Kinematic analysis of video-captured falls experienced by older adults in long-term care

Sex differences in in vivo soft tissue compressive properties of the human hip in young adults: a comparison between passive vs active state

Hip injuries are a frequent outcome of falls. Studying the biomechanics of hip injuries requires a comprehensive understanding of soft tissue properties and their responses to external loads. Particularly, muscle activity is crucial in arresting a fall and is likely to affect soft tissue properties. Failing to consider muscle activation might result in incorrect conclusions regarding the processes underlying injuries and the efficacy of preventive strategies. Soft tissue response is also affected by loading rate, sex, and mechanical testing protocols, highlighting the need for precise experimental design and interpretation. Forty individuals (age = 25.53 ± 3.41 years) were recruited (20 males and 20 females) to investigate the hip soft tissue response during a high-speed cyclic indentation testing. Muscle activity was recorded using electromyography (EMG) and soft tissue thickness was measured using ultrasound imaging. Peak force, energy, and tissue stiffness were measured using tissue indentation. The hip soft tissue exhibited hysteresis and was nonlinear during loading. Sex differences in trochanteric soft tissue stiffness resulted in males having 38% higher peak force than females and absorbed energy was 32% higher in the active state than the passive state (in combined participants). Characterizing the range of tissue responses for in vivo hip soft tissues emphasizes the natural variability in healthy human tissues and the need to consider the range of tissue behaviors in models, not just the average response. Both sex and muscle activation increased tissue mechanical variability and need to be considered in future physical and computational models of hip impact.

Estimating hip impact velocity and acceleration from video-captured falls using a pose estimation algorithm

Analyzing video footage of falls in older adults has emerged as an alternative to traditional lab studies. However, this approach is limited by the labor-intensive process of manually labeling body parts. To address this limitation, we aimed to validate the use of the AI-based pose estimation algorithm (OpenPose) in assessing the hip impact velocity and acceleration of video-captured falls. We analyzed 110 videos of 13 older adults (64.0 ± 5.9 years old) falling sideways in an experimental setting. By applying OpenPose to each video, we generated a time series of hip positions in the video, which were then analyzed using custom MATLAB code to calculate hip impact velocity and acceleration. These calculations were compared against ground truth measurements obtained from motion capture systems (VICON for hip impact velocity) and inertial measurement units (MC10 for hip impact acceleration). We examined the agreement between the ground truth and OpenPose measurements in terms of mean of absolute error (MAE), mean of absolute percentage error (MAPE), and bias (mean of error). Results showed that OpenPose had a good accuracy in estimating hip impact velocity with minimal bias (MAE: 0.17 ± 0.13 m/s, MAPE: 7.28 ± 5.21%; percent bias: - 1.27%). However, its estimation of hip impact acceleration (i.e., peak vertical hip acceleration at impact) showed poor accuracy (MAPE: 26.3 ± 19.4%), showing substantial underestimation in instances of high acceleration impacts (> 3.0 g). Further ANOVA analysis revealed OpenPose's ability to discern significant differences in hip impact velocity and acceleration based on the movement response utilized during the fall (e.g., stick-like fall, tuck-and-roll, knee block). This is the first study to validate the use of a pose estimation algorithm for identifying the hip impact kinematics in video-captured falls among older adults. Future validation studies involving diverse camera settings, fall contexts, and biomechanical parameters are warranted to extend this support for using pose estimation algorithms in this field.

Human fall simulation testing method: where we are

Falls pose a significant threat to human health and safety. Accurately assessing the protective effectiveness of fall protection products can significantly reduce the occurrence of fall accidents. This paper systematically reviews the types and risk factors of human falls and then discusses the current research status and future prospects of various test methods for human fall protection. A literature search was conducted in databases such as Web of Science, Google Scholar, and Scopus. This study focuses on experimental methods for human fall testing, simulation model experiments, and finite element simulations, providing an outlook on future development trends. In the discussion of three different fall testing methods, research indicates that human fall simulation testing faces limitations such as ethical concerns and safety issues. Although simulation experiments allow for multiple tests in a short period, the complexity and accuracy of the models may affect the reliability of the results. By integrating more experimental data, optimizing the design of human models, and incorporating finite element simulation technology, the scope of testing applications can be expanded, thereby improving the effectiveness of protective product designs. In conclusion, future research on fall protection testing methods should aim to establish unified international standards, which will enhance consistency and repeatability in testing, facilitating better comparison and evaluation of the effectiveness of various protective measures. Furthermore, the integration of more experimental data with real-world scenarios, the optimization of human models and test environments, and the promotion of finite element simulation technology will be crucial in enhancing the precision of protective assessments.

Role of the Upper Limb in Limiting Head Impact During Laboratory-Induced Falls in at Fall-Risk Older Adults

BACKGROUND

Fall-related head impact is the leading cause of traumatic brain injury in older adults. There is limited understanding of factors related to fall-related head impact. This investigation examined characteristics of upper limb movements during standing-height falls and examined their association with fall-related head impact in older adults at risk for falls.

METHODS

Older adults (n = 29) at risk for fall-related injuries underwent experimentally induced falls in multiple directions (backwards and sideways). To characterize the upper limb movements and their association with head impact, a standardized analysis tool was used to analyze a total of 164 video-recorded falls. The association between upper limb movements (and their characteristics) and head impact was analyzed through logistic regression.

RESULTS

Nearly 80% of falls involved upper limb movements. Absence of upper limb movements significantly increased head impact odds by approximately 4-fold. The odds of head impact were reduced in falls with energy absorption at the forearm (0.013-fold) and upper arm (0.018-fold), compared to falls without upper limb energy absorption. Backwards falls showed significantly higher odds of head impact (more than 4-fold).

CONCLUSIONS

Upper limb movements are common during fall descent and are associated with lower odds of experiencing head impact. Energy absorption with the upper limb seems to be an important protective mechanism. Future work should explore if these movements can be augmented with targeted training.

Investigating the biomechanics of falls in older adults in long-term care using a video camera: a scoping review

BACKGROUND

Falls are a worrying and growing phenomenon worldwide that especially affects the elderly. With the development of technology, one way of studying the real-life falls that occur in healthcare settings is by using video cameras.

AIMS

To (a) map the patterns of the research on real-life falls among older adults in healthcare settings as assessed with digital video camera supports; and (b) highlight the advances, the evidence produced, and the gaps still present regarding the biomechanics of falls as assessed technologically.

METHODS

A scoping review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews. CINAHL, PubMed and Google Scholar were searched. All studies regarding falls investigated with video cameras among older individuals in healthcare settings published from 1st January 1990 to 1st January 2022 were eligible. Findings were summarised according to the Patterns, Advances, Gaps, Evidence and Recommendations framework for Scoping Reviews.

RESULTS

In total, 1943 studies were retrieved, and 16 met the inclusion criteria. Studies were mostly conducted in Canada. They described the real-life falls that occurred mainly in common and living areas of long-term facilities among older individuals, mainly females. Thirteen studies investigated falls through biomechanics, while three provided advances in the reliability of the measures as collected with video cameras. Studies reported that the biomechanics of a fall, reflecting the direction of the fall and protective responses, increase or decrease the likelihood of serious impact. In addition, the direction of the landing after a fall has been determined as having a significant impact on the severity and outcome of the fall.

