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PubMed1999

Exercise-induced muscle damage and potential mechanisms for the repeated bout effect.

Unfamiliar, predominantly eccentric exercise, frequently results in muscle damage. A repeated bout of similar eccentric exercise results in less damage and is referred to as the 'repeated bout effect'. Despite numerous studies that have clearly demonstrated the repeated bout effect, there is little consensus as to the actual mechanism. In general, the adaptation has been attributed to neural, connective tissue or cellular adaptations. Other possible mechanisms include, adaptation in excitation-contraction coupling or adaptation in the inflammatory response. The 'neural theory' predicts that the initial damage is a result of high stress on a relatively small number of active fast-twitch fibres. For the repeated bout, an increase in motor unit activation and/or a shift to slow-twitch fibre activation distributes the contractile stress over a larger number of active fibres. Although eccentric training results in marked increases in motor unit activation, specific adaptations to a single bout of eccentric exercise have not been examined. The 'connective tissue theory' predicts that muscle damage occurs when the noncontractile connective tissue elements are disrupted and myofibrillar integrity is lost. Indirect evidence suggests that remodelling of the intermediate filaments and/or increased intramuscular connective tissue are responsible for the repeated bout effect. The 'cellular theory' predicts that muscle damage is the result of irreversible sarcomere strain during eccentric contractions. Sarcomere lengths are thought to be highly non-uniform during eccentric contractions, with some sarcomeres stretched beyond myofilament overlap. Loss of contractile integrity results in sarcomere strain and is seen as the initial stage of damage. Some data suggest that an increase in the number of sarcomeres connected in series, following an initial bout, reduces sarcomere strain during a repeated bout and limits the subsequent damage. It is unlikely that one theory can explain all of the various observations of the repeated bout effect found in the literature. That the phenomenon occurs in electrically stimulated contractions in an animal model precludes an exclusive neural adaptation. Connective tissue and cellular adaptations are unlikely explanations when the repeated bout effect is demonstrated prior to full recovery, and when the fact that the initial bout does not have to cause appreciable damage in order to provide a protective effect is considered. It is possible that the repeated bout effect occurs through the interaction of various neural, connective tissue and cellular factors that are dependent on the particulars of the eccentric exercise bout and the specific muscle groups involved.

Adaptation, Physiological↗
PubMed1999

Measures to prevent cricket injuries: an overview.

Cricket is a major international sport, generally played in British Common-wealth nations. Although strictly a non-contact sport, injuries in cricket can result in a number of ways. In high level cricket, overuse injuries are common and related to the physical demands of the sport, particularly in the delivery of the ball. The bowling action involves repetitive twisting, extension and rotation of the trunk at the same time as absorption of large ground reaction forces over a short period of time. These movements, if performed incorrectly or too frequently, can lead to overuse injuries of the back, particularly in elite and high level cricketers. Cross-sectional studies have demonstrated that spinal overuse injuries occur more frequently to cricketers adopting a mixed bowling action than to those who favour a front- or side-on bowling technique. Strategies to ensure that cricketers do not adopt the mixed action or bowl too fast for extended periods can prevent these back injuries. Injuries resulting from impacts, generally from the cricket ball, can also occur and are more common during low level competition or informal participation. Because of the potential severity of these impacts, a range of protective equipment ranging from body padding to gloves and face protectors are now common features of standard cricket equipment. Although a number of measures to prevent cricket injuries have been widely suggested in the literature, there have been very few studies that have formally assessed their effectiveness in preventing injury. Further research is needed to gain a greater understanding of the biomechanics of cricket actions, the mechanisms of resultant injuries and the role of various risk factors in injury causation.

Adolescent↗
PubMed2000

Biomechanical analysis of the effect of orthotic shoe inserts: a review of the literature.

