Showing papers in "Sports Medicine in 2003"
TL;DR: Exercise is the most effective means of alleviating pain during DOMS, however the analgesic effect is also temporary, and athletes who must train on a daily basis should be encouraged to reduce the intensity and duration of exercise for 1–2 days following intense DOMS-inducing exercise.
Abstract: Delayed onset muscle soreness (DOMS) is a familiar experience for the elite or novice athlete. Symptoms can range from muscle tenderness to severe debilitating pain. The mechanisms, treatment strategies, and impact on athletic performance remain uncertain, despite the high incidence of DOMS. DOMS is most prevalent at the beginning of the sporting season when athletes are returning to training following a period of reduced activity. DOMS is also common when athletes are first introduced to certain types of activities regardless of the time of year. Eccentric activities induce micro-injury at a greater frequency and severity than other types of muscle actions. The intensity and duration of exercise are also important factors in DOMS onset. Up to six hypothesised theories have been proposed for the mechanism of DOMS, namely: lactic acid, muscle spasm, connective tissue damage, muscle damage, inflammation and the enzyme efflux theories. However, an integration of two or more theories is likely to explain muscle soreness. DOMS can affect athletic performance by causing a reduction in joint range of motion, shock attenuation and peak torque. Alterations in muscle sequencing and recruitment patterns may also occur, causing unaccustomed stress to be placed on muscle ligaments and tendons. These compensatory mechanisms may increase the risk of further injury if a premature return to sport is attempted. A number of treatment strategies have been introduced to help alleviate the severity of DOMS and to restore the maximal function of the muscles as rapidly as possible. Nonsteroidal anti-inflammatory drugs have demonstrated dosage-dependent effects that may also be influenced by the time of administration. Similarly, massage has shown varying results that may be attributed to the time of massage application and the type of massage technique used. Cryotherapy, stretching, homeopathy, ultrasound and electrical current modalities have demonstrated no effect on the alleviation of muscle soreness or other DOMS symptoms. Exercise is the most effective means of alleviating pain during DOMS, however the analgesic effect is also temporary. Athletes who must train on a daily basis should be encouraged to reduce the intensity and duration of exercise for 1–2 days following intense DOMS-inducing exercise. Alternatively, exercises targeting less affected body parts should be encouraged in order to allow the most affected muscle groups to recover. Eccentric exercises or novel activities should be introduced progressively over a period of 1 or 2 weeks at the beginning of, or during, the sporting season in order to reduce the level of physical impairment and/or training disruption. There are still many unanswered questions relating to DOMS, and many potential areas for future research.
1,121 citations
TL;DR: This review covers some of the recent investigations into the roles of five growth factors whose activities have been best characterised during tendon healing: insulin-like growth factor-I (IGF-I), transforming growth factor β (TGFβ), vascular endothelial growthFactor (VEGF), platelet-derived growth factor (PDGF), and basic fibroblast growth factor ($FGF).
Abstract: sustained and eventually terminated by a large number and variety of molecules. Growth factors represent one of the most important of the molecular families involved in healing, and a considerable number of studies have been undertaken in an effort to elucidate their many functions. This review covers some of the recent investigations into the roles of five growth factors whose activities have been best characterised during tendon healing: insulin-like growth factor-I (IGF-I), transforming growth factor β (TGFβ), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and basic fibroblast growth factor (bFGF). All five are markedly up-regulated following tendon injury and are active at multiple stages of the healing process. IGF-I has been shown to be highly expressed during the early inflammatory phase in a number of animal tendon healing models, and appears to aid in the proliferation and migration of fibroblasts and to subsequently increase collagen production. TGFβ is also active during inflammation, and has a variety of effects including the regulation of cellular migration and proliferation, and fibronectin binding interactions. VEGF is produced at its highest levels only after the inflammatory phase, at which time it is a powerful stimulator of angiogenesis. PDGF is produced shortly after tendon
923 citations
TL;DR: There appears to be a small day-to-day variability in HR and a steady increase during exercise has been observed in most studies, and the effects of overreaching on submaximal HR are controversial, with some studies showing decreased rates and others no difference.
Abstract: Over the last 20 years, heart rate monitors (HRMs) have become a widely used training aid for a variety of sports. The development of new HRMs has also evolved rapidly during the last two decades. In addition to heart rate (HR) responses to exercise, research has recently focused more on heart rate variability (HRV). Increased HRV has been associated with lower mortality rate and is affected by both age and sex. During graded exercise, the majority of studies show that HRV decreases progressively up to moderate intensities, after which it stabilises. There is abundant evidence from cross-sectional studies that trained individuals have higher HRV than untrained individuals. The results from longitudinal studies are equivocal, with some showing increased HRV after training but an equal number of studies showing no differences. The duration of the training programmes might be one of the factors responsible for the versatility of the results. HRMs are mainly used to determine the exercise intensity of a training session or race. Compared with other indications of exercise intensity, HR is easy to monitor, is relatively cheap and can be used in most situations. In addition, HR and HRV could potentially play a role in the prevention and detection of overtraining. The effects of overreaching on submaximal HR are controversial, with some studies showing decreased rates and others no difference. Maximal HR appears to be decreased in almost all ‘overreaching’ studies. So far, only few studies have investigated HRV changes after a period of intensified training and no firm conclusions can be drawn from these results. The relationship between HR and oxygen uptake (VO2) has been used to predict maximal oxygen uptake (VO2max). This method relies upon several assumptions and it has been shown that the results can deviate up to 20% from the true value. The HR-VO2 relationship is also used to estimate energy expenditure during field conditions. There appears to be general consensus that this method provides a satisfactory estimate of energy expenditure on a group level, but is not very accurate for individual estimations. The relationship between HR and other parameters used to predict and monitor an individual’s training status can be influenced by numerous factors. There appears to be a small day-to-day variability in HR and a steady increase during exercise has been observed in most studies. Furthermore, factors such as dehydration and ambient temperature can have a profound effect on the HR-VO2 relationship.
901 citations
TL;DR: There is a strong need for basic research on the nature of the control and regulating mechanism exerted by the autonomic nervous system on cardiovascular function in athletes, preferably with a multidisciplinary approach between cardiologists, exercise physiologists, pulmonary physiologists and coaches and biomedical engineers.