CONCLUSION

The use of video cameras to investigate the biomechanics of falls is a well-established research area that offer interesting insight regarding (a) how to prevent falls and their injuries and (b) the direction of the research in the field of falls.

Finite element analysis of hip fracture risk in elderly female: The effects of soft tissue shape, fall direction, and interventions

This study investigates the effects of fall configurations on hip fracture risk with a focus on pelvic soft tissue shape. This was done by employing a whole-body finite element (FE) model. Soft tissue thickness around the pelvis was measured using a standing CT system, revealing a trend of increased trochanteric soft tissue thickness with higher BMI and younger age. In the lateroposterior region from the greater trochanter, the soft tissues of elderly females were thin with a concave shape. Based on the THUMS 5F model, an elderly female FE model with a low BMI was developed by morphing the soft tissue shape around the pelvis based on the CT data. FE simulation results indicated that the lateroposterior fall led to a higher femoral neck force for the elderly female model compared to the lateral fall. One reason may be related to the thin soft tissue of the pelvis in the lateroposterior region. Additionally, the effectiveness of interventions that can help mitigating hip fractures in lateroposterior falls on the thigh-hip and hip region was assessed using the elderly female model. The attenuation rate of the femoral neck force by the hip protector was close to zero in the thigh-hip fall and high in the hip fall, whereas the attenuation rate of the compliant floor was high in both falls. This study highlights age-related changes in the soft tissue shape of the pelvis in females, particularly in the lateroposterior regions, which may influence force mitigation for the hip joint during lateroposterior falls.

A dynamic spatiotemporal model for fall warning and protection

Early detection of falls is important for reducing fall injuries. However, existing fall detection strategies mostly focus on reducing impact injuries rather than avoiding falls. This study proposed the concept of identifying "Imbalance Point" to warn the body imbalance, allowing sufficient time to recover balance. And if falling cannot be avoided, an impact sign is released by detecting the "Fall Point" prior to the impact. To achieve this goal, motion prediction model and balance recovery model are integrated into a spatiotemporal framework to analyze dynamic and kinematic features of body motion. Eight healthy young volunteers participated in three sets of experiment: Normal trial, Recovery trial and Fall trial. The body motion in the trials was recorded using Microsoft Azure Kinect. The results show that the developed algorithm for Fall Point detection achieved 100% sensitivity and 98.6% specificity, along with an average lead time of 297 ms. Moreover, Imbalance Point was successfully detected in all Fall trials, and the average time interval between Imbalance Point and Fall Point was 315 ms, longer than reported step reaction time for elderly (approximately 270 ms). The experiment results demonstrate that the developed algorithm have great potential for fall warning and protection in the elderly.

Effects of hip joint kinematics on the effective pelvis stiffness and hip impact force during simulated sideways falls

Improved understanding is required on how hip fracture risk is influenced by landing configuration. We examined how hip impact dynamics was affected by hip joint kinematics during simulated sideways falls. Twelve young adults (7 males, 5 females) of mean age 23.5 (SD = 1.5) years, participated in pelvis release experiments. Trials were acquired with the hip flexed 15° and 30° for each of three hip rotations: +15° ("external rotation"), 0°, and -15° ("internal rotation"). During falls, force-deformation data of the pelvis were recorded. Outcome variables included the peak hip impact force (Fexperimental) and effective stiffness of the pelvis (k1st, ksecant, and kms) determined with different methods suggested in literature, and predicted hip impact force during a fall from standing height (F1st, Fsecant and Fms). The two-way repeated-measures ANOVA was used to test whether these variables were associated with hip joint angles. The Fexperimental, ksecant and Fsecant were associated with hip rotation (F = 5.587, p = 0.005; F = 9.278, p < 0.0005; F = 5.778, p = 0.004, respectively), and 15 %, 31 % and 17 % smaller in 15° external than internal rotation (848 versus 998 N; 24.6 versus 35.6 kN/m; 2,637 versus 3,170 N, respectively). However, none of the outcome variables were associated with hip flexion (p > 0.05). Furthermore, there were no interactions between the hip rotation and flexion for all outcome variables (p > 0.05). Our results provide insights on hip impact dynamics, which may help improve a hip model to assess hip fracture risk during a fall.

The Effect of Handrail Cross-Sectional Design and Age on the Speed and Quality of Reach-To-Grasp Reactions to Recover Balance

OBJECTIVE

To determine the effect of handrail cross-section on the speed and quality of reach-to-grasp movements following balance loss in younger and older adults.

BACKGROUND

Grasping a handrail is a common strategy for balance recovery. For handrails to be effective, the design must enable fast and accurate reactive grasping. Little is known about the effect of handrail cross-section on the timing or quality of the reach-to-grasp movement following balance loss.

METHODS

Twenty-four younger and 16 older adults experienced incrementally increasing magnitudes of perturbations in the forward and backward direction until they were no longer able to recover balance. We analyzed the last trial where the participant could recover using only the handrail, without stepping or relying on the harness, the maximum withstood perturbation (MWP). Seven handrail cross-sections were tested.

RESULTS

Handrail cross-section did not affect the speed or timing of the reach-to-grasp reaction for younger or older adults. However, handrail cross-section affected the MWP, the grip types used, and the likelihood of making an error or adjustment when grasping. The greatest MWP and fewest errors occurred with 1.5" round handrails.

CONCLUSION

The absence of common strategies for accurately grasping complex shapes (reaching more slowly), combined with the higher frequency of errors with larger handrails, suggests that both older and younger adults prioritized quickly reaching the handrail over prehension during reach-to-grasp balance reactions.

APPLICATION

This work provides new insights on the effect of age and handrail cross-sectional design on reach-to-grasp reactions to recover balance, which can inform safer handrail design standards.

Distinctive Geometrical Traits of Proximal Femur Fractures-Original Article and Review of Literature

Background and Objectives: The incidence of proximal femoral fractures is escalating rapidly, generating a significant challenge for healthcare systems globally and, carrying serious social and economic implications. The primarily object of this study was to discover potential distinguishing factors between fractures occurring in the femoral neck and trochanteric region. Materials and Methods: We performed a prospective cohort study of the radiographic images of 70 people over 65 years of age who were admitted to the orthopedic department with hip fracture and who fulfilled our eligibility criteria. Neck Length (NL), Offset Lenth (OL), Hip Axis Length (HAL), Neck Shaft Angle (NSA), Wiberg Angle (WA), Acetabular Angle (AA), Femoral Neck Diameter (FND), Femoral Head Diameter (FHD), Femoral Shaft Diameter (FSD), Femoral Canal Diameter (FCD) and Tonnis classification were recorded. For the comparison of the categorical variables, Pearson's χ2 criterion was used, while Student's t-test was applied for the comparison of means of quantitative variables across fracture types. Results: There were no statistically significant variances observed while comparing the selected geometric parameters of the proximal femur with the type of fracture. This finding was reaffirmed in relation to age, gender, and Tonnis classification. However, a moderate correlation was noted, revealing comparatively reduced values of HAL, FHD, and FND in women as opposed to men. Conclusions: The inability of our research to establish the differentiative geometric factors between femoral neck and trochanteric fractures underscores the need for further investigations, which would take into consideration the intrinsic characteristics of the proximal femur.

