Showing papers in "Sports Medicine in 2005"

Physiology of Soccer: An Update

Abstract: Soccer is the most popular sport in the world and is performed by men and women, children and adults with different levels of expertise. Soccer performance depends upon a myriad of factors such as technical/biomechanical, tactical, mental and physiological areas. One of the reasons that soccer is so popular worldwide is that players may not need to have an extraordinary capacity within any of these performance areas, but possess a reasonable level within all areas. However, there are trends towards more systematic training and selection influencing the anthropometric profiles of players who compete at the highest level. As with other activities, soccer is not a science, but science may help improve performance. Efforts to improve soccer performance often focus on technique and tactics at the expense of physical fitness. During a 90-minute game, elite-level players run about 10 km at an average intensity close to the anaerobic threshold (80-90% of maximal heart rate). Within this endurance context, numerous explosive bursts of activity are required, including jumping, kicking, tackling, turning, sprinting, changing pace, and sustaining forceful contractions to maintain balance and control of the ball against defensive pressure. The best teams continue to increase their physical capacities, whilst the less well ranked have similar values as reported 30 years ago. Whether this is a result of fewer assessments and training resources, selling the best players, and/or knowledge of how to perform effective exercise training regimens in less well ranked teams, is not known. As there do exist teams from lower divisions with as high aerobic capacity as professional teams, the latter factor probably plays an important role. This article provides an update on the physiology of soccer players and referees, and relevant physiological tests. It also gives examples of effective strength- and endurance-training programmes to improve on-field performance. The cited literature has been accumulated by computer searching of relevant databases and a review of the authors' extensive files. From a total of 9893 papers covering topics discussed in this article, 843 were selected for closer scrutiny, excluding studies where information was redundant, insufficient or the experimental design was inadequate. In this article, 181 were selected and discussed. The information may have important implications for the safety and success of soccer players and hopefully it should be understood and acted upon by coaches and individual soccer players.

Hormonal Responses and Adaptations to Resistance Exercise and Training

Abstract: Resistance exercise has been shown to elicit a significant acute hormonal response. It appears that this acute response is more critical to tissue growth and remodelling than chronic changes in resting hormonal concentrations, as many studies have not shown a significant change during resistance training despite increases in muscle strength and hypertrophy. Anabolic hormones such as testosterone and the superfamily of growth hormones (GH) have been shown to be elevated during 15-30 minutes of post-resistance exercise providing an adequate stimulus is present. Protocols high in volume, moderate to high in intensity, using short rest intervals and stressing a large muscle mass, tend to produce the greatest acute hormonal elevations (e.g. testosterone, GH and the catabolic hormone cortisol) compared with low-volume, high-intensity protocols using long rest intervals. Other anabolic hormones such as insulin and insulin-like growth factor-1 (IGF-1) are critical to skeletal muscle growth. Insulin is regulated by blood glucose and amino acid levels. However, circulating IGF-1 elevations have been reported following resistance exercise presumably in response to GH-stimulated hepatic secretion. Recent evidence indicates that muscle isoforms of IGF-1 may play a substantial role in tissue remodelling via up-regulation by mechanical signalling (i.e. increased gene expression resulting from stretch and tension to the muscle cytoskeleton leading to greater protein synthesis rates). Acute elevations in catecholamines are critical to optimal force production and energy liberation during resistance exercise. More recent research has shown the importance of acute hormonal elevations and mechanical stimuli for subsequent up- and down-regulation of cytoplasmic steroid receptors needed to mediate the hormonal effects. Other factors such as nutrition, overtraining, detraining and circadian patterns of hormone secretion are critical to examining the hormonal responses and adaptations to resistance training.

Physiological and Metabolic Responses of Repeated-Sprint Activities Specific to Field-Based Team Sports

Abstract: Field-based team sports, such as soccer, rugby and hockey are popular worldwide. There have been many studies that have investigated the physiology of these sports, especially soccer. However, some fitness components of these field-based team sports are poorly understood. In particular, repeated-sprint ability (RSA) is one area that has received relatively little research attention until recent times. Historically, it has been difficult to investigate the nature of RSA, because of the unpredictability of player movements performed during field-based team sports. However, with improvements in technology, time-motion analysis has allowed researchers to document the detailed movement patterns of team-sport athletes. Studies that have published time-motion analysis during competition, in general, have reported the mean distance and duration of sprints during field-based team sports to be between 10-20m and 2-3 seconds, respectively. Unfortunately, the vast majority of these studies have not reported the specific movement patterns of RSA, which is proposed as an important fitness component of team sports. Furthermore, there have been few studies that have investigated the physiological requirements of one-off, short-duration sprinting and repeated sprints (<10 seconds duration) that is specific to field-based team sports. This review examines the limited data concerning the metabolic changes occurring during this type of exercise, such as energy system contribution, adenosine triphosphate depletion and resynthesis, phosphocreatine degradation and resynthesis, glycolysis and glycogenolysis, and purine nucleotide loss. Assessment of RSA, as a training and research tool, is also discussed.

