INTRODUCTIONComputational simulations of gait under abnormal conditions provide insights into the actions of muscles, its relationships with external reaction forces, and motions of the body during slips, trips, and falls (STFs) – a leading cause of substantial injuries worldwide, especially in slip-prone environments such as hospitals and clinics. STFs are the result of a failure of normal locomotion together with a failure of attempts at equilibrium recovery following an induced gait imbalance. OpenSim, an open-source motion simulation software, was utilized to construct musculoskeletal structures and create dynamic simulations of body movements. Gaits of eighteen subjects were studied to extract experimentally difficult-to-obtained variables under slippery conditions. The joint angles and moments of hip, knee, ankle, and the forces of four prime muscle groups were analyzed for body corrective movements during slip events. Besides, the connections between one’s perception of the surrounding environment and their postural alterations to prevent falls are also discussed. Hence, this study provides a better understanding of the influence between muscle forces, joint angles, and body movements, aids in the evaluation of movement deviations, and contributes to the development of predictive injury thresholds during slip events.METHODSEighteen healthy male participants were recruited for the data acquisition procedure. A 3D motion capture system with two force plates was used to collect kinematic, kinetic, and muscle activity data during gait. Four types of gait conditions were assessed including normal gait (NG), unexpected slip (ES), alerted slip (AS), and expected slip (US). The NG trial was comprised of a repeated number of gait cycles under normal dry conditions. Whereas, in the case of US trial, the participants performed a gait cycle without the expectation of a slippery agent applied on the force plate, making them prone to slip. Then, they repeated the experiment again with an instruction that the floor ‘may be slippery’ for AS trial. Lastly, the participant performed the last ES trial with the knowledge of the slippery floor. Hence, the three trials US, AS, and ES characterized an increasing scale of participants’ perception of the slippery surface. Next, the collected data were converted using MATLAB and imported into OpenSim, which consists of a musculoskeletal model and 16 virtual markers placed based on Helen Hayes’s marker system. Finally, simulations were run and the corresponding joint angles, joint moments, and muscle forces were extracted for the three joints (hip, knee, and ankle) and four prime muscle groups (bicep femoris – BF, medial gastrocnemius – MG, tibialis anterior – TA, and vastus intermedius – VI).RESULTS AND CONCLUSIONSIn general, during the slip process, the joint angles of plantarflexion at the ankle increase to preserve the traction between the lower extremity and surface, and thus the friction force with the floor, to stabilize the body’s center of mass and reduce the slip movement. Meanwhile, the joint angles of the knee were shown to be fixed to support the body, and the hip joint angles were slightly adjusted to balance the upper body as well as accommodate the postural change. Also, the fiber forces of the MG and TA rise proportionally to the participants’ perception of slips in AS and ES trials. This result proposes that, as their perceptions for a potential slip increase, the participants tend to put more control on their ankle joints to preserve their balance in the form of leaning backward to minimize the body center of mass excursions outside the base of support of the lower limbs or reducing angular velocity to increase the coefficient of friction between the foot-floor interface. Overall, the project provides a practical alternative method to extract biomechanical variables of various muscles and joints during slip movements that are difficult to measure. Hence, the study will aid in the prediction of injury thresholds and locations for slip-trip events, while identifying new movements and relationships among muscle forces, joint angles, and posture to reduce injury risks in clinical or athletic training conditions.

Evaluation of Human Gait Under Slippery Conditions Using Opensim Musculoskeletal Simulations

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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