Impact forces in backward falls: Subject-specific video-based rigid body simulation of backward falls

A critical missing component in the study of real-world falls is the ability to accurately determine impact forces resulting from the fall. Subject-specific rigid body dynamic (RBD) models calibrated to video captured falls can quantify impact forces and provide additional insights into injury risk factors. RBD models were developed based on five backward falls captured on surveillance video in long-term care facilities in British Columbia, Canada. Model joint stiffness and initial velocities were calibrated to match the kinematics of the fall and contact forces were calculated. The effect of joint stiffnesses (neck, lumbar spine, hip, and knee joint) on head contact forces were determined by modifying the calibrated stiffness values ±25%. Fall duration, fall trajectories, and maximum velocities showed a close match between fall events and simulations. The maximum value of pelvic velocity difference between Kinovea (an open-source software 2D digitization software) and Madymo multibody modeling was found to be 6% ± 21.58%. Our results demonstrate that neck and hip stiffness values have a non-significant yet large effect on head contact force (t(3) = 1, p = 0.387 and t(3) = 2, p = 0.138), while lower effects were observed for knee stiffness, and the effect of lumbar spine stiffness was negligible. The subject-specific fall simulations constructed from real world video captured falls allow for direct quantification of force outcomes of falls and may have applications in improving the assessment of fall-induced injury risks and injury prevention methods.

A supervisory controller intended to arrest dynamic falls with a wearable cold-gas thruster

This article examines the feasibility of employing a cold-gas thruster (CGT), intended as a backpack-wearable device, for purposes of arresting backward falls, and in particular describes a supervisory controller that, for some motion described by an arbitrary combination of center-of-mass angle and angular velocity, both detects an impending fall and determines when to initiate thrust in the CGT in order to arrest the impending fall. The CGT prototype and the supervisory controller are described and experimentally assessed using a rocking block apparatus intended to approximate a backward-falling human. In these experiments, the CGT and supervisory controller restored upright stability to the rocking block in all experiment cases that would have otherwise resulted in a fall without the CGT assistance. Since the controller and experiments employ a reduced-order model of a falling human, the authors also conducted a series of simulations intended to examine the extent to which the controller might remain effective in the case of a multi-segment human. The results of these simulations suggest that the CGT controller would be nearly as effective on a multi-segment falling human as on the reduced-order model.

Evaluating femoral augmentation to prevent geriatric hip fracture: A scoping review of experimental methods

Various femoral augmentation designs have been investigated over the past decade for the prevention of geriatric hip fracture. The experimental methods used to evaluate the efficacy of these augmentations have not been critically evaluated or compared in terms of biofidelity, robustness, or ease of application. Such parameters have significant relevance in characterizing future clinical success. In this study we aimed to use a scoping review to summarize the experimental studies that evaluate femoral augmentation approaches, and critically evaluate commonly applied protocols and identify areas for concordance with the clinical situation. We conducted a literature search targeting studies that used experimental test methods to evaluate femoral augmentation to prevent geriatric fragility fracture. A total of 25 studies met the eligibility criteria. The most commonly investigated augmentation to date is the injection of bone cement or another material that cured in situ, and a popular subsequent method for biomechanical evaluation was to load the augmented proximal femur until fracture in a sideways fall configuration. We noted limitations in the clinical relevance of sideways fall scenarios being modeled and large variance in the concordance of many of the studies identified. Our review brings about recommendations for enhancing the fidelity of experimental methods modeling clinical sideways falls, which include an improved representation of soft tissue effects, using outcome metrics beyond load-to-failure, and applying loads inertially. Effective augmentations are encouraging for their potential to reduce the burden of hip fracture; however, the likelihood of this success is only as strong as the methods used in their evaluation.

The timing and amplitude of the muscular activity of the arms preceding impact in a forward fall is modulated with fall velocity

Protective arm reactions have been shown to be an important injury avoidance mechanism in unavoidable falls. Protective arm reactions have been shown to be modulated with fall height, however it is not clear if they are modulated with impact velocity. The aim of this study was to determine if protective arm reactions are modulated in response to a forward fall with an initially unpredictable impact velocity. Forward falls were evoked via sudden release of a standing pendulum support frame with adjustable counterweight to control fall acceleration and impact velocity. Thirteen younger adults (1 female) participated in this study. Counterweight load explained more than 89% of the variation of impact velocity. Angular velocity at impact decreased (p < 0.001), drop duration increased from 601 ms to 816 ms (p < 0.001), and the maximum vertical ground reaction force decreased from 64%BW to 46%BW (p < 0.001) between the small and large counterweight. Elbow angle at impact (129 degrees extension), triceps (119 ms) and biceps (98 ms) pre-impact time, and co-activation (57%) were not significantly affected by counterweight load (p-values > 0.08). Average triceps and biceps EMG amplitude decreased from 0.26 V/V to 0.19 V/V (p = 0.004) and 0.24 V/V to 0.11 V/V (p = 0.002) with increasing counterweight respectively. Protective arm reactions were modulated with fall velocity by reducing EMG amplitude with decreasing impact velocity. This demonstrates a neuromotor control strategy for managing evolving fall conditions. Future work is needed to further understand how the CNS deals with additional unpredictability (e.g., fall direction, perturbation magnitude, etc.) when deploying protective arm reactions.

Effect of Handrail Height and Age on Trunk and Shoulder Kinematics Following Perturbation-Evoked Grasping Reactions During Gait

OBJECTIVE

To characterize the effect of handrail height and age on trunk and shoulder kinematics, and concomitant handrail forces, on balance recovery reactions during gait.

BACKGROUND

Falls are the leading cause of unintentional injury in adults in North America. Handrails can significantly enhance balance recovery and help individuals to avoid falls, provided that their design allows users across the lifespan to reach and grasp the rail after balance loss, and control their trunk by applying hand-contact forces to the rail. However, the effect of handrail height and age on trunk and shoulder kinematics when recovering from perturbations during gait is unknown.

METHOD

Fourteen younger and 13 older adults experienced balance loss (sudden platform translations) while walking beside a height-adjustable handrail. Handrail height was varied from 30 to 44 inches (76 to 112 cm). Trunk and shoulder kinematics were measured via 3D motion capture; applied handrail forces were collected from load cells mounted to the rail.

RESULTS

As handrail height increased (up to 42 inches/107 cm), peak trunk angular displacement and velocity generally decreased, while shoulder elevation angles during reaching and peak handrail forces did not differ significantly between 36 and 42 inches (91 and 107 cm). Age was associated with reduced peak trunk angular displacements, but did not affect applied handrail forces.

CONCLUSION

Higher handrails (up to 42 inches) may be advantageous for trunk control when recovering from destabilizations during gait.

APPLICATION

Our results can inform building codes, workplace safety standards, and accessibility standards, for safer handrail design.

