Levels Of Impact Loading Research Articles

Assessing the Muscle-Bone Unit in Girls Exposed to Different Amounts of Impact-Loading Physical Activity-A Cross-Sectional Association Study.

In children, an association exists between muscle and bone, as well as between physical activity and osteogenesis. Impact loading is a factor in increasing bone accrual during growth. In this work, we explored the muscle-bone association in girls exposed to long-term physical activity at different levels of impact loading. Four groups of girls aged 7-16 were considered. The curricular (C; n = 22) group only had curricular physical activity at school (2 h/w). In addition to curricular physical activity, the girls in the dance (D; n = 21), gymnastics at lower training (GL; n = 14), and gymnastics at higher training (GH; n = 20) groups had 2 h/w, 4 h/w, and 4 h/w < training ≤ 12 h/w additional physical activity, respectively, for at least one year. A visual analysis estimated the respective amounts of impact-loading activity. The bone mineral content (BMC), areal bone mineral density (aBMD), and fat-free soft tissue mass (FFSTM) were assessed with dual-energy X-ray absorptiometry. The results showed that, after adjusting for several confounders, statistically significant correlations were present between muscle mass and several bone mineral variables. A regression analysis confirmed the correlation in the data, and showed the marginal role of other body composition variables and physical activity for predicting BMC and BMD. Skeletal muscle mass is a major determinant of the BMC and BMD of the TBLH, as well as of the Appendicular level, in girls exposed to different amounts of long-term impact-loading physical activity.

Upper and lower limb impact loading during artistic gymnastics foundation floor tumbling skills

AbstractThe floor apparatus is associated with the highest rate of injury for male and female gymnasts in training and competition. This study aims to determine the magnitude of the upper and lower body impact loading when performing foundation floor tumbling skills and sequences. Fourteen sub‐elite artistic gymnasts (male, n = 9; female, n = 5) performed eight tumbling skills and sequences while wearing four inertial measurement units (IMU; upper back, lower back, forearm, and tibia). The peak resultant acceleration (PRA) during all ground contacts was calculated. The forearm and upper back PRA were analyzed for hand contacts, while the lower back and tibia PRA were analyzed for foot contacts. Descriptive statistics (median and inter‐quartile range), Wilcoxon signed‐rank tests and Friedman's ANOVA were calculated between IMU positions and gymnastics skills. Distal IMUs (forearm and tibia) recorded significantly higher loading than proximal IMUs (upper and lower back) for all ground contacts. Proximal IMUs experienced dampening due to shock attenuation properties of the human body, as these positions are located further away from the impact site. Additionally, some foundation skills exposed gymnasts to higher loading when the skill was performed separately, while other skills exposed gymnasts to higher loading when the skill was performed in a tumbling sequence. Training foundation skills separately and as a part of a tumbling sequence exposes the upper and lower body structures to high levels of impact loading. These results can be used by coaches to help in the design of safe training programs.

A method for quantifying impact loads from stone impact in mountain biking

High performance mountain bike frames nowadays are commonly built of carbon composites (CFRP), because of their excellent material properties allowing very high stiffness and strength at low weights. But this material has also disadvantages as it is sensitive to transversal impact loads. Impacts damage the material inside and can therefor affect the structural safety. As impact damages are often barely visible from the outside, they are very critical for structural parts like bike frames. A mountain bike frame suffers from different types of impacts like crashes and stone impacts. In order to evaluate the effect on structural integrity, the occurring impact energies have to be known. This paper describes a method for quantifying the impact load levels of stone impacts in order to evaluate the effect on the structural safety. Therefor the down tube of a mountain bike is shot using a high speed camera Casio Exilim EX FC 100 during biking. Impact events are identified in the videos and the impact energy is assessed, analyzing the stone geometry and its speed. Therefor a correlation between the two dimensional images of the stones and its mass was developed in an empiric approach. Using the above mentioned method, relevant impact energy levels and their frequency of occurrence are investigated.

