Sophie C. Killer

The Myths Surrounding Pre-Exercise Carbohydrate Feeding

Background/Aims: Carbohydrate ingested 30–60 min before exercise may result in hypoglycaemia during exercise, a phenomenon often called rebound or reactive hypoglycaemia. There is considerable confusion regarding pre-exercise carbohydrate feeding with advice that ranges from ‘consume carbohydrate in the hour before exercise’ to ‘avoid carbohydrate in the 60 min prior to exercise’. Methods: We analysed the studies available in the literature to draw conclusions about the use of carbohydrate in the pre-exercise period. Results: Without performing a meta-analysis, it is clear that the risk of reduced performance is minimal as almost all studies point towards unaltered or even improved performance. This is despite the rather large metabolic changes that occur in response to pre-exercise carbohydrate feeding. Conclusion: It can be concluded that advice to avoid carbohydrate feeding in the hour before exercise is unfounded. Nevertheless athletes may develop symptoms similar to those of hypoglycaemia, even though they are rarely linked to actual low glucose concentrations. An individual approach may therefore be necessary to minimize these symptoms even though they do not appear to be related to exercise performance.

No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living Population

It is often suggested that coffee causes dehydration and its consumption should be avoided or significantly reduced to maintain fluid balance. The aim of this study was to directly compare the effects of coffee consumption against water ingestion across a range of validated hydration assessment techniques. In a counterbalanced cross-over design, 50 male coffee drinkers (habitually consuming 3–6 cups per day) participated in two trials, each lasting three consecutive days. In addition to controlled physical activity, food and fluid intake, participants consumed either 4×200 mL of coffee containing 4 mg/kg caffeine (C) or water (W). Total body water (TBW) was calculated pre- and post-trial via ingestion of Deuterium Oxide. Urinary and haematological hydration markers were recorded daily in addition to nude body mass measurement (BM). Plasma was analysed for caffeine to confirm compliance. There were no significant changes in TBW from beginning to end of either trial and no differences between trials (51.5±1.4 vs. 51.4±1.3 kg, for C and W, respectively). No differences were observed between trials across any haematological markers or in 24 h urine volume (2409±660 vs. 2428±669 mL, for C and W, respectively), USG, osmolality or creatinine. Mean urinary Na+ excretion was higher in C than W (p = 0.02). No significant differences in BM were found between conditions, although a small progressive daily fall was observed within both trials (0.4±0.5 kg; p<0.05). Our data show that there were no significant differences across a wide range of haematological and urinary markers of hydration status between trials. These data suggest that coffee, when consumed in moderation by caffeine habituated males provides similar hydrating qualities to water.

Evidence of disturbed sleep and mood state in well-trained athletes during short-term intensified training with and without a high carbohydrate nutritional intervention

ABSTRACT Few studies have investigated the effects of exercise training on sleep physiology in well-trained athletes. We investigated changes in sleep markers, mood state and exercise performance in well-trained cyclists undergoing short-term intensified training and carbohydrate nutritional intervention. Thirteen highly-trained male cyclists (age: 25 ± 6y, O2max: 72 ± 5 ml/kg/min) participated in two 9-day periods of intensified training while undergoing a high (HCHO) or moderate (CON) carbohydrate nutritional intervention before, during and after training sessions. Sleep was measured each night via wristwatch actigraphy. Mood state questionnaires were completed daily. Performance was assessed with maximal oxygen uptake (. Percentage sleep time fell during intensified training (87.9 ± 1.5 to 82.5 ± 2.3%; p < 0.05) despite an increase in time in bed (456 ± 50 to 509 ± 48 min; p = 0.02). Sleep efficiency decreased during intensified training (83.1 ± 5.3 to 77.8 ± 8.6%; p < 0.05). Actual sleep time was significantly higher in CON than HCHO throughout intensified training. Mood disturbance increased during intensified training and was higher in CON than HCHO (p < 0.05). Performance in the exercise protocol fell significantly with intensified training. The main findings of this study were that 9-days of intensified training in highly-trained cyclists resulted in significant and progressive declines in sleep quality, mood state and maximal exercise performance.

