Medicine and sport science最新文献

During prolonged exercise, fluid and salt losses through sweating reduce plasma volume which leads to heart rate drift in association with hyperthermia and reductions in performance. Oral rehydration with water reduces the loss of plasma volume and lessens heart rate drift and hyperthermia. Moreover, the inclusion of sodium in the rehydration solution to levels that double those in sweat (i.e., around 90 mmol/l Na(+)) restores plasma volume when ingested during exercise, and expands plasma volume if ingested pre-exercise. Pre-exercise salt and fluid ingestion with the intention of expanding plasma volume has received an increasing amount of attention in the literature in recent years. In four studies, pre-exercise salt and fluid ingestion improved performance, measured as time to exhaustion, either during exercise in a thermoneutral or in a hot environment. While in a hot environment, the performance improvements were linked to lowering of core temperatures and heart rate, the reasons for the improved performance in a thermoneutral environment remain unclear. However, when ingesting pre-exercise saline solutions above 0.9% (i.e., > 164 mmol/l Na(+)), osmolality and plasma sodium increase and core temperature remain at dehydration levels. Thus, too much salt counteracts the beneficial effects of plasma volume expansion on heat dissipation and hence in performance. In summary, the available literature suggests that pre-exercise saline ingestion with concentrations not over 164 mmol/l Na(+) is an ergogenic aid for subsequent prolonged exercise in a warm or thermoneutral environment.

An optimal post-exercise nutrition regimen is fundamental for ensuring recovery. Therefore, research has aimed to examine post-exercise nutritional strategies for enhanced training stimuli. Chocolate milk has become an affordable recovery beverage for many athletes, taking the place of more expensive commercially available recovery beverages. Low-fat chocolate milk consists of a 4:1 carbohydrate:protein ratio (similar to many commercial recovery beverages) and provides fluids and sodium to aid in post-workout recovery. Consuming chocolate milk (1.0-1.5•g•kg(-1) h(-1)) immediately after exercise and again at 2 h post-exercise appears to be optimal for exercise recovery and may attenuate indices of muscle damage. Future research should examine the optimal amount, timing, and frequency of ingestion of chocolate milk on post-exercise recovery measures including performance, indices of muscle damage, and muscle glycogen resynthesis.

Despite ongoing improvements to regulatory and manufacturing guidelines, the potential for contaminated nutritional supplements to cause a failed doping test for an athlete remains a concern. Several surveys of supplements available through the internet and at retail have confirmed that many are contaminated with steroids and stimulants that are prohibited for use in elite sport. Suggested responses to this issue include the complete avoidance of all supplements. However, this approach seems to be unrealistic as many athletes use nutritional supplements for very different reasons. In addition, the number of publications describing trials that demonstrate the benefit of certain nutritional products has also increased over the last decade or so. This ensures that for many sports the use of supplements will remain a common practice. In response to the issue of contamination in nutritional supplements, many reputable manufacturers have their products rigorously tested by sports anti-doping laboratories to help ensure as far as possible that the risks to an athlete remain minimal. In this chapter we review the issue of supplements and contamination, and look at how this might be addressed through effective quality control procedures at the manufacturing facility and through the highly sensitive testing of finished products using appropriately accredited tests.

Prevalence of rotator cuff tears after traumatic dislocation increases with advancing age, as a consequence of the age-associated deterioration of structures and mechanical properties of the tendons of the rotator cuff. These act as effective stabilizers of the joint, compressing the humeral head in the three-dimensional concavity of the glenoid. It is impossible to establish whether a lesion of the capsulo-labrum complex or of the rotator cuff causes or follows a dislocation, regardless of whether it is anterior or posterior. A peripheral nerve or a brachial plexus injury can be associated with tendon lesion and instability, developing the 'terrible triad' of the shoulder. Both conservative and surgical management are possible, and surgeons must choose the most appropriate management modality according to the biologic age of the patients, functional demands, and type of lesion.

Objectives: We critically review the existing studies comparing the features of single- and double-row repair, and discuss suggestions about the surgical indications for the two repair techniques.

Data sources: All currently available studies comparing the biomechanical, clinical and the biological features of single and double row.

Main results: Biomechanically, the double-row repair has greater performances in terms of higher initial fixation strength, greater footprint coverage, improved contact area and pressure, decreased gap formation, and higher load to failure. Results of clinical studies demonstrate no significantly better outcomes for double-row compared to single-row repair. Better results are achieved by double-row repair for larger lesions (tear size 2.5-3.5 cm).

Conclusions: Considering the lack of statistically significant differences between the two techniques and that the double row is a high cost and a high surgical skill-dependent technique, we suggest using the double-row technique only in strictly selected patients.

We review the management of rotator cuff tears, the mechanism of action of autologous blood products, principally platelet-rich plasma, and the current evidence for effective use of platelet-rich plasma, particularly in relation to the shoulder and chronic rotator cuff tears, for biological augmentation of rotator cuff repair.