The Mechanisms of Massage and Effects on Performance, Muscle Recovery and Injury Prevention

Abstract: Many coaches, athletes and sports medicine personnel hold the belief, based on observations and experiences, that massage can provide several benefits to the body such as increased blood flow, reduced muscle tension and neurological excitability, and an increased sense of well-being. Massage can produce mechanical pressure, which is expected to increase muscle compliance resulting in increased range of joint motion, decreased passive stiffness and decreased active stiffness (biomechanical mechanisms). Mechanical pressure might help to increase blood flow by increasing the arteriolar pressure, as well as increasing muscle temperature from rubbing. Depending on the massage technique, mechanical pressure on the muscle is expected to increase or decrease neural excitability as measured by the Hoffman reflex (neurological mechanisms). Changes in parasympathetic activity (as measured by heart rate, blood pressure and heart rate variability) and hormonal levels (as measured by cortisol levels) following massage result in a relaxation response (physiological mechanisms). A reduction in anxiety and an improvement in mood state also cause relaxation (psychological mechanisms) after massage. Therefore, these benefits of massage are expected to help athletes by enhancing performance and reducing injury risk. However, limited research has investigated the effects of pre-exercise massage on performance and injury prevention. Massage between events is widely investigated because it is believed that massage might help to enhance recovery and prepare athletes for the next event. Unfortunately, very little scientific data has supported this claim. The majority of research on psychological effects of massage has concluded that massage produces positive effects on recovery (psychological mechanisms). Post-exercise massage has been shown to reduce the severity of muscle soreness but massage has no effects on muscle functional loss. Notwithstanding the belief that massage has benefits for athletes, the effects of different types of massage (e.g. petrissage, effleurage, friction) or the appropriate timing of massage (pre-exercise vs post-exercise) on performance, recovery from injury, or as an injury prevention method are not clear. Explanations are lacking, as the mechanisms of each massage technique have not been widely investigated. Therefore, this article discusses the possible mechanisms of massage and provides a discussion of the limited evidence of massage on performance, recovery and muscle injury prevention. The limitations of previous research are described and further research is recommended.

Multiple sprint work : physiological responses, mechanisms of fatigue and the influence of aerobic fitness.

Abstract: The activity patterns of many sports (e.g. badminton, basketball, soccer and squash) are intermittent in nature, consisting of repeated bouts of brief (≤6-second) maximal/near-maximal work interspersed with relatively short (≤60-second) moderate/low-intensity recovery periods. Although this is a general description of the complex activity patterns experienced in such events, it currently provides the best means of directly assessing the physiological response to this type of exercise. During a single short (5- to 6-second) sprint, adenosine triphosphate (ATP) is resynthesised predominantly from anaerobic sources (phosphocreatine [PCr] degradation and glycolysis), with a small (<10%) contribution from aerobic metabolism. During recovery, oxygen uptake (V-dotO2) remains elevated to restore homeostasis via processes such as the replenishment of tissue oxygen stores, the resynthesis of PCr, the metabolism of lactate, and the removal of accumulated intracellular inorganic phosphate (Pi). If recovery periods are relatively short, V-dotO2 remains elevated prior to subsequent sprints and the aerobic contribution to ATP resynthesis increases. However, if the duration of the recovery periods is insufficient to restore the metabolic environment to resting conditions, performance during successive work bouts may be compromised. Although the precise mechanisms of fatigue during multiple sprint work are difficult to elucidate, evidence points to a lack of available PCr and an accumulation of intracellular Pi as the most likely causes. Moreover, the fact that both PCr resynthesis and the removal of accumulated intracellular Pi are oxygen-dependent processes has led several authors to propose a link between aerobic fitness and fatigue during multiple sprint work. However, whilst the theoretical basis for such a relationship is compelling, corroborative research is far from substantive. Despite years of investigation, limitations in analytical techniques combined with methodological differences between studies have left many issues regarding the physiological response to multiple sprint work unresolved. As such, multiple sprint work provides a rich area for future applied sports science research.

Designing resistance training programmes to enhance muscular fitness: a review of the acute programme variables.

Abstract: The popularity of resistance training has grown immensely over the past 25 years, with extensive research demonstrating that not only is resistance training an effective method to improve neuromuscular function, it can also be equally effective in maintaining or improving individual health status. However, designing a resistance training programme is a complex process that incorporates several acute programme variables and key training principles. The effectiveness of a resistance training programme to achieve a specific training outcome (i.e. muscular endurance, hypertrophy, maximal strength, or power) depends on manipulation of the acute programme variables, these include: (i) muscle action; (ii) loading and volume; (iii) exercise selection and order; (iv) rest periods; (v) repetition velocity; and (vi) frequency. Ultimately, it is the acute programme variables, all of which affect the degree of the resistance training stimuli, that determine the magnitude to which the neuromuscular, neuroendocrine and musculoskeletal systems adapt to both acute and chronic resistance exercise. This article reviews the available research that has examined the application of the acute programme variables and their influence on exercise performance and training adaptations. The concepts presented in this article represent an important approach to effective programme design. Therefore, it is essential for those involved with the prescription of resistance exercise (i.e. strength coaches, rehabilitation specialists, exercise physiologists) to acquire a fundamental understanding of the acute programme variables and the importance of their practical application in programme design.

Post-activation potentiation: underlying physiology and implications for motor performance.