Abstract: This review examines the influence on heart rate variability (HRV) indices in athletes from training status, different types of exercise training, sex and ageing, presented from both cross-sectional and longitudinal studies. The predictability of HRV in over-training, athletic condition and athletic performance is also included. Finally, some recommendations concerning the application of HRV methods in athletes are made.The cardiovascular system is mostly controlled by autonomic regulation through the activity of sympathetic and parasympathetic pathways of the autonomic nervous system. Analysis of HRV permits insight in this control mechanism. It can easily be determined from ECG recordings, resulting in time series (RR-intervals) that are usually analysed in time and frequency domains. As a first approach, it can be assumed that power in different frequency bands corresponds to activity of sympathetic (0.04-0.15 Hz) and parasympathetic (0.15-0.4 Hz) nerves. However, other mechanisms (and feedback loops) are also at work, especially in the low frequency band. During dynamic exercise, it is generally assumed that heart rate increases due to both a parasympathetic withdrawal and an augmented sympathetic activity. However, because some authors disagree with the former statement and the fact that during exercise there is also a technical problem related to the non-stationary signals, a critical look at interpretation of results is needed. It is strongly suggested that, when presenting reports on HRV studies related to exercise physiology in general or concerned with athletes, a detailed description should be provided on analysis methods, as well as concerning population, and training schedule, intensity and duration. Most studies concern relatively small numbers of study participants, diminishing the power of statistics. Therefore, multicentre studies would be preferable. In order to further develop this fascinating research field, we advocate prospective, randomised, controlled, long-term studies using validated measurement methods. Finally, there is a strong need for basic research on the nature of the control and regulating mechanism exerted by the autonomic nervous system on cardiovascular function in athletes, preferably with a multidisciplinary approach between cardiologists, exercise physiologists, pulmonary physiologists, coaches and biomedical engineers.
768 citations
TL;DR: It is argued that trial-to-trial movement variations within individuals and performance differences observed between individuals may be best interpreted as attempts to exploit the variability that is inherent within and between biological systems.
Abstract: In recent years, concepts and tools from dynamical systems theory have been successfully applied to the study of movement systems, contradicting traditional views of variability as noise or error. From this perspective, it is apparent that variability in movement systems is omnipresent and unavoidable due to the distinct constraints that shape each individual's behaviour. In this position paper, it is argued that trial-to-trial movement variations within individuals and performance differences observed between individuals may be best interpreted as attempts to exploit the variability that is inherent within and between biological systems. That is, variability in movement systems helps individuals adapt to the unique constraints (personal, task and environmental) impinging on them across different timescales. We examine the implications of these ideas for sports medicine, by: (i) focusing on intra-individual variability in postural control to exemplify within-individual real-time adaptations to changing informational constraints in the performance environment; and (ii) interpreting recent evidence on the role of the angiotensin-converting enzyme gene as a genetic (developmental) constraint on individual differences in physical performance. The implementation of a dynamical systems theoretical interpretation of variability in movement systems signals a need to re-evaluate the ubiquitous influence of the traditional 'medical model' in interpreting motor behaviour and performance constrained by disease or injury to the movement system. Accordingly, there is a need to develop new tools for providing individualised plots of motor behaviour and performance as a function of key constraints. Coordination profiling is proposed as one such alternative approach for interpreting the variability and stability demonstrated by individuals as they attempt to construct functional, goal-directed patterns of motor behaviour during each unique performance. Finally, the relative contribution of genes and training to between-individual performance variation is highlighted, with the conclusion that dynamical systems theory provides an appropriate multidisciplinary theoretical framework to explain their interaction in supporting physical performance.
630 citations
TL;DR: The greater professionalism of rugby union has increased scientific research in the sport; however, there is scope for significant refinement of investigations on the physiological demands of the game, and sports-specific testing procedures.
Abstract: Increased professionalism in rugby has elicited rapid changes in the fitness profile of elite players. Recent research, focusing on the physiological and anthropometrical characteristics of rugby players, and the demands of competition are reviewed. The paucity of research on contemporary elite rugby players is highlighted, along with the need for standardised testing protocols. Recent data reinforce the pronounced differences in the anthropometric and physical characteristics of the forwards and backs. Forwards are typically heavier, taller, and have a greater proportion of body fat than backs. These characteristics are changing, with forwards developing greater total mass and higher muscularity. The forwards demonstrate superior absolute aerobic and anaerobic power, and muscular strength. Results favour the backs when body mass is taken into account. The scaling of results to body mass can be problematic and future investigations should present results using power function ratios. Recommended tests for elite players include body mass and skinfolds, vertical jump, speed, and the multi-stage shuttle run. Repeat sprint testing is a possible avenue for more specific evaluation of players. During competition, high-intensity efforts are often followed by periods of incomplete recovery. The total work over the duration of a game is lower in the backs compared with the forwards; forwards spend greater time in physical contact with the opposition while the backs spend more time in free running, allowing them to cover greater distances. The intense efforts undertaken by rugby players place considerable stress on anaerobic energy sources, while the aerobic system provides energy during repeated efforts and for recovery. Training should focus on repeated brief high-intensity efforts with short rest intervals to condition players to the demands of the game. Training for the forwards should emphasise the higher work rates of the game, while extended rest periods can be provided to the backs. Players should not only be prepared for the demands of competition, but also the stress of travel and extreme environmental conditions. The greater professionalism of rugby union has increased scientific research in the sport; however, there is scope for significant refinement of investigations on the physiological demands of the game, and sports-specific testing procedures.
581 citations
TL;DR: In the child, hip pathology can present as knee pain so a careful hip exam is important in the child presenting with an insidious onset of knee pain, and other common injuries in young athletes discussed include anterior cruciate ligament injuries, ankle sprains and ankle fractures.
