Invasive dynamic electrical impedance myography during 100 s of moderate contraction in rats' gastrocnemius muscle.

GOAL: The present study aimed to investigate the behavior of dynamic electrical impedance myography (dEIM) signals during a 100-s period of the dynamic contraction of Wistar rats' gastrocnemius evoked by electrical stimulation and to link the variations in bioimpedance with muscular energy systems. METHODS: Muscle contraction used 30% of the maximum muscular force and persisted for 100 s, along which dynamic bioimpedance signals were acquired. Based on the bioimpedance signals, two parameters, ΔZc and ΔZpc, were calculated to allow the analysis of their changes with the energy systems that supplied adenosine triphosphate (ATP) to the muscle. ΔZc indicated the variation of impedance of a twitch cycle compared to the values observed during the rest period preceding the cycle, and ΔZpc indicated slow bioimpedance variations compared to the values obtained during the rest period. RESULTS: The results indicated that ΔZc followed the force behavior, achieving a change rate of ∼14%. This parameter was associated with instantaneous impedance changes owing to the occurrence of each twitch. CONCLUSION: Although the findings of this study were linked to energy system processes, future studies are required for improving the understanding of the underlying mechanisms involved in dEIM. SIGNIFICANCE: The results contributed to understanding the relation of energy systems that supply ATP to the muscles with dEIM variations that occurred during muscle activity.

Invasive electrical impedance myography at different levels of contraction of gastrocnemius muscle of rat.

Electrical impedance myography (EIM) is as an experimental technique that associates muscle impedance with muscular activity. Changes in muscle impedance during contraction occur mainly due to changes in the morphological and physiological characteristics of muscles that lead to different impeditivities in comparison with the resting condition. There is no consensus on the details of muscular impedance during muscle activity. EIM measurements on humans are also influenced by factors such as the electrode-skin interface, layers of skin and fat, and the connective tissue that can generate undesirable effects in the impedance signal. These effects can be avoided if EIM measurements are carried out directly on the muscle by using the models of animals. This study investigates changes in the EIM signal in the gastrocnemius muscles of Wistar rats during different levels of muscular contraction. In vivo experiments were conducted on 19 male rats. The muscle was exposed, fixed on a load cell, and electrically stimulated to evoke different levels of muscle contraction. Signals of the components of impedance were analyzed against the muscular force signal. The results show moderate correlations (p < 0.05) among the impedance-related parameters of resistance (r = -0.76), reactance (r = 0.57), and phase (r = 0.53). In addition to providing an experimental protocol for the invasive collection of data on electrical impedance to minimize problems associated with surface electrodes, this study shows that of the components of impedance, resistance is most affected by the intensity of muscular contractions and that morphological changes influence impedance mainly at low intensities.

Lactate threshold by muscle electrical impedance in professional rowers.

Lactate threshold (LT) is one of the physiological parameters usually used in rowing sport training prescription because it indicates the transitions from aerobic to anaerobic metabolism. Assessment of LT is classically based on a series of values of blood lactate concentrations obtained during progressive exercise tests and thus has an invasive aspect. The feasibility of noninvasive LT estimative through bioelectrical impedance spectroscopy (BIS) data collected in thigh muscles during rowing ergometer exercise tests was investigated. Nineteen professional rowers, age 19 (mean) ± 4.8 (standard deviation) yr, height 187.3 ± 6.6 cm, body mass 83 ± 7.7 kg, and training experience of 7 ± 4 yr, were evaluated in a rowing ergometer progressive test with paired measures of blood lactate concentration and BIS in thigh muscles. Bioelectrical impedance data were obtained by using a bipolar method of spectroscopy based on the current response to a voltage step. An electrical model was used to interpret BIS data and to derive parameters that were investigated to estimate LT noninvasively. From the serial blood lactate measurements, LT was also determined through Dmax method (LTDmax). The zero crossing of the second derivative of kinetic of the capacitance electrode (Ce), one of the BIS parameters, was used to estimate LT. The agreement between the LT estimates through BIS (LTBIS) and through Dmax method (LTDmax) was evaluated using Bland-Altman plots, leading to a mean difference between the estimates of just 0.07 W and a Pearson correlation coefficient r = 0.85. This result supports the utilization of the proposed method based on BIS parameters for estimating noninvasively the lactate threshold in rowing.