The study aimed to assess by an electromyographic (EMG), mechanomyographic (MMG), and force-combined approach the electrochemical and mechanical components of the overall electromechanical delay during relaxation (R-EMD). Reliability of the measurements was also assessed. To this purpose, supramaximal tetanic stimulations (50？Hz) were delivered to the gastrocnemius medialis muscle of 17 participants. During stimulations, the EMG, MMG, and force signals were detected, and the time lag between EMG cessation and the beginning of force decay ( EMG-F, as temporal indicators of the electrochemical events) and from the initial force decrease to the largest negative peak of MMG signal during relaxation ( F-MMG, as temporal indicators of the mechanical events) was calculated, together with overall R-EMD duration (from EMG cessation to the largest MMG negative peak during relaxation). Peak force (pF), half relaxation time (HRT), and MMG peak-to-peak during the relaxation phase (R-MMG p-p) were also calculated. Test-retest reliability was assessed by Intraclass Correlation Coefficient (ICC). With a total R-EMD duration of 96.9 ± 1.9？ms, EMG-F contributed for about 24% (23.4 ± 2.7？ms) while F-MMG for about 76% (73.5 ± 3.2？ms). Reliability of the measurements was high for all variables. Our findings show that the main contributor to R-EMD is represented by the mechanical components (series elastic components and muscle fibres behaviour), with a high reliability level for this type of approach. 1. Introduction Similarly to the electromechanical delay (EMD), which is generally defined as the time lag between the onset of muscle electrical activation and the onset of force production during the contraction, a delay between the cessation of EMG activity and the beginning of force decrease can be observed also during the relaxation phase [1]. While EMD has been widely investigated and has been shown to include the electrochemical and mechanical events from neuromuscular activation to force transmission to the bone [2–10], few studies approached the delay during the relaxation phase (R-EMD), which comprises (i) the cessation of the neuromuscular activation; (ii) Ca2+ reuptake by the sarcoplasmic reticulum and the block of the actomyosin interaction by troponin and tropomyosin; and (iii) the release of the elastic elements previously stretched during contraction and the return of the sarcomeres to their resting length [1, 11–15]. In those studies, the R-EMD ranged from 30？ms [15] to about 250？ms [12]. Several factors contributed to this large R-EMD variability, among which
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