Abstract: It is estimated that 30 million children in the US participate in organised sports programmes. As more and more children participate in sports and recreational activities, there has been an increase in acute and overuse injuries. Emergency department visits are highest among the school-age to young adult population. Over one-third of school-age children will sustain an injury severe enough to be treated by a doctor or nurse. The yearly costs have been estimated to be as high as 1.8 billion US dollars. There are physical and physiological differences between children and adults that may cause children to be more vulnerable to injury. Factors that contribute to this difference in vulnerability include: children have a larger surface area to mass ratio, children have larger heads proportionately, children may be too small for protective equipment, growing cartilage may be more vulnerable to stresses and children may not have the complex motor skills needed for certain sports until after puberty. The most commonly injured areas of the body include the ankle and knee followed by the hand, wrist, elbow, shin and calf, head, neck and clavicle. Contusions and strains are the most common injuries sustained by young athletes. In early adolescence, apophysitis or strains at the apophyses are common. The most common sites are at the knee (Osgood-Schlatter disease), at the heel (Sever's disease) and at the elbow (Little League Elbow). Non-traumatic knee pain is one of the most common complaints in the young athlete. Patellar Femoral Pain Syndrome (PFPS) has a constellation of causes that include overuse, poor tracking of the patellar, malalignment problems of the legs and foot problems, such as pes planus. In the child, hip pathology can present as knee pain so a careful hip exam is important in the child presenting with an insidious onset of knee pain. Other common injuries in young athletes discussed include anterior cruciate ligament injuries, ankle sprains and ankle fractures. Prevention of sports and recreation-related injuries is the ideal. There are six potential ways to prevent injuries in general: (i) the pre-season physical examination; (ii) medical coverage at sporting events; (iii) proper coaching; (iv) adequate hydration; (v) proper officiating; and (vi) proper equipment and field/surface playing conditions.
555 citations
TL;DR: A number of conclusions can be drawn regarding the effects of active warm up on performance and the role of warm up in different environmental conditions, especially for endurance events where a critical core temperature may limit performance.
Abstract: While warm up is considered to be essential for optimum performance, there is little scientific evidence supporting its effectiveness in many situations. As a result, warm-up procedures are usually based on the trial and error experience of the athlete or coach, rather than on scientific study. Summarising the findings of the many warm-up studies conducted over the years is difficult. Many of the earlier studies were poorly controlled, contained few study participants and often omitted statistical analyses. Furthermore, over the years, warm up protocols consisting of different types (e.g. active, passive, specific) and structures (e.g. varied intensity, duration and recovery) have been used. Finally, while many studies have investigated the physiological responses to warm up, relatively few studies have reported changes in performance following warm up. The first part of this review critically analyses reported changes in performance following various active warm-up protocols. While there is a scarcity of well-controlled studies with large subject numbers and appropriate statistical analyses, a number of conclusions can be drawn regarding the effects of active warm up on performance. Active warm up tends to result in slightly larger improvements in short-term performance ( 10 seconds, but <5 minutes) if it allows the athlete to begin the subsequent task in a relatively non-fatigued state, but with an elevated baseline oxygen consumption (VO2). While active warm up has been reported to improve endurance performance, it may have a detrimental effect on endurance performance if it causes a significant increase in thermoregulatory strain. The addition of a brief, task-specific burst of activity has been reported to provide further ergogenic benefits for some tasks. By manipulating intensity, duration and recovery, many different warm-up protocols may be able to achieve similar physiological and performance changes. Finally, passive warm-up techniques may be important to supplement or maintain temperature increases produced by an active warm up, especially if there is an unavoidable delay between the warm up and the task and/or the weather is cold. Further research is required to investigate the role of warm up in different environmental conditions, especially for endurance events where a critical core temperature may limit performance.
531 citations
TL;DR: Despite limited scientific evidence supporting their effectiveness, warm-up routines prior to exercise are a well-accepted practice and can be broadly classified into two major categories: passive warm up or active warm up.
Abstract: Despite limited scientific evidence supporting their effectiveness, warm-up routines prior to exercise are a well-accepted practice. The majority of the effects of warm up have been attributed to temperature-related mechanisms (e.g. decreased stiffness, increased nerve-conduction rate, altered force-velocity relationship, increased anaerobic energy provision and increased thermoregulatory strain), although non-temperature-related mechanisms have also been proposed (e.g. effects of acidaemia, elevation of baseline oxygen consumption (VO2) and increased postactivation potentiation). It has also been hypothesised that warm up may have a number of psychological effects (e.g. increased preparedness). Warm-up techniques can be broadly classified into two major categories: passive warm up or active warm up. Passive warm up involves raising muscle or core temperature by some external means, while active warm up utilises exercise. Passive heating allows one to obtain the increase in muscle or core temperature achieved by active warm up without depleting energy substrates. Passive warm up, although not practical for most athletes, also allows one to test the hypothesis that many of the performance changes associated with active warm up can be largely attributed to temperature-related mechanisms.
514 citations
TL;DR: Long-term endurance training significantly influences how the autonomic nervous system controls heart function, and increases parasympathetic activity and decreases sympathetic activity in the human heart at rest.
Abstract: Long-term endurance training significantly influences how the autonomic nervous system controls heart function. Endurance training increases parasympathetic activity and decreases sympathetic activity in the human heart at rest. These two training-induced autonomic effects, coupled with a possible reduction in intrinsic heart rate, decrease resting heart rate. Long-term endurance training also decreases submaximal exercise heart rate by reducing sympathetic activity to the heart. Physiological ageing is associated with a reduction in parasympathetic control of the heart; this decline in parasympathetic activity can be reduced by regular endurance exercise. Some research has indicated that females have increased parasympathetic and decreased sympathetic control of heart rate. These gender-specific autonomic differences probably contribute to a decreased cardiovascular risk and increased longevity observed in females.
479 citations
TL;DR: There has been a very rapid secular decline in the 20mSRT performance of children and adolescents over the last 20 years, at least in developed countries, with a sample-weighted mean decline of 0.43% of mean values per year.
