Abstract: Objective: To explore the ankle joint and knee joint movement, the ground reaction force and the muscle surface electromyography (EMG) of elderly people during stair descent. Methods: Ten elderly males (68.5±3.8 years old, 1.71±0.25 meters high, 70.2±13.5 kg weight) and ten young people (22.5±2.7 years old, 1.75±0.14 meters high, 65.9±11.3 kg weight) participated in the test. The kinematic, dynamic and surface EMG signals of the walking process of the elderly were collected through the equipment and software specific to sports biomechanics. Results: The kinematic, dynamic and surface EMG curves of both the old and young people are identical. The maximum ankle flexion angle, the maximum ankle plantar flexion angle, the first peak value of the ground reaction force and the second peak value of the ground reaction force were significantly different between the young and the elderly. During the support ting phase, the femoral lateral muscle and the activation level of gastrocnemius lateralis muscle of the elderly are slightly higher than those of the young. Conclusion: The difference in motion performance between the elderly and the young may be attributed to the difference in their muscle strength. Therefore, it is of great importance for the elderly to develop their lower extremity muscle strength to enhance their body stability during stair descent.

Key words: The Elderly, Stair Descent, Kinematics, Dynamics, Surface EMG