# Effects of Arm Swing in Lower Limb Muscle Activation and Coordination During Treadmill Walking
## 3 Results
### EMG Entvelopes and Performance Indicators  
The EMG envelopes and performance indicators obtained for all subjects during WWA and WNA are shown in Figure 3. Although the shapes of the EMG envelopes looked similar between WWA and WNA (see Figure 3a), statistically significant differences were found between the two tasks at 50% of GC for GLM (minimum \(p\)-value = 0.037, [PERSON]'s d = 0.62), at around 0% of GC (or 100% of GC) for VL (minimum \(p\)-value = 0.037, [PERSON]'s d = 0.26) and ST (minimum \(p\)-value = 0.027, [PERSON]'s d = 0.55), and at 25% of GC for ST (minimum \(p\)-value = 0.002, [PERSON]'s d = 0.27), GaM (minimum \(p\)-value = 0.037, [PERSON]'s d = 0.41), and SOL (minimum \(p\)-value = 0.037, [PERSON]'s d = 0.26). Peak muscle activity was obtained at around 0% of GC (or 100% of GC) for GLM, RF, and VL, at around 90% of GC for BF, ST, and TA, and at around 40% of GC for GaM and SOL (Figure 3b). Additional details on the timing of the EMG maximum amplitude as a function of the GC can be found in Table S4 of the Supplementary Material. The distribution of the EMG differences between WWA and WNA (\(\Delta\)) are shown in Figure 3b. Median \(\Delta\) values are around zero for all muscles, due to  
Figure 2: Cadence distribution for all subjects during walking with arms (WWA in black) and walking with no arms (WNA in grey). The cadence specified by the metronome (desired cadence) is shown as a red horizontal line. See the Supplementary Material (Table S3) for more detailed data on the cadence statistics results.  
the inter-subject variability. Subjects responded differently to walking without arms for RF (\(\Delta\in(-10,83)\)), VL (\(\Delta\in(-59,37)\)), ST (\(\Delta\in(-19,38)\)), and GaM (\(\Delta\in(-24,23)\)). Detailed data on the EMG amplitude of each subject can be found in Table S5 of the Supplementary Material. Some subjects increased RF and VL activity (17, 39, 21, and 83% for RF and 24, 27, 13, and 9% for VL Subjects 2, 3, 5, and 8, respectively) during WNA compared to WWA. Others decreased the activity of the quadriceps muscles (\(-7\%\) and \(-10\%\) for RF and \(-59\) and \(-27\%\) for VL for Subject 4 and 7, respectively) under WNA conditions compared to WWA condition. Subject 10 increased BF activity by 36% but decreased ST activity by 38% during WNA. Subjects 1, 6, and 9 showed less relevant changes (\(\Delta\) < 15%). Moreover, there was a very high cross-correlation between WWA and WNA in all muscles, with a median value of 0.99 in all muscles and a maximum lag of 3% of GC for GaM (Figure 3c). No statistically significant differences were observed in the SPM analysis.  
Figure 3: EMG envelopes and performance indicators during walking with arms (WWA in black) and walking with no arms (WNA in grey). **(a)** Normalized mean EMG envelopes for each subject (thin lines) and mean of all subjects (bold lines). Vertical red lines show statistically significant differences between WWA and WNA. **(b)** Distribution of the peak position (\(max_{x}^{EMG}\)) as a function of gait cycle (GC) (upper plot) and distribution of the EMG differences between WWA and WNA (\(\Delta\)) (lower plot). **(c)** Distribution of the cross-correlation (\(crosscorr^{EMG}\)) between WWA and WNA (upper plot) and its lag as a function of GC (lower plot) for each muscle. Black boxplots correspond to WWA and grey boxplots to WNA.