A Novel Approach to Measuring Muscle Mechanics in Vehicle Collision Conditions

Abstract

The aim of the study was to evaluate a novel approach to measuring neck muscle load and activity in vehicle collision conditions. A series of sled tests were performed on 10 healthy volunteers at three severity levels to simulate low-severity frontal impacts. Electrical activity-electromyography (EMG)-and muscle mechanical tension was measured bilaterally on the upper trapezius. A novel mechanical contraction (MC) sensor was used to measure the tension on the muscle surface. The neck extensor loads were estimated based on the inverse dynamics approach. The results showed strong linear correlation (Pearson's coefficient = 0.821) between the estimated neck muscle load and the muscle tension measured with the MC sensor. The peak of the estimated neck muscle force delayed 0.2 ± 30.6 ms on average vs. the peak MC sensor signal compared to the average delay of 61.8 ± 37.4 ms vs. the peak EMG signal. The observed differences in EMG and MC sensor collected signals indicate that the MC sensor offers an additional insight into the analysis of the neck muscle load and activity in impact conditions. This approach enables a more detailed assessment of the muscle-tendon complex load of a vehicle occupant in pre-impact and impact conditions.

Keywords: active muscle; biomechanics; impact; in vivo; vehicle occupant.

Figure 1

(a) A volunteer seated on the sled test device; (b) Two MC sensors and EMG surface electrode pairs attached bilaterally to the upper trapezius; (c) MC sensor-bottom side with indenting tip (5 mm radius).

Figure 2

(a) Local coordinate system of the head: origin $O\prime$, center of gravity (CG), occipital condyle (OC); (b) external loads on the head-neck joint at OC.

Figure 3

Average time history of (a) head displacements; (b) head rotation; (c) head translational acceleration; (d) head angular acceleration; (e) sled deceleration pulse; (f) OC bending moment; (g) OC shear force; (h) OC axial force; (i) EMG signals of upper trapezius activity; (j) MC sensor. The plots are presented for low (1.7 g), medium (2.6 g), and high impact severity level (3.8 g).

Figure 3

Average time history of (a) head displacements; (b) head rotation; (c) head translational acceleration; (d) head angular acceleration; (e) sled deceleration pulse; (f) OC bending moment; (g) OC shear force; (h) OC axial force; (i) EMG signals of upper trapezius activity; (j) MC sensor. The plots are presented for low (1.7 g), medium (2.6 g), and high impact severity level (3.8 g).

Figure 4

(a) Plot of the average muscle force vs. the average MC sensor indentation force; (b) time history of the estimated neck muscle force.