Abstract: It is widely believed that the performance of children and adolescents on aerobic fitness tests is declining. To test this hypothesis, this meta-analysis compared the results of 55 reports of the performance of children and adolescents aged 6–19 years who have used the 20m shuttle run test (20mSRT). All data were collected in the period 1981–2000. Following corrections for methodological variation, the results of all studies were expressed using the common metric of running speed (km/h) at the last completed stage. Raw data were combined with pseudodata generated from reported means and standard deviations using Monte Carlo simulation. Where data were available on children and adolescents from the same country of the same age and sex, but tested at different times, linear regression was used to calculate rates of change. This was possible for 11 (mainly developed) countries, representing a total of 129 882 children and adolescents in 151 age × sex × country slices. There has been a significant decline in performance in the 11 countries where data were available, and in most age × sex groups, with a sample-weighted mean decline of 0.43% of mean values per year. The decline was most marked in older age groups and the rate of decline was similar for boys and girls. There has been a very rapid secular decline in the 20mSRT performance of children and adolescents over the last 20 years, at least in developed countries. The rate of decline is not related to the change in the country’s relative wealth, as quantified by per capita gross domestic product (GDP).
TL;DR: The development of performance in competition is achieved through a training process that is designed to induce automation of motor skills and enhance structural and metabolic functions to improve performance at competition time.
Abstract: The development of performance in competition is achieved through a training process that is designed to induce automation of motor skills and enhance structural and metabolic functions. Training also promotes self-confidence and a tolerance for higher training levels and competition. In general, there are two broad categories of athletes that perform at the highest level: (i) the genetically talented (the thoroughbred); and (ii) those with a highly developed work ethic (the workhorse) with a system of training guiding their effort. The dynamics of training involve the manipulation of the training load through the variables: intensity, duration and frequency. In addition, sport activities are a combination of strength, speed and endurance executed in a coordinated and efficient manner with the development of sport-specific characteristics. Short- and long-term planning (periodisation) requires alternating periods of training load with recovery for avoiding excessive fatigue that may lead to overtraining. Overtraining is long-lasting performance incompetence due to an imbalance of training load, competition, non-training stressors and recovery. Furthermore, annual plans are normally constructed in macro-, meso- and microcycles around the competitive phases with the objective of improving performance for a peak at a predetermined time. Finally, at competition time, optimal performance requires a healthy body, and integration of not only the physiological elements but also the psychological, technical and tactical components.
TL;DR: The maximal lactate steady state ( MLSS) is defined as the highest blood lactate concentration (MLSSc) and work load (MLSSw) that can be maintained over time without a continualBlood lactate accumulation.
Abstract: concentration (MLSSc) and work load (MLSSw) that can be maintained over time without a continual blood lactate accumulation. A close relationship between endurance sport performance and MLSSw has been reported and the average velocity over a marathon is just below MLSSw. This work rate delineates the lowto high-intensity exercises at which carbohydrates contribute more than 50% of the total energy need and at which the fuel mix switches (crosses over) from predominantly fat to predominantly carbohydrate. The rate of metabolic adenosine triphosphate (ATP) turnover increases as a direct function of metabolic power
TL;DR: Empirical evidence strongly suggests that regular exercise confers beneficial effects on cardiovascular health, and shear stress-mediated improvement in endothelial function provides one plausible explanation for the cardioprotective benefits of exercise training.
Abstract: In the past two decades, normal endothelial function has been identified as integral to vascular health. The endothelium produces numerous vasodilator and vasoconstrictor compounds that regulate vascular tone; the vasodilator, nitric oxide (NO), has additional antiatherogenic properties, is probably the most important and best characterised mediator, and its intrinsic vasodilator function is commonly used as a surrogate index of endothelial function. Many conditions, including atherosclerosis, diabetes mellitus and even vascular risk factors, are associated with endothelial dysfunction, which, in turn, correlates with cardiovascular mortality. Furthermore, clinical benefit and improved endothelial function tend to be associated in response to interventions. Shear stress on endothelial cells is a potent stimulus for NO production. Although the role of endothelium-derived NO in acute exercise has not been fully resolved, exercise training involving repetitive bouts of exercise over weeks or months up-regulates endothelial NO bioactivity. Animal studies have found improved endothelium-dependent vasodilation after as few as 7 days of exercise. Consequent changes in vasodilator function appear to persist for several weeks but may regress with long-term training, perhaps reflecting progression to structural adaptation which may, however, have been partly endothelium-dependent. The increase in blood flow, and change in haemodynamics that occur during acute exercise may, therefore, provide a stimulus for both acute and chronic changes in vascular function. Substantial differences within species and within the vasculature appear to exist. In humans, exercise training improves endothelium-dependent vasodilator function, not only as a localised phenomenon in the active muscle group, but also as a systemic response when a relatively large mass of muscle is activated regularly during an exercise training programme. Individuals with initially impaired endothelial function at baseline appear to be more responsive to exercise training than healthy individuals; that is, it is more difficult to improve already normal vascular function. While improvement is reflected in increased NO bioactivity, the detail of mechanisms, for example the relative importance of up-regulation of mediators and antioxidant effects, is unclear. Optimum training schedules, possible sequential changes and the duration of benefit under various conditions also remain largely unresolved. In summary, epidemiological evidence strongly suggests that regular exercise confers beneficial effects on cardiovascular health. Shear stress-mediated improvement in endothelial function provides one plausible explanation for the cardioprotective benefits of exercise training.
TL;DR: It appears that trained individuals have a more rapid return of post-exercise metabolism to resting levels after exercising at either the same relative or absolute work rate; however, studies after more strenuous exercise bouts are needed.
