Scholarly Works, Industrial and Systems Engineering

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Employing Eye Trackers to Reduce Nuisance Alarms
Herdt, Katherine; Hildebrandt, Michael; LeBlanc, Katya; Lau, Nathan (MDPI, 2025-04-22)
When process operators anticipate an alarm prior to its annunciation, that alarm loses information value and becomes a nuisance. This study investigated using eye trackers to measure and adjust the salience of alarms with three methods of gaze-based acknowledgement (GBA) of alarms that estimate operator anticipation. When these methods detected possible alarm anticipation, the alarm’s audio and visual salience was reduced. A total of 24 engineering students (male = 14, female = 10) aged between 18 and 45 were recruited to predict alarms and control a process parameter in three scenario types (parameter near threshold, trending, or fluctuating). The study evaluated whether behaviors of the monitored parameter affected how frequently the three GBA methods were utilized and whether reducing alarm salience improved control task performance. The results did not show significant task improvement with any GBA methods (F(3,69) = 1.357, p = 0.263, partial η² = 0.056). However, the scenario type affected which GBA method was more utilized (X² (2, N = 432) = 30.147, p < 0.001). Alarm prediction hits with gaze-based acknowledgements coincided more frequently than alarm prediction hits without gaze-based acknowledgements (X² (1, N = 432) = 23.802, p < 0.001, OR = 3.877, 95% CI 2.25–6.68, p < 0.05). Participant ratings indicated an overall preference for the three GBA methods over a standard alarm design (F(3,63) = 3.745, p = 0.015, partial η² = 0.151). This study provides empirical evidence for the potential of eye tracking in alarm management but highlights the need for additional research to increase validity for inferring alarm anticipation.
Passive back support exoskeletons do not effectively reduce physical demands during simulated floor tiling
Usmani, Ahmad Raza; Rajabi, Mohammad Sadra; Ojelade, Aanuoluwapo; Kim, Sunwook; Harris-Adamson, Carisa; Barr, Alan; Nussbaum, Maury A. (Elsevier, 2025-05)
Back-support exoskeletons (BSEs) have the potential to reduce physical demands during many occupational tasks, but their effectiveness in flooring work remains underexplored. Eighteen participants performed simulated floor tiling work under three intervention conditions (HeroWear Apex™ = HW, Laevo Flex™ = LV, and no device = ND), across two tile sizes (small vs. large), and two task types (tiling vs. grouting). HW use increased back muscle activation by ∼13-44 % compared to ND, while LV led to minimal changes. Some participants reported concerns with both BSEs, including movement restrictions, discomfort, and skin irritation. Significant interaction effects of intervention and tile size on muscle activity and subjective outcomes suggest the importance of considering task-specificity in BSE evaluations. Overall, the BSEs examined here did not effectively reduce physical demands during simulated floor tiling. Although we assessed BSE effects on tiling, our findings could also guide future implementation of exoskeletons in other similar construction tasks.
User Experiences and Adoption Factors for a Back-Support Exosuit in Automotive Logistics: Results from Field Testing up to 18 Months
Kim, Sunwook; Porto, Ryan; Nussbaum, Maury A. (Taylor & Francis, 2025-04)
Occupational Applications: We interviewed 24 automotive logistic workers who had used (or stopped using) a soft back-support exoskeleton (exosuit). These workers generally recognized potentially benefits of back-support exosuits, with 11 continuing use. Their use was primarily influenced by usability, compatibility, and comfort factors. We found wide variability in use patterns and adaptation periods, and that there were specific design concerns and concerns regarding thermal discomfort. To enhance long-term adoption of exosuits in industrial settings, organizations should consider: 1) implementing flexible, individualized training programs addressing specific usability challenges; 2) adopting a voluntary approach accommodating varied adaptation needs; 3) providing comprehensive education on potential health benefits; 4) using peer demonstrations to promote acceptance; and 5) collaborating with manufacturers to improve designs based on user feedback. These strategies may help enhance acceptance and sustained use of exosuits, potentially contributing to more effective support for occupational health during manual material handling tasks.
