Biomechanics, Volume 1, Issue 1 (June 2021) – 13 articles

Background: Wearable technology is used by clinicians and researchers and play a critical role in biomechanical assessments and rehabilitation. Objective: The purpose of this research is to validate a soft robotic stretch (SRS) sensor embedded in a compression knee brace (smart knee brace) against a motion capture system focusing on knee joint kinematics. Methods: Sixteen participants donned the smart knee brace and completed three separate tasks: non-weight bearing knee flexion/extension, bodyweight air squats, and gait trials. Adjusted R² for goodness of fit (R²), root mean square error (RMSE), and mean absolute error (MAE) between the SRS sensor and motion capture kinematic data for all three tasks were assessed. Results: For knee flexion/extension: R² = 0.799, RMSE = 5.470, MAE = 4.560; for bodyweight air squats: R² = 0.957, RMSE = 8.127, MAE = 6.870; and for gait trials: R² = 0.565, RMSE = 9.190, MAE = 7.530 were observed. Conclusions: The smart knee brace demonstrated a higher goodness of fit and accuracy during weight-bearing air squats followed by non-weight bearing knee flexion/extension and a lower goodness of fit and accuracy during gait, which can be attributed to the SRS sensor position and orientation, rather than range of motion achieved in each task. Full article

Electromyography (EMG) is a research tool used in gait analysis, muscle coordination evaluation, clinical evaluation and sports techniques. Electromyography can provide an insight into neural adaptations, cross education effects, bilateral contraction deficiencies, and antagonist activity in exercise-related movements. While there are clear benefits to using EMG in exercise-related professions, accessibility, cost, and difficulty interpreting the data limit its use in strength and clinical settings. We propose a practical EMG assessment using the isometric squat to identify compensatory activation patterns and report early observations. Ten healthy participants were recruited. Participants performed a 2-min isometric handgrip protocol and an isometric squat protocol. The isometric handgrip was used to identify the expected EMG amplitude response solely due to fatigue. There was a significant increase in EMG amplitude after 2 min (p < 0.05), with the relative increase of 95% CI (1.4%; 27.4%). This indicates the relative increase in EMG amplitude expected if the only influence was fatigue in the 2-min protocol. In the isometric squat protocol, we identified a number of different muscle activation compensation strategies with relative EMG amplitude increases outside of this bandwidth. One subject demonstrated a quadricep compensation strategy with a 188% increase in activation, while reducing activation in both the hamstrings and lower back by 12%. Exercise professionals can use this information to design exercise programs specifically targeting the unloaded muscles during the isometric squat. Full article

Periacetabular osteotomy (PAO) is a common surgical treatment for developmental dysplasia of the hip. To obtain the optimal method of fixation during PAO, different screw fixation techniques have been proposed for stabilizing the acetabular fragment. This study assesses the biomechanical performance of two popular 3-screw fixation techniques: iliac (IS) and transverse (IT) configurations, through finite element simulations. Additionally, different 2-screw combinations are simulated to investigate the biomechanical significance of each screw of the fixation configurations. The study findings show that yield load of the pelvic bone subject to gait loading for IT configuration is on average 7% higher compared to that of the IS. Although the yield load of the IT is predicted to be slightly higher, no significant difference in bone stiffness and displacement of the acetabular fragment are found between two configurations. Simulation results, therefore, do not demonstrate a significant biomechanical advantage of the IT configuration over the IS. Furthermore, the biomechanical comparison between the 2-screw combinations of IS and IT fixations demonstrates that the most anterior screw in IS, located at the iliac crest, and the most medial screw in the IT are the most critical elements in providing sufficient stability and support for acetabular fragment. Full article

Margin of stability (MOS) is considered a measure of mechanical gait stability. Due to broad application of treadmills in gait assessment experiments, we aimed to determine if walking on a treadmill vs. overground would affect MOS during three speed-matched conditions. Eight healthy young participants walked on a treadmill and overground at Slow, Preferred, and Fast speed-matched conditions. The mean and variability (standard deviation) of the MOS in anterior-posterior and mediolateral directions at heel contact were calculated. Anterior-posterior and mediolateral mean MOS values decreased with increased speed for both overground and treadmill; although mediolateral mean MOS was always wider on the treadmill compared to overground. Due to lack of optic flow and different proprioceptive inputs during treadmill walking, subjects may employ strategies to increase their lateral stability on treadmill compared to overground. Anterior-posterior MOS variability increased with speed overground, while it did not change on treadmill, which might be due to the fixed speed of treadmill. Whereas, lateral variability on both treadmill and overground was U-shaped. Walking at preferred speed was less variable (may be interpreted as more stable) laterally, compared to fast and slow speeds. Caution should be given when interpreting MOS between modes and speeds of walking. As sagittal plane walking is functionally unstable, this raises the consideration as to the meaningfulness of using MOS as a global measure of gait stability in this direction. Full article

