Occupant Kinetics and Muscle Responses of Relaxed and Braced Small Female and Midsize Male Volunteers in Low-Speed Frontal Sled Tests

Previous volunteer studies focused on low-speed frontal events have demonstrated that muscle activation (specifically pre-impact bracing) can significantly affect occupant response. However, these tests do not always include a sufficient number of small female volunteers to compare their unique responses to the typically studied midsize male population. The purposes of this study were to quantify the occupant kinetics and muscle responses of relaxed and braced small female and midsize male volunteers during low-speed frontal sled tests and to compare between muscle states and demographic groups. Small female and midsize male volunteers experienced multiple low-speed frontal sled tests consisting of two pulse severities (1 g and 2.5 g) and two muscle states (relaxed and braced) per pulse severity. The muscle activity of 30 muscles (15 bilaterally) and reaction forces at the volunteer-test buck interfaces and seat belt were measured before and during each sled test. Compared to the relaxed muscle state, bracing generally increased pre-test muscle activity and pre-test forces, delayed muscle activation (relative to the pre-test value) in response to the sled pulse, and increased peak forces during the sled tests. However, relaxed volunteers exhibited greater changes in muscle activity and reaction forces relative to the pre-test value. Males exhibited higher peak forces across all reaction surfaces during the sled tests compared to females, but peak muscle activity varied as to whether males or females exhibited higher activation. The upper extremity muscles activated the most during pre-test bracing, while the upper extremity, trunk, and neck muscles activated the most during the sled tests.