The effects of training, immobilization and remobilization on musculoskeletal tissue

Compared with the knowledge on immobilization, the effects of remobilization on musculoskeletal tissues have not been well established. What is sure is that remobilization and rehabilitation of any component of the musculoskeletal tissues require much more time than the time needed to cause the immobilization atrophy. With intensive rehabilitation, the functional properties of skeletal muscles can be improved significantly even years after the injury and following immobilization, but no study has shown whether full recovery is possible and whether these rehabilitated muscles are able to respond normally to further training. Experimental studies have given evidence that slow-twitch muscle fibres have better capacity for recovery than fast-twitch fibres, most likely due to better circulation and higher protein turnover. Also evidence has been given that fibre regeneration is possible through satellite cell activation and myotube formation. Very little is known, however, about the effects of age, gender or the level of preimmobilization muscle performance on the restoration capacity. Also the fate of the marked structural changes (for example, connective tissue accumulation) induced by immobilization is unknown. Tendon and ligament tissues are likely to respond appropriately to remobilization, resulting in acceleration of collagen synthesis and fibril neoformation. However, there is a strong suspicion that remobilized tendons and ligaments will not achieve all the biochemical and biomechanical properties of their healthy counterparts. Specifically, the amount of weak type III collagen has been shown to be overrepresented in these tissues instead of mature, strong type I collagen. It is not known whether this is an important risk factor for ruptures during later activity. The effects of remobilization on muscle-tendon junction and proprioceptive organs are not known. It would not be surprising if the serious structural changes induced by immobilization were unrestorable. In the literature dealing with immobilization and remobilization, cartilage degeneration is always a major concern, because not only too strenuous training or immobilization, but also unskilful remobilization may activate this process leading finally to osteoarthrosis. Bone may be one of the best components of musculoskeletal tissues to respond to remobilization, probably because the immobilization atrophy of bone is largely quantitative (osteoporosis) only. The prerequisites for bony recovery are that the follow-up time is long enough (months) and that immobilization has not exceeded about 6 months, the time limit between active and inactive (irreversible) osteoporosis. Prevention of the atrophying effects of immobilization can be very successful if performed properly. According to present knowledge, there are many methods for the purpose, including preimmobilization training early, controlled mobilization; optimal positioning of the immobilized joint; muscular training during immobilization; early weightbearing; exercise with the nonimmobilized extremity; and electrical stimulation. Lots of education and information will be needed, however, before these methods are deeply rooted in the daily routines of the attending physicians, physical therapists, athletic trainers and other persons involved in the treatment of musculoskeletal problems.     

Value of resistance training for the reduction of sports injuries

Many competitive and recreational athletes perform resistance training as a part of their conditioning programmes. Resistance training in addition to increasing muscular strength and hypertrophy may also aid in the prevention of injuries. Research indicates that resistance training promotes growth and/or increases in the strength of ligaments, tendons, tendon to bone and ligament to bone junction strength, joint cartilage and the connective tissue sheaths within muscle. Studies involving humans and animal models also demonstrate resistance training can cause increased bone mineral content and therefore may aid in prevention of skeletal injuries. Investigations to date suggest resistance training can aid in injury prevention. The incidence of various types of overuse injuries, such as swimmers shoulder and tennis elbow, may be reduced by the performance of sport and/or motion specific resistance training activities. Screening of athletes for agonist and antagonist muscle strength imbalances can be utilised to identify possessing a predisposition for injury. Resistance training may then be performed to correct the imbalance and therefore reduce the incidence of injury.     

The adaptations to strength training : morphological and neurological contributions to increased strength

