The present study has investigated the characteristics of the tensile behavior of fiber bundles isolated from the spinal nerve roots. By conducting a series of uniaxial stretching tests at three different velocities, 0.2, 2, and 20 mm/s, we found a significant difference (P < 0.05) in failure strain (∼0.15), linear portion of elastic modulus (∼20 MPa), and tensile strength (∼2 MPa) between low (0.2 mm/s) and high (20 mm/s) loading rates. However, it was revealed that mechanical properties of fiber bundles were resultantly on the order of the same magnitude, indicating that their mechanical responses were relatively insensitive to a strain rate irrespective of a 100-fold increase in the applied stretching velocities. It was also confirmed that the “spinal level effect” does exist in the nerve roots, i.e., a fiber bundle isolated from the thoracic spinal level is the strongest in mechanical strength compared to that of the cervical and lumbar spinal levels (P < 0.01), which suggests we should pay more close attention to an anatomical site where excised samples are obtained. The mechanical data obtained here will be useful to improve a mathematical human body model and to assess the potential injury in crash simulations relevant to whiplash associated disorder.

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