Vibrotactile feedback in virtual motor learning: A systematic review
Islam, Md Shafiqul; Lim, Sol (Elsevier, 2022-05-01)
Vibrotactile feedback can be effectively applied to motor (physical) learning in virtual environments, as it can provide task-intrinsic and augmented feedback to users, assisting them in enhancing their motor performance. This review investigates current uses of vibrotactile feedback systems in motor learning applications built upon virtual environments by systematically synthesizing 24 peer-reviewed studies. We aim to understand: (1) the current state of the science of using real-time vibrotactile feedback in virtual environments for aiding the acquisition (or improvement) of motor skills, (2) the effectiveness of using vibrotactile feedback in such applications, and (3) research gaps and opportunities in current technology. We used the Sensing-Analysis-Assessment-Intervention framework to assess the scientific literature in our review. The review identifies several research gaps in current studies, as well as potential design considerations that can improve vibrotactile feedback systems in virtual motor learning applications, including the selection and placement of feedback devices and feedback designs.
Real-time vibrotactile feedback system for reducing trunk flexion exposure during construction tasks
Lim, Sol; Yang, Xiang (Elsevier, 2023-07)
Workplaces are increasingly evaluating the use of wearables for ergonomic assessment and providing biofeedback as a real-time postural intervention to improve workers’ posture. However, the effectiveness of such intervention systems has yet to be thoroughly investigated in different types of industrial tasks. This study tested the immediate effects of using vibrotactile feedback in simulated construction work tasks including lifting-lowering, shoveling, and tying rebar, to investigate the potential for such an intervention as a way to instruct workers in reducing excessive trunk flexion exposures. Fourteen male participants completed simulated work tasks with three different feedback locations, namely, no feedback, back, and wrist. The results demonstrate that the 95th, 90th, and 50th percentiles of trunk flexion angles are significantly lower for lifting-lowering and shoveling tasks when the feedback system is used. No significant postural changes were observed for the rebar tying task at any combination of percentile and feedback location. The rating of perceived exertion (RPE) for each task did not differ significantly between feedback conditions. Productivity remained the same with the feedback for lifting-lowering and rebar tying, while it was significantly reduced (4.5% of working rate reduction) in shoveling. Participants rated the wrist as the most preferred feedback location. The results of this study suggest that vibrotactile feedback has potential as an effective postural intervention for ergonomic risk factors in selected construction work tasks. Implications for the future design of real-time wearable, sensor-based vibrotactile feedback systems for postural control intervention during dynamic work tasks are discussed.
Use of a wearable electromyography armband to detect lift-lower tasks and classify hand loads
Taori, Sakshi; Lim, Sol (Elsevier, 2024-09)
We used an armband with embedded surface electromyography (sEMG) electrodes, together with machine-learning (ML) models, to automatically detect lifting-lowering activities and classify hand loads. Nine healthy participants (4 male and 5 female) completed simulated lifting-lowering tasks in various conditions and with two different hand loads (2.3 and 6.8 kg). We compared three sEMG signal feature sets (i.e., time, frequency, and a combination of both domains) and three ML classifiers (i.e., Random Forest, Support Vector Machine, and Logistic Regression). Both Random Forest and Support Vector Machine models, using either time-domain or time- and frequency-domain features, yielded the best performance in detecting lifts, with respective accuracies of 79.2% (start) and 86.7% (end). Similarly, both ML models yielded the highest accuracy (80.9%) in classifying the two hand loads, regardless of the sEMG features used, emphasizing the potential of sEMG armbands for assessing exposure and risks in occupational lifting tasks.
Barriers and Benefits of Online Group Exercise Programs for Older Adults
Islam, Md Shafiqul; Frazier, Mary C.; Harden, Samantha M.; Lim, Sol (Sage, 2024-10)
Engaging in regular physical activity offers a myriad of benefits, including the improvement of mental health, social well-being, and cognitive function. Unfortunately, obstacles, such as transportation constraints, time limitations, and inadequate exercise facilities, hinder the regular participation of older adults in physical activity. Online group physical activity programs present a promising solution to enhance the involvement of older adults; however, several barriers impede their effective utilization. To explore these barriers and benefits, we conducted semi-structured interviews with participants and instructors of a community-based exercise program. Thematic analysis of interviews with 12 physical activity instructors and eight program participants unveiled key hindrances, including limited awareness and accessibility of online programs, challenges in assessing performance during exercise sessions, lack of social component, and technological difficulties. On the positive side, the benefits encompass convenience, wide accessibility, and enhanced social comfort. We also deliberate on future considerations to further bolster participation in these programs.
