Background The effect of foot, especially intrinsic muscles, on postural control and its related mechanisms remain unclear due to the complex structure. Therefore, this study aims to investigate the activation of intrinsic foot muscles in the elderly under static and dynamic postural tasks. Methods Twenty-one elderly participants were included to perform different postural tests (sensory organization test (SOT), motor control test (MCT), limit of stability test (LOS), and unilateral stance test) by a NeuroCom Balance Manager System. The participants were instructed to maintain postural stability under conditions with combined different sensory inputs (vision, vestibular, and proprioception) in SOT as well as conditions with translation disturbance in MCT, and to perform an active weight-shifting tasks in LOS. During these tasks, muscle activation were simultaneously acquired from intrinsic foot muscles (abductor halluces (AbH) and flexor digitorum brevis (FDB)) and ankle muscles (anterior tibialis, medial head of gastrocnemius, lateral head of gastrocnemius, and peroneus longus). The root-mean-square amplitude of these muscles in postural tasks was calculated and normalized with the EMG activity in unilateral stance task. Results The activation of intrinsic foot muscles significantly differed among different SOT tasks ( p < 0.001). Post-hoc tests showed that compared with that under normal condition 1 without sensory interference, EMGs increased significantly under sensory disturbance (conditions 2–6). By contrast, compared with that under the single-sensory disturbed conditions (conditions 2–4; 2 for disturbed vision, 3 for disturbed vestibular sensation, 4 for disturbed proprioception), activation was significantly greater under the dual-sensory disturbed postural tasks (conditions 5 and 6; 5 for disturbed vision and proprioception, 6 for disturbed vestibular sensation and proprioception). In MCT, EMGs of foot muscles increased significantly under different translation speeds ( p < 0.001). In LOS, moderate and significant correlations were found between muscle activations and postural stability parameters (AbH, r = 0. 355–0.636, p < 0.05; FDB, r = 0.336–0.622, p < 0.05). Conclusion Intrinsic foot muscles play a complementary role to regulate postural stability when disturbances occur. In addition, the recruitment magnitude of intrinsic foot muscles is positively correlated with the limit of stability, indicating their contribution to increasing the limits of stability in the elderly.
The Fanshan alunite deposit, located in Cangnan County, Zhejiang Province, is the largest alunite deposit in China, which developed a lithocap with an extensive advanced argillic alteration. Surface alteration mapping, through field geology and shortwave infrared (SWIR) spectroscopy analyses, has defined three alteration zones including Na-alunite-dickite-pyrophyllite-topaz alteration, K-alunite-pyrophyllite-phengitic muscovite alteration, and chlorite-illite alteration from center to margin. Alunite varies from K-rich to Na-rich and has different paragenesis and texture. Na-alunite, with quartz, pyrophyllite, dickite, and topaz, mainly developed in Pingpengling area of Fanshan, forming a typical advanced argillic alteration. The wavelength position of the alunite –OH spectral absorption feature at ∼ 1480 nm (Pos1480) varies from 1478 nm to 1492 nm with increasing content of Na in alunite. There exists a positive correlation between Na/K ratio value and Pos1480 of alunite. The TESCAN Integrated Mineral Analyzer (TIMA), coupled with LA-ICP-MS analyses of alunite has been conducted, aiming to systematically characterize the texture and mineral chemistry of alunite. Fanshan alunite is rich in Ga, V, rare earth elements (REEs), and large ion lithophile elements (LILEs). Na-alunite has higher LILEs and light rare earth elements (LREEs) than K-alunite. Thorium, U, Li, and B, vary greatly in the Na-alunite and K-alunite. The ratio of Na/K in alunite, together with Pos1480 has been used to vector the magmatic-hydrothermal center. Furthermore, the content of Pb and ratios of Rb/Sr*1000, Sr/Pb, La/Pb, have illustrated the consistent results as Na/K and Pos1480. Based on the spatial distribution of these vectors in conjunction with the occurrence of Na-alunite, we concluded that Pingpengling area is the most proximal area to the magmatic-hydrothermal center, which may imply a possible causative intrusion underneath. Further exploration is suggested to be conducted under Pingpengling to verify if there is porphyry Cu(-Au-Mo) mineralization.
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