**5. Conclusions**

This article thoroughly discusses a new knee joint motion measurement system constructed using two linear accelerometers, from the basic stretch reflex to the analysis of measurement results, focused on achievements obtained up to this time.

In section 2, we first explained the mechanical structure of knee joint flexion and extension as background knowledge to understand the discussion in section 3 and subsequent subsection, briefly touching also on the movement of the knee joint axis. Next, we looked at the source of the generation of the stretch reflex, which is the subject of measurement of the knee joint motion measurement system. We also showed the phasic and tonic reflex loops centered on muscle spindle function.

In section 3, we summarized the principles and results of performance evaluation of the knee joint motion measurement system. First, we looked comprehensively at accelerometers, which are the best option among sensors that can be used to measure knee joint motion, and then discussed the principles of the knee joint motion measurement system using two linear accelerometers. Next, we showed that the detection error of this device for simple pendulum motion and the pendulum motion of subjects is about the same as with high-accuracy, rotation angle gauges.

In section 4, we showed that the angle and angular acceleration of the knee joint could be simultaneously synchronized and measured in patients showing spasticity with enhanced phasic reflexes, and that the timing at which reflexes are produced could be easily estimated. Next, we showed the principles of a simulator to analyze measured waveforms and examples of analysis using this simulator, together with an additional statement on the outlook for high-level analysis of reflexes in patients with spasticity.

As a general conclusion, we demonstrated that the developed knee joint motion measurement system does not restrict subjects' movement as other systems do, and that it has many features that other systems do not, such as simple system configuration and the ability to acquire large amounts of information with simple data processing.

Future issues are the accumulation of clinical data using the features of this knee joint motion measurement system and quantification estimates of abnormal stretch reflexes such as spasticity, rigidity, and rigidospasticity based on those data.