Abstract: In the recovery period after exercise there is an increase in oxygen uptake termed the ‘excess post-exercise oxygen consumption’ (EPOC), consisting of a rapid and a prolonged component. While some studies have shown that EPOC may last for several hours after exercise, others have concluded that EPOC is transient and minimal. The conflicting results may be resolved if differences in exercise intensity and duration are considered, since this may affect the metabolic processes underlying EPOC. Accordingly, the absence of a sustained EPOC after exercise seems to be a consistent finding in studies with low exercise intensity and/or duration. The magnitude of EPOC after aerobic exercise clearly depends on both the duration and intensity of exercise. A curvilinear relationship between the magnitude of EPOC and the intensity of the exercise bout has been found, whereas the relationship between exercise duration and EPOC magnitude appears to be more linear, especially at higher intensities. Differences in exercise mode may potentially contribute to the discrepant findings of EPOC magnitude and duration. Studies with sufficient exercise challenges are needed to determine whether various aerobic exercise modes affect EPOC differently. The relationships between the intensity and duration of resistance exercise and the magnitude and duration of EPOC have not been determined, but a more prolonged and substantial EPOC has been found after hardversus moderate-resistance exercise. Thus, the intensity of resistance exercise seems to be of importance for EPOC. Lastly, training status and sex may also potentially influence EPOC magnitude, but this may be problematic to determine. Still, it appears that trained individuals have a more rapid return of post-exercise metabolism to resting levels after exercising at either the same relative or absolute work rate; however, studies after more strenuous exercise bouts are needed. It is not determined if there is a sex effect on EPOC. Finally, while some of the mechanisms underlying the more rapid EPOC are well known (replenishment of oxygen stores, adenosine triphosphate/creatine phosphate resynthesis, lactate removal, and increased body temperature, circulation and ventilation), less is known about the mechanisms underlying the prolonged EPOC component. A sustained increased circulation, ventilation and body temperature may contribute, but the cost of this is low. An increased rate of triglyceride/fatty acid cycling and a shift from carbohydrate to fat as substrate source are of importance for the prolonged EPOC component after exhaustive aerobic exercise. Little is known about the mechanisms underlying EPOC after resistance exercise.
TL;DR: Suggestions have been made that carbohydrate availability is the main limiting factor for glycogen synthesis when large quantities of glucose are ingested following exercise.
Abstract: The pattern of muscle glycogen synthesis following glycogen-depleting exercise occurs in two phases. Initially, there is a period of rapid synthesis of muscle glycogen that does not require the presence of insulin and lasts about 30–60 minutes. This rapid phase of muscle glycogen synthesis is characterised by an exercise-induced translocation of glucose transporter carrier protein-4 to the cell surface, leading to an increased permeability of the muscle membrane to glucose. Following this rapid phase of glycogen synthesis, muscle glycogen synthesis occurs at a much slower rate and this phase can last for several hours. Both muscle contraction and insulin have been shown to increase the activity of glycogen synthase, the rate-limiting enzyme in glycogen synthesis. Furthermore, it has been shown that muscle glycogen concentration is a potent regulator of glycogen synthase. Low muscle glycogen concentrations following exercise are associated with an increased rate of glucose transport and an increased capacity to convert glucose into glycogen. The highest muscle glycogen synthesis rates have been reported when large amounts of carbohydrate (1.0–1.85 g/kg/h) are consumed immediately post-exercise and at 15.60 minute intervals thereafter, for up to 5 hours post-exercise. When carbohydrate ingestion is delayed by several hours, this may lead to ∼50% lower rates of muscle glycogen synthesis. The addition of certain amino acids and/ or proteins to a carbohydrate supplement can increase muscle glycogen synthesis rates, most probably because of an enhanced insulin response. However, when carbohydrate intake is high (≥1.2 g/kg/h) and provided at regular intervals, a further increase in insulin concentrations by additional supplementation of protein and/or amino acids does not further increase the rate of muscle glycogen synthesis. Thus, when carbohydrate intake is insufficient ( 1 g/min) of glucose are ingested following exercise.
TL;DR: Current evidence supports a 10% per decade decline in V̇O2max in men and women regardless of activity level, and aging most likely plays a role as studies have demonstrated that training maintenance becomes more difficult with advancing age.
Abstract: Because of the influence of cardiorespiratory fitness on functional independence, quality of life, and cardiovascular disease and all-cause mortality, tremendous interest has been directed towards describing the age-related change in maximal oxygen consumption (VO(2max)). Current evidence supports a 10% per decade decline in VO(2max) in men and women regardless of activity level. High-intensity exercise may reduce this loss by up to 50% in young and middle-aged men, but not older men, if maintained long term. Middle-aged and older women do not appear to be able to reduce loss rates in VO(2max) to less than 10% per decade, which may be related to estrogen status. However, maintaining high-intensity training seems limited to approximately one decade at best and to a select few individuals. While the factors limiting the ability to maintain high-intensity training are not completely known, aging most likely plays a role as studies have demonstrated that training maintenance becomes more difficult with advancing age. Age-related loss of VO(2max) seems to occur in a non-linear fashion in association with declines in physical activity. In sedentary individuals, this non-linear decline generally occurs during the twenties and thirties whereas athletic individuals demonstrate a non-linear decline upon decreasing or ceasing training. Non-linear loss rates are also demonstrated in individuals over the age of 70 years. The decline in VO(2max) seems to be due to both central and peripheral adaptations, primarily reductions in maximal heart rate (HR(max)) and lean body mass (LBM). Exercise training does not influence declines in HR(max), while LBM can be maintained to some degree by exercise. Recommendations for exercise training should include aerobic activities utilising guidelines established by the American College of Sports Medicine for improving CV fitness and health, as well as strength training activities for enhancing LBM.
TL;DR: The use of motion sensors is very promising in the measurement of EE, and has a number of advantages over the DLW method, and if used correctly, both heart rate and questionnaire methods may provide valuable estimates of EE.
Abstract: This review includes an historical overview of the techniques for measuring energy expenditure (EE). Following this overview, the "gold standard" method of measuring EE, the doubly labelled water (DLW) method, is emphasised. Other methods, such as direct calorimetry, indirect calorimetry systems, heart rate and EE relationships, questionnaires and activity recall, motion sensors, combined heart rate and motion sensors for the estimation of EE are then highlighted in relation to their validation against the DLW method. The major advantages and disadvantages for each method are then considered. The preferred method to determine EE is likely to depend principally on factors such as the number of study participants to be monitored, the time period of measurements and the finances available. Small study participant numbers over a short period may be measured accurately by means of indirect calorimetric methods (stationary and portable systems). For periods over 3-4 days, EE should ideally be measured using the DLW method. However, the use of motion sensors is very promising in the measurement of EE, and has a number of advantages over the DLW method. Furthermore, if used correctly, both heart rate and questionnaire methods may provide valuable estimates of EE. Additional studies are needed to examine the possibility of improving the accuracy of measurement by combining two or more techniques. Such information, if confirmed by scientific rigour, may lead to an improvement in the estimation of EE and population-based physical activity levels. The accurate measurement of physical activity and EE is critical from both a research and health prospective. A consideration of the relevant techniques used for the estimation of EE may also help improve the quality of these frequently reported measurements.
