ECSS Paris 2023: CP-BM01
INTRODUCTION: Observing others actions activates a brain network known as the action observation network (AON), which includes motor-related brain areas [1]. The AON activity has been reported to be stronger when observing an action that the observer has repeatedly practiced compared to an unexperienced action [2]. However, previous studies have mainly focused on how motor experience affects the AON activity during the observation of voluntary movements (e.g., dancing) and have not examined semi-automatic rhythmic movements such as walking. Therefore, the present study aimed to investigate brain activity induced by observing walking in a split-belt condition (where the left and right treadmill belts move at different speeds), which the observers had not experienced. Initially, walking under the split-belt condition becomes asymmetric, but it gradually approaches more symmetric over several minutes [3]. Using functional magnetic resonance imaging (fMRI), we investigated brain activity, while participants observed both asymmetric and symmetric walking at the initial and late periods of the split-belt condition, respectively. METHODS: Nineteen healthy adults participated in the study. From the walking video recorded from the actors left side in a tied condition (left and right speed: 1.25 m/s) for 2 minutes and a split-belt condition (left speed: 1.0 m/s, right speed: 1.5 m/s) for 10 minutes, three video clips of the actors lower limb movements were created: 8 seconds during walking in the tied condition, as well as the initial and last 8 seconds (initial and late period, respectively) of split-belt condition. The actors step lengths in the video clips were almost symmetric in the tied condition and late period of the split-belt condition, but were markedly asymmetric in the initial period of the split-belt condition. The participants observed these video clips in a random order to examine brain activity during the observation using fMRI. The differences in brain activity between conditions were analyzed using one-sample t-tests with a voxel-wise threshold of p < 0.001 (uncorrected) and a family-wise error rate-corrected extent threshold of p < 0.05. RESULTS: While observing walking video clips, AON areas, including the parietal cortex, cerebellum, and inferior frontal gyrus, were significantly activated, irrespective of the condition. Furthermore, brain regions, including the supramarginal gyrus and inferior frontal gyrus, were strongly activated during the observation of walking in both periods of the split-belt condition compared to the tied condition. CONCLUSION: Our results suggest that observation of walking under an asymmetric speed condition, which is unfamiliar to the observers, elicits stronger AON activation compared to observation of normal walking in a symmetric speed condition. [1] Caspers et al., Neuroimage, 2010 [2] Calvo-Merino et al., Cereb Cortex, 2005 [3] Reisman et al., J Neurophysiol, 2005
Read CV Masaya KitamuraECSS Paris 2023: CP-BM01
INTRODUCTION: Older adults experience more frequent falls due to sensory decline, reduced muscle strength, and other causes. While these risk factors are well-documented, less is known about how aging affects movement behavior near the stability limit. In particular, do older adults adjust their postural control strategies differently than young adults when balance becomes precarious? To investigate this, we instructed volunteers to lean forward as far as possible (“test your limits”) from an upright standing position while maintaining a straight body posture. We hypothesized that older individuals would exhibit different characteristics in their corrective movements compared to younger individuals. METHODS: Twenty young (10 males, 26 ± 3 years) and 21 older (11 males, 70 ± 7 years) healthy volunteers performed eight 30-second trials of forward leaning while their postural movements were recorded (Vicon™, 39 markers, 250 Hz). Postural movement characteristics were analyzed using principal component analysis (PCA), with relative movement variance (rVARk) reported for each principal movement. Depending on normality and variance homogeneity, group differences in rVARk were assessed using independent t-test, Welch’s t-test, or the Mann-Whitney U test. Effect sizes were reported as Cohen’s d (d = 0.2–0.5: small, d = 0.5–0.8: moderate, d > 0.8: large) or rank biserial correlation (rbc = 