural control during prolonged sitting by training local muscles of the back (i.e., multifidus and transverse abdominis) [20]. To date, despite stability ball seating having become a trend in order to challenge trunk muscles (core activation) in the (prolonged) sitting position, the current body of evidence is not sufficient to define stability ball sitting as an effective practice to obtain a beneficial postural alignment during seated activities [17].