The Effects of Ship’s Roll Motion on the Center of Mass and Margin of Stability During Walking: A Simulation Study

Abstract

Walking strategies in an unstable environment like a ship differ from walking on stable ground. Extreme ship motions may endanger the safety of the crews. Notably, a loss of balance on board can lead to an injury or an accident of falling off a ship. Keeping one's balance on board a ship is strongly influenced by the ship's motion. Therefore, the objective of this study is to determine how walking on a ship differs from walking in a stable environment and explore the effects of the ship's roll motion on balance control and stability while walking in sea environments. We hypothesized that step time variability, center of mass (COM), and margin of stability (MOS) would significantly differ between stable and unstable walking conditions. We also hypothesized that there would be an effect of rolling cycles and angles on increasing step time variability, COM excursion, and MOS variability. We recruited 30 healthy individuals between 21 and 39 years old for this study. Participants walked for two minutes at their self-selected speeds during the study with and without rolling on a computer-assisted rehabilitation environment (CAREN) system. The CAREN system was used to simulate the parametric roll motion of ships up to 20 degrees. This study quantified step time variability, peak COM excursion, and MOS variability in different rolling conditions. We found a significant difference in step time variability (p < 0.001), lateral peak COM excursion (p < 0.001), and MOS variability (p < 0.001) between waking on land and walking at sea. INDEX TERMS CAREN, center of mass, lateral balance, margin of stability, ship's roll motion, walking

Machine Learning-Based Approach to Identifying Fall Risk in Seafarers Using Wearable Sensors

“…We also found that the mediolateral and anterior-posterior directional features were mainly selected. This is because the rolling motion can affect the dynamic instability by moving the body forward or left and right [38].…”

“…Using the collected accelerations from the pelvis for nine different walking trials, we first labeled the data in terms of the fall risk as high or low. Choi et al found significant balance and stability variations in rolling above 15 degrees [38]. Thus, the data on the walking trials in 15 and 20 degrees of rolling for both the slow and fast cycles were labeled as "high risk", and the remaining data (i.e., no rolling and 5 and 10 degrees in slow and fast cycles) were labeled as "low risk".…”

“…We also randomly divided the data into training (70%) and test (30%) datasets, as shown in Table 2. In [38], we calculated the center of mass excursion (COME) and the variability in the margin of stability (vMOS) with the data collected from the motion capture system, since these two variables represent the balance or stability during walking and have been proven to be reasonable predictors of falls in many studies [39][40][41][42][43][44][45][46][47]. To verify the determination of data divided into high and low risk, we compared the difference between the two groups using an independent samples t-test for the four variables: mediolateral and anterior-posterior directional COMEs and vMOSs, denoted by ML-COME, AP-COME, ML-vMOS, and AP-vMOS, respectively.…”