Bioimpedance spectroscopy assessment of skeletal muscle tissue properties after muscle damage

High intensity and unaccustomed physical activity can induce skeletal muscle damage, while even routine movements can cause similar alterations in patients with neuromuscular disease. However, reliable assessment of muscle damage using indirect markers such as muscle function evaluation, invasive measurements, or imaging techniques is difficult to implement in routine clinical follow-up and sport field settings. Bioimpedance spectroscopy appears as a promising non-invasive, easy-to-use and transportable tool to assess indirect markers of muscle damage. The aim of this study was to determine whether bioimpedance spectroscopy data are sensitive to eccentric exercise-induced muscle damage and if these potential changes mirror responses in muscle function and tissue mechanical properties. Changes in knee extensors maximal isometric contraction torque, muscle soreness, resting rigidity of the quadriceps femoris muscle tissue, and bioimpedance parameters at rest and during maximal isometric contraction were assessed in nine healthy males before, immediately after and in the three days following 120 maximal isokinetic eccentric contractions. Maximal contraction torque was significantly reduced during the three days following the eccentric exercise (up to -24.2%) while muscle soreness and rigidity of the quadriceps femoris were elevated until the second day (+494.4% and +7.6%). Changes in bioimpedance spectroscopy parameters were transiently observed at rest immediately after the damaging exercise, but not in the days that followed. Although the changes in bioimpedance parameters correlated with that of the indirect markers of muscle damage, they had already returned to baseline while functional and mechanical impairments persisted. Therefore, bioimpedance spectroscopy measurements may represent a suitable and cost-effective means of monitoring muscle fatigue.