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Purpose Physical and hormonal changes during pregnancy are thought to affect balance and injury risk, with increased numbers of falls being reported. A maternity support belt (MSB) has been suggested to stabilize the pelvis and to enhance balance. The purpose of this study was therefore to investigate the effect of an MSB on postural stability in different trimesters of pregnancy. Methods Postural stability was assessed in the first (T1, n = 30), second (T2, n = 30) and third trimester (T3, n = 30) of pregnancy and compared to non-pregnant controls (n = 30), using a portable force plate. Postural sway during quiescent standing with and without applying an MSB was characterized by analyzing path length, velocity, amplitudes and area. Subsequently, anterior and posterior limits of stability (LoS) were determined. Results Postural sway during quiescent standing did not change with pregnancy. However, LoS performance was reduced already in T1, before body mass significantly increased. The MSB led to a small improvement in the LoS while slightly increasing postural sway in anterior-posterior direction and shifting the center of pressure posteriorly during quiescent standing. Conclusion While impairments in balance already occurred early in pregnancy before body mass significantly increased, they were subtle and only measurable in exacerbated conditions. This challenges the assumed necessity of balance enhancing interventions in pregnant women. Although the MSB significantly affected body posture, the magnitude of the LoS improvement using the MSB was very small. Thus, it remains debatable if the MSB is a meaningful tool to increase balance during pregnancy.

The assessment of muscle architecture with B-mode ultrasound is an established method in muscle physiology and mechanics. There are several manual, semi-automated and automated approaches available for muscle architecture analysis from ultrasound images or videos. However, most approaches have limitations such as workload, subjectivity, drift or they are applicable to short muscle fascicles only. Addressing these issues, an algorithm was developed to analyse architectural parameters of the vastus lateralis muscle (VL). In 17 healthy young men and women, ultrasound images were taken five times on two different days during passive knee joint flexion. From the images, fascicle length (FL), pennation angle (PAN) and muscle thickness (MTH) were calculated for both test days using the algorithm. Interday differences were determined using a two-way ANOVA. Interday and intraday reliability were assessed using intraclass correlation coefficients (ICC) and root mean square (RMS) differences. FL, MTH and PAN did not differ between day one and two. The within day ICCs were above 0.94 for all tested parameters. The average interday ICCs were 0.86 for the FL, 0.96 for MTH and 0.60 for PAN. The average RMS differences between both days were 5.0%, 8.5% and 12.0% for MTH, FL and PAN, respectively. The proposed algorithm provides high measurement reliability. However, the interday reliability might be influenced by small differences in probe position between days.

Purpose:To understand the mechanisms for the effects of resistance training on functional parameters, and to assess the injury risk of the involved tissues, it is necessary to examine the underlying morphological and structural changes of the respective tissues.Methods:The presented information on physiological adaptations have been deduced from cross-sectional studies comparing youth athletes with controls and children with adults as well as from longitudinal studies examining the effects of resistance training in untrained children and adolescents and in youth athletes.Results:The evidence indicates, that training induced changes in motor performance rely partly on enhanced neuromuscular control, and partly on morphological adaptation of muscles and tendons, such as changes in muscle, muscle fiber and tendon cross-sectional area, muscle composition, and tendon material properties, with the bone also adapting by increasing bone mineral content and cortical area.Conclusion:Although the training induced adaptations of the investigated tissues follows similar principles in children as in adults, the magnitude of the adaptive response appears to be more subtle. As studies investigating physiological adaptation in youth athletes are sparse, more research in this area is warranted to elucidate the specific physiological stimulus-response relationship necessary for effective training programs and injury prevention.

Many parents still hesitate to encourage their children to participate in resistance training programs. This is unfortunate since recent research shows that resistance training can positively affect children’s health. This narrative review aims to present an overview of the health-associated effects resistance training can provide particularly in children and adolescents with disabilities by describing its effects on muscle strength, physical function, mental health, self-concept, obesity, and injury prevention. To illustrate the variety of possible fields of application, the effects of resistance training in children and adolescents suffering from Charcot-Marie-Tooth disease, cerebral palsy, Down syndrome, Ehlers-Danlos syndrome, joint hypermobility, juvenile idiopathic arthritis, obesity, and spina bifida are discussed. Although randomized controlled trials with a sufficiently large sample size are rare, the research presented in this review indicates that this mode of training might be a potent tool to improve mental and physical health by improving muscle strength, body composition, self-concept or functionality, reducing pain or injury risk, and strengthening bone or tendons even in the most vulnerable groups of children with physical or mental disability. Furthermore, it has to be emphasized that compared with other types of treatment resistance training is considered to be without adverse effects.

Tendinopathies, chronic tendon disorders characterized by pain and functional impairment, are a common problem particularly in elite and recreational athletes. There is a high prevalence of Achilles tendinopathy in runners, while patellar tendinopathies, also referred to as jumpers knee, are very common amongst volleyball and basketball players. However, tendinopathies also occur in the sedentary population. The syndrome is associated with a variety of morphological, histopathological, biochemical and molecular changes, such as an increase in tendon cross sectional area, loss of fibre organization and infiltration of blood vessels. It has been shown that exercise or mechanical loading plays a role, which is why overuse is suspected to initiate tendinopathies. The exact mechanisms are still poorly understood, which makes the treatment problematic. A variety of treatment options are available, ranging from non-invasive procedures such as exercise treatment, topical nitroglycerin patches or shock wave therapy, over injections of various substances, such as corticosteroids, platelet-rich plasma or sclerosing agents, to surgical debridement. However, most of the treatment options focus solely on symptom relief, and the evidence for their effectiveness is often poor. The effectiveness of a treatment is furthermore likely to depend on the stage of the tendinapathy. In contrast to many therapies, exercise treatment has been relatively well investigated, has been shown to work in the majority of cases and is considered the gold standard.

