Andrew C. Laing

Effect of sagittal plane mechanics on ACL strain during jump landing

The relationships between non‐contact anterior cruciate ligament injuries and the underlying biomechanics are still unclear, despite large quantities of academic research. The purpose of this research was to study anterior cruciate ligament strain during jump landing by investigating its correlation with sagittal plane kinetic/kinematic parameters and by creating an empirical model to estimate the maximum strain. Whole‐body kinematics and ground reaction forces were measured from seven subjects performing single leg jump landing and were used to drive a musculoskeletal model that estimated lower limb muscle forces. These muscle forces and kinematics were then applied on five instrumented cadaver knees using a dynamic knee simulator system. Correlation analysis revealed that higher ground reaction force, lower hip flexion angle and higher hip extension moment among others were correlated with higher peak strain (pu2009<u20090.05). Multivariate regression analyses revealed that intrinsic anatomic factors account for most of the variance in strain. Among the extrinsic variables, hip and trunk flexion angles significantly contributed to the strain. The empirical relationship developed in this study could be used to predict the relative strain between jumps of a participant and may be beneficial in developing training programs designed to reduce an athletes risk of injury.

Compliant flooring to prevent fall-related injuries in older adults: A scoping review of biomechanical efficacy, clinical effectiveness, cost-effectiveness, and workplace safety

Background Compliant flooring, broadly defined as flooring systems or floor coverings with some level of shock absorbency, may reduce the incidence and severity of fall-related injuries in older adults; however, a lack of synthesized evidence may be limiting widespread uptake. Methods Informed by the Arksey and O’Malley framework and guided by a Research Advisory Panel of knowledge users, we conducted a scoping review to answer: what is presented about the biomechanical efficacy, clinical effectiveness, cost-effectiveness, and workplace safety associated with compliant flooring systems that aim to prevent fall-related injuries in healthcare settings? We searched academic and grey literature databases. Any record that discussed a compliant flooring system and at least one of biomechanical efficacy, clinical effectiveness, cost-effectiveness, or workplace safety was eligible for inclusion. Two independent reviewers screened and abstracted records, charted data, and summarized results. Results After screening 3611 titles and abstracts and 166 full-text articles, we included 84 records plus 56 companion (supplementary) reports. Biomechanical efficacy records (n = 50) demonstrate compliant flooring can reduce fall-related impact forces with minimal effects on standing and walking balance. Clinical effectiveness records (n = 20) suggest that compliant flooring may reduce injuries, but may increase risk for falls. Preliminary evidence suggests that compliant flooring may be a cost-effective strategy (n = 12), but may also result in increased physical demands for healthcare workers (n = 17). Conclusions In summary, compliant flooring is a promising strategy for preventing fall-related injuries from a biomechanical perspective. Additional research is warranted to confirm whether compliant flooring (i) prevents fall-related injuries in real-world settings, (ii) is a cost-effective intervention strategy, and (iii) can be installed without negatively impacting workplace safety. Avenues for future research are provided, which will help to determine whether compliant flooring is recommended in healthcare environments.

Study protocol for the Flooring for Injury Prevention (FLIP) Study: a randomised controlled trial in long-term care

Background A promising strategy for reducing the incidence and severity of fall-related injuries in long-term care (LTC) is to decrease the ground surface stiffness, and the subsequent forces applied to the body parts at impact, through installation of compliant flooring that does not substantially affect balance or mobility. Definitive evidence of the effects of compliant flooring on fall-related injuries in LTC is lacking. The Flooring for Injury Prevention (FLIP) Study is designed to address this gap. Methods The FLIP Study is a 4-year, parallel-group, 2-arm, randomised controlled superiority trial of flooring in 150 resident rooms at a LTC site. The primary objective is to determine whether compliant flooring reduces serious fall-related injuries relative to control flooring. Intervention (2.54u2005cm SmartCells compliant; 74 rooms) and control (2.54u2005cm plywood; 76 rooms) floorings were installed over the top of existing concrete floors and covered with identical 2.00u2005mm vinyl. The primary outcome is serious fall-related injury, defined as any impact-related injury due to a fall in a study room that results in Emergency Department visit or hospital admission. Secondary outcomes include minor fall-related injury, any fall-related injury, falls, number of fallers, fractures, and healthcare utilisation and costs for serious fall-related injuries. Randomisation of study rooms, and residents in rooms, was stratified by residential unit, and flooring assignments were concealed. Outcome ascertainment began September 2013. Discussion Results from the FLIP Study will provide evidence about the effects of compliant flooring on fall-related injuries in LTC and will guide development of safer environments for vulnerable older adults. Trial registration number NCT01618786.

Use of the Nintendo Wii Balance Board for Studying Standing Static Balance Control: Technical Considerations, Force-Plate Congruency, and the Effect of Battery Life.