TL;DR: There is clearly a need for longitudinal or cross-sectional studies that investigate the relationship between maturity and training with carefully monitored programmes, and it is suggested that intensities higher than 80% of maximal heart rate are necessary to expect a significant improvement in peak V̇O2.
Abstract: Training-induced adaptations in aerobic fitness have been extensively studied in adults, and some exercise scientists have recommended similar training programmes for young people. However, the subject of the response to aerobic training of children and adolescents is controversial. The effects of exercise training on prepubertal children are particularly debatable. The latter may be partly explained by different training designs, which make comparisons between studies very problematic. We have analysed the procedures applied to protocol design and training methods to highlight the real impact of aerobic training on the peak oxygen uptake (V-dotO2) of healthy children and adolescents. In accordance with previously published reviews on trainability in youngsters, research papers were rejected from the final analysis according to criteria such as the lack of a control group, an unclear training protocol, inappropriate statistical procedures, small sample size, studies with trained or special populations, or with no peak V-dotO2 data. Factors such as maturity, group constitution, consistency between training and testing procedures, drop out rates, or attendance were considered, and possible associations with changes in peak V-dotO2 with training are discussed. From 51 studies reviewed, 22 were finally retained. In most of the studies, there was a considerable lack of research regarding circumpubertal individuals in general, and particularly in girls. The results suggest that methodologically listed parameters will exert a potential influence on the magnitude of peak V-dotO2 improvement. Even if little difference is reported for each parameter, it is suggested that the sum of errors will result in a significant bias in the assessment of training effects. The characteristics of each training protocol were also analysed to establish their respective potential influence on peak V-dotO2 changes. In general, aerobic training leads to a mean improvement of 5-6% in the peak V-dotO2 of children or adolescents. When only studies that reported significant training effect were taken into account, the mean improvement in peak V-dotO2 rose to 8-10%. Results suggested that intensities higher than 80% of maximal heart rate are necessary to expect a significant improvement in peak V-dotO2. There is clearly a need for longitudinal or cross-sectional studies that investigate the relationship between maturity and training with carefully monitored programmes. Further research is also needed to compare interval training and continuous training.
TL;DR: It is suggested that the sensation of fatigue is the conscious awareness of changes in subconscious homeostatic control systems, and is derived from a temporal difference between subconscious representations of these homeostatics in neural networks that are induced by changes in the level of activity.
Abstract: In this review, fatigue is described as a conscious sensation rather than a physiological occurrence. We suggest that the sensation of fatigue is the conscious awareness of changes in subconscious homeostatic control systems, and is derived from a temporal difference between subconscious representations of these homeostatic control systems in neural networks that are induced by changes in the level of activity. These mismatches are perceived by consciousness-producing structures in the brain as the sensation of fatigue. In this model, fatigue is a complex emotion affected by factors such as motivation and drive, other emotions such as anger and fear, and memory of prior activity. It is not clear whether the origin of the conscious sensation of fatigue is associated with particular localised brain structures, or is the result of electrophysiological synchronisation of entire brain activity.
TL;DR: The current knowledge and proposed mechanisms for the exercise-induced growth hormone response, the physiological consequences of endurance, strength and power training on the EIGR and its potential effects in elderly populations, including the aged athlete are examined.
Abstract: Human growth hormone (hGH) is secreted in a pulsatile fashion, generally following a circadian rhythm. A number of physiological stimuli can initiate hGH secretion, the most powerful, non-pharmacological of which are sleep and exercise. hGH has many varied roles throughout life, from growth itself, including the turnover of muscle, bone and collagen, to the regulation of selective aspects of metabolic function including increased fat metabolism and the maintenance of a healthier body composition in later life.
TL;DR: These findings suggest that regularly menstruating female athletes, competing in strength-specific sports and intense anaerobic/aerobic sports, do not need to adjust for menstrual cycle phase to maximise performance.
Abstract: This article reviews the potential effects of the female steroid hormone fluctuations during the menstrual cycle on exercise performance. The measurement of estrogen and progesterone concentration to verify menstrual cycle phase is a major consideration in this review. However, even when hormone concentrations are measured, the combination of differences in timing of testing, the high inter- and intra-individual variability in estrogen and progesterone concentration, the pulsatile nature of their secretion and their interaction, may easily obscure possible effects of the menstrual cycle on exercise performance. When focusing on studies using hormone verification and electrical stimulation to ensure maximal neural activation, the current literature suggests that fluctuations in female reproductive hormones throughout the menstrual cycle do not affect muscle contractile characteristics. Most research also reports no changes over the menstrual cycle for the many determinants of maximal oxygen consumption (VO2max), such as lactate response to exercise, bodyweight, plasma volume, haemoglobin concentration, heart rate and ventilation. Therefore, it is not surprising that the current literature indicates that VO2max is not affected by the menstrual cycle. These findings suggest that regularly menstruating female athletes, competing in strength-specific sports and intense anaerobic/aerobic sports, do not need to adjust for menstrual cycle phase to maximise performance. For prolonged exercise performance, however, the menstrual cycle may have an effect. Even though most research suggests that oxygen consumption, heart rate and rating of perceived exertion responses to sub-maximal steady-state exercise are not affected by the menstrual cycle, several studies report a higher cardiovascular strain during moderate exercise in the mid-luteal phase. Nevertheless, time to exhaustion at sub-maximal exercise intensities shows no change over the menstrual cycle. The significance of this finding should be questioned due to the low reproducibility of the time to exhaustion test. During prolonged exercise in hot conditions, a decrease in exercise time to exhaustion is shown during the mid-luteal phase, when body temperature is elevated. Thus, the mid-luteal phase has a potential negative effect on prolonged exercise performance through elevated body temperature and potentially increased cardiovascular strain. Practical implications for female endurance athletes may be the adjustment of competition schedules to their menstrual cycle, especially in hot, humid conditions. The small scope of the current research and its methodological limitations warrant further investigation of the effect of the menstrual cycle on prolonged exercise performance.
