Changes in Gait between Successful Balance Recovery and Fall after Unexpected Slip

The most common interference causing human gait instability is slippery ground [1]. Falling caused by the interference of slippery ground is one of the serious security problems in the occupational environment [2]. Yamaguchi et al. pointed out that falling was the main accident in the industrial apartment and up to 50% of the occupational harm [3]. Therefore, a large number of researches have been conducted on gait instability. Cham et al. found that knee flexion movement and stretching the hip reduce heel slippage rate can maintain the stability of the body at the instant of the heel contact with smooth surface. Lockhart et al. [4] researched the differences of human gait biomechanics between sliding without falling and sliding to fall. They constructed the relation between biomechanics and slip or fall accident and provided a series of prevention strategies [5]. Chambers et al. used Electromyography to study the relationship between muscle activation patterns and sliding degree of slipper. Their research indicate that the effect of muscle after sliding and reaction time were reduced, and faster muscle reaction was beneficial for reducing the number of slip accidents. Based on the studies from Rectus Femoris, Tibialis Anterior and Gastrocnemius activation patterns and effort of joint motion, [6] Yang et al. suggests that the knee flexion and stretching hip could slow down the speed of base of support (BOS) interval change to ensure the center of mass (COM) projection on the ground in BOS to keep balance [7]. Xingda et al. compared the muscle reaction characteristics of calf after slipping when recovery or fall happened, and found that the calf of TA muscle response characteristics had the biggest differences [8]. Fui et al. focused on the influence of the muscle fatigue to muscle mechanical properties when falling. Their studies suggest that strengthening the awareness of body and the lower limb muscle strength could effectively prevent falling caused by sliding [9]. Li et al. concentrated on the relationship between muscular weakness and fall among community elders by comparing the muscle forces when subjects recover balance or falling after sliding and found that the muscle forces of knee when falling happened was lower than recovery balance. As slip severity increased, the reactive activation onset of the medial hamstring was significantly faster and there was a trend approaching significance for the onset of the vastus lateralis. Additionally, the peak magnitude and time-to-peak of the vastus lateral is increased with slip severity. No significant effects of age were found on any of the output variables [10]. The above studies have demonstrated that both human lower limb joints and muscles play important roles in recovery balance when slip happened.