Joint loads and muscle force distribution during classical and jazz pirouettes

Purpose: The objective of this study was to analyze the muscle force distribution and lower limb joint loading during two types of pirouettes and check which muscle in which pirouette generates the highest force and which joint is the most loaded. Methods: Skilled dancers (n = 16) performed single-turn pirouettes in jazz and classic styles. Kinematic and kinetic data were collected using the Vicon system and Kistler plates. The joint reaction forces and muscle forces were calculated using a musculoskeletal model in the AnyBody Modeling System. Results: No statistically significant differences were found for the duration of the turn in both pirouettes. The range of motion in all joints of supporting leg in sagittal plane and in hip joint in frontal plane for non-supporting leg were significantly higher in classic pirouette. The ankle joint was the most loaded joint in both pirouettes and its maximal value was significantly higher in classic pirouette. The force generated by ankle plantar flexors muscles was significantly greater in the jazz pirouette in turn phase. For the nonsupport limb, external hip rotators generated significantly greater force when performing the classic pirouette. Conclusions: It seems that early stage dancers may start their lessons with jazz pirouettes, where necessary joint mobility is lesser. They also are supposed to increase muscle strength and body awareness with such proceedings. A better awareness of the mechanical loads on the musculoskeletal system which a dancer performing pirouettes faces should have an impact on the way dance classes are conducted and choreographic elements are sequenced.

Differentiating fallers from nonfallers using nonlinear variability analyses of data from a low-cost portable footswitch device: a feasibility study

Purpose: Falls are one of the main causes of injuries in older adults. This study evaluated a low-cost footswitch device that was designed to measure gait variability and investigates whether there are any relationships between variability metrics and clinical balance tests for individuals with a history of previous falls. Methods: Sixteen older adults completed a history of falls questionnaire, three functional tests related to fall risk, and walked on a treadmill with the footswitch device. We extracted the stride times from the device and applied two nonlinear variability analyses: coefficient of variation and detrended fluctuation analysis. Results: The temporal variables and variability metrics from the footswitch device correlated with gold-standard measurements based on ground reaction force data. One variability metric (detrended fluctuation analysis) showed a significant relationship with the presence of past falls with a sensitivity of 43%. Conclusion: This feasibility study demonstrates the basis for using low-cost footswitch devices to predict fall risk.

Lower extremity stiffness in habitual forefoot strikers during running on different overground surfaces

Purpose: Sports surface is one of the known external factors affecting running performance and injury. To date, we have found no study that examined the lower extremity stiffness in habitual forefoot strikers running on different overground surfaces. Therefore, the objective of this study was to investigate lower extremity stiffness and relevant kinematic adjustments in habitual forefoot strikers while running on different surfaces. Methods: Thirty-one male habitual forefoot strikers were recruited in this study. Runners were instructed to run at a speed of 3.3 m/s (±5%) on three surfaces, named synthetic rubber, concrete, and artificial grass. Results: No significant differences were found in leg stiffness, vertical stiffness, and joint stiffness in the sagittal plane during running on the three surfaces (p > 0.05). Running on artificial grass exerted a greater displacement in knee joint angle than running on synthetic rubber (p = 0.002, 95% CI = 1.52–7.35 degrees) and concrete (p = 0.006, 95% CI = 1.04–7.25 degrees). In the sagittal plane, peak knee moment was lower on concrete than on artificial grass (p = 0.003, 95% CI = 0.11–0.58 Nm/kg), whereas peak ankle moment was lower on synthetic rubber than on concrete (p < 0.001, 95% CI = 0.03–0.07 Nm/kg) and on artificial grass (p < 0.001, 95% CI = 0.02–0.06 Nm/kg). Among the three surfaces, the maximal ground reaction forces on concrete were the lowest (p < 0.05). Conclusions: This study indicated that running surfaces cannot influence lower extremity stiffness in habitual forefoot strikers at current running speed. Kinematic adjustments of knee and ankle, as well as ground reaction forces, may contribute to maintaining similar lower extremity stiffness.

