Abstract: ObjectiveTo analyze the biomechanics of ascending and descending stairs.MethodsThe moment of force of knee joint and contract strength of quadriceps muscles were analyzed by three dimensional motion analysis system and electromyograph (EMG) in three healthy men.ResultsFor the moment of force of knee joint, there were differences among different styles of ascending and descending stairs, but there were no differences in angles of knee joint flexion. The contract strength of quadriceps muscles during ascending stairs was stronger than that during descending stairs.Conclusion There are differences of knee joint moment and quadriceps muscles activities among 4 strategies during descending, and it is shown that quadriceps muscles' activities and knee joint moment became smaller during forward stepping, double stepping on one stair, side stepping, and 45°side stepping in sequence during descending stairs.

Key words: joint moment of force, forward stepping, double stepping on one stair, side stepping, 45°side stepping