A portable, easy-to-use hardware- and software-based prototype system was designed to quantify the Achilles myotatic reflex in clinical settings. The prototype has three parts: an input stage with an instrumented hammer to measure strike force, an EMG sensor, and an accelerometer to detect responses; an Arduino UNO-based acquisition/transmission stage; and a Python software stage for signal display, recording, and processing on a PC. The hardware performance was validated by assessing the system’s sampling and transmission rates. The software was validated in a pilot study. The conduction and contraction gains of 7 healthy volunteers were obtained as the slopes of the EMG-striking force (r = 0.82 ± 0.13, p < 0.005) and EMG-acceleration (r = 0.90 ± 0.11, p < 0.005) relations, respectively. The conduction, contraction, and total latencies were computed as the times spanning from the onset of the hammer strike to the onset of the EMG signal, from the EMG to the acceleration wave, and from the strike to the acceleration wave, respectively. The gains converged to similar mean values with a small standard deviation. The portable system allowed quantitative evaluation of conduction and contraction gains, as well as latencies of the Achilles myotatic reflex using a clinical method. These validation and pilot studies produced promising results, supporting the device’s potential for clinical use.