The efficacy of femoral augmentation for hip fracture prevention using ceramic-based cements: A preliminary experimentally-driven finite element investigation

Femoral fractures due to sideways falls continue to be a major cause of concern for the elderly. Existing approaches for the prevention of these injuries have limited efficacy. Prophylactic femoral augmentation systems, particularly those involving the injection of ceramic-based bone cements, are gaining more attention as a potential alternative preventative approach. We evaluated the mechanical effectiveness of three variations of a bone cement injection pattern (basic ellipsoid, hollow ellipsoid, small ellipsoid) utilizing finite element simulations of sideways fall impacts. The basic augmentation pattern was tested with both high- and low-strength ceramic-based cements. The cement patterns were added to the finite element models (FEMs) of five cadaveric femurs, which were then subject to simulated sideways falls at seven impact velocities ranging from 1.0 m/s to 4.0 m/s. Peak impact forces and peak acetabular forces were examined, and failure was evaluated using a strain-based criterion. We found that the basic HA ellipsoid provided the highest increases in both the force at the acetabulum of the impacted femur ("acetabular force", 55.0% ± 22.0%) and at the force plate ("impact force", 37.4% ± 15.8%). Changing the cement to a weaker material, brushite, resulted in reduced strengthening of the femur (45.2% ± 19.4% acetabular and 30.4% ± 13.0% impact). Using a hollow version of the ellipsoid appeared to have no effect on the fracture outcome and only a minor effect on the other metrics (54.1% ± 22.3% acetabular force increase and 35.3% ± 16.0% impact force increase). However, when the outer two layers of the ellipsoid were removed (small ellipsoid), the force increases that were achieved were only 9.8% ± 5.5% acetabular force and 8.2% ± 4.1% impact force. These results demonstrate the importance of supporting the femoral neck cortex to prevent femoral fractures in a sideways fall, and provide plausible options for prophylactic femoral augmentation. As this is a preliminary study, the surgical technique, the possible effects of trabecular bone damage during the augmentation process, and the effect on the blood supply to the femoral head must be assessed further.

Analysis of loading to the hip joint in fall using whole-body FE model

Hip fractures caused by falls are important health problems for the elderly. Many studies used finite element (FE) models of the femur and its surroundings to evaluate the hip fracture risk during the impact phase in a fall. In this study, the whole-body human FE model (THUMS) of a small female was applied from the descent to the impact phase in a fall to understand the effect of the whole body. Brosh's material model was used for the soft tissue of the hip. A low-BMI and high-BMI model were developed based on THUMS (middle-BMI). For the middle-BMI model, the torso angle and the pelvis impact velocity were 45.2° and 2.62 m/s at the time of pelvis impact. The effective mass changed with time, and was 18.3 kg when the femoral neck force was maximum. The femoral neck force was 2.11 kN for the low-BMI model. The femoral neck forces when wearing a soft and a hard hip protector, and when falling on an energy-absorbing floor were compared for the FE models of human and a hip protector testing system. Though the force attenuation of the protective devices was 32.0-44.3 % in the testing system, the force attenuation in the middle-BMI was 0.1-22.2 %. In the low-BMI model, the attenuation of the soft protector was limited (4.2 %) because the hip protector protruded from the outer surface, so the contact force was concentrated at the hip region. This research suggests the importance of including the whole body to evaluate the hip fracture risk.

Effects of the Mobility-Fit Physical Activity Program on Strength and Mobility in Older Adults in Assisted Living: A Feasibility Study

Physical activity programs focusing on fall prevention often overlook upper-limb strength, which is important for transferring, balance recovery, and arresting a fall. We developed and evaluated a physical activity program, Mobility-Fit for older adults in Assisted Living (AL) that includes upper-limb strengthening, agility, coordination, and balance exercises. Thirty participants (85 ± 6 years) were recruited from two AL facilities; 15 were assigned to Mobility-Fit (three times/week, 45 min/session for 12 weeks) and 15 maintained usual care. Twenty-two participants (11 in each group) completed the study. We compared outcome changes between groups and interviewed participants and staff to explore the effectiveness and feasibility of the program. Among participants who attended Mobility-Fit, knee extension strength increased by 6%, reaction time decreased by 16%, and five-time sit-to-stand duration decreased by 15%. Conversely, participants in the usual care group had a 6% decrease in handgrip strength. Changes of these outcomes were significantly different between two groups (p < 0.05). Participants enjoyed the program and staff suggested some changes to improve attendance. Our results indicate that Mobility-Fit is feasible to deliver and beneficial for older adults in AL and may guide future clinical trials to evaluate the effectiveness of upper limb strengthening on safe mobility of older adults in care facilities.

Test-retest reliability of the FALL FIT system for assessing and training protective arm reactions in response to a forward fall

The use of the hands and arms is an important protective mechanism in avoiding fall-related injury. The aim of this study was to evaluate the test-retest reliability of fall dynamics and evokd protective arm response kinematics and kinetics in forward falls simulated using the FALL simulator For Injury prevention Training and assessment system (FALL FIT). Fall FIT allows experimental control of the fall height and acceleration of the body during a forward fall. Two falls were simulated starting from 4 initial lean angles in Experiment 1 and with 4 different fall accelerations in Experiment 2. Fourteen younger adults (25.1±3.5 years) and 13 older adults (71.3±3.7 years) participated in Experiment 1 and 13 younger adults (31.8±5.7 years) participated in Experiment 2. Intraclass correlation coefficients (ICC) were used to the evaluate absolute agreement of single measures at each condition and averages across conditions. Average measures of fall dynamics and evoked kinematics and kinetics exhibited excellent reliability (ICC(A,4)>0.86). The reliability of single measures (ICC(A,1) > 0.59) was good to excellent, although 18% of single measures had a reliability (ICC(A,1)) between 0.00 and 0.57. The FALL FIT was shown to have good to excellent reliability for most measures. FALL FIT can produce a wide range of fall dynamics through modulation of initial lean angle and body acceleration. Additionally, the range of fall velocities and evoked kinematics and kinetics are consistent with previous fall research.•

The FALL FIT can be used to gain further insight into the control of protective arm reactions and may provide a therapeutic tool to assess and train protective arm reactions.

The Influence of Fall Direction and Hip Protector on Fracture Risk: FE Model Predictions Driven by Experimental Data

Hip fractures in older adults, which often lead to lasting impairments and an increased risk of mortality, are a major public health concern. Hip fracture risk is multi-factorial, affected by the risk of falling, the load acting on the femur, and the load the femur can withstand. This study investigates the influence of impact direction on hip fracture risk and hip protector efficacy. We simulated falls for 4 subjects, in 7 different impact directions (15° and 30° anterior, lateral, and 15°, 30°, 60°, and 90° posterior) at two different impact velocities (2.1 and 3.1 m/s), all with and without hip protector, using previously validated biofidelic finite element models. We found the highest number of fractures and highest fragility ratios in lateral and 15° posterior impacts. The hip protector attenuated femur forces by 23-49 % for slim subjects under impact directions that resulted in fractures (30° anterior to 30° posterior). The hip protector prevented all fractures (6/6) for 2.1 m/s impacts, but only 10% of fractures for 3.1 m/s impacts. Our results provide evidence that, regarding hip fracture risk, posterior-lateral impacts are as dangerous as lateral impacts, and they support the efficacy of soft-shell hip protectors for anterior- and posterior-lateral impacts.