Evaluation of brain injury criteria based on reliability analysis

Purpose: Among the proposed brain injury metrics, Brain Injury Criteria (BrIC) is a promising tool for performing safety assessment of vehicles in the future. In this paper, the available risk curves of BrIC were re-evaluated with the use of reliability analysis and new risk curves were constructed for different injury types based on literature data of tissue-level tolerances. Moreover, the comparison of different injury metrics and their corresponding risk curves were performed. Methods: Tissue-level uncertainties of the effect and resistance were considered by random variables. The variability of the tissue-level predictors was quantified by the finite element reconstruction of 100 frontal crash tests which were performed in Simulated Injury Monitor environment. The applied tests were scaled to given BrIC magnitudes and the injury probabilities were calculated by Monte Carlo simulations. New risk curves were fitted to the observed results using Weibull and Lognormal distribution functions. Results: The available risk curves of diffuse axonal injury (DAI) could be slightly improved, and combined AIS 4+ risk curves were obtained by considering subdural hematoma and contusion as well. The performance of several injury metrics and their risk curves were evaluated based on the observed correlations with the tissue-level predictors. Conclusions: The cumulative strain damage measure and the BrIC provide the highest correlation (R2 = 0.61) and the most reliable risk curve for the evaluation of DAI. Although the observed correlation is smaller for other injury types, the BrIC and the associated reliability analysis-based risk curves seem to provide the best available method for estimating the brain injury risk for frontal crash tests.

Stress relaxation of porcine tendon under simulated biological environment: experiment and modeling

Purpose: The aim of the study was to investigate the viscoelastic response in the low and high physiological strain with the use of experimental and modeling approach. Methods: Viscoelastic response in the low, transition and high physiologic strain (3, 6 and 9%) with consideration of simulated biological environment (0.9% saline solution, 37 °C) was measured in relaxation tests. Preconditioning of tendons was considered in the testing protocol and the applied range of load was obtained from tensile testing. The quasi-linear viscoelasticity theory was used to fit experimental data to obtain constants (moduli and times of relaxation), which can be used for description of the viscoelastic behavior of tendons. The exponential non-linear elastic representation of the stress response in ramp strain was also estimated. Results: Differences between stress relaxation process can be seen between tendons stretched to the physiological strain range (3%) and exceeding this range (6 and 9%). The strains of 6% and 9% showed a similar stress relaxation trend displaying relatively rapid relaxation for the first 70 seconds, whereas the lowest strain of 3% displayed relatively slow relaxation. Conclusions: Results of the model fitting showed that the quasi-linear viscoelastic model gives the best fit in the range of low physiological strain level.

Muscle co-contraction of ankle joint in young adults in functional reach test at different distances

Purpose: It has been reported that young people may be able to modulate simultaneous contraction depending on the task. The functional reach test (FRT) is widely used as a method to assess dynamic balance. Although there are several reports on the center of pressure (COP), there are few reports on muscle activity and no studies focus on muscle co-contraction during FRT at different distances. We aimed to clarify how the differences in reach distance affect the activity of the lower limb muscles by measuring COP and muscle activity during FRT at different distances. Methods: Eighteen healthy young adults performed FRT at different distances (maximum, 75%, and 50%) and measured COP and muscle activity of tibialis anterior (TA) and soleus (SOL). Postural control variables were calculated from the COP, and mean muscle activity and muscle co-contraction index (CI) were calculated from muscle activity. Each variable was compared between the reach distance conditions and the correlation between the variable was examined. Results: Most COP variables were significantly higher as the reach distance increased. A significant increase in muscle activity and CI was similarly observed with increasing distance. There was no consistent correlation between COP variables and CI, but there was a positive correlation between TA muscle activity and CI. Conclusions: The results of the present study showed that the young people used task-specific strategies by modulating lower limb muscle contraction and varying the degree of simultaneous muscle contraction during reaching movements at different distances.

Numerical insights into the determinants of stent performance for the management of aneurysm with a visceral vessel attached

Purpose: As the factors affecting the efficacy of the bare-metal stent in the treatment of aneurysm with a visceral vessel attached were not fully understood, we aimed to discuss the effects of different characteristics of the stent on the hemodynamics and flexibility in the treatment of the aneurysm. Methods: Single-layer (with different strut widths) and multi-layer (with a different number of struts) stent models divided into three porosity groups, with porosities of 72.3, 60.5, and 52.4%, were modeled for a comparison of their hemodynamic isolation and flexibility performance via computational fluid dynamics and finite element methods. Results: The velocity and timeaveraged wall shear stress decreased more noticeably with multi-layer stent interventions. A higher oscillatory shear index and relative residence time occurred at the aneurysmal sac wall after multi-layer stents were employed. Time-averaged wall shear stress on the aneurysmal wall decreased with an increase in the number of struts or a decrease in pore size, but oscillatory shear index and relative residence time increased as the number of struts increased or the pore size decreased. Besides, all stents affect the branch patency slightly. In the bending test, when the porosity exceeded 60.5%, multi-layer stents were more flexible. Conclusion: The number of struts or pore size of stent dominated the isolation in the management of the aneurysm and affected the flexibility significantly when the porosity was below 60.5%. These findings may contribute to the special design of the stent in the treatment of such types of aneurysms.