Exposures to select risk factors can be estimated from a continuous stream of inertial sensor measurements during a variety of lifting-lowering tasks
Lim, Sol (Taylor & Francis, 2024-11-01)
Wearable inertial measurement units (IMUs) are used increasingly to estimate biomechanical exposures in lifting-lowering tasks. The objective of the study was to develop and evaluate predictive models for estimating relative hand loads and two other critical biomechanical exposures to gain a comprehensive understanding of work-related musculoskeletal disorders in lifting. We collected 12,480 lifting-lowering phases from 26 subjects (15 men and 11 women) performing manual lifting-lowering tasks with hand loads (0–22.7 kg) at varied workstation heights and handling modes. We implemented a Hierarchical model, that sequentially classified risk factors, including workstation height, handling mode, and relative hand load. Our algorithm detected lifting-lowering phases (>97.8%) with mean onset errors of 0.12 and 0.2 seconds for lifting and lowering phases. It estimated workstation height (>98.5%), handling mode (>87.1%), and relative hand load (mean absolute errors of 5.6–5.8%) across conditions, highlighting the benefits of data-driven models in deriving lifting-lowering occurrences, timing, and critical risk factors from continuous IMU-based kinematics.
Verbal and nonverbal communication differences between in-person and live-streamed group physical activity: a specific investigation into yoga instruction
Islam, Md Shafiqul; Harden, Samantha M.; Lee, Sang Won; Lim, Sol (Taylor & Francis, 2025-03-25)
Live-streamed group exercise programmes are used increasingly to start or maintain physical activity behaviours. However, participants’ performance and long-term engagement can be impacted in live-streamed programmes due to communication gaps with the instructors and peers. We analysed verbal and nonverbal communication differences between in-person and live-streamed group yoga classes to understand current challenges in live-streamed exercise programmes. A total of 29 group yoga class videos (14 live-streamed and 15 in-person) were annotated and analysed for verbal and nonverbal communication events. We found significantly reduced individual feedback in live-streamed vs. in-person sessions, while the trend was reversed for physical pose demonstrations. Environmental incidents hindered fluent communication in live-streamed sessions. The study identified interaction gaps in live-streamed group physical training in both verbal and nonverbal communication, especially in relation to providing personalised feedback for performance improvement. Potential ways to improve instructor-participant interactions in future designs for remote exercise platforms are discussed.
Sensitivity to Vibrotactile Stimulation in the Hand and Wrist: Effects of Motion, Temporal Patterns, and Biological Sex
Tajdari, Mahdis; Forsyth, Jason; Lim, Sol (Sage, 2025-04)
Objective: We investigated the impact of low-tempo, repetitive hand movements on vibrotactile sensitivity by employing various temporal and spatial patterns in the hand and wrist area. Background: The investigation of a human’s ability to perceive vibrotactile stimuli during dynamic hand movements remains understudied, despite the prevalence of slow to mild hand motions in applications such as hand navigation or gesture control using haptic gloves in Virtual Reality (VR) and Augmented Reality (AR). Method: We investigated vibrotactile sensitivity, analyzing the impact of various factors, including Motion (static and low-tempo repetitive hand movements), Temporal Patterns (Single or Double vibrations with varying onset times), Tactor Placements (hand and wrist), Spatial Patterns, and Biological Sex. Results: Our study revealed that Motion significantly influences vibrotactile sensitivity in the hand and wrist areas, leading to reduced accuracy rates during dynamic conditions. Additionally, as the stimulus onset approached in Double vibrations, accuracy rates markedly decreased. Notably, Hand Placement resulted in significantly higher accuracy rates compared to the Wrist Placement. Conclusion: Our findings underscore the impact of motion in reducing vibrotactile sensitivity on the back of the hand and around the wrist. Application: This research has wide-ranging practical applications, particularly in the field of VR/AR experiences, rehabilitation programs, and accessibility solutions through the use of haptic gloves. Insights from our study can be harnessed to enhance the efficacy of haptic gloves in conveying vibrotactile cues within these contexts.
