Biomechanics, Volume 1, Issue 2 (September 2021) – 9 articles

The liver and kidneys are the most commonly injured organs due to traumatic impact forces applied to the abdomen and pose a challenge to physicians due to a hard-to-diagnose risk of internal bleeding. A better understanding of the mechanism of injury will improve diagnosis, treatment, forensics, and other fields. Finite element modelling is a tool that can aid in this understanding, but accurate material properties are required including the strain rate dependency and the feasibility of using animal tissue properties instead of human. The elastic modulus in a probing protocol and the elastic modulus, failure stress, and failure strain in a compression protocol were found for both liver and kidney tissue from human and porcine specimens at varying strain rates. Increases in the elastic modulus were seen for both the human kidney and liver, but only for the porcine kidney, when comparing the unconfined compression and probing protocols. A strain rate dependency was found for both the liver and kidney properties and was observed to have a larger saturation effect at higher rates for the failure stress than for the elastic modulus. Overall, the material properties of intact liver and kidney were characterized, and the strain rate dependency was numerically modelled. The study findings suggest that some kidney and liver material properties vary from human to porcine tissue. Therefore, it is not always appropriate to use material properties of porcine tissue in computational or physical models of the human liver and kidney. Full article

The human motor system is a complex neuro-musculo sensory system that needs further investigations of neuro-muscular commands and sensory-motor coupling to decode movement execution. Some researchers suggest that the central nervous system (CNS) activates a small set of modules termed muscle synergies to simplify motor control. Further, these modules form functional building blocks of movement as they can explain the neurophysiological characteristics of movements. We can identify and extract these muscle synergies from electromyographic signals (EMG) recorded in the laboratory by using linear decomposition algorithms, such as principal component analysis (PCA) and non-Negative Matrix Factorization Algorithm (NNMF). For the past three decades, the hypothesis of muscle synergies has received considerable attention as we attempt to understand and apply the concept of muscle synergies in clinical settings and rehabilitation. In this article, we first explore the concept of muscle synergies. We then present different strategies of adaptation in these synergies that the CNS employs to accomplish a movement goal. Full article

Background: The aim is to evaluate methods to quantify the interstitial splitting force and thermal load input of self-tapping and self-drilling osteosynthesis screws. Methods: A specialized modular test bench was developed to measure the induced splitting force of self-drilling and self-tapping osteosynthesis screws using porcine mandibular bone. In addition, a fundamentally new approach to measure the temperature near the contact zone of osteosynthesis screws (fiber-optic sensor in the axis of the screw) was established. Results: The self-drilling screw type induces a splitting force of about 200 N in the surrounding tissue, so that microdamage of the bone and increased resorption can be assumed. Even pre-drilling induces a short-time force into the tissue, which is comparable to the splitting force of the self-tapping screw. The temperature increase in the screw is clearly higher compared to the temperature increase in the surrounding tissue, but no significant difference in temperature between the two screw types could be measured. Based on the measured temperatures of both screw types, the temperature increase in the contact zone is considered critical. Complications during the screwing process caused by the manual tool guidance resulted in numerous breakages of the fiber-optic sensors. Conclusions: The developed methods provide additional insight regarding the thermomechanical load input of self-drilling and self-tapping screws. However, based upon the optical fiber breakages, additional refinement of this technique may still be required. Full article

Articular cartilage, as a hydrated soft tissue which covers diarthrodial joints, has a pivotal role in the musculoskeletal system. Osteoarthritis is the most common degenerative disease that affects most individuals over the age of 55. This disease affects the elasticity, lubrication mechanism, damping function, and energy absorption capability of articular cartilage. In order to investigate the effect of osteoarthritis on the performance of articular cartilage, the mechanical behavior of human knee articular cartilage was experimentally investigated. Progressive cyclic deformation was applied beyond the physiological range to facilitate degradation of the tissue. The relaxation response of the damaged tissue was modeled by means of a fractional-order nonlinear viscoelastic model in the framework of finite deformations. It is shown that the proposed fractional model well reproduces the tissue’s mechanical behavior using a low number of parameters. Alteration of the model parameters was also investigated throughout the progression of tissue damage. This helps predict the mechanical behavior of the osteoarthritic tissue based on the level of previous damage. It is concluded that, with progression of osteoarthritis, the articular cartilage loses its viscoelastic properties such as damping and energy absorption capacity. This is also accompanied by a loss of stiffness which deteriorates more rapidly than viscosity does throughout the evolution of tissue damage. These results are thought to be significant in better understanding the degradation of articular cartilage and the progression of OA, as well as in the design of artificial articular cartilages. Full article

While it is generally recognized that prolonged sitting periods at work can harm the locomotor system, little attention has been paid to the impact of sitting behavior on muscle stiffness. This study investigated the effect of sitting posture and postural activity on lower back muscle stiffness in a controlled experiment in which participants sat at a desk for 4.5 h. Lower back muscle stiffness was measured before and after the sitting period. In addition, continuous recording of kinematic data of the lower back using an eight-camera motion analysis system was applied to quantify sitting posture and the level of postural activity. The results show that the prolonged sitting period led to a significant increase in muscle stiffness. Further, all participants spent a substantial amount of time in a slumped sitting posture, and the level of postural activity varied significantly throughout the 4.5 h sitting period. Those results suggest that the increase in lumbar muscle stiffness is presumably related to the often-preferred slump sitting posture and may help to understand how prolonged sitting periods can increase susceptibility to common pathological conditions such as low back pain. However, the results also leave some uncertainties that need further investigation. Full article