Abstract: The response of muscle to volitional or electrically induced stimuli is affected by its contractile history. Fatigue is the most obvious effect of contractile history reflected by the inability of a muscle to generate an expected level of force. However, fatigue can coexist with post-activation potentiation (PAP), which serves to improve muscular performance, especially in endurance exercise and activities involving speed and power. The measured response of muscular performance following some form of contractile activity is the net balance between processes that cause fatigue and the simultaneous processes that result in potentiation. Optimal performance occurs when fatigue has subsided but the potentiated effect still exists. PAP has been demonstrated using electrically induced twitch contractions and attributed to phosphorylation of myosin regulatory light chains, which makes actin and myosin more sensitive to Ca(2+). The potentiated state has also been attributed to an increase in alpha-motoneuron excitability as reflected by changes in the H-reflex. However, the significance of PAP to functional performance has not been well established. A number of recent studies have applied the principles of PAP to short-term motor performance as well as using it as a rationale for producing long-term neuromuscular changes through complex training. Complex training is a training strategy that involves the execution of a heavy resistance exercise (HRE) prior to performing an explosive movement with similar biomechanical characteristics, referred to as a complex pair. The complex pair is then repeated for a number of sets and postulated that over time will produce long-term changes in the ability of a muscle to generate power. The results of these studies are equivocal at this time and, in fact, no training studies have actually been undertaken. The discrepancies among the results of the various studies is due in part to differences in methodology and design, with particular reference to the mode and intensity of the HRE, the length of the rest interval within and between the complex pairs, the type of explosive activity, the training history of the participants, and the nature of the dependent variables. In addition, few of the applied studies have actually included measures of twitch response or H-reflex to determine if the muscles of interest are potentiated. There is clearly more research required in order to clarify the functional significance of PAP and, in particular, the efficacy of complex training in producing long-term neuromuscular adaptations.

Exercise-induced oxidative stress: Myths, realities and physiological relevance

Abstract: Although assays for the most popular markers of exercise-induced oxidative stress may experience methodological flaws, there is sufficient credible evidence to suggest that exercise is accompanied by an increased generation of free radicals, resulting in a measurable degree of oxidative modifications to various molecules. However, the mechanisms responsible are unclear. A common assumption that increased mitochondrial oxygen consumption leads per se to increased reactive oxygen species (ROS) production is not supported by in vitro and in vivo data. The specific contributions of other systems (xanthine oxidase, inflammation, haem protein auto-oxidation) are poorly characterised. It has been demonstrated that ROS have the capacity to contribute to the development of muscle fatigue in situ, but there is still a lack of convincing direct evidence that ROS impair exercise performance in vivo in humans. It remains unclear whether exercise-induced oxidative modifications have little significance, induce harmful oxidative damage, or are an integral part of redox regulation. It is clear that ROS play important roles in numerous physiological processes at rest; however, the detailed physiological functions of ROS in exercise remain to be elucidated.

Models to Explain Fatigue during Prolonged Endurance Cycling

Abstract: Much of the previous research into understanding fatigue during prolonged cycling has found that cycling performance may be limited by numerous physiological, biomechanical, environmental, mechanical and psychological factors. From over 2000 manuscripts addressing the topic of fatigue, a number of diverse cause-and-effect models have been developed. These include the following models: (i) cardiovascular/anaerobic; (ii) energy supply/energy depletion; (iii) neuromuscular fatigue; (iv) muscle trauma; (v) biomechanical; (vi) thermoregulatory; (vii) psychological/motivational; and (viii) central governor. More recently, however, a complex systems model of fatigue has been proposed, whereby these aforementioned linear models provide afferent feedback that is integrated by a central governor into our unconscious perception of fatigue. This review outlines the more conventional linear models of fatigue and addresses specifically how these may influence the development of fatigue during cycling. The review concludes by showing how these linear models of fatigue might be integrated into a more recently proposed nonlinear complex systems model of exercise-induced fatigue.

Physical activity in the prevention and amelioration of osteoporosis in women : interaction of mechanical, hormonal and dietary factors.

Abstract: levies a financial burden on those who fear and experience bone fractures. Physical activity as a way to prevent osteoporosis is based on evidence that it can regulate bone maintenance and stimulate bone formation including the accumula

The Use of Vibration Training to Enhance Muscle Strength and Power

Abstract: Vibration has been combined with conventional resistance training in an attempt to attain greater gains in neuromuscular performance than from conventional resistance training alone. Although there is a lack of strictly controlled studies on the vibration training effect, current findings in this area suggest that vibration may have a beneficiary acute and/or chronic training effect on strength and power enhancement. However, the effect of vibration on strength and power development appears dependent upon the vibration characteristics (method of application, amplitude and frequency) and exercise protocols (training type, intensity and volume) employed. Vibration amplitude and frequency determine the load that vibration imposes on the neuromuscular system. This vibration load should be in an optimal range to elicit strength and power enhancement. To activate the muscle most effectively, vibration frequency should be in the range of 30-50 Hz. It is less clear to what the optimal amplitude should be, but smaller amplitudes may be insufficient to elicit an enhancement. It should also be noted that the method of vibration application (i.e. vibration applied directly or indirectly to a targeted muscle) may have an influence on the magnitude of amplitude and frequency that are delivered to the muscle and, therefore, may have an influence on vibration training effect. The employment of a greater exercise intensity and volume within a vibration training programme may facilitate a larger enhancement in strength and power. In addition, benefits from vibration training may be greater in elite athletes than non-elite athletes. Further studies are required to examine these inter-dependencies, especially in relation to chronic adaptation to dynamic exercises, which are the most relevant response to practitioners, but where the least amount of research has been undertaken.

