Medicine and sport science最新文献

Prolonged and high-intensity exercise affects immune function and leads to an increased risk of upper respiratory tract infections (URTIs) in endurance athletes. The increased incidence of URTI symptoms may negatively affect athletic performance. Various nutritional supplements have been tested in the last decade for their ability to prevent developing of URTIs or reduce their incidence. One of the most promising nutritional supplements is β-glucan, a well-known immunomodulator with positive effects on functioning of immunocompetent cells. However, β-glucans are a diverse group of molecules that vary in macromolecular structure, solubility, viscosity, molecular weight and biological activity. This fact is supported by results from recent human clinical studies where β-glucans of different origin and properties differed in ability to prevent or reduce incidence of URTIs in athletes. It has been found that pleuran, a unique insoluble β-glucan isolated from mushroom Pleurotus ostreatus, significantly reduced the incidence of URTI symptoms in athletes. In addition, it was able to increase the number of circulating natural killer cells and to prevent reduction of natural killer cell activity. Contrarily, soluble oat β-glucan supplementation did not alter URTI incidence in endurance athletes. This difference suggests that the immunomodulatory capacity of β-glucans is strongly dependent on solubility and structural factors such as backbone structure and degree of branching. This review refers to using pleuran as a natural supplement that is able to protect endurance athletes against development of URTI.

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.

The aquatic environment is a complex mix of waterways with varying uses and hazards. It is the intersection of the use of the water and the hazards which provides enjoyment to those who use them as well as risk to a person's health. Canoeing, kayaking and rafting have and continue to be popular recreation sports in aquatic environments. This chapter explores participation in, risks associated with and prevention strategies for keeping canoeists, kayakers and rafters safe and healthy. There is a dearth of good quality descriptive studies exploring these issues, particularly around the risks involved and the effectiveness of proposed prevention strategies. According to Outdoor Foundation, there are 23.9 million people in the USA who undertake paddling activities per annum, with canoeing (10.1 million) being the most popular activity followed by recreational kayaking (6.2 million). There were 141 deaths of canoeists (89) and kayakers (52) identified by the US Coast Guard in their recreational boating statistics data for 2009. The crude rate of death per 100,000 participants for canoeing ranges between 0.72 and 0.92 and for kayaking between 0.37 and 0.41 per annum. Although death is the most severe consequence of a misadventure while paddling, there are a range of other hazards faced such as hitting objects, waterborne diseases, hypothermia from unintended submersion, blisters, muscle strain, cuts and abrasions. There are a range of prevention strategies which have been proposed and provided in this chapter. However, there is very little evidence of their effectiveness. Further research is required in understanding the risk associated with paddling activities, the effectiveness of prevention strategies and how these strategies might be delivered.

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.

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.

There is no definite consensus on the best management for patients with rotator cuff tears. No randomized controlled studies have compared the outcome of surgical versus conservative treatment. The described successful rate of conservative treatment varies widely, from 33 to 92%. Even though current evidence is not sufficient to allow definitive conclusions on conservative treatment of rotator cuff tears, non-operative management is often recommended in such patients. Prognostic factors seem to be clinical presentation, duration of symptoms and tear size. The best programme for conservative treatment is not defined. Physical therapy consists of stretching and strengthening exercises. The characteristics of exercise programmes are not standardized. In clinical practice, intra-articular injections are commonly used for treatment of shoulder pain. Systemic pharmacotherapy for patients with shoulder pain consists of non-steroidal anti-inflammatory drugs. Recently, cyclo-oxygenase-2-selective inhibitors have been introduced for management of shoulder pain. To date, few randomized controlled trials are available on conservative management of rotator cuff tears, and therefore further studies are required to clarify its role in such patients.