Abstract
Coactivation is the concomitant contraction of synergistic and antagonistic muscle pairs. Studies using linear coactivation assessments have shown greater coactivation in older than younger adults during gait. Coactivation is a nonlinear phenomenon that may be better examined with nonlinear methods, such as symbolic transfer entropy (STE), which provides the magnitude of information flow and its directionality index (DI). Through analyzing system uncertainty, information flow may provide insight into the communication between coactivating muscles. PURPOSE: To assess the effects of aging on information flow between knee muscles during gait using STE. METHODS: The publicly available dataset used comprises 40 healthy older adults (Age: 76 ± 6.3 yrs., Height: 164.3 ± 10.5 cm, Weight: 75.3 ± 11.4 Kg) and 45 healthy young adults (Age: 28.4 ± 5.1 yrs., Height: 172.7 ± 8.6 cm, Weight: 75.7 ± 18.4 Kg). Surface electromyographic data was recorded bilaterally from the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and semitendinosus (ST). STE was calculated with
STE_{Y \to X} = \sum P(\widehat{x}_{t+\delta}, \widehat{x}_t, \widehat{y}_t) \log \frac{p(\widehat{x}_{t+\delta}|\widehat{x}_t, \widehat{y}_t)}{p(\widehat{x}_{t+\delta}|\widehat{x}_t)}
, where {$\widehat{x}_t$ }, {$\widehat{y}_t$ } are symbolic sequences of sEMG, and δdenotes a time step. The DI was calculated by subtracting the two STEs for each direction (\[DI = STE_{X \to Y} - STE_{Y \to X}\]). The STE was calculated for RF-ST, RF-VL, and VL-BF for the left leg during left stride and used for statistical analysis. A one-way analysis of variance (ANOVA) with an adjusted Bonferroni post hoc test was used to identify differences in information flow and DI between the young and old groups. RESULTS: During left stride, the VL-BF for the left leg was statistically significant for STEX→Y (F(1,51) = 7.855, P = 0.007), while the STEY→X (P = 0.215) and DI (P = 0.789) were not significant. The pairwise test indicated that older adults had greater STE from VL to BF. For RF-ST, the STEX→Y (P = 0.394), STEY→X (P = 0.284), and DI (P = 0.913) were not statistically significant. Finally, the RF-VL muscle pairs showed no statistical significance for the STEX→Y (P = 0.61), STEY→X (P = 0.052), and DI (P = 0.73). The older adult’s DIs were VL-BF: -0.0026 ± 0.007, RF-ST: 0.0005 ± 0.015, and RF-VL: 0.0064 ± 0.013. Younger adult’s DIs were VL-BF: -0.0032 ± 0.0078, RF-ST: 0.00093 ± 0.016, and RF-VL: 0.0047 ± 0.01. CONCLUSION: The STE analysis showed that information flow increases from VL to BF in older adults; however, its directionality remained unchanged. The DI results indicated that information flow from RF to ST and VL reduced their activity uncertainty, while VL information flow reduced the uncertainty in BF activity in older and younger adults. The increase in VL-BF information flow may manifest as greater coactivation in older adults and decreased variation in BF activation. Previous literature indicates that aging reduces inhibitory inputs to antagonistic motoneurons, while no differences in excitatory input were reported. Increased information flow in older adults may be attributed to a reduction in inhibitory input, leading to net excitatory input to antagonistic motoneurons. However, further investigation is required to assess differences in information flow in the case of increased inhibitory input to antagonistic motoneurons.
Recommended Citation
Hoang, Kiefer A.; Champion, Reece K.; and Alighanbari, Mohsen
(2026)
"Analyzing the Effect of Aging on Information Flow Among Knee Muscles During Gait Using Symbolic Transfer Entropy,"
International Journal of Exercise Science: Conference Proceedings: Vol. 2:
Iss.
18, Article 80.
Available at:
https://digitalcommons.wku.edu/ijesab/vol2/iss18/80