Fig. 4　 Summary measurements of shoulder stress for abduction during laparoscopic simulation surgery, represented as the amplitude probability distribution function（ APDF） in %MVC. White bar: control group; dotted bar: SAS- group; grey bar: SAS＋group; error bar: S. D. No significant differences were found between the SAS- or SAS＋ vs. control groups（ t-test, Mann-Whitney U test）. N. S.: not significant.