Physical activity is increasingly recognised as an important component of primary disease prevention. Overuse injuries are common sequelae of exercise and sporting activities in general, and of running in particular, frequently resulting in cessation of activity. It has been proposed that there is a link between foot shape, foot function and the occurrence of injury. As a means of treatment and prevention of further injury, orthoses and shoe inserts are widely prescribed in the belief that they can alter the pattern of lower extremity joints' alignment and movement. Although this is an assumption widely made in the treatment of many joint conditions, the manner through which this treatment could be effective is not clear. This article aims to examine the literature to gain an improved understanding of the present state of knowledge regarding the effect of foot shape and orthotic use on foot kinematic and plantar pressure characteristics. The effects of foot type on the occurrence of lower limb injury during sporting activities and different aspects of biomechanics are reviewed, and the effects of applying orthoses on injury treatment and prevention and on various aspects of biomechanics of the lower limb joints are discussed. Further research is required, firstly to establish the casual effect of foot type and function on the risk of lower extremity overuse injury, and secondly to document the specific effect of orthotic therapy on injury treatment and prevention. Specifically, more prospective studies are necessary to investigate the long term effect of orthotic intervention.

Biomechanical Phenomena↗
PubMed2001

Magnetic resonance imaging of the knee.

Magnetic resonance imaging (MRI) has revolutionised diagnostic imaging of the knee. It has evolved significantly since Kean described healthy and pathologic knee anatomy in 1983. This innovative technology allows superior soft-tissue detail with multiplanar imaging capability that provides accurate evaluation of intra- and extra-articular structures of the knee not demonstrated with other imaging modalities. The development and advancements in MRI and the introduction of high-resolution coils have provided a noninvasive, nonoperator dependent, cost effective means to diagnose knee pathology. MRI is well tolerated by patients, widely accepted by evaluating physicians, and assists in distinguishing pathologic knee conditions that may have similar clinical signs and symptoms (i.e. meniscal tears, osteochondral lesions). This paper presents an overview of MRI of the knee and focuses on the MRI findings in a number of common pathologic conditions.

Cumulative Trauma Disorders↗
PubMed2002

Musculoskeletal problems of the chest wall in athletes.

Chest pain in the athlete has a wide differential diagnosis. Pain may originate from structures within the thorax, such as the heart, lungs or oesophagus. However, musculoskeletal causes of chest pain must be considered. The aim of this review is to help the clinician to diagnose chest wall pain in athletes by identifying the possible causes, as reported in the literature. Musculoskeletal problems of the chest wall can occur in the ribs, sternum, articulations or myofascial structures. The cause is usually evident in the case of direct trauma. Additionally, athletes' bodies may be subjected to sudden large indirect forces or overuse, and stress fractures of the ribs caused by sporting activity have been extensively reported. These have been associated with golf, rowing and baseball pitching in particular. Stress fractures of the sternum reported in wrestlers cause pain and tenderness of the sternum, as expected. Diagnosis is by bone scan and limitation of activity usually allows healing to occur. The slipping rib syndrome causes intermittent costal margin pain related to posture or movement, and may be diagnosed by the 'hooking manoeuvre', which reproduces pain and sometimes a click. If reassurance and postural advice fail, good results are possible with resection of the mobile rib. The painful xiphoid syndrome is a rare condition that causes pain and tenderness of the xiphoid and is self-limiting. Costochondritis is a self-limiting condition of unknown aetiology that typically presents with pain around the second to fifth costochondral joints. It can be differentiated from Tietze's syndrome in which there is swelling and pain of the articulation. Both conditions eventually settle spontaneously although a corticosteroid injection may be useful in particularly troublesome cases. The intercostal muscles may be injured causing tenderness between the ribs. Other conditions that should be considered include epidemic myalgia, precordial catch syndrome and referred pain from the thoracic spine.

Adolescent↗
PubMed2002

Aetiology of rib stress fractures in rowers.