The Role of Biomechanics in Maximising Distance and Accuracy of Golf Shots

Abstract: Golf biomechanics applies the principles and technique of mechanics to the structure and function of the golfer in an effort to improve golf technique and performance. A common recommendation for technical correction is maintaining a single fixed centre hub of rotation with a two-lever one-hinge moment arm to impart force on the ball. The primary and secondary spinal angles are important for conservation of angular momentum using the kinetic link principle to generate high club-head velocity. When the golfer wants to maximise the distance of their drives, relatively large ground reaction forces (GRF) need to be produced. However, during the backswing, a greater proportion of the GRF will be observed on the back foot, with transfer of the GRF on to the front foot during the downswing/acceleration phase. Rapidly stretching hip, trunk and upper limb muscles during the backswing, maximising the X-factor early in the downswing, and uncocking the wrists when the lead arm is about 30° below the horizontal will take advantage of the summation of force principle. This will help generate large angular velocity of the club head, and ultimately ball displacement. Physical conditioning will help to recruit the muscles in the correct sequence and to optimum effect. To maximise the accuracy of chipping and putting shots, the golfer should produce a lower grip on the club and a slower/shorter backswing. Consistent patterns of shoulder and wrist movements and temporal patterning result in successful chip shots. Qualitative and quantitative methods are used to biomechanically assess golf techniques. Two- and three-dimensional videography, force plate analysis and electromyography techniques have been employed. The common golf biomechanics principles necessary to understand golf technique are stability, Newton’s laws of motion (inertia, acceleration, action reaction), lever arms, conservation of angular momentum, projectiles, the kinetic link principle and the stretch-shorten cycle. Biomechanics has a role in maximising the distance and accuracy of all golf shots (swing and putting) by providing both qualitative and quantitative evidence of body angles, joint forces and muscle activity patterns. The quantitative biomechanical data needs to be interpreted by the biomechanist and translated into coaching points for golf professionals and coaches. An understanding of correct technique will help the sports medicine practitioner provide sound technical advice and should help reduce the risk of golfing injury.

The science of cycling: physiology and training - part 1.

Abstract: The aim of this review is to provide greater insight and understanding regarding the scientific nature of cycling. Research findings are presented in a practical manner for their direct application to cycling. The two parts of this review provide information that is useful to athletes, coaches and exercise scientists in the prescription of training regimens, adoption of exercise protocols and creation of research designs. Here for the first time, we present rationale to dispute prevailing myths linked to erroneous concepts and terminology surrounding the sport of cycling. In some studies, a review of the cycling literature revealed incomplete characterisation of athletic performance, lack of appropriate controls and small subject numbers, thereby complicating the understanding of the cycling research. Moreover, a mixture of cycling testing equipment coupled with a multitude of exercise protocols stresses the reliability and validity of the findings. Our scrutiny of the literature revealed key cycling performance-determining variables and their training-induced metabolic responses. The review of training strategies provides guidelines that will assist in the design of aerobic and anaerobic training protocols. Paradoxically, while maximal oxygen uptake (VO2max) is generally not considered a valid indicator of cycling performance when it is coupled with other markers of exercise performance (e.g. blood lactate, power output, metabolic thresholds and efficiency/economy), it is found to gain predictive credibility. The positive facets of lactate metabolism dispel the ‘lactic acid myth’. Lactate is shown to lower hydrogen ion concentrations rather than raise them, thereby retarding acidosis. Every aspect of lactate production is shown to be advantageous to cycling performance. To minimise the effects of muscle fatigue, the efficacy of employing a combination of different high cycling cadences is evident. The subconscious fatigue avoidance mechanism ‘teleoanticipation’ system serves to set the tolerable upper limits of competitive effort in order to assure the athlete completion of the physical challenge. Physiological markers found to be predictive of cycling performance include: (i) power output at the lactate threshold (LT2); (ii) peak power output (Wpeak) indicating a power/weight ratio of ≥5.5 W/kg; (iii) the percentage of type I fibres in the vastus lateralis; (iv) maximal lactate steady-state, representing the highest exercise intensity at which blood lactate concentration remains stable; (v) Wpeak at LT2; and (vi) Wpeak during a maximal cycling test. Furthermore, the unique breathing pattern, characterised by a lack of tachypnoeic shift, found in professional cyclists may enhance the efficiency and metabolic cost of breathing. The training impulse is useful to characterise exercise intensity and load during training and competition. It serves to enable the cyclist or coach to evaluate the effects of training strategies and may well serve to predict the cyclist’s performance. Findings indicate that peripheral adaptations in working muscles play a more important role for enhanced submaximal cycling capacity than central adaptations. Clearly, relatively brief but intense sprint training can enhance both glycolytic and oxidative enzyme activity, maximum short-term power output and VO2max. To that end, it is suggested to replace ~15% of normal training with one of the interval exercise protocols. Tapering, through reduction in duration of training sessions or the frequency of sessions per week while maintaining intensity, is extremely effective for improvement of cycling time-trial performance. Overuse and over-training disabilities common to the competitive cyclist, if untreated, can lead to delayed recovery.

