Determining fall direction and impact location for various disturbances and gait speeds using the articulated total body model

Design and Performance Analysis of a Mecanum-Built Perturbation-Based Balance Training Device

This study proposes a mecanum-built perturbation-based balance training device aimed at improving motor adaptive skills for fall prevention in individuals with neurological disorders or the elderly. Incorporating multidirectional fall simulations in line with modified constraint-induced movement therapy, the device's efficacy was evaluated by measuring the distance traveled and peak acceleration under different static loads (20, 30, and 40 kg) and input accelerations (1, 2, and 3 m/s2). A pilot study with 10 subjects was conducted to assess device performance, utilizing repeated measures analysis of variance and Bonferroni's post hoc analysis. Results indicated a load-dependent reduction in distance traveled, with an average mean difference of 0.74-1.23 cm between the 20 and 40 kg loads for trials of 9 and 18 cm, respectively. Despite varying loads, the device consistently achieved near-anticipated peak accelerations, suggesting its capability to induce effective perturbations. The study also observed a significant lateral movement preference, suggesting adjustments to pulse width modulation and time period may optimize lateral movement performance.

A Cross-Sectional Study on Fall Direction and Lower Limb Loading in Response to a Perturbation on Laterally Inclined Platform

Perturbation-based balance training (PBT) improves reactive stepping in older adults and people with neurological disorders. Slip-induced falls are a threat to older adults, leading to hip fractures. Fall-prone individuals must be trained to regain balance during a fall in the posterolateral direction. This study aims to analyze the characteristics of the reactive step induced by a laterally inclined platform. This cross-sectional study included 46 healthy participants who performed a "lean and release" backward fall using a platform with two inclined angles on each side. Kinovea software was used to analyze the step width. Reactive steps, characterized by crossover or medial foot placement, are preventive measures against posterolateral falls. The first objective was on the narrowed step width that was subjected to analysis using analysis of variance (ANOVA) and Tukey's post hoc assessment, indicating a tendency toward posterolateral falls. As part of our second objective, the inclined platform resulted in uneven loading between the legs, with a preference for the unloaded leg as the reactive leg (p < 0.001), as determined by Fisher's exact test and Cramer's V. These characteristics align closely with those observed in modified constraint-induced movement therapy (mCIMT). The angled platform had a significant effect on selecting the reactive leg, particularly at higher angles (p < 0.001). Thus, the study suggested that the device is capable of inducing posterolateral falls and exhibited mCIMT characteristics.

Slip-induced fall-risk assessment based on regular gait pattern in older adults

Aging-associated fall-risk assessment is crucial for fall prevention. Thus, this study aimed to develop a prognostic model to predict fall-risk following an unexpected over-ground slip perturbation based on normal gait pattern in healthy older adults. 112 healthy older adults who experienced a novel slip in a safe laboratory environment were included. Their slip trial and natural walking trial immediately prior to it were analyzed. To identify the best fall-risk predictive model, gait related variables including step length, segment angles, center of mass state, and ground reaction force (GRF) were determined and inputted into a stepwise logistic regression. The optimal slip-induced fall prediction model was based on the right thigh angle at slipping foot touchdown (TD), the maximum GRF of the slipping limb after TD, and the momentum change from TD to recovery foot liftoff (LO), with an overall prediction accuracy of 75.9%, predicting 74.5% of falls (sensitivity) and 77.2% of recoveries (specificity). Conversely, a model based on clinical and demographic measures predicted 78.2% of falls and 47.4% of recoveries, resulting in a much lower overall accuracy of 62.5%. The fall-risk model based on normal gait pattern which was developed for slip-induced perturbations in healthy older adults was able to provide a high predictive accuracy. This information could provide insight about the ideal normal gait measures which could be used to contribute towards development of therapeutic strategies related to dynamic balance and fall prevention to enhance preventive interventions in populations with high-risk for slip-induced falls.

Can Recovery Foot Placement Affect Older Adults' Slip-Fall Severity?

Following a slip occurred in the overground walking, a fall can be classified into two exclusive categories: feet-forward fall or split fall. The purposes of this study were to investigate whether the placement of the recovery foot would determine the slip types, the likelihood of fall, and the severity associated with each fall. The fall severity was estimated based on the impact velocity of body segments or trunk orientation upon fall arrest. One hundred ninety-five participants experienced a novel, unannounced slip while walking on a 7-m walkway. Kinematics of a full-body marker set was collected by a motion capture system which was synchronized with the force plates and loadcell. The results showed that the recovery foot landing position relative to the projected center of mass position at the recovery foot touchdown determined the slip type by 90.8%. Feet-forward slips led to significantly lower rate of falls than did split slips (47.6 vs. 67.8%, p < 0.01). Yet, feet-forward falls were much more dangerous because they were associated with significantly greater estimated maximum hip impact velocity (p < 0.001) and trunk backward leaning angle (p < 0.001) in comparison to split falls.

Two types of slip-induced falls among community dwelling older adults

Little is known about the landing behavior of the trailing (recovery) foot and ensuing types of falls following a forward slip in walking. The purposes of this study were to (1) determine if community-dwelling older adults experienced bilateral slips at the same rate as had been previously observed for young adults during over-ground walking; (2) determine if fall rate in older adults was dependent on slip type (unilateral vs. bilateral); and (3) identify differences in spatiotemporal variables of the trailing leg step between unilateral and bilateral slips. One-hundred-seventy-four participants experienced an unannounced, unrehearsed slip while walking on a 7-m walkway. Each trial was monitored with a motion capture system and bilateral ground reaction force plates. Although the experimental design, developed with original data from a young adult population, favored bilateral slips, more older adults (35%) than anticipated (10% previously observed in young, p<0.001) displayed a unilateral slip. The probability of fall was equal in the two types of slips. Eighty-two people recovered from the slip, while the remaining 92 (53%) fell. These 92 were classified into two exclusive categories based on the heel distance at the time of fall arrest using cluster analysis: those which resembled a fall into a "splits" position (n=47) or a feet-forward fall (n=45). All (100%) unilateral slips led to splits falls, as expected. Yet, not all bilateral slips (only 83%) resulted in feet-forward falls. A longer forward recovery step with a prolonged step time led to both feet slipping, nearly together, hence a feet-forward fall.

Forensic injury biomechanics

Forensic injury biomechanics is the science that relates mechanical forces to disruption of anatomical regions of the human body. In this review, we introduce (a) how scaling techniques can be used to describe injury severity and probability of death; (b) how a simple ratio, the factor of risk, and more sophisticated injury risk functions can be used to determine the probability of injury; and (c) how injury criteria (also known as tolerance limits) are defined for the head and neck. Methods for establishing injury causation are then illustrated by real-world examples drawn from litigation involving motor vehicle collisions and slips, trips and falls. Those factors that distinguish litigation from basic and applied research are also discussed, including the criteria for admissibility of expert opinions and the level of certainty used as the basis for these opinions. The criteria that must be met to support opinions on causation at both epidemiological and individual levels are also noted. If the expert appreciates the difference between the demands of ligation and those of basic and applied research, expert opinion can play a crucial role in the decision-making process that characterizes litigation. Because forensic injury biomechanics is central to opinions on injury causation, and because causation is often the key to determinations of who is at fault, forensic injury biomechanics can be the deciding factor in many personal injury, products and premises liability, wrongful death, and criminal cases.