Influence of Hydration Status on Changes in Plasma Cortisol, Leukocytes, and Antigen-Stimulated Cytokine Production by Whole Blood Culture following Prolonged Exercise

Elevated antigen-stimulated anti-inflammatory cytokine production appears to be a risk factor for upper respiratory tract illness in athletes. The purpose of this study was to determine the effects of prolonged exercise and hydration on antigen-stimulated cytokine production. Twelve healthy males cycled for 120 min at 60% V˙O2max⁡ on two occasions, either euhydrated or moderately hypohydrated (induced by fluid restriction for 24 h). Blood samples were collected before and after exercise and following 2 h recovery for determination of cell counts, plasma cortisol, and in vitro antigen-stimulated cytokine production by whole blood culture. Fluid restriction resulted in mean body mass loss of 1.3% and 3.9% before and after exercise, respectively. Exercise elicited a significant leukocytosis and elevated plasma cortisol, with no differences between trials. IL-6 production was significantly reduced 2 h postexercise (P < 0.05), while IL-10 production was elevated postexercise (P < 0.05). IFN-γ and IL-2 production tended to decrease postexercise. No significant effect of hydration status was observed for the measured variables. Prolonged exercise appears to result in augmented anti-inflammatory cytokine release in response to antigen challenge, possibly coupled with acute suppression of proinflammatory cytokine production, corresponding with studies using mitogen or endotoxin as stimulant. Moderate hypohydration does not appear to influence these changes.

Intensified training increases salivary free light chains in trained cyclists: Indication that training volume increases oral inflammation

Periods of short-term intensified training (IT) are often used by athletes during training cycles over the season and undergoing phases of increased physical stress may impact upon the immune system. This study investigated the effects of a period of IT on free light chains (FLCs) in saliva - an emerging immune biomarker of oral inflammation - and matched serum samples in well-trained athletes. It also examined if IT influences basal FLC levels and FLC flux during acute exercise. Highly trained male cyclists (n = 10) underwent a 9-day period of IT; before and after IT participants performed a 1 h time trial (TT) on a cycle ergometer, with blood and saliva samples collected pre- and post-exercise. FLCs were assessed in serum and saliva, and IgG, IgA, IgM and creatinine were also measured in serum. Weekly training volume increased by 143% (95% CI 114-172%), p < 0.001, during IT compared with pre-trial baseline training. Following IT, the cyclists demonstrated higher salivary FLC levels. Both salivary lambda FLC concentrations (p < 0.05, η2 = 0.384) and secretion rates, and kappa FLC concentrations and secretion rates increased after IT. Salivary FLCs concentration and secretion rates decreased in response to the TT following IT (p < 0.05, η2 = 0.387-0.428), but not in response to the TT prior to IT. No significant effects of IT on serum FLCs were observed. There were no significant changes in serum FLCs in response to the TT, before or after the IT period, nor did IT impact upon other serological responses to the TT. In conclusion, IT increased basal salivary FLC parameters and amplified decreases in salivary FLCs in response to acute exercise. Increases in salivary FLC concentration likely reflects alterations to oral inflammation during times of heavy training, and we show for the first time that FLCs may have utility as a marker of exercise stress and oral health status.

Immune nutrition and exercise: Narrative review and practical recommendations

Abstract Evidence suggests that periods of heavy intense training can result in impaired immune cell function, and whether this leaves elite athletes at greater risk of infections and upper respiratory symptoms (URS) is still debated. There is some evidence that episodes of URS do cluster around important periods of competition and intense periods of training. Since reducing URS, primarily from an infectious origin, may have implications for performance, a large amount of research has focused on nutritional strategies to improve immune function at rest and in response to exercise. Although there is some convincing evidence that meeting requirements of high intakes in carbohydrate and protein and avoiding deficiencies in nutrients such as vitamin D and antioxidants is integral for optimal immune health, well-powered randomised controlled trials reporting improvements in URS beyond such intakes are lacking. Consequently, there is a need to first understand whether the nutritional practices adopted by elite athletes increases their risk of URS. Second, promising evidence in support of efficacy and mechanisms of immune-enhancing nutritional supplements (probiotics, bovine colostrum) on URS needs to be followed up with more randomised controlled trials in elite athletes with sufficient participant numbers and rigorous procedures with clinically relevant outcome measures of immunity.