High-resistance strength training (HRST) is one of the most widely practiced forms of physical activity, which is used to enhance athletic performance, augment musculo-skeletal health and alter body aesthetics. Chronic exposure to this type of activity produces marked increases in muscular strength, which are attributed to a range of neurological and morphological adaptations. This review assesses the evidence for these adaptations, their interplay and contribution to enhanced strength and the methodologies employed.The primary morphological adaptations involve an increase in the cross-sectional area of the whole muscle and individual muscle fibres, which is due to an increase in myofibrillar size and number. Satellite cells are activated in the very early stages of training; their proliferation and later fusion with existing fibres appears to be intimately involved in the hypertrophy response. Other possible morphological adaptations include hyperplasia, changes in fibre type, muscle architecture, myofilament density and the structure of connective tissue and tendons.Indirect evidence for neurological adaptations, which encompasses learning and coordination, comes from the specificity of the training adaptation, transfer of unilateral training to the contralateral limb and imagined contractions. The apparent rise in whole-muscle specific tension has been primarily used as evidence for neurological adaptations; however, morphological factors (e.g. preferential hypertrophy of type 2 fibres, increased angle of fibre pennation, increase in radiological density) are also likely to contribute to this phenomenon. Changes in inter-muscular coordination appear critical. Adaptations in agonist muscle activation, as assessed by electromyography, tetanic stimulation and the twitch interpolation technique, suggest small, but significant increases. Enhanced firing frequency and spinal reflexes most likely explain this improvement, although there is contrary evidence suggesting no change in cortical or corticospinal excitability.The gains in strength with HRST are undoubtedly due to a wide combination of neurological and morphological factors. Whilst the neurological factors may make their greatest contribution during the early stages of a training programme, hypertrophic processes also commence at the onset of training.     

Magnetic resonance imaging of entheses. Part 1

Entheses are the sites of attachment of a tendon, ligament, or joint capsule to bone. Many features of entheses are adapted to disperse stress and accommodate compressive and shear forces at, or near, boundaries between tendons or ligaments and bone. Of particular interest is calcified and uncalcified fibrocartilage, which has mechanical properties that differ from those of tensile regions of tendons or ligaments, and from bone. Ultrashort echo time (UTE) pulse sequences can identify the specific tissue components of entheses and differentiate cortical bone, calcified fibrocartilage, uncalcified fibrocartilage, and fibrous connective tissue. Magic angle imaging can also differentiate tissues, such as fibrocartilage and tendon, which have different fibre orientations. Understanding the magnetic resonance (MR) appearance of entheses involves consideration of tissue properties, fibre-to-field angle, magic angle effects, pulse sequences, and geometrical factors including fibre-to-section orientation and partial volume effects. New approaches using MR imaging, allow entheses to be visualised with much greater detail than previously possible, and this may help in biomechanical studies, diagnosis of disease including overuse syndromes and spondyloarthropathies, as well as monitoring tissue repair and healing.     

大强度训练对动物肌肉和结缔组织生物力学性质的影响

利用兔进行大强度跳跑练习，测定其股骨、膝内侧副韧带、屈趾肌腱、胫前肌的生物力学特性，结果表明上述组织在一段时间大强度训练后，其生物力学性质均有不同程度增强，表明组织对大强度训练仍有良好的适应。     

高山滑雪运动踝关节急性期损伤MRI表现

目的:探讨高山滑雪运动(AS)踝关节急性期损伤MRI特点。方法:搜集27例AS运动踝关节急性损伤患者(共29个踝关节损伤)作为实验组;随机选取30例普通外伤踝关节患者(共30个踝关节损伤)作为对照组。采用3.0T MRI和相控阵线圈进行踝关节扫描。由2名放射科主治医师评估膝关节骨、软骨、韧带、肌腱等损伤。结果:实验组多结构联合损伤29(100%)个;对照组多结构联合损伤24(80.00%)个。MRI显示实验组内踝、外踝、胫骨滑车、距骨、跟骨、舟骨、骰骨挫伤/骨折分别为14、12、12、17、15、13、14个,对照组分别为7、5、5、9、8、6、6个;实验组内侧胫距关节软骨、外侧胫骨关节软骨、距下关节软骨、距跟舟关节软骨、距骰关节软骨损伤分别为16、15、14、12、13个,对照组分别为8、6、7、5、5个;实验组三角韧带、距腓前韧带、距腓后韧带、跟腓韧带、下胫腓前韧带、下胫腓后韧带损伤分别为16、17、13、16、15、12个,对照组分别为8、9、6、9、7、5个;实验组拇长屈肌肌腱、趾长屈肌肌腱、胫骨后肌肌腱、腓骨长短肌肌腱、拇长伸肌肌腱,趾长伸肌肌腱、胫骨前肌肌腱损、跟腱损伤分别为14、15、14、14、14、13、14、15个,对照组分别为7、7、6、7、6、6、7、8个。两组损伤发生率差异具有统计学意义(P均<0.05)。实验组关节软骨损伤0、Ⅰ、Ⅱ、Ⅲ、Ⅳ级分别为75、33、16、11、10个,对照组分别为119、12、7、6、6个;实验组韧带损伤0、Ⅰ、Ⅱ、Ⅲ级分别为68、58、31、17个,对照组分别为124、31、13、12个;实验组肌腱损伤0、Ⅰ、Ⅱ、Ⅲ级分别为105、82、31、14个,对照组分别为171、45、15、9个。两组损伤程度差异具有统计学意义(P均<0.001)。实验组常见多个解剖部位、多发性骨挫伤/骨折,而对照组常见直接撞击部位的骨挫伤/骨折。实验组关节软骨常表现≥Ⅱ级损伤,而对照组软骨损伤常表现Ⅰ级损伤。实验组多表现为多条韧带联合损伤,以Ⅱ级损伤居多;对照组以单条韧带损伤为主,以Ⅰ级损表现居多。实验组常表现多条肌腱Ⅰ级损伤,对照组常表现单条Ⅰ级损伤。结论:滑雪运动踝关节损伤为骨髓、软骨、韧带及肌腱的联合损伤,正确认识滑雪运动踝关节急性期损伤的MRI表现,对早期诊断、踝关节功能恢复有重要意义。     