Classification algorithms trained on simple (symmetric) lifting data perform poorly in predicting hand loads during complex (free-dynamic) lifting tasks
Taori, Sakshi; Lim, Sol (Elsevier, 2025-05)
The performance of machine learning (ML) algorithms is dependent on which dataset it has been trained on. While ML algorithms are increasingly used for lift risk assessment, many algorithms are often trained and tested on controlled simulation datasets, lacking the diversity of the lifting conditions. Consequently, concerns arise regarding their applicability in real-world scenarios characterized by substantial variations in lifting scenarios and postures. Our study investigates the impact of different lifting scenarios on the performance of ML algorithms trained on surface electromyography (sEMG) armband sensor data to classify hand-load levels (2.3 and 6.8 kg). Twelve healthy participants (6 male and 6 female) performed repetitive lifting tasks employing various lifting scenarios, including symmetric (S), asymmetric (A), and free-dynamic (F) techniques. Separate algorithms were developed using diverse training datasets (S, A, S+A, and F), ML classifiers, and sEMG features, and tested using the F dataset, representing unconstrained and naturalistic lifts. The mean accuracy and sensitivity were significantly lower in models trained on constrained (S) datasets compared to those trained on naturalistic lifts (F). The accuracy, precision, and sensitivity of models trained with frequency-domain sEMG features were greater than those trained with the time-domain features. In conclusion, ML algorithms trained on controlled symmetric lifts showed poor performance in predicting loads for dynamic, unconstrained lifts; thus, particular attention is needed when using such algorithms in real-world scenarios.
Use of wearable sensors for continuous field monitoring of upper arm and trunk postures among construction workers
Porta, Micaela; Casu, Giulia; Lim, Sol; Nussbaum, Maury A.; Pau, Massimiliano (Taylor & Francis, 2025-02-28)
Construction is considered amongst the highest risk sectors for the development of work-related musculoskeletal disorders (MSDs) considering the large number of unfavourable environmental and task-specific factors typical in this sector. Thus, it is important to have quantitative tools to support the assessment of the exposure to physical MSD risk factors. We employed wearable inertial sensors (ISs) to perform a real-world characterisation of static postures and repetitive movements involving the trunk and upper arms (UA), among 15 workers during 2 hours of their regular shifts. IS data were processed according to ISO 11226 and EN 1005-4 standards. We found that workers spent ∼25% of the monitored time in static trunk flexion >20% and more than 50% of the time with UA elevations >20°. The ability to assess working postures for prolonged periods may represent a useful tool for different stakeholders involved in the protection of construction worker health.
Cognitive workload assessment during VR forklift training
Zahabi, Saman Jamshid Nezhad; Islam, Md Shafiqul; Kim, Sunwook; Lau, Nathan; Nussbaum, Maury A.; Lim, Sol (Elsevier, 2025-05)
Virtual Reality (VR)-based training offers a safe and engaging environment for training forklift operators. Given the complexity of forklift operation, monitoring the cognitive workload of novice operators in these virtual settings is essential for optimizing the training process. This study investigated cognitive workload variation during a VR-based training for forklift operators due to varying levels of task difficulty and repeated training. Twenty novice participants completed two sessions in a VR simulator with each session including three forklift driving lessons at three difficulty levels. Perceived workload (NASA-TLX) and normalized encephalographic (EEG) activity were employed to assess cognitive workload. Five of the six NASA-TLX subscales and EEG activity in three distinct frequency bands (theta, alpha and beta) all significantly increased with increasing task difficulty. However, we did not observe significant changes in cognitive workload as measured by EEG in the second training session, highlighting a potential limitation in using EEG to track workload variations across days. Perceived workload and EEG measures showed moderate, positive correlations. Our results highlight the potential of EEG for real-time monitoring of workload during VR-based forklift training, particularly in differentiating tasks of varying difficulty. While more research is needed to confirm measurement consistency across sessions, this capability could facilitate worker monitoring to deliver timely alerts or assistance when workload levels exceed optimal thresholds.
Perspectives of Mining Personnel on Adopting Occupational Exoskeletons: Comparisons Between a Developed and a Developing Country
Akinwande, Feyisayo; Kim, Sunwook; Ojelade, Aanuoluwapo; Muslim, Khoirul; Iridiastadi, Hardianto; Nasarwanji, Mahiyar; Kim, Jeong Ho; Nussbaum, Maury A. (Springer, 2025-03-01)
Occupational exoskeletons (EXOs) have received growing attention as a new ergonomic intervention to reduce physical demands in various industries (e.g., manufacturing, logistics, construction, and agriculture). However, their potential use in mining has not yet been reported. Survey data (n = 135) were obtained from mining workers in the United States (US) and Indonesia (ID). Qualitative and frequency analyses were used to summarize and compare respondents’ perceived barriers, benefits, and promoters to EXO use and adoption. Beta regression analyses were also used to examine whether the perceived likelihood to use arm-support EXOs or back-support EXOs differed between the countries and was affected by demographic or job characteristics, or by perceptions regarding EXOs. Both US and ID respondents reported potential benefits of EXOs for physically demanding tasks such as lifting and overhead work, and they shared concerns about adaptation, uncertainty or lack of knowledge, confined spaces, device weight, potential failure or damage, and costs. However, some key differences also emerged: US respondents were more likely to consider using arm-support EXOs and back-support EXOs, despite expressing concerns about their use; ID respondents, although they reported more existing health and safety hazards, appeared more hesitant about adopting EXOs, possibly due to these additional hazards. These results demonstrate that miners appear to have an interest in EXOs but also emphasize the need to ensure task compatibility, comfort, and affordability to ensure the safe and effective adoption of EXO technology in mining in both developed and developing countries.
