# The Effect of Bodyweight Support and Incline Running on Triceps Surae Electromyographic Activity
## 4 Discussion  
The main finding of the present study was that running with a slope of 7% and 30% of BWS results in EMG activity comparable to that observed during level running, verifying our hypothesis. Furthermore, as was hypothesized, BWS can decrease running-induced muscle fatigue (LFF). Our results correspond to previous studies that confirmed an increase in EMG for GL, SOL, and GM at 7% incline running [9], as well as in mechanical power [35]. As shown in Figure 1, the EMG of SOL seemed less impacted by the slope and a BWS of 15% than the GL and the GM. Indeed, the SOL EMG increased by 10.8% from the LR to IR7%, but that of the GL and GM increased by 23.6% and 16%, respectively. On the other hand, with a BWS of 15%, the SOL EMG decreased by 4.8%, and the GL and GM by 29.4% and 13.8%, respectively. This is mainly due to differences in the muscle insertion; the SOL is a monoarticular muscle that only participates in plantar flexion, and the gastrocnemius is a bi-articular muscle used for knee flexion. Another explanation of this phenomenon could be the different roles of the gastrocnemius and soleus. A previous study has shown that, in the single-leg-stance period, the SOL is mainly responsible for forward trunk progression and support, and the gastrocnemius for leg swing [36]. However, this study focused on walking locomotion; it could be interesting to elucidate the behavior of these two muscles while running. After that, the EMG of the VL and triceps surae was decreased by 15% of the BWS compared to incline running and had an almost-similar muscular activity to level running (VL (\(-\)0.6%), SOL (0.6%), GM (\(-\)2.1%)). Only the GL (\(-\)11.3%) appeared more affected by unloading 15% of the body weight. Moreover, 30% BWS was effective, having an EMG activity lower than for level running: VL (\(-\)20.5%), GL (\(-\)10.5%), SOL (\(-\)10.8%), except for GM (1.1%). However, the EMG activity of the gastrocnemius muscle did not decrease while unloading from 15% to 30%. Conversely, the VL EMG significantly decreased from BWS 15% to BWS 30%. We hypothesize that as the IR from 5% to 10% modifies the running pattern (increase GM/GL EMG and mechanical work), adding more BWS could also change the running pattern. During the single-leg stance from BWS 15% to BWS 30%, it could be possible that the percentage of work from the Gastrocnemius increases, but as the weight decreases, the EMG does not change. Those results would be similar to [PERSON] et al. [37], who found a significant decrease in muscle activity at the push-off phase at 20% of BWS, but not at 40%, for both gastrocnemius. Our results showed a decrease in EMG activity \begin{table}
\begin{tabular}{c c c c} \hline  & **Flight Time** & **Contact Time** & **Step Frequency** \\ \cline{2-4}  & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** & **Mean \(\pm\) SD** \\ \hline IR\({}_{0}\)BWS\({}_{0}\) & 47 \(\pm\) 1.3 *b & 338 \(\pm\) 29 & 156 \(\pm\) 9 \\ IR\({}_{P}\)BWS\({}_{0}\) & 35 \(\pm\) 1.2 *a,d & 340 \(\pm\) 44 & 161 \(\pm\) 14 \\ IR\({}_{P}\)BWS\({}_{15}\) & 38 \(\pm\) 1.3 & 340 \(\pm\) 36 & 159 \(\pm\) 12 \\ IR\({}_{P}\)BWS\({}_{30}\) & 47 \(\pm\) 1.7 *b & 336 \(\pm\) 27 & 155 \(\pm\) 9 \\ \hline  & \(p\) \textless{} 0.006 & \(p\) \textgreater{} 0.05 & \(p\) \textgreater{} 0.05 \\ \hline \end{tabular}
\end{table} 
Table 4: Gait parameter data between each condition. a, b and d represent significant differences between IR0 BWS0, IR7 BW50 and IR7 BWS30. Level running without BWS (IR0 BWS0), incline running at 7% and 0% of BWS (IR7 BWS0), incline running at 7% and 30% of BWS (IR7 BWS30). * Means significative difference (\(p\) \textless{} 0.05). \begin{table}
\begin{tabular}{c c c} \hline  & **Contact Time** & **Flight Duration** & **Step Frequency** \\ \hline Condition & 0.306 & 0.001 * & 0.107 \\ Time & 0.344 & 0.208 & 0.641 \\ Interaction & 0.618 & 0.911 & 0.594 \\ \hline \end{tabular}
\end{table} 
Table 3: \(p\) values with ANOVA analysis for gait spatiotemporal parameters. * Means significative difference (\(p\) \textless{} 0.05).