Neural adaptations to resistive exercise: mechanisms and recommendations for training practices

It is generally accepted that neural factors play an important role in muscle strength gains. This article reviews the neural adaptations in strength, with the goal of laying the foundations for practical applications in sports medicine and rehabilitation.An increase in muscular strength without noticeable hypertrophy is the first line of evidence for neural involvement in acquisition of muscular strength. The use of surface electromyographic (SEMG) techniques reveal that strength gains in the early phase of a training regimen are associated with an increase in the amplitude of SEMG activity. This has been interpreted as an increase in neural drive, which denotes the magnitude of efferent neural output from the CNS to active muscle fibres. However, SEMG activity is a global measure of muscle activity. Underlying alterations in SEMG activity are changes in motor unit firing patterns as measured by indwelling (wire or needle) electrodes. Some studies have reported a transient increase in motor unit firing rate. Training-related increases in the rate of tension development have also been linked with an increased probability of doublet firing in individual motor units. A doublet is a very short interspike interval in a motor unit train, and usually occurs at the onset of a muscular contraction. Motor unit synchronisation is another possible mechanism for increases in muscle strength, but has yet to be definitely demonstrated.There are several lines of evidence for central control of training-related adaptation to resistive exercise. Mental practice using imagined contractions has been shown to increase the excitability of the cortical areas involved in movement and motion planning. However, training using imagined contractions is unlikely to be as effective as physical training, and it may be more applicable to rehabilitation.Retention of strength gains after dissipation of physiological effects demonstrates a strong practice effect. Bilateral contractions are associated with lower SEMG and strength compared with unilateral contractions of the same muscle group. SEMG magnitude is lower for eccentric contractions than for concentric contractions. However, resistive training can reverse these trends. The last line of evidence presented involves the notion that unilateral resistive exercise of a specific limb will also result in training effects in the unexercised contralateral limb (cross-transfer or cross-education). Peripheral involvement in training-related strength increases is much more uncertain. Changes in the sensory receptors (i.e. Golgi tendon organs) may lead to disinhibition and an increased expression of muscular force.Agonist muscle activity results in limb movement in the desired direction, while antagonist activity opposes that motion. Both decreases and increases in co-activation of the antagonist have been demonstrated. A reduction in antagonist co-activation would allow increased expression of agonist muscle force, while an increase in antagonist co-activation is important for maintaining the integrity of the joint. Thus far, it is not clear what the CNS will optimise: force production or joint integrity.The following recommendations are made by the authors based on the existing literature. Motor learning theory and imagined contractions should be incorporated into strength-training practice. Static contractions at greater muscle lengths will transfer across more joint angles. Submaximal eccentric contractions should be used when there are issues of muscle pain, detraining or limb immobilisation. The reversal of antagonists (antagonist-to-agonist) proprioceptive neuromuscular facilitation contraction pattern would be useful to increase the rate of tension development in older adults, thus serving as an important prophylactic in preventing falls. When evaluating the neural changes induced by strength training using EMG recording, antagonist EMG activity should always be measured and evaluated.     