0.1–0.3: small, rbc = 0.3–0.5: moderate, rbc > 0.5: large). RESULTS: PCA revealed no significant differences in the first two principal movements, which accounted for 71% of explained variance. However, older adults exhibited greater lateral sway (rVAR3, p = .005, d = -1.79), while younger adults showed higher contributions of an ankle strategy with arm movements (rVAR4, p < .001, d = 2.22), a hip strategy with arm movements (rVAR6, p = .016, d = 1.51), and elbow flexion, lateral trunk flexion, and ankle movement (rVAR8-12, p < .038, d > 1.21 / rbc > .63). CONCLUSION: Our findings reveal age-related differences in corrective motor responses near the stability boundary. The lack of differences in the first two principal components, which account for most of the movement variance, suggests that fundamental movement strategies remain similar across age groups (Haid et al., 2018). However, younger adults exhibited greater variance in higher components, indicating more adaptable movement strategies. In contrast, older adults showed increased lateral sway, a pattern associated with a higher fall risk (Rogers & Mille, 2003). REFERENCES: Haid, Doix, Nigg, Federolf, (2018). Front. Aging Neurosci., 10, 22. doi: 10.3389/fnagi.2018.00022 Rogers, Mille, (2003). Exercise and Sport Sciences Reviews, 31(4), 182–187. doi: 10.1097/00003677-200310000-00005
Read CV Anna WargelECSS Paris 2023: CP-BM01
INTRODUCTION: Foot stabilization for maintaining standing posture has been attributed to intrinsic foot muscles, particularly the abductor hallucis muscle (1). However, our previous study indicated that the towel curl exercise, which activates the abductor digiti minimi (ADM) along with other intrinsic foot muscles, improves balance during single-leg standing (2). Despite this, exercise alone struggles to effectively target ADM, making its role in balance control difficult to evaluate. Therefore, we combined exercise with neuromuscular electrical stimulation (NMES) to selectively activate the ADM and investigate its role in balance control. NMES enhances muscle strength, neural adaptations, and intermuscular coordination (3), with effects further augmented when combined with voluntary exercise (4). This study examined the effects of combining NMES with ADM-focused exercise and hypothesized that it would improve balance and activate extrinsic foot muscles during standing. METHODS: Twenty-six participants were divided into two groups: NMES combined with towel curl exercise (NMES group) and exercise alone (CON group). They performed single leg standing tasks under eyes-open and eyes-closed conditions before and after intervention. NMES at 20 Hz for 20 minutes was applied to the NMES group before exercise. During the exercise, they used their little toe side to gather the towel. Balance was assessed using the root mean square (RMS) of CoP displacement in the anteroposterior and mediolateral (ML) directions and rectangular area (RA). Electromyogram of the lower limb was recorded, and the RMS of each muscle were analyzed. They were analyzed by two-way repeated measures ANOVA (α = 0.05). RESULTS: During single leg standing with eyes closed, both groups showed reduced ML-RMS (CON: p = 0.003, NMES: p = 0.003) and RA (CON: p = 0.037, NMES: p < 0.001) after the intervention. Additionally, in the NMES group, RMS of the gastrocnemius (p = 0.033) and peroneus longus (p = 0.003) decreased with eyes open. With eyes closed, RMS of the tibialis anterior (p = 0.024) and peroneus longus (p = 0.004) decreased in the NMES group. CONCLUSION: In single leg standing with eyes closed, ML CoP sway decreased in both groups, likely due to ADM activation supporting lateral stability (5). Furthermore, improvements in eyes-closed conditions, where somatosensory input dominates (6), suggest that NMES and exercise enhanced somatosensory function. The NMES group showed reduced extrinsic foot muscles activity, implying ADM activation minimized compensatory extrinsic muscles use (1). These findings indicate that activation of intrinsic muscles enhances stability and reduces reliance on extrinsic muscles. In conclusion, NMES combined with ADM-focused exercise improves standing balance and reduces extrinsic foot muscles activity. REFERENCES 1. McKeon et al. (2013) 2. Nishino et al. (2024) 3. Enoka et al. (2019) 4. Namsawang et al. (2022) 5. Neumann (2017) 6. Brodoehl et al. (2016)
Read CV Aoi NishinoECSS Paris 2023: CP-BM01