Author(s): FOURÉ, A., DE FREITAS, S.M.1, LETOURNEUR, A.2, GOURAUD, E.2, BOUVIER, J.1, Institution: UNIVERSITY OF LYON (UCBL), Country: FRANCE, Abstract-ID: 1006

INTRODUCTION:
Reliable assessment of exercise-induced muscle damage (EIMD) using indirect markers such as muscle function evaluation, invasive measurements, or imaging techniques is difficult to implement in field settings. On the other hand, bioimpedance spectroscopy is a non-invasive, easy-to-use and transportable tool, whose data seem to be affected in the presence of EIMD (1). The aim of this study was to determine which bioimpedance spectroscopy parameters are sensitive to eccentric EIMD and if these potential changes mirror responses in classical outome measures, such as muscle function and tissue mechanical properties.

METHODS:
Nine healthy males performed 120 maximal eccentric contractions of the knee extensors. Changes in knee extensors maximal isometric contraction torque, muscle soreness, resting rigidity (i.e., shear wave speed) of quadriceps femoris muscle, and bioimpedance spectroscopy parameters at rest and during maximal isometric contraction were assessed before (PRE), immediately after (POST) and in the three days (D1-D2-D3) following the exercise.

RESULTS:
Maximal contraction torque was significantly reduced during the three days following the eccentric exercise (up to -24.6% at D1, p < 0.001) while muscle soreness and rigidity of the whole quadriceps femoris were elevated until the second day (p < 0.05). Changes in bioimpedance (phase angle and reactance at 5 kHz, p < 0.001) and spectroscopy (membrane capacitance and characteristic frequency, p < 0.05) parameters were transiently observed at rest immediately after the damaging exercise, but not in the days that followed. Repeated-measures correlations revealed significant associations across time points between the rigidity of the whole muscle and the four biompedance parameters affected by the exercise (p < 0.05, 0.391 < r < 0.503), while maximal isometric contraction torque was only negatively correlated with characteristic frequency (p < 0.01, r = -0.362). None of the bioimpedance and spectroscopy parameters measured during contraction were affected by the eccentric exercise (p > 0.05).

CONCLUSION:
Maximal contraction torque, muscle soreness and resting rigidity followed the typical kinetics reported in cases of EIMD (2). Although the changes in bioimpedance spectroscopy parameters correlated with that of the indirect markers of EIMD, they returned to baseline by D1, while functional and mechanical impairments persisted. Therefore, bioimpedance spectroscopy measurements are not appropriate for monitoring EIMD in field settings, but may represent a cost-effective option for monitoring muscle fatigue (3).

(1) Shiose K. et al (2019). J Physiol Sci, 69:895-901.
(2) Paulsen G. et al (2012). Exerc Immunol Rev, 18:42-97.
(3) Vescio G. et al (2011). 5th Eur Conf Int Fed Med and Biol Eng, 1257-1260.