The bone-ligament junction: A comparison between biological and artificial ACL reconstruction

The physiological bone-ligament junction is composed of four zones: ligament, fibrocartilage, calcified fibrocartilage and bone. It plays a very important part in the distribution of mechanical loads applied to ligaments so as to diminish stress concentration or shearing at the interface. This paper examines types of bone and neoligament insertion after anterior cruciate ligament (ACL) reconstruction with a Dacron prothesis, the Leeds-Keio scaffold ligament (LK), patellar tendon with LAD augmentation (PT+LAD) and bone patellar tendon bone alone (PT). The anterior cruciate reconstructions were implanted in 16 sheep via double-isometric bone tunnels without postoperative knee immobilization. Histological examination of the new insertions (using haematoxylin-cosin, Giemsa, Masson, and Mallory stains) was performed following animal sacrifice after 2, 3, 6 and 9 months. A layer of fibrocartilage between the bone and the ligament was observed with PT, followed by a nearly normal insertion after 6 months. With PT, followed by PT+LAD, the augmentation was surrounded by fibrous tissue (also noted inside the LAD). The PT insertion was virtually physiological after 3–6 months. With the LK scaffold, fibrous tissue was noted in and around the scaffold, even after 6 and 9 months. With the Dacron prosthesis, fibrous tissue around the ligament was unaccompanied by ingrowth into the prosthesis. Nerve endings (pacinian corpuscles) were only present in the PT. These findings show that even after 9 months artificial ligaments are separated from bone by fibrous tissue and devoid of the histological and biomechanical features of a physiological junction. PT alone was the only technique that resulted in formation of a structure very similar to the physiological junction, capable of protecting the bone against excessive shearing stress and the tendon against excessive strains.     

Effects of training, immobilization and remobilization on tendons

Since a tendon is a living tissue, it is not a surprise that tendon shows the capacity to adapt its structure and mechanical properties to the functional demands of the entire muscle-tendon unit. However, compared with muscle, the experimental knowledge of the effects of strength or endurance-type training on tendon tissue is scarce and clinical human experiments are completely lacking (1). Research should, however, be able to improve the true understanding of the biomechanical, functional, morphological and biochemical changes that occur in tendons due to training and physical activity, since understanding of the basic physiology of a tissue is the key to understanding its pathological processes (1,2). Compared with muscle tissue, the metabolic turnover of tendon tissue is many times slower due to poorer vascularity and circulation (1, 3). The adaptive responses of tendons to training are therefore also slower than those in muscles, but they may finally be considerable if the time frame is long enough (3, 4).     

Nonoperative treatment of acute knee ligament injuries. A review with special reference to indications and methods

Nonoperative treatment has received little attention in the numerous scientific reports on knee ligament injuries. Great controversy still exists concerning the proper treatment of a knee with a ruptured ligament, especially the anterior cruciate ligament. However, according to the studies of the authors and an extensive review of the literature the indications for conservative management can be established to be all grade I and II sprains (partial tears) of knee ligaments as well as an isolated grade III sprain (complete tear) of the posterior cruciate ligament. In addition, an isolated complete rupture of an anterior cruciate, or medial or lateral collateral ligament may be treated nonoperatively in an older sedentary person. Other injuries obviously call for an operative approach at the acute stage. Nonoperative therapy protocols must be based on the knowledge of the biological phenomenon occurring during connective tissue healing process. In the first phase of ligament healing the injured knee needs 2 to 3 weeks immobilisation for undisturbed fibroblast invasion and proliferation of collagen fibres. This is achieved by immobilising the knee in a rehabilitative knee brace locked in 40 to 45 degrees of flexion. Thereafter, a gradually increasing controlled mobilisation is allowed in the brace to avoid the deleterious effects of immobilisation to cartilage, bone, muscles, tendons and ligaments, and to enhance the orientation of collagen fibres to the stress lines of the healing ligament. After 4 to 8 weeks the goal for rehabilitation is rapid and full recovery to work and sports. A functional knee brace may be used at this phase to give extra protection before final strengthening of the injured ligament. During the mobilisation and muscle training of the therapy protocol various specific techniques can be used for strengthening of the hamstring and quadriceps muscles, including isometric, isotonic, isokinetic and eccentric exercises with or without resistive equipments. In addition, electrical stimulation may help prevent muscle wasting due to immobilisation, and continuous passive motion may be used to correct persistent extension or flexion deficit. Normally, jogging is allowed approximately 3 to 6 months after the injury, and an athlete is generally able to return to full activity and competitive sports after 6 to 12 months. Quite frequently the whole question of successful rehabilitation after a knee ligamentous injury is more motivational rather than methodological and is thus often independent of attending physician's or physiotherapist's skill or will. Therefore, one of the most important things during rehabilitation is to motivate and encourage the patient for longstanding, intensive work.     