Challenges in Understanding the Influence of Maximal Power Training on Improving Athletic Performance

Abstract: The ability to optimise muscular power output is considered fundamental to successful performance of many athletic and sporting activities. Consequently, a great deal of research has investigated methods to improve power output and its transference to athletic performance. One issue that makes comparisons between studies difficult is the different modes of dynamometry (isometric, isokinetic and isoinertial) used to measure strength and power. However, it is recognised that isokinetic and isometric assessment bear little resemblance to the accelerative/decelerative motion implicit in limb movement during resistance training and sporting performance. Furthermore, most people who train to increase power would have limited or no access to isometric and/or isokinetic dynamometry. It is for these reasons and for the sake of brevity that the findings of isoinertial (constant gravitational load) research will provide the focus of much of the discussion in this review.

Does neuromuscular electrical stimulation strengthen the quadriceps femoris? A systematic review of randomised controlled trials.

Abstract: Devices for neuromuscular electrical stimulation (NMES) are increasingly used by individuals without specific injuries and are standard equipment in most physical therapy practices. The most often stimulated muscle group is the quadriceps femoris. We designed a systematic review and meta-analysis of randomised controlled trials to determine whether NMES is an effective modality for strength augmentation of the quadriceps femoris. A full content search for randomised controlled trials was performed in Medline, Embase, Cinahl, the Cochrane Controlled Trials Register and the Physical Therapy Evidence Database. Maximum volitional isometric or isokinetic muscle torque in Nm was used as main outcome measure. Thirty-five trials were included and evaluated. A fundamental distinction was made between the trials using subjects with unimpaired quadriceps femoris muscles and the trials using post-injury or post-operative subjects. In the unimpaired quadriceps subgroup, meta-analyses were performed for the comparisons 'NMES versus no exercises' and 'NMES versus volitional exercises'. All other comparisons were evaluated descriptively. The included trials were generally of poor quality and meta-analytic data indicate that publication bias may be present. The evaluated data suggest that, both for the unimpaired and impaired quadriceps, NMES makes sense compared with doing no exercises but volitional exercises appear to be more effective in most situations. Based on the available evidence, NMES may only be preferred over volitional training for within-cast muscle training and perhaps in specific situations where volitional training does not receive sufficient patient compliance. Further research should be directed toward identifying the clinical impact at activity and participation levels and the optimal stimulation parameters of this modality.

Contribution of school programmes to physical activity levels and attitudes in children and adults

Abstract: Although children and youth currently form the most active segments of the population in developed societies, there is a marked trend toward an increase in sedentary lifestyle among school-age children. The purpose of this review is to analyse the effects of school physical education (PE) programmes on: (i) the physical activity (PA) levels of participants as children and adults; and (ii) attitudes toward PE and PA in the same groups. Based on the literature analysed, it can be suggested that a sufficient quantity of a quality PE programme can contribute significantly to the overall amount of moderate-to-intense PA of the school-age child. Schools also have the potential to influence the habitual PA of children by encouraging increased participation in extracurricular sports activities, by favouring active commuting to school and by providing exercise equipment and supervision for youth in their neighbourhoods. Most young children have a very positive attitude towards PE. However, as they grow older, their perception of PE as a positive experience seems to become more ambiguous. From the few studies available, it seems likely that quality PE programmes help to maintain initial positive perceptions. Future research should address factors influencing the change of perceptions as a child matures. In addition to offering a quality PE programme, schools should ensure that the total weekly amount of PE is sufficient not only to maintain but also to enhance a child’s physical fitness. More research is needed to determine the ability of school PE programmes to influence PA behaviour in adult life and to evaluate strategies that will make optimal use of the curricular time allocated to PE.

Creatine supplementation and exercise performance: recent findings.

Abstract: Creatine monohydrate (Cr) is perhaps one of the most widely used supplements taken in an attempt to improve athletic performance. The aim of this review is to update, summarise and evaluate the findings associated with Cr ingestion and sport and exercise performance with the most recent research available. Because of the large volume of scientific literature dealing with Cr supplementation and the recent efforts to delineate sport-specific effects, this paper focuses on research articles that have been published since 1999. Cr is produced endogenously by the liver or ingested from exogenous sources such as meat and fish. Almost all the Cr in the body is located in skeletal muscle in either the free (Cr: ~40%) or phosphorylated (PCr: ~60%) form and represents an average Cr pool of about 120–140g for an average 70kg person. It is hypothesised that Cr can act though a number of possible mechanisms as a potential ergogenic aid but it appears to be most effective for activities that involve repeated short bouts of high-intensity physical activity. Additionally, investigators have studied a number of different Cr loading programmes; the most common programme involves an initial loading phase of 20 g/day for 5–7 days, followed by a maintenance phase of 3–5 g/day for differing periods of time (1 week to 6 months). When maximal force or strength (dynamic or isotonic contractions) is the outcome measure following Cr ingestion, it generally appears that Cr does significantly impact force production regardless of sport, sex or age. The evidence is much more equivocal when investigating isokinetic force production and little evidence exists to support the use of Cr for isometric muscular performance. There is little benefit from Cr ingestion for the prevention or suppression of muscle damage or soreness following muscular activity. When performance is assessed based on intensity and duration of the exercises, there is contradictory evidence relative to both continuous and intermittent endurance activities. However, activities that involve jumping, sprinting or cycling generally show improved sport performance following Cr ingestion. With these concepts in mind, the focus of this paper is to summarise the effectiveness of Cr on specific performance outcomes rather than on proposed mechanisms of action. The last brief section of this review deals with the potential adverse effects of Cr supplementation. There appears to be no strong scientific evidence to support any adverse effects but it should be noted that there have been no studies to date that address the issue of long-term Cr usage.