Assessment of Residual Tensile Strength of Carbon/Epoxy Composites Subjected to Low-Energy Impact

This paper presents the results of an experimental study to investigate the effects of impact loading on the residual tensile strength of woven graphite epoxy laminates with a toughened resin system. In this study, both cross-ply, [0∕90]6, and angle-ply, [±45]6, laminate lay-up configurations were studied and compared. Test specimens were subjected to various levels of impact loading, after which tensile pull tests were performed to determine the residual tensile strength properties. The study results demonstrated that impact damage causes a significant reduction in tensile strength properties of woven cross-ply [0°/90°] laminates. For example, cross-ply laminated composite specimens subjected to the lowest impact level, 6.8J, exhibited a 25% decrease in ultimate tensile strength. Angle-ply woven laminates [±45°], however, exhibited an 18% increase in ultimate tensile strength after being subjected to 6.8(J) impact. This characteristic of increasing tensile strength in [±45°] specimens is an example of increased fiber reorientation in composite laminates with limited fiber damage.

Temporal Effects of Impact on Articular Cartilage Cell Death, Gene Expression, Matrix Biochemistry, and Biomechanics

Articular cartilage injury can cause post-traumatic osteoarthritis, but early processes leading to the disease are not well understood. The objective of this study was to characterize two levels of impact loading at 24 h, 1 week, and 4 weeks in terms of cell death, gene expression, extracellular matrix biochemistry, and tissue biomechanical properties. The data show cell death increased and tissue stiffness decreased by 24 h following High impact (2.8 J). These degradative changes persisted at 1 and 4 weeks, and were further accompanied by measurable changes in ECM biochemistry. Moreover, following High impact at 24 h there were specific changes in gene expression that distinguished injured tissue from adjacent tissue that was not loaded. In contrast, Low impact (1.1 J) showed little change from control specimens at 24 h or 1 week. However, at 4 weeks, a significant increase in cell death and significant decrease in tissue stiffness were present. The constellation of findings indicates Low impacted tissue exhibited a delayed biological response. The study characterizes a model system for examining the biology of articular cartilage post-impact, as well as identifies possible time points and success criteria to be used in future studies employing intervention agents.

Effects of doxycycline on articular cartilage GAG release and mechanical properties following impact

The effects of doxycycline were examined on articular cartilage glycosaminoglycan (GAG) release and biphasic mechanical properties following two levels of impact loading at 1 and 2 weeks post-injury. Further, treatment for two continuous weeks was compared to treatment for only the 1st week of a 2-week culture period. Following impact at two levels, articular cartilage explants were cultured for 1 or 2 weeks with 0, 50, or 100 microM doxycycline. Histology, GAG release to the media, and creep indentation biomechanical properties were examined. The "High" (2.8 J) impact level had gross surface damage, whereas "Low" (1.1 J) impact was indiscernible from non-impacted controls. GAG staining decreased after High impact, but doxycycline did not visibly affect staining. High impact resulted in decreased aggregate moduli at both 1 and 2 weeks and increased permeability at 2 weeks, but tissue mechanical properties were not affected by doxycycline treatment. At 1 week, High impact resulted in more GAG release compared to non-impacted controls. However, following High impact, 100 microM doxycycline reduced cumulative GAG release at 1 and 2 weeks by 30% and 38%, respectively, compared to no treatment. Interestingly, there was no difference in GAG release comparing 2 weeks continuous treatment with 1 week on, 1 week off. These results support the hypothesis that doxycycline can mitigate GAG release from articular cartilage following impact loads. However, doxycycline was unable to prevent the loss of tissue stiffness observed post-impact, presumably due to initial matrix damage resulting solely from mechanical trauma.

Rail wheel removal and its implication on track life: A fracture mechanics approach

Wheel/rail forces generated by wheel defects is known to be one of the contributing factors to track failure. Current strategy of removing wheels from service is dependent on the magnitude of the impact forces generated by these defects. These impact forces are estimated with wheel impact monitor established along a section of the railway track. This is also known as wayside monitoring. The impact load levels recorded by these monitors are recorded and the wheels that generate impact loads above a stated level (e.g. 400 kN) will be removed from service for maintenance. The question one poses is “What if the impact force generated by a given wheel is just below this level and stays at this level for extended period of time?” Will this, e.g. 380 kN, impact force do as much damage to the track as a 400 kN impact force if it is allowed in service? What are the implications of allowing a wheel that generate a seemingly acceptable level of 250 kN impact load to remain in service for extended period of time? In an attempt to answer these questions, a series of investigations were carried out to investigate the effect of impact loads on the propagation of a Vertical Split Head (VSH) defect found in the head of a 50 kg/m rail.

