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Purpose：The purpose of this study was to assess the effects of the lower extremity muscle activity on bridging exercise according to the knee joint angle. Methods：Twenty-five healthy adults volunteered to participate in this study. Subjects were required to complete following four bridging exercises; knee joint flexion 120°, 90°, 60°, 45°. Surface electromyography from selected lower extremity muscles was normalized to maximum voluntary isometric contraction. Muscle activity was measured by QEMG-4 system (LXM 3204, Laxtha Korea). A repeated measures of one-way ANOVA was used to determine the influence of bridging exercise on muscle activity for each muscle and descriptive statistics was used to determine muscle ratio. Results：The biceps femoris of all bridging exercises showed significantly(p<.05). The vastus medialis and lateralis of all bridging exercises showed significant excepted 120°(p<.05). The rectus femoris of all bridging exercises showed no significant. Median of vastus medialis/rectus femoris ratio of 120° was 2.03, 90° was 2.16, 60° was 2.67, 45° was 4.10. Median of vastus lateralis/rectus femoris ratio of 120° was 1.70, 90° was 1.70, 60° was 2.08, 45° was 2.58. Median of vastus medialis/vastus lateralis ratio of 120° was 1.26, 90° was 1.50, 60° was 1.52, 45° was 1.47. Conclusion：Angular motion decreasing with knee joint flexion made increase biceps femoris and vastus medialis activation. This result will be use knee joint stabilizing exercises during bridging or unstable surface training and biceps femoris strength training.