Author(s): LONGO, S., CORATELLA, G., TONINELLI, N., BORRELLI, M., RAMPICHINI, S., DORIA, C., LIMONTA, E., CÈ, E., ESPOSITO, F., Institution: UNIVERSITÀ DEGLI STUDI DI MILANO, Country: ITALY, Abstract-ID: 1371

INTRODUCTION:
Electrical impedance myography (EIM) is a painless technique deriving from the classical bioelectrical impedance analysis. In EIM, the electrodes are applied locally over a body segment to describe its bioelectrical tissue properties (i.e., impedance, Z) by resistance (R), reactance (Xc), and phase angle (PhA) analysis. EIM components seem to change in response to different level of muscle contraction, fatiguing tasks, and eccentric exercise. However, there is still a lack of studies about its potential use to assess the recovery following potential eccentric exercise-induced performance impairment. Therefore, the aim of this study was to measure changes in EIM components induced by a typical dose of Nordic hamstring exercise (NHE) and the time-course of recovery.
METHODS:
Thirteen men (mean±SD; age=25.2±2.9 years; body mass=77.5±11.3 kg; height=176.4±8.4 cm) were recruited. Knee flexors maximum voluntary isometric contraction (MVC), muscle soreness by visual-analogue scale of 100 mm (VAS), 50-kHz EIM components (i.e., Z, R, Xc, and PhA), echo intensity (EI), and anatomical cross-sectional area (ACSA) of the posterior thigh were assessed at baseline (PRE). Then, 4 sets of 6 repetitions of NHE were performed. The participants were subsequently assessed on day 1 to day 4 (Day1, Day2, Day3, Day4) after the NHE. Data were analysed by repeated-measure ANOVA and non-parametric Friedman tests with p<0.05.
RESULTS:
After the NHE protocol, MVC decreased at Day1 (-14%, p<0.01), Day2 (-17%, p<0.01), and Day3 (-17%, p<0.01), recovering at Day4 (-7%, p>0.05) compared to baseline. VAS increased at Day1 (16±13 mm, p<0.01), Day2 (22±16 mm, p<0.01), Day3 (19±14 mm, p<0.01), and was still higher than baseline at Day4 (11±8 mm, p<0.05). Conversely, EIM components (Z, R, Xc, and PhA) did not change significantly from baseline throughout the protocol (p>0.05). Similarly, hamstrings EI and ACSA did not change significantly from baseline throughout the protocol (p>0.05).
CONCLUSION:
These results showed that the proposed NHE protocol induced an impairment in muscle function, which recovered within 4 days. Muscle soreness increased and persisted up to Day4. However, muscle impedance and structural characteristics were not affected by 4 x 6 NHE. Therefore, further research with different eccentric exercise-induced performance impairment is needed to assess the potential use of EIM to monitor muscle-performance recovery.

Freeborn T.J., Regard G., Fu B. Localized Bicep Tissue Bioimpedance Alterations Following Eccentric Exercise in Healthy Young Adults. 2020. IEEE Access, vol. 8, pp. 23100-23109