Passive arm-support and back-support exoskeletons have distinct phase-dependent effects on physical demands during cart pushing and pulling: An exploratory study
Park, Hanjun; Noll, Alex; Kim, Sunwook; Nussbaum, Maury A. (Elsevier, 2025-03-20)
Arm-support exoskeletons (ASEs) and back-support exoskeletons (BSEs) can be effective in reducing physical demands during various occupational tasks, yet evidence of their effects in pushing and pulling tasks remains limited. We examined the effects of using a passive ASE and a BSE on task completion time, shoulder and trunk kinematics, and muscle activity in the shoulder and back while pushing and pulling a moderately loaded (100 kg) cart. Forty volunteers (24 M and 16 F) completed the study. Using the BSE substantially reduced thoracic and lumbar erector spinae muscle activity for males, especially during the initial and ending phases of pushing (by up to ∼31.4 %) and pulling (by up to ∼25.4 %) compared to the No Device (ND) condition. In contrast, using the ASE showed no significant benefits, with females experiencing an increase in anterior deltoid muscle activity (by up to ∼46.3 %) compared to ND. Findings from this study help to understand the effects of BSEs and ASEs in pushing and pulling tasks and support the development of more versatile exoskeletons.
Gait variability predicts post-fatigue obstacle course performance among military cadets: An exploratory study
Ulman, Sophia; Srinivasan, Divya; Nussbaum, Maury A. (Elsevier, 2025-03-12)
We explored the extent to which pre-fatigue gait variability during load carriage is associated with the ability of an individual to perform an obstacle course post-fatigue. Twenty-four military cadets were monitored during treadmill gait and completed an obstacle course before and after a full-body fatigue protocol. Gait variability measures were determined from spatiotemporal stride characteristics, joint angle trajectories, and inter-joint coordination. These measures were then used in multiple linear regression models to predict three measures of post-fatigue performance (i.e., hurdle completion time, maximum jump height, and maximum jump distance). Measures of joint kinematic variability predicted 73–89% of the variance in post-fatigue performance. Specifically, the significant predictors were sagittal plane variability of 1) hip angle and hip-knee coordination during swing phase; and 2) knee-ankle coordination during both stance and swing phase. Measures of joint kinematic variability obtained from gait thus appear relevant for predicting individual differences in adapting to fatigue, and such measures could aid in predicting post-fatigue performance in diverse dynamic tasks.
Understanding the drivers of and barriers to adopting passive back- and arm-support exoskeletons in construction: Results from interviews and short-term field testing
Ashtiani, Mohamad Behjati; Morris, Wallace; Ojelade, Aanuoluwapo; Kim, Sunwook; Akinwande, Feyisayo; Barr, Alan; Harris-Adamson, Carisa; Akanmu, Abiola; Nussbaum, Maury A. (Elsevier, 2025-05)
Construction workers experience high rates of work-related musculoskeletal disorders (WMSDs), particularly affecting the back and shoulders. Exoskeletons (EXOs), including arm-support (ASEs) and back-support (BSEs) devices, have clear potential as ergonomic interventions for reducing WMSD risks, yet the specific benefits and limitations in the construction industry remain largely unclear. We aimed to identify drivers and barriers to adopting EXOs in construction, which was done using a two-phase approach: an interview study involving 24 construction stakeholders, followed by a field study with 22 construction workers. Participants in the interview study had hands-on experiences with diverse EXOs, then provided feedback on initial impressions, perceived barriers, and potential benefits of EXO use. Interview recordings were analyzed for sentiment, systematically categorizing responses as positive, neutral, and negative. During the field study, workers wore EXOs while performing their job tasks for up to 1 h, then completed structured exit surveys that assessed usability, comfort, safety, and overall satisfaction. We found a generally positive view of EXO technology in construction, with stakeholders open to adoption for enhancing productivity and reducing physical demands. However, usability, safety, and social acceptance concerns indicated a need for design improvements focused on comfort and compatibility. Notably, safety concerns expressed by interviewees contrasted with positive field study responses, suggesting that the input obtained can vary between assessment conditions. Future research should include longitudinal studies to track shifts in perception and assess diverse designs. These findings highlight the need for refined EXOs to meet construction demands and support broader industry adoption.
