The impact of obesity on skeletal muscle strength and structure through adolescence to old age.

Obesity is associated with functional limitations in muscle performance and increased likelihood of developing a functional disability such as mobility, strength, postural and dynamic balance limitations. The consensus is that obese individuals, regardless of age, have a greater absolute maximum muscle strength compared to non-obese persons, suggesting that increased adiposity acts as a chronic overload stimulus on the antigravity muscles (e.g., quadriceps and calf), thus increasing muscle size and strength. However, when maximum muscular strength is normalised to body mass, obese individuals appear weaker. This relative weakness may be caused by reduced mobility, neural adaptations and changes in muscle morphology. Discrepancies in the literature remain for maximal strength normalised to muscle mass (muscle quality) and can potentially be explained through accounting for the measurement protocol contributing to muscle strength capacity that need to be explored in more depth such as antagonist muscle co-activation, muscle architecture, a criterion valid measurement of muscle size and an accurate measurement of physical activity levels. Current evidence demonstrating the effect of obesity on muscle quality is limited. These factors not being recorded in some of the existing literature suggest a potential underestimation of muscle force either in terms of absolute force production or relative to muscle mass; thus the true effect of obesity upon skeletal muscle size, structure and function, including any interactions with ageing effects, remains to be elucidated

Combined effects of body composition and ageing on joint torque, muscle activation and co-contraction in sedentary women

This study aimed to establish the interplay between body mass, adiposity, ageing and determinants of skeletal muscle strength. One hundred and two untrained healthy women categorised by age into young (Y) (mean ± SD, 26.7 ± 9.4 years) vs. old (O) (65.1 ± 7.2 years) were assessed for body fat, lean mass, plantar flexion and dorsiflexion maximum voluntary isometric contraction (MVC) torque, muscle activation capacity and antagonist muscle co-contraction. MVC torque normalised to body mass in the obese group was 35 and 29 % lower (p < 0.05) in Y and 34 and 31 % lower (p < 0.05) in O, compared with underweight and normal weight individuals, respectively. Y with ≥40 % body fat had significantly lower activation than Y with <40 % body fat (88.3 vs. 94.4 %, p < 0.05), but O did not exhibit this effect. Co-contraction was affected by ageing (16.1 % in O vs. 13.8 % in Y, p < 0.05) but not body composition. There were significant associations between markers of body composition, age, strength and activation capacity, with the strongest correlation between muscle strength and total body mass (r = 0.508 in Y, p < 0.001, vs. r = 0.204 in O, p < 0.01). Furthermore, the age-related loss in plantar flexion (PF) MVC torque was exacerbated in obese compared to underweight, normal weight and overweight individuals (-0.96 vs. -0.54, -0.57 and -0.57 % per year, p < 0.05). The negative impact of adiposity on muscle performance is associated with not only muscular but also neural factors. Overall, the effects of ageing and obesity on this system are somewhat cumulative. © 2014 The Author(s)

Finite element model to simulate impact on a soft tissue simulant

A finite element model of an impact test on a soft tissue simulant, used as part of a shoulder surrogate, was developed in Ansys© LS-DYNA®. The surrogate consisted of a metal hemicylindrical core, with a diameter of 75 mm, covered with a 15 mm thick relaxed muscle simulant. The muscle simulant consisted of a 14 mm thick layer of silicone covered with 1 mm thick chamois leather to represent skin. The material properties of the silicone were obtained via quasi-static compression testing (curve fit with hyperelastic models) and compressive stress relaxation testing (curve fit with a Prony series). Outputs of the finite element models were compared against experimental data from impact tests on the shoulder surrogate at energies of 4.9, 9.8 and 14.7 J. The accuracy of the finite element models was assessed using four parameters: peak impact force, maximum deformation, impact duration and impulse. A 5-parameter Mooney-Rivlin material model combined with a 2-term Prony series was found to be suitable for modelling the soft tissue simulant of the shoulder surrogate. This model had under 10% overall mean deviation from the experimental values for the four assessment parameters across the three impact energies. Overall, the model provided a repeatable test method that can be adapted to help predict injuries to skin tissue and the performance/efficacy of personal protective equipment