Rib stress fractures are a common and significant problem in the rowing population. They occur in approximately 6.1 to 12% of rowers and account for the most time lost from on-water training and competition. This review discusses possible causative factors for rib stress fractures in rowers. Central to the establishment of causative factors is the identification that each rib forms part of a closed ring of bone that is completed anteriorly by the sternum and posteriorly by the thoracic vertebrae. Because of the shared sternum anteriorly each ring of bone is mechanically connected. Subsequently, during rowing individual ribs are not loaded in isolation, rather the rib cage is loaded as a complete unit. Incorporating this functioning as a complete unit a possible mechanism by which different factors contribute to rib stress fracture can be developed. In rowing, muscle factors generate loading of the rib cage. The characteristics of this loading stimulus are influenced by equipment, technique and joint factors. Rib-cage loading generates bone strain in individual ribs with the response of each rib depending upon site-specific skeletal factors. Depending on the characteristics of the bone strain in terms of the magnitude and rate of strain, microdamage may develop. The bone response to this microdamage is reparative remodelling. Whether this response is capable of repairing the damage to prevent progression to a stress fracture is dependent upon training and gender factors. Identification of these factors will generate a better understanding of the aetiology of this injury, which is required for improved prevention and treatment strategies.

Athletic Injuries↗
PubMed2002

Little league elbow: valgus overload injury in the paediatric athlete.

This article describes a variety of elbow injuries often seen in young, throwing athletes. Understandings of normal skeletal development, as well as the biomechanics of throwing, provide a basis on which to evaluate, diagnose and manage "little league elbow". With emphasis on an anatomically-based differential diagnosis, the pathologic forces placed upon the young thrower's elbow, and the subsequent injury patterns, are reviewed. Medial side injuries are the most common and relate to chronic forces of valgus overload produced during the early and late cocking phases of throwing. The majority of this force is placed on the medial epicondyle and produces age-dependent injury patterns, such as apophysitis in childhood and epicondylar avulsion fractures in the more mature athlete. With repetitive valgus overload, lateral side injuries such as Panner's disease and osteochondritis dissecans of the capitellum and radial head become more apparent. These injuries relate to the compressive forces produced by the late cocking and early acceleration phases of throwing. Finally, posterior injury patterns consistent with olecranon apophysitis and posteromedial impingement, as well as flexion and capsular contracture, can be seen. The key in the treatment of "little league elbow" is prevention and this responsibility lies not only with the evaluating or team physician, but also with the coach, trainer, parents and officials. Proper throwing mechanics must be emphasised at an early age, and the determinants of elbow injury among young pitchers better understood. Early recognition and proper treatment of such injuries will then prevent later sequelae or functional disability.

Athletic Injuries↗
PubMed2004

Neuromuscular function after exercise-induced muscle damage: theoretical and applied implications.

Exercise-induced muscle damage is a well documented phenomenon particularly resulting from eccentric exercise. When eccentric exercise is unaccustomed or is performed with an increased intensity or duration, the symptoms associated with muscle damage are a common outcome and are particularly associated with participation in athletic activity. Muscle damage results in an immediate and prolonged reduction in muscle function, most notably a reduction in force-generating capacity, which has been quantified in human studies through isometric and dynamic isokinetic testing modalities. Investigations of the torque-angular velocity relationship have failed to reveal a consistent pattern of change, with inconsistent reports of functional change being dependent on the muscle action and/or angular velocity of movement. The consequences of damage on dynamic, multi-joint, sport-specific movements would appear more pertinent with regard to athletic performance, but this aspect of muscle function has been studied less often. Reductions in the ability to generate power output during single-joint movements as well as during cycling and vertical jump movements have been documented. In addition, muscle damage has been observed to increase the physiological demand of endurance exercise and to increase thermal strain during exercise in the heat. The aims of this review are to summarise the functional decrements associated with exercise-induced muscle damage, relate these decrements to theoretical views regarding underlying mechanisms (i.e. sarcomere disruption, impaired excitation-contraction coupling, preferential fibre type damage, and impaired muscle metabolism), and finally to discuss the potential impact of muscle damage on athletic performance.