Age-related changes in protective arm reaction kinematics, kinetics, and neuromuscular activation during evoked forward falls

Fall related injuries in older adults are a major healthcare concern. During a fall, the hands and arms play an important role in minimizing trauma from ground impact. Although older adults are able to orient the hands and arms into a protective orientation after falling and prior to ground impact, an inability to avoid increased body impact occurs with age. Previous investigations have generally studied rapid arm movements in the pre-impact phase or absorbing energy in the post-impact phase. There are no known studies that have directly examined both the pre-impact and post-impact phase in sequence in a forward fall. The aim of this study was to identify age-related biomechanical and neuromuscular changes in evoked arm reactions in response to forward falls that may increase fall injury risk. Fourteen younger and 15 older adults participated. Falls were simulated while standing with torso and legs restrained via a moving pendulum system from 4 different initial lean angles. While there was not a significant age-related difference in the amount of energy absorbed post-impact (p = 0.68), older adults exhibited an 11% smaller maximum vertical ground reaction force when normalized to body weight (p = 0.031), and 8 degrees less elbow extension at impact (p = 0.045). A significant interaction between age and initial lean angle (p = 0.024), indicated that older adults required 54%, 54%, 41%, and 57% greater elbow angular displacement after impact at the low, medium, medium-high, and high initial lean angles compared to younger adults. These results suggested older adults may be at greater risk of increased body impact due to increased elbow flexion angular displacement after impact when the hands and arms are able to contact the ground first. Both groups exhibited robust modulation to the initial lean angle with no observed age-related differences in the initial onset timing or amplitude of muscle activation levels. There were no significant age-related differences in the EMG timing, amplitude or co-activation of muscle activation preceding impact or following impact indicating comparable neuromotor response patterns between older and younger adults. These results suggest that aging changes in muscular elements may be more implicated in the observed differences than changes in neuromuscular capacity. Future work is needed to test the efficacy of different modalities (e.g. instruction, strength, power, perturbation training, fall landing techniques) aimed at reducing fall injury risk.

Prophylactic augmentation implants in the proximal femur for hip fracture prevention: An in silico investigation of simulated sideways fall impacts

Femoral fractures from sideways falls in the elderly are associated with significant rates of morbidity and mortality. Approaches to prevent these catastrophic injuries include pharmacological treatments, which have limited efficacy. Prophylactic femoral augmentation systems are a promising alternative that are gaining prominence by addressing the most debilitating osteoporosis-related fracture. We have developed finite element models (FEMs) of a novel experimental sideways fall simulator for cadavers. By virtue of the range of specimens and injury outcomes, these FEMs are well-suited to the evaluation of such implants. The purpose of this study was to use the FEMs to evaluate the mechanical effectiveness of three different prophylactic femoral augmentation systems. Models of the Y-Strut® (Hyprevention®, Pessac, France), Gamma Nail® (Stryker, Kalamazoo, USA), and a simple lag screw femoral fracture implant systems were placed into FEMs of five cadaveric pelvis-femur constructs embedded in a soft tissue surrogate, which were then subject to simulated sideways falls at seven impact velocities. Femur-only FEMs were also evaluated. Peak impact forces and peak acetabular forces were examined, and failure was evaluated using a strain-based criterion. We found that the femoral augmentation systems increased the peak forces prior to fracture, but were unable to prevent fracture for severe impacts. The Gamma Nail® system consistently produced the largest strength increases relative to the unaugmented femur for all five specimens in both the pendulum-drop FEMs and the femur-only simulations. In some cases, the same implant appeared to cause fractures in the acetabulum. The femur-only FEMs showed larger force increases than the pendulum-drop simulations, which suggests that the results of the femur-only simulations may not represent sideways falls as accurately as the soft tissue-embedded pendulum-drop simulations. The results from this study demonstrate the ability to simulate a high energy phenomenon and the effect of implants in an in silico environment. The results also suggest that implants could increase the force applied to the proximal femur during impact. Fracture outcomes from the tested implants can be used to inform the design of future devices, which reaffirms the value of modelling with biofidelic considerations in the implant design process. To the authors' knowledge, this is the first paper to use more complex biofidelic FEMs to assess prophylactic femoral augmentation methods.

Accuracy of Kinovea software in estimating body segment movements during falls captured on standard video: Effects of fall direction, camera perspective and video calibration technique

Falls are a major cause of unintentional injuries. Understanding the movements of the body during falls is important to the design of fall prevention and management strategies, including exercise programs, mobility aids, fall detectors, protective gear, and safer environments. Video footage of real-life falls is increasingly available, and may be used with digitization software to extract kinematic features of falls. We examined the validity of this approach by conducting laboratory falling experiments, and comparing linear and angular positions and velocities measured from 3D motion capture to estimates from Kinovea 2D digitization software based on standard surveillance video (30 Hz, 640x480 pixels). We also examined how Kinovea accuracy depended on fall direction, camera angle, filtering cut-off frequency, and calibration technique. For a camera oriented perpendicular to the plane of the fall (90 degrees), Kinovea position data filtered at 10 Hz, and video calibration using a 2D grid, mean root mean square errors were 0.050 m or 9% of the signal amplitude and 0.22 m/s (7%) for vertical position and velocity, and 0.035 m (6%) and 0.16 m/s (7%) for horizontal position and velocity. Errors in angular measures averaged over 2-fold higher in sideways than forward or backward falls, due to out-of-plane movement of the knees and elbows. Errors in horizontal velocity were 2.5-fold higher for a 30 than 90 degree camera angle, and 1.6-fold higher for calibration using participants’ height (1D) instead of a 2D grid. When compared to 10 Hz, filtering at 3 Hz caused velocity errors to increase 1.4-fold. Our results demonstrate that Kinovea can be applied to 30 Hz video to measure linear positions and velocities to within 9% accuracy. Lower accuracy was observed for angular kinematics of the upper and lower limb in sideways falls, and for horizontal measures from 30 degree cameras or 1D height-based calibration.

Factors that influence the distribution of impact force relative to the proximal femur during lateral falls

In-vivo fall simulations generally evaluate hip fracture risk through differences in impact force magnitude; however, the distribution of force over the hip likely modulates loading and subsequent injury risk of the underlying femur. The current study characterized impact force distribution over the hip during falls, and the influence of biological sex and trochanteric soft tissue thickness (TSTT). Forty young adults completed fall simulation protocols (FSP) including highly controlled vertical pelvis and more dynamic kneeling and squat releases. At the instant of peak force, percentage of impact force applied in a circular region (r = 5 cm) centered over the greater trochanter (F_GT%) was determined to characterize force localization. To assess the need for anatomically aligned pressure analysis, this process was repeated utilizing peak pressure location as a surrogate for the greater trochanter (F_PP%). F_GT% was 10.8 and 21.9% greater in pelvis release than kneeling and squat releases respectively. F_GT% was 19.1 and 30.4% greater in males and low-TSTT individuals compared to females and high-TSTT individuals. TSTT explained the most variance (43.7-55.3%) in F_GT% across all protocols, while sex explained additional variance (5.3-19.0%) during dynamic releases. In all FSP, TSTT-groups and sexes, average peak pressure location was posterior and distal to the GT. F_PP% overestimated F_GT% by an average of 15.7%, highlighting the need for anatomically aligned pressure analysis. This overestimation was FSP and sex dependent, minimized during pelvis release and in males. The data have important implications from clinical and methodological perspectives, and for implementation in tissue-level computational models.