A force capacity evaluation for a given posture may provide better understanding of human motor abilities for applications in sport sciences, rehabilitation and ergonomics. From data on posture and maximum isometric joint torques, the upper-limb force feasible set of the hand was predicted by four models called force ellipsoid, scaled force ellipsoid, force polytope and scaled force polytope, which were compared with a measured force polytope. The volume, shape and force prediction errors were assessed. The scaled ellipsoid underestimated the maximal mean force, and the scaled polytope overestimated it. The scaled force ellipsoid underestimated the volume of the measured force distribution, whereas that of the scaled polytope was not significantly different from the measured distribution but exhibited larger variability. All the models characterized well the elongated shape of the measured force distribution. The angles between the main axes of the modelled ellipsoids and polytopes and that of the measured polytope were compared. The values ranged from 7.3° to 14.3°. Over the entire surface of the force ellipsoid, 39.7% of the points had prediction errors less than 50 N; 33.6% had errors between 50 and 100 N; and 26.8% had errors greater than 100 N. For the force polytope, the percentages were 56.2%, 28.3% and 15.4%, respectively. Full article

Side-step cutting is an action associated with non-contact anterior cruciate ligament (ACL) injury with a plethora of negative economical, health, and psychological implications. Although ACL injury risk factors are multifactorial, biomechanical and neuromuscular deficits which contribute to “high-risk” and aberrant movement patterns are linked to ACL injury risk due to increasing knee joint loads and potential ACL loading. Importantly, biomechanical and neuromuscular deficits are modifiable; thus, being able to profile and classify athletes as potentially “high-risk” of injury is a crucial process in ACL injury mitigation. The Cutting Movement Assessment Score (CMAS) is a recently validated field-based qualitative screening tool to identify athletes that display high-risk postures associated with increased non-contact ACL injury risk during side-step cutting. This article provides practitioners with a comprehensive and detailed overview regarding the rationale and implementation of the CMAS. Additionally, this review provides guidance on CMAS methodological procedures, CMAS operational definitions, and training recommendations to assist in the development of more effective non-contact ACL injury risk mitigation programmes. Full article

Background: Handheld dynamometers are used for diagnosis and rehabilitation at several pathologies. Grip force is essential for a person’s quality of life. Most dynamometers are not equipped with rehabilitation or training protocols, although the bibliography highlights this need. Objective: To compare the validity and reliability of Jamar and K-Force Grip dynamometers in patients with shoulder impingement syndrome and healthy people. Methods: Concurrent validity was assessed using known weights. Forty-four (44) patients and 69 healthy adults performed three maximum repetitions in random order with each hand, at each instrument. Reliability was evaluated using ICCs for each instrument separately, and between the two instruments. The differences between the two dynamometers were evaluated using repeated t-tests. Results: Concurrent validity of the two instruments did not reveal fix or proportional bias. Analyses for reliability yield high correlation coefficients for both groups with the lower one being between the two instruments r = 0.90, p < 0.05, (0.72–0.91) for the healthy group. T-tests showed that all participants had lower force values when using the K-Force Grip (p < 0.05). Conclusion: Both dynamometers were reliable in measuring hand grip strength for both groups. K-Force Grip was reliable and valid with respect to Jamar that was used as a benchmark. The different handle dimensions between the two dynamometers may be the reason for the different force values. Full article

To better understand the pathophysiology and functional outcomes of musculoskeletal and neuromotor pathologies, research is often conducted in mice models. As a key component of such research, metrics of movement, loading, symmetry, and stability all have to be assessed, ideally requiring the measurement of 3D ground reaction forces, which can be difficult. While the measurement of ground reaction forces (GRF) is well developed for humans, appropriate devices for mice remain rare or inadequate. Such devices need to combine high sensitivity with small dimensions, especially when the forces for each individual paw should be measured. As preparation for building such a device that can measure 3D GRF per paw in mice in an upcoming study, this systematic review of the literature identified 122 articles and 49 devices that measured the ground reaction forces for mice and other small animals. Based on a variety of criteria, such as sensitivity and resonance frequency, the miniaturisation of each device and/or its capability to measure the three components of the ground reaction forces in individual paws were judged. The devices were consequently classified; eight devices were classified as “can be adapted”, nine as “hard to be adapted”, and 24 as “cannot be adapted”. Full article

