Figure 3. Dose-related increases in the duration of motor block of the (A) abdominal muscles as assessed by electromyography (bupivacaine, R²= 0.89; P < 0.0001; ropivacaine, R²= 0.67; P < 0.0001) and (B) the right quadriceps muscle as assessed by isometric force dynamometry (bupivacaine, R (²)= 0.97; P < 0.0001; ropivacaine, R²= 0.75; P < 0.0001). Mean and 95% confidence intervals of the slope of linear regression are plotted for bupivacaine and ropivacaine. In A, for the 4-mg and 12-mg dose, n = 5; for the 8-mg dose, n = 6. In B, n = 6 for all doses.