## 4 Discussion
### Improvement of Measuring Techniques for the Past 10 Years  
As discussed earlier, one of the aims of this systematic review is to analyse the improvement of the techniques used for measuring the residual limb volume, and this study acts as an extension of the study by [PERSON] and [PERSON] [4]. Since the last publication in the year 2011, a lot of researchers have shown their interest in measuring the residual limb volume. There are 21 publications from the past 10 years related to the techniques for measuring the residual limb, and a lot of improvements were conducted by researchers to make the techniques more accurate, user-friendly, and easy to apply. Apart from that, for the past 10 years, based on the published articles, researchers have presented their methods and data in a clear and easy-to-understand way to allow for any replications of the techniques. This systematic review also found that there is an increase in the number of studies in both the laser scanning and bioimpedance techniques. In recent years, the bioimpedance technique has shown an improvement. Some researchers made the technique easy to use and more sensitive to any changes in the residual limb. There are 12 publications on using the bioimpedance technique to measure the residual limb from the past 10 years, and this number of publications shows a drastic increase compared to the number of publications before 10 years ago, when there were only 2 publications related to this measuring technique. Researchers conducted some modifications to the techniques, especially in relation with the electrodes, as they can suit the residual limb and, at the same time, make the electrodes more sensitive to any volume measurement changes. [PERSON] et al. [53] improved and developed their own electrode that can suit the usage of bioimpedance instruments in the residual limb volume measurement studies. The developed electrode was thin with a thickness of 0.09 mm, flat, and could withstand mechanical and shear stresses inside the prosthetic socket. These features can to help give good results since the electrode will not disturb the normal prosthetic socket configuration. Moreover, compared to the electrode used by [PERSON] et al. [48] before 10 years ago, they just used the commercial bioimpedance instruments that had a thickness of 0.81 mm, which led to less accuracy in the signal reading. Another study also discovered that a thin layer of hydrogel ensured a good electrical coupling [53]. Later, in the year 2019, [PERSON] et al. [55] developed a portable bioimpedance instrument that helped researchers to monitor the residual limb volume changes outside of the lab setting. With the development of the bioimpedance instrument, the results were more accurate and reliable, showing that the instrument can be used to measure the volume changes inside or outside of laboratory settings. As mentioned earlier, this technique can measure the volume changes in real time only without knowing the residual limb volume. Thus, this allowed the researchers to measure the residual limb volume changes in every step of the gait cycle. This technique can determine the possible causes of residual limb volume changes without worrying about the post-doffing effect. As reported by [PERSON] et al. [6; 49; 50; 51; 54] and [PERSON] et al. [56], some factors such as the type of socket suspension system (vacuum, non-vacuum [49], and suction socket [56]); the post-doffing effect [51]; the amount of residual limb volume changes within one day [50]; daily activity such as walking, standing, and resting [6]; and the effect of the socket size (oversize, normal, and smaller sizes) [54] were found to be the causes of volume changes in the residual limb. Apart from the bioimpedance technique, the laser scanning method also shows an increased trend since the past 10 years. There are six publications related to the laser scanning technique from the years 2011 to 2021 as opposed to only three publications before the past 10 years.