Summary The aim of this study was to evaluate the suitability of ultrasonography for the quantification of gastrocnemius muscle architecture in healthy young children. The variation and reliability of measurement of muscle thickness, pennation angle and fibre length of the medial gastrocnemius were determined, using stationary and portable ultrasound machines, in 13 boys and eight girls aged 4‐10. Ultrasound images were obtained from each leg, in duplicate, with the ankle at 90� , then at maximal plantar flexion, with the two machines within the same session. The same set of 16 scans was repeated in four children 4‐6 weeks later. The mean muscle thickness, pennation angle and fibre length differed between ankle positions and between legs. Measurements obtained using the two machines established similar values with no significant differences in absolute values and coefficients of variation (CV). For duplicate images taken during the same session for the same leg, ankle position and machine, the CV and intraclass correlation coefficients (ICC) ranged, respectively, from 2AE1% to 3AE1% and 0AE94‐0AE98 for muscle thickness, from 4AE1% to 6AE0% and 0AE85‐0AE96 for pennation angle and from 4AE5% to 6AE3% and 0AE87‐0AE96 for fibre length. Corresponding values for variables for the same child measured on two separate occasions were within the same ranges, all being similar to reliability data reported previously for adult muscle. Muscle thickness, pennation angle and fibre length of the medial gastrocnemius can therefore be quantified reliably, using either a stationary or portable ultrasound machine, in healthy young children.

Introduction It has yet to be explained why female athletes appear to suffer more often from non‐contact ligament injuries during the first half of the menstrual cycle. Fluctuations in balance, caused by impaired proprioception due to increased fluid retention, may be relevant factors contributing to this anomaly in distribution. The aim of this study was therefore to uncover relationships between dynamic stability, proprioception and fluid retention in association with the menstrual cycle as a possible explanation for the observed changes in injury rates. Methods Nine healthy, female, well trained ice hockey players on hormonal contraception with regular cycles were tested at least twelve times during one menstrual cycle. Bioimpedance analysis was applied to investigate body composition and fluid distribution. A joint position sense test was performed to characterize changes in proprioception, while unexpected perturbations on a balance board were used to obtain measures for dynamic postural control. Results No distinct changes in proprioception, dynamic stability and fluid retention were identified across the menstrual cycle in this population. Weak correlations were found between parameters for dynamic stability and proprioception. Conclusion Variations in proprioception, dynamic stability and fluid retention seem unlikely to be major contributors to injury risk peaks, at least in this population of healthy trained athletes using hormonal contraception.

Overuse tendinopathies are often considered to be the result of repeated microstrain below the failure threshold, analogous to the fatigue failure of materials under repeated loading [1, 2]. Investigation of tendon overuse in vitro is thus of potential benefit towards characterizing the progression of damage.

Objectives. Histological examination of pathological tendon generally does not reveal signs of inflammation. However, the inflammatory cytokine IL-6 has been shown to be expressed in ruptured rotator cuff tendon. The aim of this study was to investigate the expression of IL-6 family members in painful posterior tibialis tendon (PTT) and in painful and ruptured Achilles tendon (AT) compared with normal tendon. Methods. AT samples were obtained from cadavers (normal) or from patients undergoing surgical procedures to treat chronic painful tendinopathy or ruptured tendon. PTT samples were obtained from patients undergoing surgery for other reasons (normal) and from patients with PTT dysfunction (painful). Total RNA was extracted and mRNA expression was analysed by quantitative real-time PCR. Results. Collagen type I α-chain I (COL1A1) expression was increased in both painful PTT and AT compared with normal. Ciliary neurotrophic factor levels were increased in painful PTT only. In the painful AT, cyclooxygenase-2 (COX2) and IL-6 expression increased compared with normal. In the ruptured AT, levels of VEGF A, COX2, oncostatin-M, leukaemia inhibitory factor and IL-6 expression were higher compared with both normal and painful AT. IL-6R expression decreased in both painful and ruptured AT compared with normal. Conclusion. Painful AT and PTT show different expression patterns, indicating a substantial difference between those two tendinopathies. Inflammatory markers are up-regulated in painful and particularly in ruptured AT, pointing towards a role of inflammation not only in rupture healing, but also in Achilles tendinopathy.

We appreciate the detailed response from Professor Horgan, discussing our letter to the editor concerned with end effects when mechanical testing soft tissues (Anssari-Benam et al., 2012a), and providing further insightful analysis. The concepts of end effects and characteristic decay length have indeed been well established for a long time in the context of solid mechanics, with substantial contributions from Professor Horgan, towards establishing theoretical and analytical criteria for their characterisation, as referenced in our previous publication (Anssari-Benam et al., 2012b; from Horgan (1972), Choi and Horgan (1977).