A decade of aerobic endurance training: histological evidence for fibre type transformation

BACKGROUND: Researchers employing a variety of training methods have demonstrated a fast-to-slow fibre transformation in animal skeletal muscle. The observation as to whether this occurs in exercise trained humans is limited and equivocal. METHODS: Experimental design: to examine this issue, skeletal muscle from seven subjects who had participated in a decade or more of high intensity aerobic training (DT) and six nontrained (NT) subjects was obtained by muscle biopsy from the vastus lateralis muscle (VL) and subjected to a modified myofibrillar ATPase technique to identify muscle fibre types. Muscle tissue was histochemically treated by exposure to an alkaline preincubation (pH 9.9), an acid preincubation (pH 4.3 or 4.6) and the formate-KCI preincubation buffer (pH 4.54), previously employed in animal studies. RESULTS: The formate-KCl preincubation medium identified all major fibre types at a single pH in human subjects. The percentage of type I fibres in DT was 70.9% vs 37.7% in NT (p<0.01), while the type IIa fibres in DT (25.3%) was much lower (p<0.01) than NT (51.8%). Surprisingly, type IIa fibres in the DT group displayed lesser oxidative staining intensity (p<0.01) than type IIa fibres from the NT group. Mean cross-sectional area of type I fibres for DT (6233.9+/-1421.7 microm2) was greater (p<0.05) than either type I (5746.8+/-1135.2 microm2) or II (5693.5+/-1214.6 microm2) from NT. CONCLUSIONS: The results revealed that endurance training may promote a transition from type II to type I muscle fibre types and occurs at the expense of the type II fibre population.     

Entheses: tendon and ligament attachment sites

The current brief review focuses on certain issues relating to form–function relationships that are evident at tendon or ligament attachment sites (entheses). It evaluates the development of entheses (both fibrocartilaginous and fibrous) and highlights again an issue largely ignored for decades – i.e. how entheses attached to the metaphyses of long bones manage to keep the same relative position as the bones grow in length. Attention is drawn to the manner in which enthesis fibrocartilage prevents direct cell–cell communication between osteocytes and tendon/ligament cells and how (in a healthy enthesis) it presents a physical barrier separating the blood supply of bone from that of tendon/ligament. The possibility that the thoracolumbar fascia, with its multitude of muscular associations and numerous sites of ligamentous attachment could increase stress concentration at entheses is raised, the structure and development of enthesophytes (bony spurs) is reviewed as is the concept of a synovio-entheseal complex (SEC). How these functional anatomical units (SECs) could trigger pain and inflammation in athletes is briefly discussed.     

踝关节运动损伤的MRI表现

运动造成的踝关节损伤的发病率有升高的趋势。MRI是目前诊断踝关节损伤的主要手段,可以明确踝关节骨及软骨、韧带和肌腱的损伤,同时还能评估损伤的程度及范围。就踝关节运动损伤所致的骨损伤、骨软骨损伤、韧带损伤、肌腱损伤的影像表现及其损伤程度的评估进行综述。     

The effects of immobilization on the quality of Achilles tendon in rats

Immobilization of an Achilles tendon in a shortened position for 1 and 3 weeks did not change pyridinoline and mature collagen concentrations. Although a significant decrease in the biosynthesis of collagen was observed simultaneously in the soleus muscle of the same hindlimb, these results suggest that the stability of collagen provided by the nonreducible cross-link, pyridinoline, is not altered during this type of immobilization. The significance of stable cross-links for the known decrease in tensile strength during immobilization remains open.     