Action Potentials↗
PubMed2004

Biomechanics and pathophysiology of overuse tendon injuries: ideas on insertional tendinopathy.

Tendons behave viscoelastically and exhibit adaptive responses to conditions of increased loading and disuse. High-resolution, real-time ultrasound scanning confirms the applicability of these findings in human tendons in vivo. In addition, recent biomechanical studies indicate that strain patterns in tendons may not be uniform, as tendons show stress-shielded areas and areas subjected to compressive loading at the enthesis. These areas correspond to the sites where tendinopathic characteristics are typically seen. This indicates that some tendinopathies may, paradoxically, be considered as 'underuse' lesions despite the common beliefs that they are overuse injuries. Classic inflammatory changes are not frequently seen in chronic athletic tendon conditions and histopathology features in tendinopathic tendons are clearly different from normal tendons, showing an exaggerated dysfunctional repair response. Tendinopathies are traditionally considered overuse injuries, involving excessive tensile loading and subsequent breakdown of the loaded tendon. Biomechanical studies show that the strains within the tendons near their insertion site are not uniform. If the material properties are similar throughout the tendon, forces transferred through the insertion site preferentially load the side of the tendon that is usually not affected initially in tendinopathy. In that case, the side affected by tendinopathy is generally 'stress shielded'. Thus, the presence of differential strains opens the possibility of alternative biomechanical explanations for the pathology found in these regions of the tendon. The traditional concept of tensile failure may not be the essential feature of the pathomechanics of insertional tendinopathy. Certain joint positions are more likely to stress the area of the tendon commonly affected by tendinopathy. Incorporating different joint position exercises may exert more controlled stresses on these affected areas of the tendon, possibly allowing better maintenance of the mechanical strength of that tendon region and, therefore, prevent injury. Such exercises could stress a healing area of the tendon in a controlled manner and thus stimulate healing once an injury has occurred. Additional work is needed to prove whether such principles should be incorporated in current rehabilitation techniques.

Aging↗
PubMed2005

Iliotibial band syndrome in runners: innovations in treatment.

Iliotibial band syndrome (ITBS) is the most common cause of lateral knee pain in runners. It is an overuse injury that results from repetitive friction of the iliotibial band (ITB) over the lateral femoral epicondyle, with biomechanical studies demonstrating a maximal zone of impingement at approximately 30 degrees of knee flexion. Training factors related to this injury include excessive running in the same direction on a track, greater-than-normal weekly mileage and downhill running. Studies have also demonstrated that weakness or inhibition of the lateral gluteal muscles is a causative factor in this injury. When these muscles do not fire properly throughout the support phase of the running cycle, there is a decreased ability to stabilise the pelvis and eccentrically control femoral abduction. As a result, other muscles must compensate, often leading to excessive soft tissue tightness and myofascial restrictions. Initial treatment should focus on activity modification, therapeutic modalities to decrease local inflammation, nonsteroidal anti-inflammatory medication, and in severe cases, a corticosteroid injection. Stretching exercises can be started once acute inflammation is under control. Identifying and eliminating myofascial restrictions complement the therapy programme and should precede strengthening and muscle re-education. Strengthening exercises should emphasise eccentric muscle contractions, triplanar motions and integrated movement patterns. With this comprehensive treatment approach, most patients will fully recover by 6 weeks. Interestingly, biomechanical studies have shown that faster-paced running is less likely to aggravate ITBS and faster strides are initially recommended over a slower jogging pace. Over time, gradual increases in distance and frequency are permitted. In the rare refractory case, surgery may be required. The most common procedure is releasing or lengthening the posterior aspect of the ITB at the location of peak tension over the lateral femoral condyle.

Cumulative Trauma Disorders↗
PubMed1989

Occupational health, stress, and work organization in Australia.