A nonlinear dynamic approach for evaluating postural control: new directions for the management of sport-related cerebral concussion.

Abstract: Recent research suggests that traditional biomechanical models of postural stability do not fully characterise the nonlinear properties of postural control. In sports medicine, this limitation is manifest in the postural steadiness assessment approach, which may not be sufficient for detecting the presence of subtle physiological change after injury. The limitation is especially relevant given that return-to-play decisions are being made based on assessment results. This update first reviews the theoretical foundation and limitations of the traditional postural stability paradigm. It then offers, using the clinical example of athletes recovering from cerebral concussion, an alternative theoretical proposition for measuring changes in postural control by applying a nonlinear dynamic measure known as ‘approximate entropy’. Approximate entropy shows promise as a valuable means of detecting previously unrecognised, subtle physiological changes after concussion. It is recommended as an important supplemental assessment tool for determining an athlete’s readiness to resume competitive activity.

Exercise training in obese children and adolescents: current concepts.

Abstract: Childhood obesity has reached epidemic proportions worldwide and is associated with increased cardiovascular mortality and morbidity in adult life. The increase in fat mass in children and adolescents has occurred concomitantly with a decline in reported time for exercise. Evidence suggests that non-physically active children are more likely to become non-physically active adults and that encouraging the development of physical activity habits in children helps establish patterns that continue into adulthood. Dietary treatment of obesity is relatively ineffective in adults and it has been suggested that prevention of obesity in childhood and adolescence should emphasise increased physical activity rather than diet because of fears relating to the adverse effects of inappropriate eating patterns. Despite this, there are very few randomised controlled studies investigating the efficacy of exercise training in obese children or adolescents and many of the extant studies have been poorly controlled and have not specifically stratified the independent effect of exercise versus dietary modification. This review focuses on the well designed controlled trials that have evaluated the effect of exercise training in obese children and adolescents on body composition, haemodynamic and metabolic variables, cardiovascular fitness, muscular strength and vascular function. These studies indicate that, although exercise training does not consistently decrease bodyweight or body mass index, it is associated with beneficial changes in fat and lean body mass, emphasising the importance of comprehensive assessment of body composition in future exercise-training studies. Exercise training improves cardiovascular fitness and muscular strength; however, it seems to have little effect on blood lipid profile or blood pressure in obese young people. Importantly, recent studies have demonstrated that exercise training improves vascular endothelial function, an important surrogate measure that may predict future atherosclerotic risk in obese children and adolescents. Given that improvement in vascular function in these training studies occurred in the absence of changes in lipid fractions, haemodynamic variables or glucose metabolism, exercise appears to have a direct beneficial effect on the vasculature, in addition to its putative benefits through risk-factor modification.

Patellar tendinopathy in athletes: current diagnostic and therapeutic recommendations.

Abstract: Formerly known as ‘jumper’s knee’, patellar tendinopathy gives rise to considerable functional deficit and disability in recreational as well as professional athletes. It can interfere with their performance, often perseveres throughout the sporting career and may be the primary cause to end it. The diagnosis of patellar tendinopathy is primarily a clinical one but new imaging techniques, such as Doppler ultrasonography, may provide additional diagnostic value. Current therapeutic protocols are characterised by wide variability ensuing from anecdotal experience rather than evidence. Moreover, numerous reports in recent years have shattered previous doctrines and dogmatic belief on tendon overuse. Histopathological and biochemical evidence has indicated that the underlying pathology of tendinopathy is not an inflammatory tendinitis but a degenerative tendinosis. Consequently, pain in chronic patellar tendinopathy is not inflammatory in nature, but its exact origin remains unexplained. In pursuit of pathology- and evidence-based management, conservative therapy should be shifted from anti-inflammatory strategies towards a complete rehabilitation with eccentric tendon strengthening as a key element. If conservative management fails, surgery is opted for. However, considering the heterogeneity of surgical procedures and the absence of randomised studies, no conclusive evidence can be drawn from the literature regarding the effectiveness of surgical treatment for patellar tendinopathy. Parallel with the improved knowledge on the pathophysiology and pain mechanisms in patellar tendinopathy, new treatment strategies are expected to emerge in the near future.

The impact of instability resistance training on balance and stability.

Abstract: logical mechanisms controlling stability Topics range from extrinsic factors (environment) to intrinsic factors (ie muscle coordination, vestibular response) Balance is achieved through an interaction of central anticipatory and reflexive actions as well as the active and passive restraints imposed by the muscular system However, less research has attempted to document the effects of balance on performance measures (ie force, power) Furthermore, short- and long-term adaptations to unstable environments need more substantial research While force and other performance measures can be adversely affected by a lack of balance, the transferability of instability training to activities of daily living and sport is not precisely known The applicability of instability and resistance training using unstable platforms or implements may have strong relevance in a rehabilitative or athletic setting Therefore, a comprehensive review of the literature in this area may possibly be of benefit to practitioners who deal with the general population, athletes or persons debilitated by balance and/or stability disabilities

The science of cycling: Factors affecting performance - Part 2

Abstract: This review presents information that is useful to athletes, coaches and exercise scientists in the adoption of exercise protocols, prescription of training regimens and creation of research designs. Part 2 focuses on the factors that affect cycling performance. Among those factors, aerodynamic resistance is the major resistance force the racing cyclist must overcome. This challenge can be dealt with through equipment technological modifications and body position configuration adjustments. To successfully achieve efficient transfer of power from the body to the drive train of the bicycle the major concern is bicycle configuration and cycling body position. Peak power output appears to be highly correlated with cycling success. Likewise, gear ratio and pedalling cadence directly influence cycling economy/efficiency. Knowledge of muscle recruitment throughout the crank cycle has important implications for training and body position adjustments while climbing. A review of pacing models suggests that while there appears to be some evidence in favour of one technique over another, there remains the need for further field research to validate the findings. Nevertheless, performance modelling has important implications for the establishment of performance standards and consequent recommendations for training.

