Biomechanics

Quantifying stair gait stability and plantar pressure in an aging community, with modifications to insoles and lighting

Introduction: Stair gait is an activity performed daily. Inherently falls during stair gait continue to be a concern especially for older adults 65 years +. Recently falls have become the most common cause of injury-related deaths in individuals over the age of 75 y.o. Stair descent falls account for 75% of stair falls and also present a greater injury severity. Poor shoes or insoles and lighting condition can contribute to an increased risk of falls during stair locomotion. Stability can be measured using the COM-BOS ‘stability margin’ relationship. Center of pressure (COP), another stability measure,can be calculated from a multi-axis force-plate system. As well, plantar pressure is an important indicator of gait pattern efficiency. Aim: To identify aspects of stair gait that increase the risk of falls. By measuring the COM-BOS ‘stability margin’, the COP and plantar pressure patterns of individuals during stair gait, while modifying insoles and lighting. Methods: Young and older adults will ascend and descend a 4 level staircase, with two imbedded AMTI-force platforms in varying lighting condition (low, normal). Participants will be fitted with standardized footwear with Medi-logic insoles placed under varying hardnesses of insoles. An Optotrak motion capture system will record 12 IRED markers placed on the individual to determine the COM trajectory and BOS of location. Hypothesis: Partipants should demonstrate a greater lateral displacement in the single support phase during dim lighting as opposed to normal lighting. The stability of older adults will be compromised with alteration to the insoles (soft and hard).


Listed In: Biomechanics, Gait, Other


Stress influences performance: Insights into designing high cognitive load rehab tasks

The objective of this study was to investigate the effect of induced stress on the performance of each task during high cognitive load situations(HCLS). We hypothesized that induced stress leads to performance decrements during HCLS. In this study, the HCLS included standing while completing a secondary task(wire maze). The wire maze was composed of a metal wire path(maze) and a single ring, held in one hand that was moved over the maze without contacting the maze itself. Stress was induced through a loud buzzer when the ring contacted the maze. Participants were asked to randomly stand 1)quietly, or while completing the wire maze 2)with or 3)without the buzzer. Trials were three-minute long. A sample of 18 healthy young participants, (24.76±3.56 years) were randomly recruited. Perceived stress was obtained after each trial. Regularity of ground-reaction-force (GRF) in anterior-posterior and medial-lateral directions as well as wire maze error (ring-to-path contact) were calculated as primary and secondary task performance. GRF was more irregular during quietly standing compared to HCLS with and without the buzzer in both the AP and ML directions(p=0.02, p=0.001, respectively in anterior-posterior,η^2=0.28)&(p=0.004, p<0.0001, respectively in medial-lateral, η^2=0.39). Perceived stress was significantly lower during quietly standing compared to HCLS with(p=0.001, η^2=0.45) and without buzzer(p=0.007) conditions. Overall, the hypothesis was supported partially; during the most stressful HCLS, the high level of perceived stress coincided with less wire maze errors(P<0.0001, d= 0.72). Identifying the strategies underlying task prioritization can help clinicians design appropriate interventions to challenge patients appropriately to improve performance during HCLS.
Listed In: Biomechanical Engineering, Biomechanics, Physical Therapy, Posturography


Gait biomechanics after total hip arthroplasty: using statistical parametric mapping to identify differences between various surgical approaches

Biomechanical studies have tried to assess the impact of the surgical approach on gait characteristics and recovery after total hip arthroplasty (THA). Some studies which used discrete analyses have shown that some surgical approaches provide better hip joint function after one year post-surgery, but several studies did not find any differences. The goal of this study was to compare hip biomechanics during gait using statistical parametric mapping (SPM) in patients who underwent THA with either a lateral (LAT), anterior (ANT), or posterior (POS) approach. Forty-five patients underwent unilateral THA with either a LAT, ANT, or approach, and were compared with 15 healthy controls (CTRL). All patients underwent biomechanical gait analysis approximately 9 months following surgery. Hip biomechanics were compared between groups throughout the entire gait cycle using a One-Way ANOVA SPM. Alpha was set to 0.05 and Bonferroni post hoc comparisons were completed. The POS group had a significantly lower hip flexion moment just prior to toe-off compared to the ANT and CTRL groups. The ANT group had significantly lower hip abduction moment for most of the stance phase compared to the LAT and CTRL groups. The POS group had a significantly lower hip abduction moment compared to the LAT and CTRL groups. These findings tend to contradict existing literature. Future studies should complete both pre- and post-operative assessments with a larger cohort in each group, as well as standardize the implants as much as possible to determine if observed differences are due to the approach and no other factors.
Listed In: Biomechanics, Orthopedic Research


An Investigation of Factors Affecting Dynamic Postural Stability in Collegiate Cross Country Runners

