['To explore the most effective parameters of Yi Zhi Chan Tuina manipulation for improving peripheral blood circulation.', 'A total of 45 volunteers were recruited from Pudong district in Shanghai, China, from October to December 2010, and randomly divided into nine groups using computer-generated random numbers. Participants received Yi Zhi Chan Tuina manipulation on Chengjin (BL 56) acupoint; each group received a particular combination of manipulation force and treatment time. We used a two-factor, three-level factorial design to examine the effects of force and treatment time on changes in popliteal artery average volume flow, pulsatility index, and vessel diameter to determine the optimal parameter group. Outcomes were assessed at baseline and after Tuina manipulation by interviewers blind to treatment group status.', 'After manipulation, two of the nine groups showed an increase in popliteal artery volume flow. An inter-participants effect test showed that for main effect of time, F = 0.331, P = 0.720; for main effect of force, F = 2.934, P = 0.066; and for the force-time interaction effect, F = 1.072, P = 0.385, indicating no interaction between force and time. However, a pairwise comparison of the three levels of time showed that a treatment time of 10 min was significantly more effective than that of 2 min (P = 0.024). A pairwise comparison of light force, medium force, and heavy force showed a statistically significant effect for medium force (P = 0.035).'] Does optimization of parameters of Yi Zhi Chan Tuina manipulation promote peripheral circulation?