Long-term phase angle muscle imaging under electrical muscle stimulation (EMS) by phase angle electrical impedance tomography.

Objectives . Phase angle muscle imaging has been proposed by phase angle electrical impedance tomography (ΦEIT) under electrical muscle stimulation (EMS) for long-term monitoring of muscle quality improvement, especially focusing on calf muscles. Approach . In the experiments, twenty-four subjects are randomly assigned either to three groups: control group (CG, n = 8), low voltage intensity of EMS training group (LG, n = 8), and optimal voltage intensity of EMS training group (OG, n = 8). Main results . From the experimental results, phase angle distribution images Ф are cleared reconstructed by ФEIT as four muscle compartments over five weeks experiments, which are called the M ₁ muscle compartments composed of gastrocnemius muscle, M ₂ muscle compartments composed of soleus muscle, M ₃ muscle compartments composed of tibialis-posterior muscle, flexor digitorum longus muscle, and flexor pollicis longus muscle, and M ₄ muscle compartment composed of the tibialis anterior muscle, extensor digitorum longus muscle, and peroneus longus muscle. Ф is inversely correlated with age, namely the Ф decreases with increasing age. A paired samples t -test was conducted to elucidate the statistical significance of spatial-mean phase angle in all domain < Ф > _Ω and in each muscle compartment < Ф > _M with reference to the conventional phase angle Ф by bioelectrical impedance analysis, muscle grey-scale G _muscle by ultrasound, and maximal dynamic strength S _Max by one-repetition maximum test. Significance . From the t -test results, < Ф > _Ω have good correlation with Ф and S _Max . In the OG, < Ф ^W5 > _Ω , Ф ^W5 , and ( S _Max ) ^W5 were significantly higher than in the first week ( n = 8, p < 0.05). A significant increase in the phase angle of both M ₁ and M ₄ muscle compartments is observed after five weeks in LG and OG groups. Only the OG group shows a significant increase in the phase angle of M ₂ muscle compartment after five weeks. However, no significant changes in the spatial-mean phase angle of M ₃ compartment are observed in each group. In conclusion, ФEIT satisfactorily monitors the response of each compartment in calf muscle to long-term EMS training.
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