Monitoring of performance and training in rowing

Abstract: Rowing is a strength-endurance type of sport and competition performance depends on factors such as aerobic and anaerobic power, physical power, rowing technique and tactics. Therefore, a rower has to develop several capacities in order to be successful and a valid testing battery of a rower has to include parameters that are highly related to rowing performance. Endurance training is the mainstay in rowing. For the 2000m race, power training at high velocities should be preferred to resistance training at low velocities in order to train more specifically during the off-season. The specific training of the international rower has to be approximately 70% of the whole training time. Several studies have reported different biochemical parameters for monitoring the training of rowers. There is some evidence that plasma leptin is more sensitive to training volume changes than specific stress hormones (e.g. cortisol, testosterone, growth hormone). In rowing, the stress hormone reactions to training volume and/or intensity changes are controversial. The Recovery-Stress Questionnaire for Athletes measures both stress and recovery, and may therefore be more effective than the previously used Borg ratio scale or the Profile of Mood States, which both focus mainly on the stress component. In the future, probably the most effective way to evaluate the training of rowers is to monitor both stress and recovery components at the same time, using both psychometric data together with the biochemical and performance parameters.

Running performance differences between men and women:an update.

Abstract: More than a decade ago it was reported in the journal Nature that the slope of improvement in the men's and women's running records, extrapolated from mean running velocity plotted against historical time, would eventually result in a performance intersection of the sexes across a variety of running distances. The first of these intersections was to occur for 42 000 m before the 21st century. Most of the error in this prediction is probably explained by the linear mathematical treatment and extrapolation of limited performance data, since including world record-setting running performances for women before and after 1985 results in a non-linear data fit. The reality of early, disproportionate improvements in women's running that gave the appearance of an impending convergence with men is best explained by an historical social sports bias. Women's times have now reached a plateau similar to that observed for men at comparative performance milestones in the marathon. Sex differences at distances from 100 to 10 000 m show similar trends. The remaining sex gaps in performance appear biological in origin. Success in distance running and sprinting is determined largely by aerobic capacity and muscular strength, respectively. Because men possess a larger aerobic capacity and greater muscular strength, the gap in running performances between men and women is unlikely to narrow naturally.

Physiological Aspects of Surfboard Riding Performance

Abstract: Surfboard riding (surfing) has experienced a 'boom' in participants and media attention over the last decade at both the recreational and the competitive level. However, despite its increasing global audience, little is known about physiological and other factors related to surfing performance. Time-motion analyses have demonstrated that surfing is an intermittent sport, with arm paddling and remaining stationary representing approximately 50% and 40% of the total time, respectively. Wave riding only accounts for 4-5% of the total time when surfing. It has been suggested that these percentages are influenced mainly by environmental factors. Competitive surfers display specific size attributes. Particularly, a mesomorphic somatotype and lower height and body mass compared with other matched-level aquatic athletes. Data available suggest that surfers possess a high level of aerobic fitness. Upper-body ergometry reveals that peak oxygen uptake (VO2peak) values obtained in surfers are consistently higher than values reported for untrained subjects and comparable with those reported for other upper-body endurance-based athletes. Heart rate (HR) measurements during surfing practice have shown an average intensity between 75% and 85% of the mean HR values measured during a laboratory incremental arm paddling VO2peak test. Moreover, HR values, together with time-motion analysis, suggest that bouts of high-intensity exercise demanding both aerobic and anaerobic metabolism are intercalated with periods of moderate- and low-intensity activity soliciting aerobic metabolism. Minor injuries such as lacerations are the most common injuries in surfing. Overuse injuries in the shoulder, lower back and neck area are becoming more common and have been suggested to be associated with the repetitive arm stroke action during board paddling. Further research is needed in all areas of surfing performance in order to gain an understanding of the sport and eventually to bring surfing to the next level of performance.

Haemorheology in exercise and training.

