Electrical-tomographic imaging of physiological-induced conductive response in calf muscle compartments during voltage intensity change of electrical muscle stimulation (vic-EMS)

Abstract

Objectives. The electrical-tomographic imaging has been achieved for exploring differential tendency of physiological-induced conductive response in calf muscle compartments during voltage intensity change of electrical muscle stimulation (vic-EMS). Approach. In the experiments, the differential tendency of conductivity distribution images σ during vic-EMS were clearly imaged as three responsive muscle compartments, which are called M 1 compartment composed of gastrocnemius muscle, M 2 compartment composed of tibialis anterior, extensor digitorum longus, and peroneus longus muscles, and M 3 compartment composed of soleus muscle. Main results. The differential tendency of spatial-mean conductivity 〈σ〉 M1 is the same as the differential tendency of venous blood flow velocity v bl and blood lactate concentration C bl during vic-EMS by the increased tendency of spatial-mean conductivity difference Δ〈σ〉 M1, venous blood flow velocity difference Δv bl and blood lactate concentration difference ΔC bl . The 〈σ〉 M1 is increased with the increase of voltage intensity from 〈σ pre 〉 M1 = 0.142 [-] to 〈σ l14 〉 M1 = 0.442 [-] (pre: pre-training, l14: voltage level during vic-EMS l = 14) by Δ〈σ l14-pre 〉 M1 = 204.2% (n = 16, p < 0.01). Correspondingly, the v bl and C bl are increased with the increase of voltage intensity by Δv bl l14-pre = 1480.5% (n = 16, p < 0.01) and ΔC bl l14-pre = 230.1% (n = 16, p < 0.01) respectively. Significance: The reason for the differential tendency of increase in <σ> M1 suggests an increase in muscle extracellular volumes during vic-EMS due to the co-effect of venous blood flow velocity and blood lactate metabolism. Based on the conductivity second-order difference images and spatial-mean conductivity second-order difference optimum voltage intensity φ OVI is discussed among sixteen volunteer subjects, which increased with a thicker subcutaneous fat layer.