The startle response during whiplash: a protective or harmful response?

Abstract

Whiplash injuries are common following rear-end collisions. During such collisions, initially relaxed occupants exhibit brisk, stereotypical muscle responses consisting of postural and startle responses that may contribute to the injury. Using prestimulus inhibition, we sought to determine if the startle response elicited during a rear-end collision contributes to head stabilization or represents a potentially harmful overreaction of the body. Three experiments were performed. In the first two experiments, two groups of 14 subjects were exposed to loud tones (124 dB) preceded by prestimulus tones at either four interstimulus intervals (100-1,000 ms) or five prestimulus intensities (80-124 dB). On the basis of the results of the first two experiments, 20 subjects were exposed to a simulated rear-end collision (peak sled acceleration = 2 g; speed change = 0.75 m/s) preceded by one of the following: no prestimulus tone, a weak tone (85 dB), or a loud tone (105 dB). The prestimulus tones were presented 250 ms before sled acceleration onset. The loud prestimulus tone decreased the amplitude of the sternocleidomastoid (16%) and cervical paraspinal (29%) muscles, and key peak kinematics: head retraction (17%), horizontal head acceleration (23%), and head angular acceleration in extension (23%). No changes in muscle amplitude or kinematics occurred for the weak prestimulus. The reduced muscle and kinematic responses observed with loud tones suggest that the startle response represents an overreaction that increases the kinematics in a way that potentially increases the forces and strains in the neck tissues. We propose that minimizing this overreaction during a car collision may decrease the risk of whiplash injuries.

Comparison of control strategies for the cervical muscles of an average female head-neck finite element model

“…This was because the optimal neural processing time constants, obtained from the optimization simulations for APF and MLF, were different. A wide range of muscle onset delays was observed in various volunteer studies as summarized by Mang et al (2012) and Siegmund et.al (2002) therefore, it might be worthy to investigate further regarding how it affects the head motion during rear impact collision. The APF controller exhibited the best performance based on the historic data.…”

“…To further study the effects of muscle contractions on whiplash injuries, activation time and force time histories for the cervical muscles should be considered (Siegmund et al 2002). Data from the literature as summarized by Mang et al (2012) have shown that the activation of cervical muscles occurs about 50-100ms after the onset of vehicle acceleration. This muscle response is considered to occur early enough in a rear impact event to alter the head and neck kinematics and affect the risk of injury.…”

Decreased postural control in people with moderate hearing loss

“…Different efforts have been also made to associate posture and muscular activation patterns. [ 33 , 34 ] Functionally, neck muscles can be divided into superficial and deep muscles. Superficial muscles, such as the sternocleidomastoid, that we analyzed in our study, are engaged during wide movements.…”

Protective balance and startle responses to sudden freefall in standing humans

“…To minimize such effects, 15–20 minutes were allotted between two successive EXT trial blocks and comparisons between them showed no differences in neck and arm muscle FTR amplitudes indicating no habituation carryover effects between conditions with this rest interval. [16]. …”

“…Freefall onset occurred without warning in EXT trials, and was determined by participants who initiated it at a self-selected time once the signal for the trial was given during SLF trials. To minimize habituation participants received no practice trials, and twenty minutes were allotted between the end of EXT trials and the start of SLF trials [16]. To evaluate the effectiveness of the washout interval in minimizing possible order effects, a different cohort of five (one female) untested participants (age 23.6 ± 2.51 years) received sequential EXT trial blocks with a 20 minute seated rest period between them..…”