Anatomically Aligned Loading During Falls: Influence of Fall Protocol, Sex and Trochanteric Soft Tissue Thickness

Fall simulations provide insight into skin-surface impact dynamics but have focused on vertical force magnitude. Loading direction and location (relative to the femur) likely influence stress generation. The current study characterized peak impact vector magnitude, orientation, and center of pressure over the femur during falls, and the influence of biological sex and trochanteric soft tissue thickness (TSTT). Forty young adults completed fall simulations including a vertical pelvis release, as well as kneeling and squat releases, which incorporate lateral/rotational motion. Force magnitude and direction varied substantially across fall simulations. Kneeling and squat releases elicited 57.4 and 38.8% greater force than pelvis release respectively, with differences accentuated in males. With respect to the femoral shaft, kneeling release had the most medially and squat release the most distally directed loading vectors. Across all fall simulations, sex and TSTT influenced force magnitude and center of pressure. Force was 28.0% lower in females and was applied more distally than in males. Low-TSTT participants had 16.8% lower force, applied closer to the greater trochanter than high-TSTT participants. Observed differences in skin-surface impact dynamics likely interact with underlying femur morphology to influence stress generation. These data should serve as inputs to tissue-level computational models assessing fracture risk.

Wrist and hand postures when falling and description of the upper limb falling reflex

INTRODUCTION

Falling studies, i.e. assessing what happens when an individual falls, have been conducted in controlled environments but not in field studies for ethical reasons; this potentially limits the validity and applicability of previous studies. We performed field studies on existing YouTube © videos of skateboarders falling. The aims of these studies were to measure the wrist angle at impact on videos of real unprotected falls and to study the dynamics of the upper limbs when falling.

METHODS

Youtube © videos of skateboarders falling were studied assessing the direction of the fall, the positions of both upper limbs and especially the wrists on impact quantitatively and qualitatively. This study would not be ethical by other means.

RESULTS

In study one (the more quantitative study) there were 48 men and 50 falls. The mean elbow flexion was 30⁰ (range 0⁰ to 80⁰) and the mean maximal wrist extension was 80⁰ (range 50⁰ to 110⁰). The second wrist extended less or the same in > 90%. The second wrist only once (of 31) extended > 90⁰ which should minimise the risk of toppling. Falls onto only one wrist gave significantly greater maximal wrist extension. In the second more qualitative study we observed the "upper limb falling reflex" where the response to falling is for the upper limb(s) to align the upper limb with the direction of falling of the body with the elbow mostly but not fully extended. Initially the wrists extend c. 40⁰-50⁰ with the fingers held mildly flexed. Immediately before impact the fingers hyper-extend with some compensatory wrist flexion to c. 30⁰ of extension. The fingertips impact the ground first followed by the hand.

CONCLUSION

These studies confirm wrist extension at impact around 80⁰ but the wrist(s) may hyper-extend risking toppling. Falls on both wrists minimise the risk of toppling. The "upper limb falling reflex" is defined; it is a rapid dynamic response leading to the fingers impacting the ground first on falling. Abnormalities with the upper limb falling reflex may indicate problems with development in young children and may increase the risk of injury in older people.

Impact attenuation provided by older adult protective headwear products during simulated fall-related head impacts

INTRODUCTION

While protective headwear products (PHP) are designed to protect older adults from fall-related head injuries, there are limited data on their protective capacity. This study's goal was to assess the impact attenuation provided by commercially available PHP during simulated head impacts.

METHODS

A drop tower and Hybrid III headform measured the decrease in peak linear acceleration (g atten ) provided by 12 PHP for front- and back-of-head impacts at low (clinically relevant: 3.5 m/s) and high (5.7 m/s) impact velocities.

RESULTS

The range of g atten across PHP was larger at the low velocity (56% and 41% for back and frontal impacts, respectively) vs. high velocity condition (27% and 38% for back and frontal impacts, respectively). A significant interaction between impact location and velocity was observed (p < .05), with significantly greater g atten for back-of-head compared to front-of-head impacts at the low impact velocity (19% mean difference). While not significant, there was a modest positive association between g atten and product padding thickness for back-of-head impacts (p = .095; r = 0.349).

CONCLUSION

This study demonstrates the wide range in impact attenuation across commercially available PHP, and suggests that existing products provide greater impact attenuation during back-of-head impacts. These data may inform evidence-based decisions for clinicians and consumers and help drive industry innovation.

Acceleration Magnitude at Impact Following Loss of Balance Can Be Estimated Using Deep Learning Model

Pre-impact fall detection can detect a fall before a body segment hits the ground. When it is integrated with a protective system, it can directly prevent an injury due to hitting the ground. An impact acceleration peak magnitude is one of key measurement factors that can affect the severity of an injury. It can be used as a design parameter for wearable protective devices to prevent injuries. In our study, a novel method is proposed to predict an impact acceleration magnitude after loss of balance using a single inertial measurement unit (IMU) sensor and a sequential-based deep learning model. Twenty-four healthy participants participated in this study for fall experiments. Each participant worn a single IMU sensor on the waist to collect tri-axial accelerometer and angular velocity data. A deep learning method, bi-directional long short-term memory (LSTM) regression, is applied to predict a fall's impact acceleration magnitude prior to fall impact (a fall in five directions). To improve prediction performance, a data augmentation technique with increment of dataset is applied. Our proposed model showed a mean absolute percentage error (MAPE) of 6.69 ± 0.33% with r value of 0.93 when all three different types of data augmentation techniques are applied. Additionally, there was a significant reduction of MAPE by 45.2% when the number of training datasets was increased by 4-fold. These results show that impact acceleration magnitude can be used as an activation parameter for fall prevention such as in a wearable airbag system by optimizing deployment process to minimize fall injury in real time.

Re-Enactment as a Method to Reproduce Real-World Fall Events Using Inertial Sensor Data: Development and Usability Study

BACKGROUND

Falls are a common health problem, which in the worst cases can lead to death. To develop reliable fall detection algorithms as well as suitable prevention interventions, it is important to understand circumstances and characteristics of real-world fall events. Although falls are common, they are seldom observed, and reports are often biased. Wearable inertial sensors provide an objective approach to capture real-world fall signals. However, it is difficult to directly derive visualization and interpretation of body movements from the fall signals, and corresponding video data is rarely available.

OBJECTIVE

The re-enactment method uses available information from inertial sensors to simulate fall events, replicate the data, validate the simulation, and thereby enable a more precise description of the fall event. The aim of this paper is to describe this method and demonstrate the validity of the re-enactment approach.

METHODS

Real-world fall data, measured by inertial sensors attached to the lower back, were selected from the Fall Repository for the Design of Smart and Self-Adaptive Environments Prolonging Independent Living (FARSEEING) database. We focused on well-described fall events such as stumbling to be re-enacted under safe conditions in a laboratory setting. For the purposes of exemplification, we selected the acceleration signal of one fall event to establish a detailed simulation protocol based on identified postures and trunk movement sequences. The subsequent re-enactment experiments were recorded with comparable inertial sensor configurations as well as synchronized video cameras to analyze the movement behavior in detail. The re-enacted sensor signals were then compared with the real-world signals to adapt the protocol and repeat the re-enactment method if necessary. The similarity between the simulated and the real-world fall signals was analyzed with a dynamic time warping algorithm, which enables the comparison of two temporal sequences varying in speed and timing.