Bicuspid aortic valve (BAV) patients are usually excluded from transcatheter aortic valve implantation (TAVI) as this valve anatomy likely leads to oval expansion. This study presents a numerical study of TAVI using both self-expanding and balloon expandable transcatheter heart valve (THV) in bicuspid patients with severe stenosis. The simulation framework included a patient-specific anatomy of the aortic root, calcifications and BAV leaflets extracted from medical imaging analysis as well as a realistic crimping and deployment of the THV. Tissue stress analysis highlighted local maxima in the contact area between the inner aortic lumen and the THV stent frame. Flow analysis based on the smoothed particle hydrodynamics (SPH) technique displayed the area at risk of paravalvular leakage (PVL). These findings provide insights on the TAVI in BAV and thus represents a further step towards the use of in-silico for the virtual planning of TAVI, aiming at improving not only the efficacy of the implantation but also the exploration of borderline anatomy as the case of TAVI in BAVs. Full article

Simulating diaphyseal fracture healing via numerical models has been investigated for a long time. It is apparent from in vivo studies that metaphyseal fracture healing should follow similar biomechanical rules although the speed and healing pattern might differ. To investigate this hypothesis, a pre-existing, well-established diaphyseal fracture healing model was extended to study metaphyseal bone healing. Clinical data of distal radius fractures were compared to corresponding geometrically patient-specific fracture healing simulations. The numerical model, was able to predict a realistic fracture healing process in a wide variety of radius geometries. Endochondral and mainly intramembranous ossification was predicted in the fractured area without callus formation. The model, therefore, appears appropriate to study metaphyseal bone healing under differing mechanical conditions and metaphyseal fractures in different bones and fracture types. Nevertheless, the outlined model was conducted in a simplified rotational symmetric case. Further studies may extend the model to a three-dimensional representation to investigate complex fracture shapes. This will help to optimize clinical treatments of radial fractures, medical implant design and foster biomechanical research in metaphyseal fracture healing. Full article

Effects of barefoot and minimal footwear conditions on performance during jumping (i.e., jump displacement) are unclear with traditional group-level studies because of intra- and interindividual variability. We compared barefoot, minimal, and conventional athletic footwear conditions relative to countermovement vertical jump (CMVJ) performance and muscle activation using a single-subject approach. Fifteen men (1.8 ± 0.6 m; 84.5 ± 8.5 kg; 23.8 ± 2.3 y) performed three CMVJ trials in barefoot, minimal, and conventional footwear conditions while ground reaction forces (GRF) and electromyograms of eight lower extremity muscles were recorded. The Model Statistic procedure (α = 0.05) compared conditions for CMVJ displacement, net impulse, durations of unloading, eccentric, and concentric phases, and average muscle activation amplitudes during the phases. All variables were significantly altered by footwear (p < 0.05) in some participants, but no participant displayed a universal response to all variables with respect to the footwear conditions. Seven of 15 participants displayed different CMVJ displacements among footwear conditions. Additional characteristics should be evaluated to reveal unique individual traits who respond similarly to specific footwear conditions. Considerations for footwear selection when aiming for acute performance enhancement during CMVJ tests should not be determined according to only group analysis results. The current single-subject approach helps to explain why a consensus on the effects of barefoot, minimal, and conventional footwear conditions during the CMVJ remains elusive. Full article

The purpose of this study was to identify whether ten repetitions and three trials were necessary to achieve stability in peak reactive strength index (RSI) during the 10/5 repeated jumps test (RJT). Twenty-five males, from multiple sports, performed three trials of the RJT on an in-ground force plate, with 90 seconds’ rest between trials. Intraclass correlation coefficients (ICC = 0.916–0.986) and coefficients of variation (CV ≤ 14.5%) were considered acceptable for all variables. Repeated-measures analysis of variance and Freidman’s tests revealed large and significant differences (p ≤ 0.006, η² = 0.159–0.434, power ≥ 0.859) in ground contact time (GCT), jump height (JH), and subsequently RSI both between trials and repetitions. Pairwise comparisons revealed that repetitions 1–3 produced longer GCTs (p ≤ 0.05, d = 0.41–1.40), lower JHs (p ≤ 0.05, d = 0.31–0.56), and lower RSI values (p ≤ 0.05, d = 0.35–1.24). The shortest GCTs, greatest JHs and greater RSIs occurred between repetitions 7 and 10, with approximately 60% of peak RSIs occurring during these ranges. The sequential estimate technique revealed that seven repetitions were needed to attain stability in mean peak RSI. Non-significant (p = 0.554) and negligible differences (d ≤ 0.09) in the five best RSIs between trials were noted. One trial of the 10/5 RJT is sufficient to evaluate peak RSI in athletes and should reduce data collection time and fatigue. Full article