Injury could lead to impaired postural stability which is commonly assessed during return-to-sport rehabilitation. The Dynamic Postural Stability Index (DPSI) estimates variability in tri-axial ground reaction forces. DPSI is higher in injured runners and predicts performance in soccer players. DPSI has also been related to ankle range of motion (ROM) and strength in military personnel. PURPOSE: To explore relationship between previous injury, ankle ROM and strength with DPSI in collegiate runners. METHODS: Twenty-seven Division I collegiate cross country athletes (19.8±1.3 years) participated. Athletes jumped over a hurdle on to an AMTI force plate and landed on a single leg for DPSI estimation. Three trials were performed bilaterally. Ankle ROM was assessed via active dorsiflexion and gastrocnemius length measurement. Ankle and hip strength were measured using a handheld dynamometer. An independent samples t-test was used to compare DPSI between injured (IG – those injured in the past 3 years) and uninjured (UG) groups. Pearson’s correlation coefficients were determined between DPSI and other variables. RESULTS: No significant difference was found for DPSI on left (IG: 0.30±0.03 vs. UG: 0.32±0.04) and right (IG: 0.30± 0.03 vs. UG: 0.31±0.03) sides. There was a significant moderate negative correlation between dorsiflexion ROM and DPSI (right side r= -0.605, p= 0.001; left side r= -0.452, p= 0.001). There were no correlations between strength and DPSI except for right inversion strength and right DPSI (r= 0.446, p=0.020). CONCLUSION: DPSI seems to be influenced to a greater extent by ankle dorsiflexion than strength or previous injury in a collegiate runners.
Listed In: Biomechanics, Physical Therapy, Posturography, Sports Science


SOURCES OF ERROR WHEN MEASURING ACHILLES TENDON MECHANICS DURING RUNNING ACTIVITIES

Accurate measurements of tendon mechanics are necessary for biomechanists when trying to identify injury risk factors, optimise athletic performance and develop musculoskeletal models. Measuring Achilles tendon (AT) mechanics dynamically is now possible by combining motion capture and ultrasound (US). The aim of this study was to quantify sources of error when measuring AT length using motion capture and US, and establish their effect on calculated strain values. Errors in AT insertion tracking and data synchronisation caused differences in AT length and moment arm of 5.3 ± 1.1 mm and 11.2 ± 0.9 mm, respectively; this decreased calculated AT peak strain from 11.6 ± 3.5% to 5.4 ± 2.5%. These differences could significantly impact a researcher‘s interpretation of the effects of footwear, technique, and specific kinematics on AT loading.
Listed In: Biomechanics, Sports Science


Identifying key movements contributing to ground reaction forces in sports

Body-worn sensors are commonly used for field-based movement and load measurements to asses injury risks in sports. To further explore the feasibility of using accelerometers for assessing whole-body biomechanical loading, this study used principal component analysis (PCA) to identify important movements and their contribution to the ground reaction force (GRF) for tasks that are frequently performed during running-based sports. Fifteen team-sport athletes performed accelerated, decelerated and constant low- (2-3 m/s), moderate- (4-5 m/s) and high-speed (>6 m/s) running, and 90° cutting trials, while full-body kinematics and GRF data were collected with a three-dimensional motion capture system and force platform respectively. A PCA was performed on the combined marker trajectory matrices for each task to identify task-specific principal movements (PMs). Resultant principal ground reaction forces (PGRFs) were calculated from each PM and assessed by the root mean square error (RMSE) of the summed PGRFs (∑PGRF). Across tasks, PM1 primarily described anteroposterior body movements, but PGRF1 errors were very high (>4 N/kg). Vertical body compression was the dominant contributor to the overall GRF and was described by PM3 (cutting), PM2 (low-speed) or PM5 (moderate- and high-speed), but less important for accelerated (PM10) and decelerated running (PM7). These results demonstrate that fundamental movement features contributing to GRF profiles are task-specific, making generalised evaluations of GRF features across different activities using predefined movements (e.g. segment accelerations) is difficult. Future research should investigate if PMs and PGRFs can also be related to structure-specific measures of biomechanical load (e.g. joint moments).
Listed In: Biomechanics, Sports Science


Standing steadiness and variability of older adults on a step ladder

MOTIVATION: Ladder fall injury rates are highest among older adults. While standing stability has been quantified using center of pressure (COP) to classify general fall risk of older adults, it has not been applied to older adults’ balance and performance on ladders. This study investigates the standing stability of older adults while performing a task on a ladder. METHODS: One-hundred four older adults completed the Physiological Profile Assessment (PPA) to classify fall risk and climbed to the second step of a household step ladder to change a light bulb. Force plates under the step ladder were used to calculate the COP. COP parameters were extracted to assess stability on the step ladder including path length (time-normalized), RMS and elliptical area. Task time and COP parameters were compared between 10 participants with the highest fall risk and 10 participants with the lowest fall risk based on the PPA. RESULTS: Task time was 8.4 seconds (63.9%) longer for the high fall risk group. Time-normalized path lengths were similar between the two groups. The high fall risk group showed an increase in RMS by 18.1% and elliptical area by 44.6%. CONCLUSIONS: Differences in tasks time, RMS and elliptical area were observed between low and high fall risk groups. Larger RMS values and elliptical area indicate more movement away from the average COP location. This suggests high fall risk older adults to be more variable than low fall risk older adults in their standing stability when completing a task on a step ladder.
Listed In: Biomechanical Engineering, Biomechanics, Posturography