RESULTS

A fall example from the FARSEEING database was used to show the feasibility of producing a similar sensor signal with the re-enactment method. Although fall events were heterogeneous concerning chronological sequence and curve progression, it was possible to reproduce a good approximation of the motion of a person's center of mass during fall events based on the available sensor information.

CONCLUSIONS

Re-enactment is a promising method to understand and visualize the biomechanics of inertial sensor-recorded real-world falls when performed in a suitable setup, especially if video data is not available.

Protective arm movements are modulated with fall height

Protective arm reactions were evoked in 14 younger adults to determine the effect of fall height on protective arm reaction biomechanics. Participants were supported in a forward-leaning position on top of an inverted pendulum that isolated arm reaction by preventing any fall arresting contribution that may come from the ankle, knees, or hip. At an unpredictable time, the pendulum was released requiring participants to rapidly orient their arms to protect the head and body. Vertical ground reaction force (vGRF), arm kinematics, and electromyographic (EMG) measures of the biceps and triceps were compared at four initial lean angles. The time following perturbation onset and prior to impact consisted of two phases: rapid extension of the elbows and co-activation of the biceps and triceps in preparation for impact. The rapid orientation phase was modulated with fall height while the co-activation of the biceps and triceps in preparation for landing was minimally affected. Larger lean angles resulted in increased vGRF, increased elbow extension at impact, decreased elbow angular extension velocity at impact, and increased neck velocity at impact while hand velocity at impact was not significantly affected. The neuromuscular control strategy appears to optimize elbow extension angle/angular velocity prior to co-activation of the biceps and triceps that occurs about 100 ms prior to impact. Future work should investigate how the neuromuscular control strategy handles delayed deployment of protective arm reactions.

Development of a stick-on hip protector: A multiple methods study to improve hip protector design for older adults in the acute care environment

Introduction

Over 90% of hip fractures in older adults result from falls, and hospital patients are at especially high risk. Specific types of wearable hip protectors have been shown to reduce hip fracture risk during a fall by up to 80%, but user compliance has averaged less than 50%. We describe the development and evaluation of a "stick-on" hip protector (secured over the hip with a skin-friendly adhesive) for older patients in acute care.

Methods

An initial version of the product was evaluated with six female patients (aged 76-91) in a hospital ward, who were asked to wear it for one week. We subsequently refined the product through biomechanical testing and solicited feedback from 43 health professionals on a second prototype.

Results

The first prototype was worn by five of six patients for the full week or duration of their hospital stay. The second prototype (20 mm thick, surface area 19 × 15.5 cm) provided 36% force attenuation, more than common garment-based models (20-21%). Feedback from patients and health professionals highlighted usability, comfort, cost, and appearance.

Conclusions

Our results from biomechanical and user testing support the need for further work to determine the value of stick-on hip protectors in acute care.

Effect of handrail height and age on the timing and speed of reach-to-grasp balance reactions during slope descent

We investigated the effect of handrail height on the timing and speed of reach-to-grasp balance reactions during slope descent, in fourteen younger and thirteen older adults. Participants walked along an 8° slope mounted to a robotic platform. Platform perturbations evoked reach-to-grasp reactions. Handrail height did not significantly affect handrail contact time (i.e., time from perturbation onset to handrail contact) or movement time (i.e., time from EMG latency to handrail contact). Participants appeared to compensate for the increased hand-handrail distance with higher rails via increased peak upward hand speed, and decreased vertical handrail overshoot. Aging was associated with slower EMG latency, reduced hand acceleration time, and increased hand deceleration time. Our findings suggest that participants were not disadvantaged by higher handrails from reach-to-grasp timing or speed perspectives, and that other metrics (e.g., center-of-mass control after grasping) may be more important when evaluating handrail designs for balance recovery.

Ecology of falls

In this chapter, we consider how falls result from interactions between humans and their environment, and the implications of these interactions on the prevention of falls and fall-related injuries. We take a lifespan approach, and examine the human behaviors that create risk for falls and injuries in various environments, and the social and biologic factors that shape those behaviors. While not always stated explicitly, we draw on our experience in collecting and analyzing video footage of hundreds of falls. We consider that most falls do not result in significant injury, and issues of self-autonomy for pursuing a lifestyle that may create risk for falls. To help guide falls management, we propose a mechanism for classifying falls as "acceptable" versus "unacceptable." We also provide an ecology of falls checklist to guide stakeholders in identifying ecologic aspects of falls that may be useful targets for intervention.

Neuromuscular determinants of slip-induced falls and recoveries in older adults

Is there a neuromuscular basis for falls? If so, it may provide new insight into falls and their assessment and treatment. We hypothesized that falls and recoveries from a laboratory-induced slip would be characterized by differences in multimuscle coordination patterns. Using muscle synergy analysis, we identified different multimuscle coordination patterns between older adults who fell and those who recovered from a laboratory-induced "feet-forward" slip. Participants who fell recruited fewer muscle synergies than participants who recovered. This suggests that a fall may result from recruitment of an inadequate number of muscle synergies to produce the necessary mechanical functions required to maintain balance. Participants who fell also recruited different muscle synergies, including one with high levels of coactivity consistent with a startle-like response. These differences in multimuscle coordination between slip outcomes were not accompanied by differences in slip difficulty or gait kinematics before or during the slip response. The differences in neuromuscular control may therefore reflect differences in sensorimotor control rather than kinematic constraints imposed by the slip, or the musculoskeletal system. Further research is required to test the robustness of these results and their interpretation with respect to additional mechanical variables (e.g., joint torques, ground reaction forces), responses to other fall types (e.g., trips), and within rather than between individuals. NEW & NOTEWORTHY Do falls and recoveries possess distinct neuromuscular features? We identified differences in neuromuscular control between older adults who fell and those who recovered from a "feet-forward" slip. Differences in neuromuscular control were not accompanied by differences in gait or slip kinematics before or during the slip response, suggesting differences in sensorimotor control rather than kinematics dictated the observed differences in neuromuscular control. An analysis of additional mechanical variables is required to confirm this interpretation.

Does Fall Arrest Strategy Training Added to a Fall Prevention Programme Improve Balance, Strength, and Agility in Older Women? A Pilot Study

Purpose: The purpose of this study was to determine the effect of a unique exercise programme (Fall Arrest Strategy Training, or FAST) on upper body strength, range of motion (ROM), and fall risk in older women. FAST was designed to improve upper body capacity to prevent injury when a fall cannot be avoided. Method: A quasi-randomized site design included 71 older women (aged 67-95 y, mean age 83 years), who participated either in a standard fall prevention programme (Staying on Your Feet, or SOYF; n=29) or in SOYF combined with FAST (n=42). The women were measured three times-at baseline, after the 12-week intervention, and again 12 weeks later-for upper body strength, ROM, and fall risk factors (fall risk questionnaire, balance, mobility, and leg strength). Results: No significant differences were found in age, physical activity, or cognitive or functional status between the SOYF-standard and the SOYF-FAST groups. Both groups improved their fall risk status after the intervention, with no significant differences between them; however, the SOYF-FAST group showed greater improvements in upper extremity strength and ROM (p=0.007). Conclusion: FAST can feasibly be integrated into fall prevention programming, with additional gains in upper body strength and ROM in older women.