TL;DR: In this paper, the authors hypothesise that exercise-related immunosuppression is due to tissue trauma sustained during intense exercise, producing cytokines, which drive the development of a T(H)2 lymphocyte profile.
Abstract: Overtraining syndrome (OTS) occurs where an athlete is training vigorously, yet performance deteriorates. One sign of OTS is suppressed immune function, with an increased incidence of upper respiratory tract infection (URTI). An increased incidence of URTIs is also associated with high volume/intensity training, as well as with excessive exercise (EE), such as a marathon, manifesting between 3-72 hours post-race. Presently, there is no encompassing theory to explain EE and altered immune competence. Recently, it has been conclusively established that T helper lymphocytes (T(H)), a crucial aspect of immune function, represent two distinct functional subsets: T(H)1 and T(H)2 lymphocytes. T(H)1 lymphocytes are associated with cell-mediated immunity (CMI) and the killing of intracellular pathogens, while T(H)2 lymphocytes are associated with humoral immunity and antibody production. When T(H)-precursor cells are activated, the balance is tipped in favour of one or the other. Furthermore, the most appropriate means of determining the T(H)-subset, is by the prevailing cytokine 'pattern'. This paper hypothesises that exercise-related immunosuppression is due to tissue trauma sustained during intense exercise, producing cytokines, which drive the development of a T(H)2 lymphocyte profile. A T(H)2 cell response results in simultaneous suppression of CMI, rendering the athlete susceptible to infection. Additionally, increased levels of circulating stress hormones (cortisol and catecholamines), as well as prostaglandin E(2), support up-regulation of T(H)2 lymphocytes. Marathon-related data are presented to support this hypothesis. It is concluded that an increased incidence of illness associated with OTS and in response to EE is not due to immunosuppression per se, but rather to an altered focus of immune function, with an up-regulation of humoral immunity and suppression of CMI.
TL;DR: The observation that exercise-induced hyperthermia reduces the central activation percentage during maximal isometricmuscle contractions supports the idea that central fatigue is involved in the aetiology ofhyperthermia-induced fatigue.
Abstract: This review focuses on cerebral changes during combined exercise and heat stress, and their relation to fatigue. Dynamic exercise can elevate the core temperature rapidly and high internal body temperatures seem to be an independent cause of fatigue during exercise in hot environments. Thus, in laboratory settings, trained participants become exhausted when they reach a core temperature of approximately 40 degrees C. The observation that exercise-induced hyperthermia reduces the central activation percentage during maximal isometric muscle contractions supports the idea that central fatigue is involved in the aetiology of hyperthermia-induced fatigue. Thus, hyperthermia does not impair the ability of the muscles to generate force, but sustained force production is lowered as a consequence of a reduced neural drive from the CNS. During ongoing dynamic exercise in hot environments, there is a gradual slowing of the electroencephalogram (EEG) whereas hyperthermia does not affect the electromyogram. The frequency shift of the EEG is highly correlated with the participants' perception of exertion, which furthermore may indicate that alterations in cerebral activity, rather than peripheral fatigue, are associated with the hyperthermia-induced development of fatigue. Cerebral blood flow is reduced by approximately 20% during exercise with hyperthermia due to hyperventilation, which causes a lowering of the arterial CO(2) pressure. However, in spite of the reduced blood flow, cerebral glucose and oxygen uptake does not seem to be impaired. Removal of heat from the brain is also an important function of the cerebral blood flow and the lowered perfusion of the brain during exercise and heat stress appears to reduce heat removal by the venous blood. Heat is consequently stored in the brain. The causal relationship between the circulatory changes, the EEG changes and the hyperthermia-induced central fatigue is at the present not well understood and future studies should focus on this aspect.
TL;DR: The importance and relevance of chronic physical activity in the induction of mitochondrial biogenesis is considered, with particular emphasis on how an endurance training programme could positively affect the age-related decline in mitochondrial content and delay the progression of age- and physical inactivity-related diseases.
Abstract: Behavioural and hereditary conditions are known to decrease mitochondrial volume and function within skeletal muscle. This reduces endurance performance, and is manifest both at high- and low-intensity levels of exertion. A programme of regular endurance exercise, undertaken over a number of weeks, produces significant adaptations within skeletal muscle such that noticeable improvements in oxidative capacity are evident, and the related decline in endurance performance can be attenuated. Notwithstanding the important implications that this has for the highly trained endurance athlete, an improvement in mitochondrial volume and function through regular physical activity also endows the previously sedentary and/or aging population with an improved quality of life, and a greater functional independence. An understanding of the molecular and cellular mechanisms that govern the increases in mitochondrial volume with repeated bouts of exercise can provide insights into possible therapeutic interventions to care for those with mitochondrially-based diseases, and those unable to withstand regular physical activity. This review focuses on the recent developments in the molecular aspects of mitochondrial biogenesis in chronically exercising muscle. Specifically, we discuss the initial signalling events triggered by muscle contraction, the activation of transcription factors involved in both nuclear and mitochondrial DNA transcription, as well as the post-translational import mechanisms required for mitochondrial biogenesis. We consider the importance and relevance of chronic physical activity in the induction of mitochondrial biogenesis, with particular emphasis on how an endurance training programme could positively affect the age-related decline in mitochondrial content and delay the progression of age- and physical inactivity-related diseases.
TL;DR: The impact of RTM on the design and interpretation of investigations has as yet received little consideration by exercise scientists and sports physicians.
Abstract: Regression to the mean (RTM) can bias any investigation where the response to treatment is classified relative to initial values for a given variable without the use of an appropriate control group. The phenomenon and resulting errors of interpretation have been recognised by clinicians in a number of disciplines. The causes of RTM include both intra-individual variance and measurement error. The magnitude of RTM can be estimated quite simply, given a knowledge of intra- and inter-individual variance. RTM can be avoided by using a fully controlled experimental design. Difficulties can also be minimised by making duplicate measurements prior to the experimental manipulation, the first measurement serving for classification, and the second (with randomly distributed variance) allowing an assessment of the response to treatment. Less satisfactorily, surrogate measurements (for example, plasma volume for maximal oxygen intake [VO2max]) can assess the bias introduced by an initial non-random sorting of study participants. The impact of RTM on the design and interpretation of investigations has as yet received little consideration by exercise scientists and sports physicians. The response to training is often related to initial measurements of a dependent variable such as heart size, ST segmental depression, fitness or level of physical activity. In particular, analyses of this type have been adduced to support the belief that the response to aerobic training is inversely related to an individual’s VO2max. In fact, RTM may account for a major part of this apparent relationship.