Developing maximal neuromuscular power: Part 1--biological basis of maximal power production

This series of reviews focuses on the most important neuromuscular function in many sport performances, the ability to generate maximal muscular power. Part 1 focuses on the factors that affect maximal power production, while part 2, which will follow in a forthcoming edition of Sports Medicine, explores the practical application of these findings by reviewing the scientific literature relevant to the development of training programmes that most effectively enhance maximal power production. The ability of the neuromuscular system to generate maximal power is affected by a range of interrelated factors. Maximal muscular power is defined and limited by the force-velocity relationship and affected by the length-tension relationship. The ability to generate maximal power is influenced by the type of muscle action involved and, in particular, the time available to develop force, storage and utilization of elastic energy, interactions of contractile and elastic elements, potentiation of contractile and elastic filaments as well as stretch reflexes. Furthermore, maximal power production is influenced by morphological factors including fibre type contribution to whole muscle area, muscle architectural features and tendon properties as well as neural factors including motor unit recruitment, firing frequency, synchronization and inter-muscular coordination. In addition, acute changes in the muscle environment (i.e. alterations resulting from fatigue, changes in hormone milieu and muscle temperature) impact the ability to generate maximal power. Resistance training has been shown to impact each of these neuromuscular factors in quite specific ways. Therefore, an understanding of the biological basis of maximal power production is essential for developing training programmes that effectively enhance maximal power production in the human.     

肘关节后外侧旋转不稳定的解剖与生物力学研究

目的 研究肘关节外侧软组织对维持肘关节后外侧旋转稳定的作用。方法 通过解剖肘关节,观察外侧软组织的形态结构特点;将16侧上肢标本分为两组,通过生物力学试验,研究按顺序切断桡侧软组织结构时肘关节旋转度的变化。结果 肘关节伸肌起始于肱骨外髁的肌腱膜上,肌腱膜部分随肌肉走行成为肌间隔,部分止于尺骨鹰嘴外侧骨面;桡侧副韧止于尺骨冠突的部分为桡侧尺副韧带,其与桡骨环状韧带在尺度上的止点有2种类型。肘关节桡侧副韧带复合体对维持关节外侧稳定的作用约占50％,伸肌及伸肌腱膜的作用约占11％;在桡侧副韧带复合体中,桡侧副韧带（包括桡侧尺副韧带）起主要作用,桡骨环状韧带起协同作用。结论 肘关节后侧旋转不稳定除桡侧副韧带的损伤外,可能还有外侧伸肌及伸肌腱膜的损伤。     

Insertion of autologous tendon grafts to the bone: a histological and immunohistochemical study of hamstring and patellar tendon grafts

This study examined the structure of the insertion of autologous tendon grafts used for anterior cruciate ligament reconstruction. Biopsy specimens of the femoral ¶and tibial bone graft interface were obtained at revision surgery in 14 patients (6 with hamstring grafts, 8 with a patella tendon graft). The specimens were analyzed by light microscopy and immunohistochemistry (confirming type I, type II, and type III collagen). The insertions of hamstring autografts to the bone tunnel have three characteristic histological zones. Zone 1 is composed of the dense connective tissue of the graft. The collagen fibers of the graft enter the bone under oblique angles. Zone 2 is composed of woven bone with ¶a sharp transition to the lamellar bone of the tibia (zone 3). Immunohistochemistry revealed the presence of type I and type III collagen within the dense connective tissue of the graft. The woven and lamellar bone showed positive immunostaining for antibodies against type I collagen only. This structure resembled a fibrous ligament or tendon insertion. In the majority of patients with a patella tendon graft the structure of the insertion resembled a chondral enthesis. The chondral insertion of the graft to the bone is composed of four characteristic zones. Between the dense connective tissue of the graft (zone 1) and bone (zone 4) there is a zone of fibrocartilage (zone 2). Close to the bone the fibrocartilage is mineralized (zone 3). Within the fibrocartilage the immunohistochemical analysis confirmed type II collagen. This structure resembled the chondral enthesis of the normal anterior cruciate ligament. However, in cases in which the distal bone bloc has been fixated outside the tibial tunnel, the tibial insertion of the patellar tendon graft resembled a fibrous insertion. While both types of tendon grafts heal to the bone of femur and tibia, the insertion of patella tendon grafts healing by bone plug incorporation resembles the chondral insertion of the normal anterior cruciate ligament and may have a more physiological connection to the bone than hamstring grafts.     

The influence of physical activity on ligaments and tendons.

