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Slips and falls often occur in the industrial environments. They are not only caused by environmental hazards but also by some biomechanical factors related to deficient ability of postural control to arrest impending falls. The purpose of this study is to simulate the slip condition in human walking and to find out the possible related factors of biomechanics.

Eleven male and 9 female recruited were healthful without any musculoskeletal and neurological impairments. In order to provide different disturbance level, three lean angles of tilting boards were designed as 10, 20, 30 degrees with respect to horizontal plane. Subjects wore a safety harness, stood on the tilting board and were released without awareness. A forceplate applied a soap patch was in front of the tilting board to serve the slippery perturbation and to measure the fool/floor reactions. Movements of body segments were measured using the motion analysis system.

The results were shown that lean angle had a significant effect to all parameters except step length, response time, maximum ankle forward velocity, hip forward velocity, and ankle flex angle. The gender significantly affected on the step length, response time, maximum ankle forward velocity, and knee forward velocity. Larger lean angle made subjects to take a more rapid step. In order to absorb the shock in foot strike, subjects flexed more their knee and increased the foot landing angle in larger lean angle. Male tended to adopt the long step-length strategy to respond to the slippery perturbation and female tended to use the short step-length strategy instead. The results of maximum ankle forward velocity suggested that short step-length strategy could be belter to reduce the foot slip than long step-length strategy.

The passive extensibility of skeletal muscles is an important health-related component of physical fitness. Tight gastrocnemius is a common orthopedic problem and frequently leads to overuse injuries of the lower extremity. Moreover, gastrocnemius tightness is commonly associated with lower back pain. Previous studies have reported that tight gastrocnemius results in kinematic and kinetic deviations of the ankle and knee during gait and a greater hip flexion at the moment of maximal ankle dorsiflexion. Accordingly, this study performs an experimental investigation into the effects of tight gastrocnemius on the hip and pelvic movements in gait. Sixteen subjects with tight gastrocnemius (defined as $<10^{\circ }$ of ankle dorsiflexion with knee extended) and 16 healthy individuals matched by age and gender participated in the study. The three-dimensional angles of the hip and pelvis and moments of the hip were obtained for both groups during the stance phase of gait using force plates and a motion analysis system. Compared with the control group, the peak hip flexion angle is significantly higher in the tight group ($p=0.001$), while the peak hip extension angle is significantly lower ($p=0.001$). Moreover, the peak pelvic anterior tilt is significantly higher than that of the control group ($p=0.001$), while the peak pelvic posterior tilt is significantly lower ($p=0.001$). Finally, the peak extensor moment of the tight group is significantly higher than that of the control group ($p=0.049$), while the peak flexor moment is significantly lower ($p=0.003$). The results confirm that tight gastrocnemius leads to changes in the three-dimensional hip and pelvic angles and hip moments during gait. Disturbance of the hip and pelvic movement is thus a critical clinical consideration when evaluating soft tissue injuries in patients with tight gastrocnemius.