Dietary L-citrulline malate supplements may increase levels of nitric oxide (NO) metabolites, although this response has not been related to an improvement in athletic performance. NO plays an important role in many functions in the body regulating vasodilatation, blood flow, mitochondrial respiration and platelet function. L-Arginine is the main precursor of NO via nitric oxide synthase (NOS) activity. Additionally, L-citrulline has been indicated to be a second NO donor in the NOS-dependent pathway, since it can be converted to L-arginine. The importance of L-citrulline as an ergogenic support derives from the fact that L-citrulline is not subject to pre-systemic elimination and, consequently, could be a more efficient way to elevate extracellular levels of L-arginine by itself. L-Citrulline malate can develop beneficial effects on the elimination of NH(3) in the course of recovery from exhaustive muscular exercise and also as an effective precursor of L-arginine and creatine. Dietary supplementation with L-citrulline alone does not improve exercise performance. The ergogenic response of L-citrulline or L-arginine supplements depends on the training status of the subjects. Studies involving untrained or moderately healthy subjects showed that NO donors could improve tolerance to aerobic and anaerobic exercise. However, when highly-trained subjects were supplemented, no positive effect on performance was indicated.

The purpose of this report is to review the available literature to provide an epidemiological overview of skateboarding injuries, as well as to suggest possible areas for future research. A literature search was performed with the databases of PubMed, Sport Discus, Google and Google Scholar using the search terms 'skateboard', 'skateboarding', 'injury' and 'injuries', with all articles published in refereed journals in the English language being considered. An ancestry approach was also used. Articles from non-juried journals were also infrequently included to provide anecdotal information on the sport. Comparison of study results was compromised by the diversity of different study populations and variability of injury definitions across studies. The majority of injuries affect young males although conflicting arguments arise over the issues of age and experience in relation to injury severity. Most injuries are acutely suffered, and the most commonly affected body part was the wrist and forearm, with lower leg and ankle injuries also common. The incidence was relatively high but reports on severity differed. Clear conclusions could not be drawn on environmental location and risk factors. Most injuries tend to occur from a loss of balance leading to a fall, in more recent times due to a failed trick. Research on injury prevention is not conclusive although protective equipment and skatepark use are recommended. Further research using more rigorous study designs is required to gain a clearer picture of the incidence and determinants of injury, and to identify risk factors and viable injury countermeasures.

Recent studies have investigated the influence of dietary nitrate supplementation on the physiological responses to exercise. Specifically, it has been reported that enhancing nitric oxide (NO) bioavailability through supplementation of the diet with nitrate salts or nitrate-rich beetroot juice reduces the O(2) cost of exercise and improves exercise performance. The lower O(2) cost for a given sub-maximal work rate following nitrate ingestion indicates that muscle efficiency is enhanced either as a consequence of a reduced energy cost of contraction or enhanced mitochondrial efficiency. The positive effects of nitrate supplementation on the O(2) cost of sub-maximal exercise can be manifested acutely (i.e. 2.5 h following ingestion) and maintained for at least 15 days if supplementation is continued. Most recently, the influence of dietary nitrate supplementation on time trial performance in competitive cyclists has been investigated. Studies have shown a 1-2% reduction in the time to complete time trial distances between 4 and 16 km. The dose of nitrate that has been shown to improve exercise efficiency can readily be achieved through the consumption of 0.5 litre of beetroot juice or an equivalent high-nitrate foodstuff. Following a 5- to 6-mmol bolus of nitrate, plasma [nitrite] typically peaks within 2-3 h and remains elevated for a further 6-9 h before declining towards baseline. Therefore, consuming nitrate approximately 3 h prior to competition or training is recommended if athletes wish to explore the ergogenic potential of nitrate supplementation.

The rotator cuff has an important role in the stability and function of the glenohumeral joint. To understand the biomechanical proprieties of the rotator cuff, it is essential to understand the pathogenesis and effects of rotator cuff tears. The rotator cuff provides a stabilizing effect to the shoulder, because of compression of the humeral head against the glenoid cavity. The wide range of motion of the shoulder is allowed by the variety of rotational moments of the cuff muscles. Rotator cuff muscles action must be precisely coordinated to obtain the desired movement. Rotator cuff tendons are subjected to complex tension loads. The rotator cuff is also subjected to compressive loads. Upwardly directed humeral load squeezes the cuff between the humeral head and the coracoacromial arch. Extrinsic factors have always been considered among causes of cuff tears. However, evidence shows that acromial impingement is not the primary cause of rotator cuff tears. Tears of the rotator cuff change load distribution and determine a pattern that induces tear progression and extension. Progressive tears of the rotator cuff compromise glenohumeral stability and determine superior translation of the humeral head.