Using either a bone-ligament-bone or a muscle-tendon-bone preparation, numerous investigators have demonstrated that the usual site of separation is in the transitional zone between the ligament (or tendon) and bone; hence, the term junction strength or load at separation is used to describe functional changes in these preparations. Junction strength is decreased with inactivity (immobilization) and increased with chronic activity (training) provided that the exercise program is of an endurance nature. Training also increases junction strength in thyroidectomized and hypophysectomized rats. Besides in junction strength, training results in heavier ligaments and higher ligament weight/length ratios. However, water content, collagen concentrations/dry weight or collagen concentration per weight/length unit are not significantly influenced by repeated bouts of exercise. Although immobilization is associated with lower elastic stiffness values (kg/mm), training appears to have little influence on this measure in normal animals. Rats and dogs with surgically repaired ligaments are weaker and the strength results are markedly lower if the leg is immobilized. Exercise training improves the repair strength of ligaments but does not result in normal values twelve weeks after the surgery. Exogenous administration of ICSH or testosterone results in higher repair strength whereas TSH, thyroxine, ACTH and growth hormone decreases this measure. It was concluded that the mechanical stress produced by chronic exercise is an important determination of the strength of repaired ligaments and of the junctions between ligaments (or tendons) and bones.     

Physiological considerations in training young athletes

Healthy children evidence smaller values of cardiorespiratory function than adults, but these are in proportion to the smaller body size. At birth, the distribution of muscle fibres and the activity of enzymes in muscle are different from in adults, but these differences disappear at about age 6. On the other hand, muscle fibre thickness increases from birth to about 18 years of age and this is concurrent with increases in muscular strength. The increase in maximal oxygen consumption (VO2max) that accompanies growth and maturation in the human has been attributed in the main to appreciating muscle mass. During exercise, heart rate and cardiac output increase in the child as in the adult, but the heart rate in the child is greater and the stroke volume smaller. Furthermore, the arteriovenous difference in oxygen is greater in the exercising child than in the adult. Children also evidence a diminished blood pressure response to exercise. It seems that control of ventilation at exercise is the same in children as in adults, but exercise ventilation has been reported to be less efficient in the child. The young are less capable of regulating core temperature at exercise than adults and are more readily dehydrated. Very limited data suggest that muscle energy substrate storage and utilisation in children are such that they are less capable of anaerobic metabolism than adults. Generally, children respond to aerobic training as do adults, but such training in the first decade of life has been reported to have negligible effects. Blood lipid levels in children seem to be favourably influenced by persistent endurance activity. Ventilatory efficiency of children at exercise is augmented by aerobic training. Maximal values of ventilation and breathing frequency are increased in children and youth by endurance training. Conflicting data exist regarding the influence of training upon the child's vital capacity. Pulmonary diffusion capacity in well trained children has been seen to be greater than in untrained youngsters and many workers have reported increased VO2max as an outcome of endurance training. Limited data indicate that the nature of training may alter muscle fibre distribution in youthful athletes, and that muscle fibre hypertrophy can be induced in the young by means of strength and power training.(ABSTRACT TRUNCATED AT 400 WORDS)     

Specific injuries induced by the practice of trampoline, tumbling and acrobatic gymnastics

Purpose

The recreational and competitive practice of acrobatic sports, that is, trampoline, tumbling and acrobatic gymnastics (ACRO), is growing rapidly around the world. Many studies described the injuries affecting young artistic gymnasts, but only few concerned acrobatic sports.

Methods

During a 5-year period, 357 traumatic events were collected in young acrobats practicing trampoline, tumbling or ACRO. Accident characteristics, level of expertise and training, injury location (upper limb, spine and lower limb), type of tissue injured (bone, cartilage, muscle, ligament and tendon) and provoking factors (intrinsic/behavioural and extrinsic) were investigated.

Results

Acrobats of national and international levels were mostly injured. Injuries occurring in acrobatic sports concerned predominantly the lower limbs and concerned in this body part mainly damages to ligaments. Forearm and knee injuries were preferentially related to trampoline. Ankle injuries were preferentially related to tumbling. Wrist injuries were preferentially related to ACRO. Upper limb bone damage and upper limb tendon damage were preferentially related to trampoline and ACRO, respectively. Intrinsic/behavioural factors were the main injury determinant in the three acrobatic sports.

Conclusions

The main injuries in acrobatic sports (i.e. lower limbs) are similar to those observed in artistic gymnastics. Specific injuries may result from falls and incomplete and/or erroneous figure’s landing and may also depend to the type of the landing surface.

Level of evidence

II.