## 3 Results
### Kinematic Analysis  
The results of the kinematic analysis showed that the angular ROM between C7 and _temple_, as well as the distances from the _land_ to _temple_, did not change for each condition during the 10-s period of the sEMG measurement. Similarly, no changes in _asis-psis_ and great trochanter marker positions were observed during the experimental conditions in the lumbopelvic-hip complex. Specifically, the averaged full angular ROM for the craniofacial flexion-extension, measured from C7 to _temple_, was 102.01 \(\pm\) 17.99\({}^{\circ}\). Within this  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Experimental Conditions**} \\ \hline  & & _Neutral_ & & & _Flexion_ & & _Extension_ & \\ \hline
**Muscles** & **Mean \(\pm\) SD** & **95\% CI** & **ICC\({}_{\text{L,D}}\)** & **Mean \(\pm\) SD** & **95\% CI** & **ICC\({}_{\text{L,D}}\)** & **Mean \(\pm\) SD** & **95\% CI** & **ICC\({}_{\text{L,D}}\)** \\ \hline RA & 33.20 \(\pm\) 26.23 & 20.93–45.47 & 0.986 & 60.69 \(\pm\) 40.51 & 41.73–79.65 & 0.939 & 33.71 \(\pm\) 32.06 & 18.71–48.71 & 0.942 \\ ES & 4.28 \(\pm\) 1.49 & 3.58–4.98 & 0.968 & 5.19 \(\pm\) 2.20 & 4.16–6.23 & 0.740 & 5.33 \(\pm\) 2.34 & 4.23–6.43 & 0.974 \\ LEO & 29.84 \(\pm\) 12.44 & 23.21–36.47 & 0.975 & 42.84 \(\pm\) 23.12 & 30.52–55.16 & 0.945 & 31.44 \(\pm\) 16.74 & 22.52–40.36 & 0.939 \\ REO & 27.39 \(\pm\) 12.04 & 21.75–33.02 & 0.946 & 34.65 \(\pm\) 16.72 & 26.82–42.48 & 0.759 & 29.67 \(\pm\) 14.51 & 22.88–36.46 & 0.926 \\ LIO & 28.64 \(\pm\) 14.86 & 21.69–35.60 & 0.982 & 55.41 \(\pm\) 26.96 & 42.79–68.03 & 0.943 & 36.87 \(\pm\) 22.65 & 24.68–49.06 & 0.951 \\ RIO & 31.46 \(\pm\) 19.32 & 22.42–40.50 & 0.992 & 56.87 \(\pm\) 29.66 & 42.99–70.75 & 0.982 & 36.82 \(\pm\) 22.22 & 26.42–47.21 & 0.976 \\ \hline \hline \end{tabular}  
* MVIC = maximal voluntary isometric contraction; RA = recuts abdominal; LES = lumbar effector spine; LEO = left external oblique; REO = right external oblique; LD = left internal oblique; SD = standard deviation; CI = confidence Interval; ICC\({}_{2,1}\) = intraclass correlation coefficient; _neutral_ = traditional prone plank; _flexion_ = traditional prone plank with head active full flexion; _extension_ = traditional prone plank with head active full extension.  
\end{table}
Table 2: Muscle activation (%MVIC) during the three experimental conditions *.  
angular full ROM, the _neutral_ condition showed measured values of 0\({}^{\circ}\) for each participant, as reference point of initial angular ROM. Then, the measured angular values for _flexion_ were 60.88 \(\pm\) 11.14\({}^{\circ}\), and for _extension_ were 41.13 \(\pm\) 10.35\({}^{\circ}\). The resulting values for the distance from the _land_ to _temple_ was for _neutral_ 28.25 \(\pm\) 2.27 cm; for _flexion_ 19.89 \(\pm\) 2.95 cm; and for _extension_ 44.84 \(\pm\) 3.09 cm.  
Figure 3: Bar chart with typical error for change of normalised electromyographic activity (\(\Delta\)%MVIC) of the rectus abdominis (RA), lumbar erector spinate (LES), left external oblique (LEO), right external oblique (REO), left internal oblique (LIO), and right internal oblique (RIO) across experimental conditions with p values for the differences. N = traditional prone plank; F = traditional prone plank with head active full flexion; E = traditional prone plank with head active full extension. * \(p<\) 0.05.