Vehicle rollovers account for 3% of motor vehicle crashes yet cause one-third of all crashrelated fatalities. Despite advanced cervical spine injury models, a discrepancy exists between clinically reported injuries and cadaver test pathologies. One possible explanation for this discrepancy is that the intervertebral posture and simulated muscle tone used in cadaver models (and some computer models) typically mimic an upright and relaxed condition that may not exist during a rollover. The aim of this study was to characterize vertebral alignment and neck muscle responses in the cervical spine by studying a human subject in a simulated impending head-first impact, in an upside-down configuration. A custom inversion device was built to expose human subjects to a 312 ms inverted free-fall. An onboard fluoroscopic c-arm captured cervical vertebral motion while indwelling electromyography (EMG) captured the response of 8 superficial and deep neck muscles. The subject showed consistent muscular responses in 4 repetitions of the free-fall exposure. Moreover, the muscle response pattern was different from the scheme used in existing cervical spine injury models, and observed in previous quasi-static tests conducted in our lab. The general trends in muscle-induced changes to vertebral alignment were consistent with our previous work. C3-C6 translated anteriorly and inferiorly in response to the inverted free-fall stimulus, and the head moved into flexion. These observations suggest that, at the time of impact, the in vivo state of the neck may differ considerably from its initial alignment prior to the forewarned impact. The in vivo data set acquired from this experiment of vertebral and muscular responses could be used to improve and validate current injury models and advance injury prevention strategies in rollover crashes.