Effect of neck flexor muscle activation on impact velocity of the head during backward falls in young adults

Falls are a common cause of traumatic brain injuries (TBI) across the lifespan. A proposed but untested hypothesis is that neck muscle activation influences impact severity and risk for TBI during a fall. We conducted backward falling experiments to test whether activation of the neck flexor muscles facilitates the avoidance of head impact, and reduces impact velocity if the head contacts the ground. Young adults (n=8) fell from standing onto a 30cm thick gymnastics mat while wearing a helmet. Participants were instructed to fall backward and (a) prevent their head from impacting the mat ("no head impact" trials); (b) allow their head to impact the mat, but with minimal impact severity ("soft impact" trials); and (c) allow their head to impact the mat, while inhibiting efforts to reduce impact severity ("hard impact" trials). Trial type associated with peak magnitude of electromyographic activity of the sternocleidomastoid (SCM) muscles (p<0.017), and with the vertical and horizontal velocity of the head at impact (p<0.001). Peak SCM activations, expressed as percent maximal voluntary isometric contraction (%MVIC), averaged 75.3, 67.5, and 44.5%MVIC in "no head impact", "soft impact", and "hard impact" trials, respectively. When compared to "soft impact" trials, vertical impact velocities in "hard impact" trials averaged 87% greater (3.23 versus 1.73m/s) and horizontal velocities averaged 83% greater (2.74 versus 1.50m/s). For every 10% increase in SCM %MVIC, vertical impact velocity decreased 0.24m/s and horizontal velocity decreased 0.22m/s. We conclude that SCM activation contributes to the prevention and modulation of head impact severity during backward falls.

Sideways fall-induced impact force and its effect on hip fracture risk: a review

Osteoporotic hip fracture, mostly induced in falls among the elderly, is a major health burden over the world. The impact force applied to the hip is an important factor in determining the risk of hip fracture. However, biomechanical researches have yielded conflicting conclusions about whether the fall-induced impact force can be accurately predicted by the available models. It also has been debated whether or not the effect of impact force has been considered appropriately in hip fracture risk assessment tools. This study aimed to provide a state-of-the-art review of the available methods for predicting the impact force, investigate their strengths/limitations, and suggest further improvements in modeling of human body falling.

METHODS

We divided the effective parameters on impact force to two categories: (1) the parameters that can be determined subject-specifically and (2) the parameters that may significantly vary from fall to fall for an individual and cannot be considered subject-specifically.

RESULTS

The parameters in the first category can be investigated in human body fall experiments. Video capture of real-life falls was reported as a valuable method to investigate the parameters in the second category that significantly affect the impact force and cannot be determined in human body fall experiments.

CONCLUSIONS

The analysis of the gathered data revealed that there is a need to develop modified biomechanical models for more accurate prediction of the impact force and appropriately adopt them in hip fracture risk assessment tools in order to achieve a better precision in identifying high-risk patients. Graphical abstract Impact force to the hip induced in sideways falls is affected by many parameters and may remarkably vary from subject to subject.

Developing safe fall strategies for lower limb exoskeletons

One of the main challenges in the use of a powered lower limb exoskeleton (LLE) is to ensure that balance is maintained throughout the operation of the device. Since no control strategy has yet been implemented that prevents falls in the case of a loss of balance, head or other serious injuries may occur during independent use of LLEs in the event of a fall. These safety concerns limit LLEs in the community to supervised use only. Using the backward fall as a model, we used optimization techniques to develop safe fall control strategies in order to avoid head impact and mitigate the impact velocity of the hips. From available human biomechanics data, we first developed an optimization methodology to study falls of healthy people. The results showed similar kinematic and dynamic characteristics to findings of previous studies on real-life human falls. Second, we extended the optimization methodology to include characteristics of a hypothetical LLE and to generate optimal joint trajectories and optimal torque profiles for the fall duration. The results revealed that by applying the optimal fall strategy, the severity of a simulated fall was minimized compared to when the device fell with locked joints (i.e., how currently used exoskeletons fall): head impact was avoided and hip impact velocity was reduced by more than 50%.

Female Age-Related Differences in Biomechanics and Muscle Activity During Descents on the Outstretched Arms

The purposes of this study were to examine female age differences in: (1) upper extremity (UE) and trunk muscle activity, elbow joint moment, loading force, and UE energy absorption during a controlled forward body descent; and (2) UE muscle strength. Twenty young (mean 24.8 ± 3.4 years) and 20 older (68.4 ± 5.7 years) women were assessed via dynamometry for isometric, concentric, and eccentric UE strength and performed forward descents on force plates at three body lean angles (60°, 45°, and 30° from horizontal). Significant differences (p < .05) were found for muscle strength, biomechanics, and muscle activity. Concentric UE strength averaged 15% lower in older women. At 30° body lean, older women absorbed less energy. Older women had greater biceps brachii activation and less external oblique activation at all body lean angles. Age differences in muscle strength, activation, and energy absorption may contribute to fall-related injury risk.

The dynamics of electric powered wheelchair sideways tips and falls: experimental and computational analysis of impact forces and injury

Background

To reduce the occurrence of wheelchair falls and to develop effective protection systems, we aimed to quantify sideways tip and fall dynamics of electric power wheelchairs (EPWs). We hypothesized that driving speed, curb height and angle of approach would affect impact forces and head injury risk for wheelchair riders. We further expected that fall dynamics and head injury risk would be greater for unrestrained riders compared to restrained riders.

Methods

Sideways wheelchair tip and fall dynamics were reconstructed using a remotely operated rear wheel drive EPW and a Hybrid III test dummy driving at different approach angles (5 to 63°) over an adjustable height curb (0.30 to 0.41 m) at speeds of 0.6–1.5 m/s. Rigid body dynamics models (Madymo, TASS International, Livonia, MI) were developed in parallel with the experiments to systematically study and quantify the impact forces and the sideways tip or fall of an EPW user in different driving conditions.

Results

Shallower approach angles (25°) (p < 0.05) and higher curbs (0.4 m) (p < 0.05) were the most significant predictors of tipping for restrained passengers. Unrestrained passengers were most affected by higher curbs (0.4 m) (p < 0.005) and fell forward from the upright wheelchair when the approach angle was 60°. Head impact forces were greater in unrestrained users (6181 ± 2372 N) than restrained users (1336 ± 827 N) (p = 0.00053). Unrestrained users had significantly greater head impact severities than restrained users (HIC = 610 ± 634 vs HIC = 29 ± 38, p = 0.00013) and several tip events resulted in HICs > 1000 (severe head injury) in unrestrained users.

Conclusions

Sideways tips and forward falls from wheelchairs were most sensitive to curb height and approach angle but were not affected by driving speed. Sideways tips and falls resulted in impact forces that could result in concussions or traumatic brain injury and require injury prevention strategies. Seat belts eliminated the risk of falling from an upright chair and reduced head impact forces in sideways wheelchair tips in this study; however, their use must be considered within the ethical and legal definitions of restraints.