Fig. 5. Difference in VAS scores at the back: At time = 1 and 2, there were no significant differences in VAS scores. By time = 3 (80min), the 20 min interval group (•) showed a significant difference between VAS scores, which persisted throughout the remainder of the recording session. By time = 4 (2 h), the other groups showed a marginal significance, which became highly significant by the third hour (time = 6).