The Nintendo Wii Balance Board (WBB) has become popular as a low-cost alternative to research-grade force plates. The purposes of this study were to characterize a series of technical specifications for the WBB, to compare balance control metrics derived from time-varying center of pressure (COP) signals collected simultaneously from a WBB and a research-grade force plate, and to investigate the effects of battery life. Drift, linearity, hysteresis, mass accuracy, uniformity of response, and COP accuracy were assessed from a WBB. In addition, 6 participants completed an eyes-closed quiet standing task on the WBB (at 3 battery life levels) mounted on a force plate while sway was simultaneously measured by both systems. Characterization results were all associated with less than 1% error. R2 values reflecting WBB sensor linearity were > .99. Known and measured COP differences were lowest at the center of the WBB and greatest at the corners. Between-device differences in quiet stance COP summary metrics were of limited clinical significance. Lastly, battery life did not affect WBB COP accuracy, but did influence 2 of 8 quiet stance WBB parameters. This study provides general support for the WBB as a low-cost alternative to research-grade force plates for quantifying COP movement during standing.

The influence of muscle activation on impact dynamics during lateral falls on the hip

Muscle activation has been demonstrated to influence impact dynamics during scenarios including running, automotive impacts, and head impacts. This study investigated the effects of targeted muscle activation magnitude on impact dynamics during low energy falls on the hip with human volunteers. Fifteen university-aged participants (eight females, seven males) underwent 12 lateral pelvis release trials. Half of the trials were muscle-relaxed; in the remaining contracted trials participants isometrically contracted their gluteus medius to 20-30% of maximal voluntary contraction before the drop was initiated onto a force plate. Peak force applied to the femur-pelvis complex averaged 9.3% higher in contracted compared to relaxed trials (Fu202f=u202f6.798, pu202f=u202f.022). Muscle activation effects were greater for females, resulting in (on average) an 18.5% increase in effective pelvic stiffness (Fu202f=u202f5.838, pu202f=u202f.046) and a 23.4% decrease in time-to-peak-force (Fu202f=u202f5.109, pu202f=u202f.042). In the relaxed trials, muscle activation naturally increased during the impact event, reaching levels of 12.8, 7.5, 11.1, and 19.1% MVC at the time of peak force for the gluteus medias, vastus lateralis, erector spinae, and external oblique, respectively. These findings demonstrated that contraction of trunk and hip musculature increased peak impact force across sexes. In females, increases in the magnitude and rate of loading were accompanied (and likely driven) by increases in system stiffness. Accordingly, incorporating muscle activation contributions into biomechanical models that investigate loading dynamics in the femur and/or pelvis during lateral impacts may improve estimate accuracy.

Stooping, crouching, and standing - Characterizing balance control strategies across postures.

BACKGROUNDnWhile stooping and crouching postures are critical for many activities of daily living, little is known about the balance control mechanisms employed during these postures. Accordingly, the purpose of this study was to characterize the mechanisms driving net center of pressure (COPNet) movement across three postures (standing, stooping, and crouching) and to investigate if control in each posture was influenced by time.nnnMETHODSnTen young adults performed the three postures for 60s each. Kinetic signals were collected via a force platform under each foot. To quantify mechanisms of control, correlations (CorrelLR) were calculated between the left and right COP trajectories in the anterior-posterior (AP) and medio-lateral (ML) directions. To examine the potential effects of time on balance control strategies, outcomes during the first 30s were compared to the last 30s.nnnRESULTSnCorrelLR values did not differ across postures (AP: p = 0.395; ML: p = 0.647). Further, there were no main effects of time on CorrelLR (AP: p = 0.976; ML: p = 0.105). A significant posture-time interaction was observed in the ML direction (p = 0.045) characterized by 35% decreases in CorrelLR over time for stooping (p = 0.022).nnnCONCLUSIONnThe dominant controllers of sway (i.e., AP: ankle plantar/dorsi flexors; ML: hip load/unload mechanism) are similar across quiet stance stooping, and crouching. Changes in ML control strategies over time suggests that fatigue could affect prolonged stooping more so than crouching or standing.

Measurement of peak impact loads differ between accelerometers – Effects of system operating range and sampling rate