Muscle damage following maximal eccentric knee extensions in males and females

Aim To investigate whether there is a sex difference in exercise induced muscle damage. Materials and Method Vastus Lateralis and patella tendon properties were measured in males and females using ultrasonography. During maximal voluntary eccentric knee extensions (12 reps x 6 sets), Vastus Lateralis fascicle lengthening and maximal voluntary eccentric knee extensions torque were recorded every 10° of knee joint angle (20–90°). Isometric torque, Creatine Kinase and muscle soreness were measured pre, post, 48, 96 and 168 hours post damage as markers of exercise induced muscle damage. Results Patella tendon stiffness and Vastus Lateralis fascicle lengthening were significantly higher in males compared to females (p0.05). Creatine Kinase levels post exercise induced muscle damage were higher in males compared to females (p<0.05), and remained higher when maximal voluntary eccentric knee extension torque, relative to estimated quadriceps anatomical cross sectional area, was taken as a covariate (p<0.05). Conclusion Based on isometric torque loss, there is no sex difference in exercise induced muscle damage. The higher Creatine Kinase in males could not be explained by differences in maximal voluntary eccentric knee extension torque, Vastus Lateralis fascicle lengthening and patella tendon stiffness. Further research is required to understand the significant sex differences in Creatine Kinase levels following exercise induced muscle damage

A study of low cycle fatigue life and its correlation with microstructural parameters in IN713C nickel based superalloy

Up to date, IN713C Nickel-based superalloy has been continued to be the best alloy candidate for turbocharger wheel applications due to its adequate fatigue property and resistance to degradation under harsh operating environments. Throughout this study, three different batches of as-cast IN713C nickel based superalloys with different microstructures including columnar, equiaxed and transition microstructures were investigated. Strain control Low Cycle fatigue (LCF) tests were conducted for the three different microstructures, achieving fatigue life between 100 and runout at 100,000 cycles, depending on the testing parameters. The fracture mechanics and failure mechanism were correlated to the alloy's microstructure, texture and chemical composition under various LCF conditions using optical microscopy, SEM, EDX and EBSD. In the current study an exact correlation between alloy's microstructure/microtexture and LCF endurance is established. The results showed that equiaxed microstructure has a superior fatigue life than the transition microstructure by 10% and columnar microstructure by > 200% at a given temperature and strain rate. This large discrepancy was mainly due to the grain size differences between the studied microstructures. Here, it was evidenced that the grain size controls the dendrites length. It is also demonstrated that all microstructures exhibited a longer fatigue life at room temperature than at 650 °C, doubling or tripling the fatigue life of the tested IN713C. Furthermore, the high presence of precipitates between dendritic arms in all three microstructures was found to have great influence on crack propagation path. It was apparent that segregated carbides in between dendritic arms caused secondary crack initiation and crack path undulations during the LCF tests

Gender associated muscle-tendon adaptations to resistance training

© 2018 McMahon et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Purpose To compare the relative changes in muscle-tendon complex (MTC) properties following high load resistance training (RT) in young males and females, and determine any link with circulating TGFβ-1 and IGF-I levels. Methods Twenty-eight participants were assigned to a training group and subdivided by sex (T males [TM] aged 20±1 year, n = 8, T females [TF] aged 19±3 year, n = 8), whilst age-matched 6 males and 6 females were assigned to control groups (ConM/F). The training groups completed 8 weeks of resistance training (RT). MTC properties (Vastus Lateralis, VL) physiological cross-sectional area (pCSA), quadriceps torque, patella tendon stiffness [K], Young’s modulus, volume, cross-sectional area, and length, circulating levels of TGFβ-1 and IGF-I were assessed at baseline and post RT. Results Post RT, there was a significant increase in the mechanical and morphological properties of the MTC in both training groups, compared to ConM/F (p0.05) in IGF-I or TGFβ-1. Interestingly, pooled population data showed that TGFβ-1 correlated with K at baseline, with no correlations identified between IGF-I and MTC properties. Conclusions Greater resting TGFβ-1 levels are associated with superior tendon mechanical properties. RT can impact opposite ends of the patella tendon force-elongation relationship in each sex. Thus, different loading patterns may be needed to maximize resistance training adaptations in each sex

The effects of microstructure and microtexture generated during solidification on deformation micromechanism in IN713C nickel-based superalloy