Contemporary issues and changes in occupational health are reviewed in this article, with particular reference to salient historical and ideological influences on industrial relations in Australia. Comprehensive occupational health and safety legislation has been introduced recently, and the views of employers and unions are analyzed. Research into occupational stress has continued to provide guidelines for work reform, but the controversy generated by the Australian phenomenon known as Repetition Strain Injury (RSI) has raised important issues for the work reform movement.

Australia↗
PubMed2006

MRI of stress reaction of the distal humerus in elite tennis players.

OBJECTIVE: The purpose of this study was to describe the MRI appearance of stress reaction in the distal humerus in 12 elite tennis players. In addition, we aimed to determine whether any MRI findings were associated with changes in recovery times. CONCLUSION: Stress injury to the distal humerus is a cause of chronic arm pain among elite tennis players and may be exacerbated during full competition. The degree of marrow edema on STIR MRI may be predictive of time to return to competition.

Adolescent↗
PubMed1988

Bone stress lesions in ballet dancers: scintigraphic assessment.

Ballet dancers are athletes susceptible to ligamentous and bony injury. We reviewed retrospectively the bone scans (technetium-99m methylene diphosphonate) of 23 ballet dancers with pain in the back and/or lower extremities to determine the usefulness of scintigraphy in the detection of stress lesions of bone. The scintigraphic studies in 19 dancers identified multiple areas of stress injury in both symptomatic and asymptomatic locations. Thirteen dancers had 22 stress fractures (microfractures of trabeculae with associated bone repair) manifested by an intense focus of increased uptake of radiopharmaceutical, and 19 dancers had stress reactions (areas of accelerated remodeling and resorption of bone) demonstrated by diffusely increased uptake of radiotracer. Ten of the 13 dancers with stress fractures were symptomatic and six of the 19 dancers with stress reactions were symptomatic. The radiographs of 10 dancers with positive bone scans were normal or showed no distinction between acute and chronic injuries. Stress fractures were most prevalent in the feet, and stress reactions were most prevalent in the tibiae. The study confirmed that ballet dancers sustain significant bone stress in their legs and feet. Our results show that scintigraphy can be used to detect stress fractures and stress reactions at both symptomatic and asymptomatic sites in this population.

Adolescent↗
PubMed1991

Do asymptomatic marathon runners have an increased prevalence of meniscal abnormalities? An MR study of the knee in 23 volunteers.

Excessive repetitive musculoskeletal loads and stresses associated with intense physical activity may lead to deterioration of the menisci of the knee. Therefore, MR imaging was performed on the knees of 23 asymptomatic marathon runners (eight men, 15 women; average age, 40 years; average number of years training, 10; average training distance per week, 41 miles) to determine the prevalence of meniscal signal abnormalities. None of the runners had previous knee injuries or surgery and each of them regularly competes in 26-mile, 50-mile, or 100-mile marathon races. T1-weighted coronal MR images and proton density-weighted and T2-weighted sagittal images were obtained with a 1.5-T MR system and a transmit/receive extremity coil. The medial and lateral menisci were divided into four portions, or horns, and a total of 92 horns were evaluated (i.e., four horns per knee: medial posterior, medial anterior, lateral posterior, and lateral anterior). Two meniscal horns (2%) had grade 3 signal (grade 3 indicates a meniscal tear), 12 (13%) had grade 2 signal, 29 (32%) had grade 1 signal (grades 1 and 2 are indicative of meniscal degeneration), and 49 (53%) had grade 0 signal (grade 0 is normal). Overall, the prevalence of meniscal tears was 9% (two meniscal tears found in 23 runners). This is lower than the prevalence of MR signal abnormalities indicative of meniscal tears reported for asymptomatic, nonrunner athletes (20% of 20 athletes) and for asymptomatic nonathletes (16% of 74 subjects). Fifty-three percent of the meniscal horns of the nonrunner athletes had grade 1 or 2 signal, indicative of meniscal degeneration. Our results indicate that the prevalence of meniscal tears in marathon runners is no higher than the prevalence reported for sedentary persons, and the runners have the same amount of meniscal degeneration as do nonrunner athletes.

Adult↗