Estimating dynamic external hand forces during overhead work with and without an exoskeleton: Evaluating an approach using electromyography signals and random forest regression
Ashtiani, Mohamad Behjati; Ojelade, Aanuoluwapo; Kim, Sunwook; Nussbaum, Maury A. (Elsevier, 2025-05)
We developed a model to estimate hand contact forces during dynamic overhead tasks completed with and without passive arm-support exoskeletons (ASEs). One approach to assessing ASE effectiveness is evaluating shoulder joint forces through inverse dynamics, which requires data on both external kinetics and body kinematics. However, obtaining the former (e.g., hand contact forces) is challenging. To address this, our model estimates these forces using electromyographic (EMG) signals. For model development, we used data from a study in which participants completed dynamic overhead task simulations under various conditions, both with and without three ASEs. A random forest regression was used to map EMG signals to time series of hand contact force, considering task conditions and biological sex. Overall, the model produced reasonable force estimations, with errors generally consistent across conditions and regardless of ASE use. However, the model tended to underestimate peak forces, especially for upward vs. forward exertions and among males vs. females. Overall, the proposed model has the potential to support musculoskeletal modeling for assessing the effect of ASE use on workers. We provide several suggestions for improving future model performance.
Effects of exercise-induced low back pain on intrinsic trunk stiffness and paraspinal muscle reflexes
Miller, Emily M.; Bazrgari, Babak; Nussbaum, Maury A.; Madigan, Michael L. (Elsevier, 2012-11-23)
The purpose of this study was to (1) compare trunk neuromuscular behavior between individuals with no history of low back pain (LBP) and individuals who experience exercise-induced LBP (eiLBP) when pain free, and (2) investigate changes in trunk neuromuscular behavior with eiLBP. Seventeen young adult males participated including eight reporting recurrent, acute eiLBP and nine control participants reporting no history of LBP. Intrinsic trunk stiffness and paraspinal muscle reflex delay were determined in both groups using sudden trunk flexion position perturbations 1-2 days following exercise when the eiLBP participants were experiencing an episode of LBP (termed post-exercise) and 4-5 days following exercise when eiLBP had subsided (termed post-recovery). Post-recovery, when the eiLBP group was experiencing minimal LBP, trunk stiffness was 26% higher in the eiLBP group compared to the control group (p=0.033) and reflex delay was not different (p=0.969) between groups. Trunk stiffness did not change (p=0.826) within the eiLBP group from post-exercise to post-recovery, but decreased 22% within the control group (p=0.002). Reflex delay decreased 11% within the eiLBP group from post-exercise to post-recovery (p=0.013), and increased 15% within the control group (p=0.006). Although the neuromuscular mechanisms associated with eiLBP and chronic LBP may differ, these results suggest that previously-reported differences in trunk neuromuscular behavior between individuals with chronic LBP and healthy controls reflect a combination of inherent differences in neuromuscular behavior between these individuals as well as changes in neuromuscular behavior elicited by pain.
Effects of Age-Related Differences in Femoral Loading and Bone Mineral Density on Strains in the Proximal Femur During Controlled Walking
Anderson, Dennis E.; Madigan, Michael L. (Human Kinetics, 2012-11-21)
Maintenance of healthy bone mineral density (BMD) is important for preventing fractures in older adults. Strains experienced by bone in vivo stimulate remodeling processes, which can increase or decrease BMD. However, there has been little study of age differences in bone strains. This study examined the relative contributions of age-related differences in femoral loading and BMD to age-related differences in femoral strains during walking using gait analysis, static optimization, and finite element modeling. Strains in older adult models were similar or larger than in young adult models. Reduced BMD increased strains in a fairly uniform manner, whereas older adult loading increased strains in early stance but decreased strains in late stance. Peak ground reaction forces, hip joint contact forces, and hip flexor forces were lower in older adults in late stance phase, and this helped older adults maintain strains similar to those of young adults despite lower BMD. Because walking likely represents a "baseline" level of stimulus for bone remodeling processes, increased strains during walking in older adults might indicate the extent of age-related impairment in bone remodeling processes. Such a measure might be clinically useful if it could be accurately determined with age-appropriate patient-specific loading, geometry, and BMD.

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