Application of closed kinematic chain exercises with eccentric and strength exercises for the shoulder injuries prevention in student rock climbers: a randomized controlled trial

Purpose: The aim of this work to determine the influence of a program containing exercises in a closed kinematic chain, eccentric and strength exercises on injuries of students – rock climbers. Methods: Participants in this study were 84 male amateur climbing students, aged 18–19, 40 athletes were in the intervention group and 44 in the control group. In the intervention group, the program for the injuries prevention has been stalled. The program included exercises that are performed in a closed kinematic chain in combination with exercises that are performed in eccentric mode and strength exercises. We determined the Incidence rate ratio and confidence intervals. The Incidence rate ratio was determined by the by Fisher exact test. Results: The significant influence of the developed program on the reduction of injuries among the athletes of the intervention group was revealed. Injury rate per 1000 AEs recorded of all shoulder injuries in the control group was 3.182, in the intervention group was 0.5, P < 0.001. The incidence rate ratio for mild shoulder injuries was 0.861 (0.737; 1.007). The incidence rate ratio for moderate shoulder injuries was 0.862 (0.751; 0.990; P = 0.039). The incidence rate ratio for severe shoulder injuries was 0.864 (0.768; 0.971; P = 0.017). Conclusions: The use of exercises in a closed kinematic chain and exercises in an eccentric mode reduces the Incidence rate ratio of shoulders among students – amateur climbers. The incidence rate ratio decreases in the intervention group for mild, moderate, and severe shoulder injuries.

The impact of obesity and age on the risk of falls in elderly women

Purpose: The aim of this study was to examine the effect of obesity and age on body balance disorders in women over 60, especially whether obesity increases the FR in older females and whether age and obesity affect the same stabilographic parameters when it comes to the FR. Methods: The study consisted of 56 inactive females aged 71.77 ± 7.43 (SD). They were divided into groups according to age and obesity. Results: Obesity separately affects FRI12-6, static indicators with eyes closed (OSI EC, APSI EC, MLSI EC), and age affects FRI12-6 and static indices with eyes open (OSI EO, APSI EO). After considering design factors (age and obesity), there were statistically significant differences in OSI EO (p = 0.027), APSI EO (p = 0.034), FRI12-6 (p = 0.0002) between obese and non-obese participants in the age groups. There were no statistical differences between non-obese old and obese-young participants (p = 0.863). The interaction between obesity and age in the FR in static indices and in FRI12-6 (p = 0.73047) was not significant. Conclusions: Age and obesity affect the stabilographic parameters individually, but there is no interaction effect between them. The presence of only one of the above risk factors may increase the FR. Obesity affects stability, while age depends on other factors. If older people are not obese or fit, involutional changes could be reversed. The type of obesity and the location of the fat tissue should be taken into account in FR assessment.

Assessment of myofascial stiffness of flexor digitorum superficialis muscles in rock climbers

Purpose: Myofascial stiffness is the biomechanical property that can be considered as a modifiable risk factor injury of athletes. Moreover, the level of muscle stiffness can be crucial to assessment muscle adaptation to exercise. However, stiffness of flexor muscles in rock climbers has never been investigated. The purpose of this study was to evaluate the myofascial stiffness of the flexor digitorum superficialis (FDS) in the rock climbers. Methods: The group of rock climbers (n = 16) has been compared to the non-climbers group (n = 16), matched in terms of anthropometric measures and an average level of physical fitness. Moreover, the impact of the one-time rock climbing training on FDS stiffness was assessed in the rock climbers group. The measurement of myotonometric myofascial stiffness of FDS muscles was performed, when the elbow was flexed and fully extended. In both positions, the measurements were taken with the hand open and closed. Results: It has been shown that rock climber’s FDS muscle stiffness before training was significantly higher (from 15 to 20%) compared to non-climbers group. Moreover, after climbing myofascial stiffness of FDS muscles increased significantly from 25 to 40%. Conclusions: Rock climbers have significantly higher stiffness of FDS muscles after rock climbing training. Moreover, the increased stiffness in the FDS differentiates rock climbers from the active and healthy control group. Results may indicate that decrease of muscle stiffness of FDS can be an important factor for the improvement of the climbing effectiveness and prevention of overload in the forearm flexor muscles and their recovery.