Nickel-based superalloy IN713C produced through investment casting route is widely used for turbocharger turbine wheels in the automotive industry. The produced microstructure and microtexture are not homogeneous across the turbine component due to geometrical factors and localised cooling rate during the casting process, which give rise to inhomogeneous deformation during service. In the present paper, two kinds of in-house fatigue tests, Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF), were conducted at 600 °C in attempt to simulate the actual fatigue conditions experienced by turbine wheels in turbocharger. From Geometrically Necessary Dislocation (GND) distributions and strain analyses, it is concluded that microstructure heterogeneity such as carbide precipitates distribution within dendritic structure network determine the failure micromechanics during LCF tests. In the early stage of LCF loading, crack principally initiated within near surface carbides that have been oxidised during high temperature exposure. The higher GND density at the tip of carbide precipitates due to oxidation volume expansion are found to facilitate easy cracks initiation and propagation. Moreover, the cluster-like carbides network and its distribution can accelerate oxidation process and crack growth effectively. Furthermore, in the later stage of crack propagation during LCF, the weak interdendrite areas rotate to accommodate increased strain leading to faster cracks propagation and hence final catastrophic failure. Serial section technique for 3-D visualisation was employed to investigate the crystallographic grain orientation correlation with fracture mechanics during HCF loading. It appears that the microtexure and grain orientations are more critical than the alloy microstructure in an area with a relatively uniform carbides distribution and weak dendrite structure where HCF failure occurred. Based on the slip trace analysis, it was found that most faceting occurred in Goss grains (//LD) and on slip system with the highest Schmid factor. It is concluded that cracks were initiated on planes with high Schmid factors and assisted by the presence of porosity

Repeatability of a bending stiffness test for snowboarding wrist protectors

Snowboarding wrist protectors are typically designed to limit impact forces and prevent wrist hyperextension. The standard for snowboarding wrist protectors (ISO 20320:2020) includes a test for measuring their bending stiffness, when fitted to a wrist surrogate. This test serves as a simple means of assessing the ability of wrist protectors to prevent wrist hyperextension. Wrist protector bending stiffness measurements have been shown to be influenced by surrogate design, protector strapping condition, and surrogate surface compliance. Currently, there is a lack of knowledge on the repeatability of bending stiffness measurements, as previous studies have conducted tests during one session. This study investigated the repeatability of a bending stiffness test, by testing two snowboarding wrist protectors (short and long) on two wrist surrogates (compliant and stiff), under three protector strapping conditions (loose, moderate, tight), across three repeated test sessions. Test session had a significant effect (p 0.14), indicating the test had limited repeatability between test sessions. Despite this limited repeatability, torque values increased with both wrist angle and strap tightness, as reported before, indicating consistent trends in results. The outer surface compliance of the surrogate did not significantly affect the protector’s sensitivity to test session nor strapping condition

Review of Modelling and Additive Manufacturing of Auxetic Materials for Application in Sport, 8th Asia-Pacific Congress on Sports Technology

The unconventional way that auxetic materials behave can result in advantageous mechanical properties, which could be made use of in applications such as protective equipment and clothing in sport. Much of the work to date demonstrates advantageous properties of auxetic materials well, but their application in sport is underdeveloped. This review paper demonstrates how modelling has helped develop auxetics research, highlighting how further work in this area could contribute to improved implementation of auxetics within sport. Additive manufacturing as a production technology for auxetic structures is also considered and discussed. Future work could look at creating a systematic finite element modelling process to design, optimise and apply auxetic structures for use in sports protective equipment

Achilles tendon moment arm in humans is not affected by inversion/eversion of the foot: a short report

The triceps surae primarily acts as plantarflexor of the ankle joint. However, the group also causes inversion and eversion at the subtalar joint. Despite this, the Achilles tendon moment arm is generally measured without considering the potential influence of inversion/eversion of the foot during plantarflexion. This study investigated the effect of foot inversion and eversion on the plantarflexion Achilles tendon moment arm. Achilles tendon moment arms were determined using the centre-of-rotation method in MR images of the left ankle of 11 participants. The foot was positioned at 15° dorsiflexion, 0° or 15° plantarflexion using a Styrofoam wedge. In each of these positions the foot was either 10° inverted, neutral or 10° everted using an additional Styrofoam wedge. Achilles tendon moment arm in neutral foot position was 47.93 ± 4.54 mm and did not differ significantly when the foot was positioned in 10° inversion and 10° eversion. Hence, inversion/eversion position of the foot may not considerably affect the length of the Achilles tendon moment arm. This information could be useful in musculoskeletal models of the human lower leg and foot and when estimating Achilles tendon forces during plantarflexion with the foot positioned in inversion or eversion