Abstract: Disruption of the normal rheological properties of blood is considered an independent risk factor for cardiovascular disease and plays a significant role in the aetiology of atherothrombogenesis. The acute increase in whole blood viscosity may unfavourably affect the microcirculatory blood flow and oxygen delivery to the tissues. It is universally accepted that exercise and physical activity performed on a regular basis has health benefits. However, the effects of exercise on the rheological properties of blood have not received much research attention. Recent, limited evidence indicates that the viscosities of whole blood and plasma increase in response to a variety of exercise protocols. The increase in whole blood viscosity is mainly attributed to an increase in haematocrit and plasma viscosity, whereas the deformability and aggregability of red blood cells remain unaltered. The increases in plasma viscosity and haematocrit have been ascribed to exercise-induced haemoconcentration as a result of fluid transfer from the blood to the interstitial spaces. The haemorheological changes associated with strenuous exercise appear to be linked with enhanced oxidative stress and depletion of antioxidant capacity, and that may affect oxygen delivery and availability to the tissues. Although significant advances have been made in many areas of exercise haematology, the long-term effects of endurance training on blood rheology have been very briefly examined and the exact effect of training has not as yet been determined. Available cross-sectional and longitudinal studies indicate that the blood of endurance athletes is more dilute and this has been attributed to an expansion of blood volume, particularly plasma volume as a result of training. The low haematocrit values in trained athletes represent a hydration condition rather than iron stores deficiency. It has been suggested that this hypervolaemia and blood dilutional effect of endurance training may be advantageous for heat dissipation and greater cardiac stroke volume and lower heart rates during exercise. Enhanced blood fluidity also facilitates oxygen delivery to the exercising muscles because of a reduced resistance to blood flow within the microcirculation. Furthermore, the increase in plasma volume may contribute to the body water pool and help offset dehydration. The influence of strength and power training on blood rheology is not known. The physiological mechanisms responsible for and the functional consequences of the haemorheological changes associated with exercise to a large extent remain speculative. The paradox of haematocrit and blood rheology in exercise and training warrants additional studies. Likewise, further investigations are necessary to determine the possible link between overtraining and blood rheological profiles.

Interactions of Metabolic Hormones, Adipose Tissue and Exercise

Abstract: Physiological and psychological systems work together to determine energy intake and output, and thus maintain adipose tissue. In addition, adipose tissue secretes leptin and cytokines, which induces satiety and has been linked to catecholamines, cortisol, insulin, human growth hormone, thyroid hormones, gonadotropin and lipolysis. Thus, adipose tissue is acted upon by a number of physiological stimuli, including hormones, and simultaneously, is an active component in the regulation of its own lipid content. All of the hormones mentioned above are associated with each other and respond to exercise and exercise training. Thus, exercise is one of the major links between the hormonal modulators of energy intake and output. It appears that the sympathetic nervous system and the catecholamines are key components facilitating the lipolytic activity during exercise. These two neuroendocrine factors directly affect adipose metabolism and metabolic hormones that influence adipose metabolism. Acute low- and moderate-intensity exercise causes hormonal changes that facilitate lipolytic activity. Exercise training reduces these hormonal responses, but the sensitivity to these hormones increases so that lipolysis may be facilitated. Large amounts of adipose tissue blunt the metabolic hormonal responses to exercise, but the sensitivity of these hormones is increased; thus maintaining normal lipolytic activity. Although the physiological role of the endocrine system during exercise and training is significant, other training effects may have as great, or greater influence on lipolytic activity in adipose tissue.

Nutritional Considerations in Triathlon

Abstract: Triathlon combines three disciplines (swimming, cycling and running) and competitions last between 1 hour 50 minutes (Olympic distance) and 14 hours (Ironman distance). Independent of the distance, dehydration and carbohydrate (CHO) depletion are the most likely causes of fatigue in triathlon, whereas gastrointestinal (GI) problems, hyperthermia and hyponatraemia are potentially health threatening, especially in longer events. Although glycogen supercompensation may be beneficial for triathlon performance (even Olympic distance), this does not necessarily have to be achieved by the traditional supercompensation protocol. More recently, studies have revealed ways to increase muscle glycogen concentrations to very high levels with minimal modifications in diet and training. During competition, cycling provides the best opportunity to ingest fluids. The optimum CHO concentration seems to be in the range of 5–8% and triathletes should aim to achieve a CHO intake of 60–70 g/hour. Triathletes should attempt to limit body mass losses to 1% of body mass. In all cases, a drink should contain sodium (30–50 mmol/L) for optimal absorption and prevention of hyponatraemia. Post-exercise rehydration is best achieved by consuming beverages that have a high sodium content (>60 mmol/L) in a volume equivalent to 150% of body mass loss. GI problems occur frequently, especially in long-distance triathlon. Problems seem related to the intake of highly concentrated carbohydrate solutions, or hyperosmotic drinks, and the intake of fibre, fat and protein. Endotoxaemia has been suggested as an explanation for some of the GI problems, but this has not been confirmed by recent research. Although mild endotoxaemia may occur after an Ironman-distance triathlon, this does not seem to be related to the incidence of GI problems. Hyponatraemia has occasionally been reported, especially among slow competitors in triathlons and probably arises due to loss of sodium in sweat coupled with very high intakes (8–10L) of water or other low-sodium drinks.

Iliotibial band syndrome in runners: innovations in treatment.

Abstract: 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° 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

The role of apoptosis in age-related skeletal muscle atrophy.

Abstract: Skeletal myocyte atrophy and death contribute to sarcopenia, a condition associated with normal aging. By 80 years of age, it is estimated that humans generally lose 30-40% of skeletal muscle fibres. The mechanism for this loss is unknown; however, it may involve apoptosis. Mitochondrial dysfunction and sarcoplasmic reticulum (SR) stress that occurs with age may be possible stimuli inducing apoptosis. Hence, mitochondria and SR may be important organelles within skeletal myocytes responsible for apoptosis signalling. The activation of apoptosis may be partly responsible for the initiation of muscle protein degradation, loss of muscle nuclei associated with local atrophy, and cell death of the myocyte. Exercise training and caloric restriction are two interventions known to enhance skeletal muscle function. The effects of these interventions on apoptosis are discussed.