Articular Cartilage, Degenerative Process, and Repair: Current Progress

The aim of this paper is to review the current knowledge about degenerative and repair process of articular cartilage, and relationship between osteoarthritis and physical activities. Data Pubmed, ScienceDirect data base are interrogated for the period 1994 - 2003. Key words are: cartilage, osteoarthritis, exercise, rehabilitation. The mechanical biology of the cartilage and the chondrocytes, the effects of physical activity on the cartilage, the main studies on clinical trials on rehabilitation are reviewed. Chondrocyte and cartilage structure and function change with mechanical stresses. Mechanical loads can modulate cartilage matrix turnover. Joint injury increases the risk of osteoarthritis, and sports that subjects joints to repetitive high levels of impact loading increase the risk of injury and degeneration. In human, intensive physical exercises seem associated with osteoarthritis development. None of the current procedures for repairing articular cartilage restores a normal articular zone, however, selected procedures can predictably benefit selected subjects. This article presents the biology and discusses the alteration of cartilage as well as the osteoarthritis process which is not yet well understood. Current medical approaches to the treatment of osteoarthritis also are presented. Rehabilitation programme could be beneficial in the therapeutic management of osteoarthritis.

Shock Loading Effect on the MHz-Range Amplitude-Independent Internal Friction and Elastic Properties of the ??1 Martensite Phase in Cu-Al-Ni Alloys

The internal friction spectrum at 5 MHz in the martensite β' 1 -phase of CuAlNi alloys shows two prominent internal friction peaks at 270 and 170 K. Corresponding anomalies in the sound wave velocity-temperature dependence have been observed. Detailed analysis of the behaviour of the peaks in dependence on different levels of impact loading and γ-irradiation points to dislocation-point defect interaction. It is assumed that grain boundary dislocations are responsible for the 270 K peak while lattice dislocation, existing within the martensite variants are responsible for the 170 K peak.

Impact-fatigue behavior of composite tube/metal end fitting bonded joints

The relatively high specific strengths and moduli of advanced composite materials make them an attractive option for use in high speed industrial equipment. Hence, a potential market exists for integrating composites into existing machinery to replace critical metallic components. An application of such is the replacement of a high speed reciprocating steel bodymaker ram with one fabricated from a filament wound carbon fiber tube with bonded steel end fittings. Due to the dynamic forces which are inherent in the operation of high speed machinery, components are often subjected to impact, fatigue, and combined high cycle impact-fatigue. The behavior of composites as well as adhesives subjected to either impact or fatigue is well established. However, the combined impact-fatigue behavior of adhesive joints between filament wound carbon-fiber reinforced epoxy tubes and steel end fittings has not been investigated and is the focus of this study. An impact-fatigue testing machine was designed and fabricated specifically for these tests. The impact pulses generated by the machine closely resemble those of a conventional drop weight impact test machine. In addition, the impact-fatigue machine is capable of completing high cycle impact-fatigue tests (10 6 impacts) within a relatively short period of time by operating in excess of 10 impacts per second. Tests were performed at several impact load levels ranging from 15% to as much as 40% of the joint U ltimate S tatic C ompressive F ailure - L oad. These impact load levels were monitored throughout the specimen lifetime. Furthermore, three bondline thicknesses were investigated to attain an initial indication of the sensitivity to bondline thickness variation. Results indicate that the specimens exhibit an initial plateau region for a number of cycles during which time no decrease in load carrying capacity is measured. After a critical number of impacts, damage becomes apparent as the sample is no longer capable of maintaining the initial load. At this point, these constant-displacement tests show a load drop and a corresponding compliance change is noted as the sample begins to show less resistance to impact. Post-impact compression test results also show this drop in strength and modulus. Further, the percentage of the U ltimate S tatic - C ompressive - F ailure Load being applied dynamically determines the length of the plateau as well as the rate of degradation. Thus, the determination of the performance of composite tube/metal end fitting bonded joints using this impact-fatigue test approach gives information critical for lifetime design of dynamically loaded composite components.