In this study, we performed in vivo impact experiments emulating physical contact between humans and personal care robots and evaluated the conditions resulting in bruise injury due to subcutaneous hemorrhage and injury resistance. Anesthetized live pigs were used as alternate specimens, and the experiments were performed using a self-made free-fall impact tester. We investigated the existence of subcutaneous hemorrhage and performed its quantitative evaluation by hematoxylin and eosin (HE) staining of soft tissue samples at the site of the impact load. The results showed that bleeding, adopted as the indicator of bruise injury, occurred when the total energy transferred (an index of injury resistance) was 46.8 kJ/m 2 . Further, when the net energy transferred was used as the injury resistance evaluation index, the threshold value for bleeding was 30.3 kJ/m 2 . When the maximum stress was used as the injury resistance evaluation index, the threshold value for bleeding was 1.14 MPa. To investigate the possibility of adopting the injury resistance threshold of the alternate specimens obtained in this study as the injury resistance threshold of humans, we studied the capillary bleeding resistances of the test specimens experimentally. We compared these values with the capillary resistance of humans and examined the bleeding capillaries' fragility.

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