The effect of a specific fatigue protocol in force propulsion and postural sway in female handball athletes

Fatigue is a case of interaction between different factors and is characterized by the increase in the perceived effort to exercise and produce force. However, the effect on balancing tasks are not completely understood, especially the time course of the postural sway parameters during the recovery phase. Twenty female handball athletes participated in this study. They stood upright in a one-leg posture supported by the non-dominant limb on a force plate. The center of pressure (COP) and the maximum propulsion force (FMAX) were obtained at baseline, immediately after the exhaustion due to the fatigue protocol and every minute during the first 10 min of the recovery phase. For the postural-sway measures, participants stood on the force plate for 30 s with eyes opened looking to a target. Based on the COP displacement, the ellipse area containing 95% of the COP data points (Area) was computed. The FMAX was measured during a countermovement jump. Specific handball actions composed the fatigue protocol in the format of a circuit with the gradual increment of laps. The force decreased ~9.5% after the fatigue protocol (p = 0.01) and returned to baseline values during the recovery phase at the fifth minute. For the postural sway, the Area decreased during the recovery phase until the fourth minute (p = 0.007). The fatigue protocol affected postural sway and force variables, which returned to baseline values after four minutes of the protocol. Therefore, we suggest that future fatigue analyses should be tested during this time window.
Listed In: Biomechanics, Posturography, Sports Science


Influence of Generalized Joint Laxity on Landing Ground Reaction Force in Ballet and Modern Dancers

Generalized joint laxity (GJL) is a condition in which most joints of the body move beyond the accepted normal range of motion. It allows for greater flexibility, which is beneficial to sports such as dance, but can lead to musculoskeletal injuries and decreases in strength. The ability to control landings with strength and stability is key to high level dance performance. Therefore, the purpose of this study was to evaluate differences in peak ground reaction force (GRF; vertical, medial-lateral, and anterior-posterior), during landing between dancers with and without GJL. Twenty healthy female volunteers with experience in ballet or modern dance were screened for GJL using the Beighton Scale. 10 subjects with GJL (score of 6 or higher) and 10 without GJL (score of 3 or below) were selected for testing. Subjects performed three forward, unshod, single-leg drop landings from a height of 40 cm onto a portable force plate (Bertec Corporation, OH, USA). Peak GRF for each landing was found and averaged for each subject, and for each group. No significant differences were found in peak GRF in any direction (p=0.71). We believe the similarity in peak forces between groups is due to dancers’ training and technique, as dancers are expected to control and soften their landings. GRF provides information about the load placed on the body, but lacks details related to landing technique. Further research describing 3D landing kinematics, joint moments, and muscle activation is required to determine if different landing techniques exist between dancers with and without GJL.
Listed In: Biomechanics


Flexion Angle Dependent Differences in Joint Kinematics and ACL Force In Response to Applied Loads Are Conserved Throughout Skeletal Growth in the Porcine Stifle Joint

The anterior cruciate ligament (ACL) stabilizes the lower limb against translational and rotational loads while the knee is is multiple postures. Surgical reconstruction, the most common treatment for ACL tears, is intended to replicate the biomechanical function of the native ACL in the postures and activities related to daily living and high-impact activities. In order to improve outcomes from ACL reconstructions in patients in pediatric and adolescent age groups, we need to improve our understanding of the knee posture dependent biomechanical function of the ACL. As such, the objective of this study was to quantify flexion angle dependent changes in the response of the ACL and the total knee to applied loads in the anterior-posterior and varus-valgus directions using a skeletally immature porcine model. To do this, we collected stifle (knee) joints from female Yorkshire-cross pigs at ages ranging from 1.5 to 18 months (n=30 total). The joints were tested using a 6 degree-of-freedom universal force sensing robotic system under applied anterior-posterior loads and varus-valgus moments at 40° and 60° of flexion. Studied parameters included anterior-posterior tibial translation (APTT), varus-valgus rotation (VVR), and anterior force carried by the ACL and its anteromedial and posterolateral bundles. We found increased knee laxity (APTT and VVR) was associated with both younger age and increased knee flexion. Greater anterior force carried in the ACL, and specifically in the anteromedial bundle, was associated with increased flexion, regardless of age. These findings have implications in intraoperative graft assessment and biomechanical models.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science