TL;DR: The majority of strength studies examining changes during growth and maturation have investigated isometric actions, which tell us little about the muscle under dynamic conditions, but several studies have indicated that children can be reliably assessed isokinetically using both concentric and eccentric actions.
Abstract: The majority of strength studies examining changes during growth and maturation have investigated isometric actions, which tell us little about the muscle under dynamic conditions. There are numerous methodological issues in the isokinetic testing of paediatric populations that require further investigation. However, several studies have indicated that children can be reliably assessed isokinetically using both concentric and eccentric actions. Most paediatric studies have examined the knee joint and more data are needed to elucidate the reliability of upper body isokinetic strength testing. The age- and sex-associated development of isokinetic strength is less well understood. Studies have indicated that isokinetic strength increases with age but the mechanisms associated with this increase require further investigation. Current data are also conflicting regarding the age at which sex differences become apparent in isokinetic strength. More work is needed to examine the influence of maturation on isokinetic strength development, but available data suggest that maturation is a non-significant contributory factor once stature and body mass are accounted for. Most studies have demonstrated a significant relationship between stature, body mass and isokinetic strength during growth and maturation. The importance that changes in body composition during growth have on isokinetic strength has been investigated using fat-free mass and muscle cross-sectional area. Data have shown that although fat-free mass and muscle cross-sectional area are important contributors to isokinetic strength, other unexplained factors also influence isokinetic strength development. Additional work needs to investigate possible qualitative changes in muscle during growth and maturation. More work is also needed to examine changes in eccentric strength with age and to investigate sex differences in upper body isokinetic strength. Future studies should preferably be longitudinal in nature and examine known covariates simultaneously using appropriate statistical techniques.
TL;DR: The technique of the differential global positioning system (dGPS) has been put forward as a way to monitor the position and speed of an athlete during outdoor activities with acceptable precision, thus controlling the two most important factors of performance in endurance athletics.
Abstract: Most physiological testing of athletes is performed in well-controlled situations in the laboratory. Multiple factors that are hard to control for have limited the use of sport-specific field testing. Recently, the technique of the differential global positioning system (dGPS) has been put forward as a way to monitor the position and speed of an athlete during outdoor activities with acceptable precision, thus controlling the two most important factors of performance in endurance athletics, i.e. inclination and speed. A detailed analysis of performance has been shown to be possible in combination with metabolic gas measurements. The combination of accelerometry and dGPS has also been shown to improve physiological field testing. The technique of dGPS could probably also be combined with other bio-measurements (e.g. electromyography and cycling cadence and power) and may enable other studies of exercise physiology in the field, otherwise restricted to the laboratory environment. This technique may also be of use in general exercise physiology where monitoring of patients with, for example, cardiovascular and pulmonary diseases, could be of interest for the future.
TL;DR: Current research suggests that neither the inclusion of modest amounts of clothing nor the clothing fabric alter thermoregulation or thermal comfort during exercise in warm conditions, but in the cold, most reports do not support an effect of clothing fabric on thermoreGulation; however, there are reports demonstrating an effect.
Abstract: Exercise increases heat production. During exercise in both warm and cold conditions, the major dilemma is the dissipation of the heat produced from muscular activity. The use of clothing generally represents a layer of insulation and as such imposes a barrier to heat transfer and evaporation from the skin surface. In warm environments, additional clothing increases thermal insulation causing more rapid increases in temperature during exercise and imposes a barrier to sweat evaporation. However, clothing can serve a protective function by reducing radiant heat gain and thermal stress. Recent research suggests that neither the inclusion of modest amounts of clothing nor the clothing fabric alter thermoregulation or thermal comfort during exercise in warm conditions. In the cold, most reports do not support an effect of clothing fabric on thermoregulation; however, there are reports demonstrating an effect. Clothing construction does alter thermoregulation during and following exercise in the cold, where fishnet construction offers greater heat dissipation. Future research should include conditions that more closely mimic outdoor conditions, where high work rates, large airflow and high relative humidity can significantly impact thermoregulation.
TL;DR: In conclusion, ‘priming’ exercise has the potential to significantly enhance exercise tolerance and athletic performance, and the optimal combination of the intensity, duration and mode of ‘warm-up’ Exercise, andThe recovery period allowed before the criterion exercise challenge, remain to be determined.
Abstract: 'Warm-up' activity is almost universally performed by athletes prior to their participation in training or competition. However, relatively little is known about the optimal intensity and duration for such exercise, or about the potential mechanisms primed by warm-up that might enhance performance. Recent studies demonstrate that vigorous warm-up exercise that normally results in an elevated blood and presumably muscle lactate concentration has the potential to increase the aerobic energy turnover in subsequent high-intensity exercise. The reduced oxygen deficit is associated with a reduction in both the depletion of the intramuscular phosphocreatine stores and the rate at which lactic acid is produced. Furthermore, the oxygen uptake 'slow component' that develops during high-intensity, ostensibly submaximal, exercise is attenuated. These factors would be hypothesised to predispose to increased exercise tolerance. Interestingly, the elevation of muscle temperature by prior exercise does not appear to be implicated in the altered metabolic and gas exchange responses observed during subsequent exercise. The physiological mechanism(s) that limit the rate and the extent to which muscle oxygen uptake increases following the onset of exercise, and which are apparently altered by the performance of prior heavy exercise, are debated. However, these mechanisms could include oxygen availability, enzyme activity and/or availability of metabolic substrate, and motor unit recruitment patterns. Irrespective of the nature of the control mechanisms that are influenced, 'priming' exercise has the potential to significantly enhance exercise tolerance and athletic performance. The optimal combination of the intensity, duration and mode of 'warm-up' exercise, and the recovery period allowed before the criterion exercise challenge, remain to be determined.