ACL injuries are associated with a high risk of developing knee osteoarthritis in the future. In the landing motion, which is the most common injury movement, it is recommended that the vertical component of floor reaction force be lowered by landing softly to reduce the load on the knee joint. However, muscle contraction also affects joint loading, and especially in rapid deceleration movements such as landing, co-contraction of antagonist muscles is likely to occur, but joint loading has not been discussed due to differences in the magnitude of co-contraction depending on the landing method. In this study, one-leg landing movements (comfortable landing, soft landing, and stiff landing) from the 200 mm platform were measured in 11 healthy male subjects. The shock absorption capacity (loading rate) and quadriceps and hamstrings co-contraction index (CCI) were compared, and the relationship between CCI and loading rate was analyzed. The results showed that soft landing resulted in significantly smaller loading rate and CCI compared to other landing methods. In addition, the relationship between loading rate and CCI was shown to increase as CCI increased regardless of the landing method. These results suggest that reducing the co-contraction of the quadriceps and hamstrings improves shock absorption capacity, confirming the usefulness of landing softly to reduce the burden on the knee joint.

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The influence of gender difference in observers on the aesthetic impression of young female gait was investigated. First, we examined the evaluation terms that evoke a specific image of the impression of gait. As a result of multiple regression analysis, the terms were selected to express the impression of attractiveness: sexy, smooth, and unbalanced. Twenty gait patterns were selected and animated using a female digital mannequin, and 45 males and 49 females were asked to respond to the extent to which each term applied to them using a five-point scale. Male observers showed significantly higher values for the impressions of sexy (“iroppoi ” in Japanese) in the gait of young women than did female observers. No significant correlation was found between the scores of the impression of sexy of the male and female observers, indicating that the gait of women perceived as sexy by male and female observers is different. We comprehensively analyzed the entire time series of walking motion capture data used for the presented images using principal component analysis. The correlation analysis between the evaluation scores and the principal component scores revealed a significant negative correlation between the evaluation scores of the male observers and the fifth principal component score, and a significant negative correlation between the evaluation scores of the female observers and the third and fifth principal component scores. Male and female observers had different gait characteristics that gave the impression of being sexy, and the gait characteristics that gave the impression of being sexy were not necessarily related to the walker's large waist motion, unlike in previous studies.

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