Background: Occupational footwear and a prolonged duration of walking have been previously reported to play a role in maintaining postural stability. The purpose of this paper was to analyze the impact of three types of occupational footwear: the steel-toed work boot (ST), the tactical work boot (TB), and the low-top work shoe (LT) on previously unreported lower extremity muscle activity during postural stability tasks. Methods: Electromyography (EMG) muscle activity was measured from four lower extremity muscles (vastus medialis (VM), medial hamstrings (MH), tibialis anterior (TA), and medial gastrocnemius (MG) during maximal voluntary isometric contractions (MVIC) and during a sensory organization test (SOT) every 30 min over a 4 h simulated workload while wearing ST, TB, and LT footwear. The mean MVIC and the mean and percentage MVIC during each SOT condition from each muscle was analyzed individually using a repeated measures ANOVA at an alpha level of 0.05. Results: Significant differences (p < 0.05) were found for maximal exertions, but this was limited to only the time main effect. No significant differences existed for EMG measures during the SOT. Conclusion: The findings suggest that occupational footwear type does not influence lower extremity muscle activity during both MVIC and SOT. Significantly lower muscle activity during maximal exertions over the course of the 4 h workload was evident, which can be attributed to localized muscular fatigue, but this was not sufficient to impact muscle activity during postural stability tasks. Full article

There is a lack of evidence about the ways in which balance ability influences the kinematic and kinetic parameters and muscle activities during gait among healthy individuals. The hypothesis is that balance ability would be associated with the lower limb kinematics, kinetics and muscle activities during gait. Twenty-nine healthy volunteers (Age 32.8 ± 9.1; 18 males and 11 females) performed a Star Excursion Balance test to measure their dynamic balance and walked for at least three trials in order to obtain a good quality of data. A Vicon^® 3D motion capture system and AMTI^® force plates were used for the collection of the movement data. The selected muscle activities were recorded using Delsys^® Electromyography (EMG). The EMG activities were compared using the maximum values and root mean squared (RMS) values within the participants. The joint angle, moment, force and power were calculated using a Vicon Plug-in-Gait model. Descriptive analysis, correlation analysis and multivariate linear regression analysis were performed using SPSS version 23. In the muscle activities, positive linear correlations were found between the walking and balance test in all muscles, e.g., in the multifidus (RMS) (r = 0.800 p < 0.0001), vastus lateralis (RMS) (r = 0.639, p < 0.0001) and tibialis anterior (RMS) (r = 0.539, p < 0.0001). The regression analysis models showed that there was a strong association between balance ability (i.e., reaching distance) and the lower limb muscle activities (i.e., vastus medialis–RMS) (R = 0.885, p < 0.0001), and also between balance ability (i.e., reaching distance) and the lower limb kinematics and kinetics during gait (R = 0.906, p < 0.0001). In conclusion, the results showed that vastus medialis (RMS) muscle activity mainly contributes to balance ability, and that balance ability influences the lower limb kinetics and kinematics during gait. Full article

The drop jump (DJ) is commonly utilised to assess athletes. The criterion two force platform (2FP) method of assessing DJ performance involves two adjacent force platforms, one for the box and one for the athlete to rebound from. Most researchers and practitioners only have access to one force platform (1FP) and they rarely account for the often considerable discrepancy between box height and drop height (DH). Therefore, this study aimed to determine the criterion validity of evaluating DJ performance with 1FP. Twenty-six young male sports students performed three DJs, from a 0.30 m and 0.40 m high box, on two adjacent force platforms. The DH, touchdown velocity and several performance variables were calculated using the 2FP and 1FP methods. Ordinary least-products regression identified no fixed or proportional bias between methods for any DJ variable. The mean DH was 10% lower than the 0.30 m box and 14% lower than the 0.40 m high box. This discrepancy highlights the importance of accounting for DH when conducting DJ assessments. In conclusion, the 1FP method of evaluating DJ performance is a valid alternative to the criterion 2FP method and could be embedded into automated force analysis software for researchers and practitioners to utilise. Full article

Knowledge of the kinematics of young fencers is important when teaching fencing, but it has been minimally investigated in the literature, especially in young subjects, and further research is needed. Our aims were to assess whether anthropometric factors or kinematic factors are more closely related to lunge performance (speed and range of motion) in young fencers and to investigate gender differences in relation to kinematics. Fifteen fencers participated in this study (8 females and 7 males; age 12.9 ± 2.7 years, height 157.4 ± 15.1 cm, weight 49.7 ± 11.7 kg). Lunge kinematics and anthropometrics were collected with a 10-camera optoelectronic system. Descriptive statistics, bivariate correlation, t-test, and simple regression were performed. Peak lunge velocity was mainly correlated with posterior knee extension (r = 0.56, p = 0.031). The lunge distance and mean hip velocity were mostly correlated with the fencers’ height (r = 0.85, p = 0.000 and r = 0.76, p = 0.001) and fat-free mass (r = 0.79, p = 0.000 and r = 0.73, p = 0.002). Young fencers use a lower limb-driven strategy to perform the lunge, while adults are reported to use an upper limb-driven strategy for the lunge attack. Linear and angular velocities and ranges of motion were lower in young fencers in comparison to those of adults. Based on these results, we suggest a different approach to teaching the lunge action in young foil fencers. The implications of our study are that when teaching the lunge technique to this age group, a different approach for males and females is not required, and that strength is not a discriminant physical quality for the correctness of performance. Full article