A wide variety of accelerometer systems, with differing sensor characteristics, are used to detect impact loading during physical activities. The study examined the effects of system characteristics on measured peak impact loading during a variety of activities by comparing outputs from three separate accelerometer systems, and by assessing the influence of simulated reductions in operating range and sampling rate. Twelve healthy young adults performed seven tasks (vertical jump, box drop, heel drop, and bilateral single leg and lateral jumps) while simultaneously wearing three tri-axial accelerometers including a criterion standard laboratory-grade unit (Endevco 7267A) and two systems primarily used for activity-monitoring (ActiGraph GT3X+, GCDC X6-2mini). Peak acceleration (gmax) was compared across accelerometers, and errors resulting from down-sampling (from 640 to 100Hz) and range-limiting (to ±6g) the criterion standard output were characterized. The Actigraph activity-monitoring accelerometer underestimated gmax by an average of 30.2%; underestimation by the X6-2mini was not significant. Underestimation error was greater for tasks with greater impact magnitudes. gmax was underestimated when the criterion standard signal was down-sampled (by an average of 11%), range limited (by 11%), and by combined down-sampling and range-limiting (by 18%). These effects explained 89% of the variance in gmax error for the Actigraph system. This study illustrates that both the type and intensity of activity should be considered when selecting an accelerometer for characterizing impact events. In addition, caution may be warranted when comparing impact magnitudes from studies that use different accelerometers, and when comparing accelerometer outputs to osteogenic impact thresholds proposed in literature.

The Influence of Body Mass Index, Sex, & Muscle Activation on Pressure Distribution During Lateral Falls on the Hip

Hip fracture incidence rates are influenced by body mass index (BMI) and sex, likely through mechanistic pathways that influence dynamics of the pelvis-femur system during fall-related impacts. The goal of this study was to extend our understanding of these impact dynamics by investigating the effects of BMI, sex, and local muscle activation on pressure distribution over the hip region during lateral impacts. Twenty participants underwent “pelvis-release experiments” (which simulate a lateral fall onto the hip), including muscle-‘relaxed’ and ‘contracted’ trials. Males and low-BMI individuals exhibited 44 and 55% greater peak pressure, as well as 66 and 56% lower peripheral hip force, compared to females and high-BMI individuals, respectively. Local muscle activation increased peak force by 10%, contact area by 17%, and peripheral hip force by 11% compared to relaxed trials. In summary, males and low-BMI individuals exhibited more concentrated loading over the greater trochanter. Muscle activation increased peak force, but this force was distributed over a larger area, preventing increased localized loading over the greater trochanter. These findings suggest potential value in incorporating sex, gender, and muscle activation-specific force distributions as inputs into computational tissue-level models, and have implications for the design of personalized protective devices including wearable hip protectors.

Pelvis and femur geometry: Relationships with impact characteristics during sideways falls on the hip

While metrics of pelvis and femur geometry have been demonstrated to influence hip fracture risk, attempts at linking geometry to underlying mechanisms have focused on fracture strength. We investigated the potential effects of femur and pelvis geometry on applied loads during lateral falls on the hip. Fifteen female volunteers underwent DXA imaging to characterize two pelvis and six femur geometric features. Additionally, participants completed low-energy sideways falls on the hip; peak impact force and pressure, contact area, and moment of force applied to the proximal femur were extracted. No geometric feature was significantly associated with peak impact force. Peak moment of force was significantly associated with femur moment arm (pu202f=u202f0.005). Peak pressure was positively correlated with pelvis width and femur moment arm (pu202f<u202f0.05), while contact area was negatively correlated with metrics of pelvis width and femur neck length (pu202f<u202f0.05). This is the first study to link experimental measures of impact loads during sideways falls with image-based skeletal geometry from human volunteers. The results suggest that while skeletal geometry has limited effects on overall peak impact force during sideways falls, it does influence how impact loads are distributed at the skin surface, in addition to the bending moment applied to the proximal femur. These findings have implications for the design of protective interventions (e.g. wearable hip protectors), and for models of fall-related lateral impacts that could incorporate the relationships between skeletal geometry, external load magnitude/distribution, and tissue-level femur loads.

Standing Versus Stepping - Exploring the Relationships Between Postural Steadiness and Dynamic Reactive Balance Control

While the literature has characterized balance control during quasi-static and/or dynamic tasks, comparatively few studies have examined relationships across paradigms. This study investigated whether quiet-stance postural steadiness metrics were associated with reactive control parameters (during both stepping and restabilisation phases) following a lean-and-release perturbation. Forty older adults participated. Postural steadiness (centre of pressure range, root mean square, velocity, and frequency) was evaluated in feet together and tandem stance positions. During the reactive control trials, step length, step width, movement time and reaction time were measured, in addition to the postural steadiness variables measured during the restabilisation phase following the stepping response. Out of 64 comparisons, only ten moderate correlations were observed between postural steadiness and reactive spatio-temporal stepping parameters (p≤0.05, r=-.312 to -.534). However, postural steadiness metrics were associated with centre of pressure velocity and frequency during the restabilisation phase of the reactive control trials (p≤0.015, r= 0.383 to 775 for velocity; p≤0.014, r= 0.386 to 0.550 for frequency). Although some elements of quasi-static centre of pressure control demonstrated moderate associations with dynamic stepping responses, relationships were stronger for restabilisation phase dynamics after foot-contact. Future work should examine the potential association between restabilisation phase control and older adult fall-risk.