An athlete's carbohydrate intake can be judged by whether total daily intake and the timing of consumption in relation to exercise maintain adequate carbohydrate substrate for the muscle and central nervous system (''high carbohydrate availability'') or whether carbohydrate fuel sources are limiting for the daily exercise programme (''low carbohydrate availability''). Carbohydrate availability is increased by consuming carbohydrate in the hours or days prior to the session, intake during exercise, and refuelling during recovery between sessions. This is important for the competition setting or for high-intensity training where optimal performance is desired. Carbohydrate intake during exercise should be scaled according to the characteristics of the event. During sustained high-intensity sports lasting *1 h, small amounts of carbohydrate, including even mouth-rinsing, enhance performance via central nervous system effects. While 30-60 g Á h 71 is an appropriate target for sports of longer duration, events 42.5 h may benefit from higher intakes of up to 90 g Á h 71 . Products containing special blends of different carbohydrates may maximize absorption of carbohydrate at such high rates. In real life, athletes undertake training sessions with varying carbohydrate availability. Whether implementing additional ''train-low'' strategies to increase the training adaptation leads to enhanced performance in well-trained individuals is unclear.

Measures of substrate oxidation have traditionally been calculated from indirect calorimetry measurements using stoichiometric equations. Although this has proven to be a solid technique and it has become one of the standard techniques to measure whole body substrate metabolism, there are also several limitations that have to be considered. When indirect calorimetry is used during exercise most of the assumptions on which the method is based hold true although changes in the size of the bicarbonate pool at higher exercise intensities may invalidate the calculations of carbohydrate and fat oxidation. Most of the existing equations are based on stoichiometric equations of glucose oxidation and the oxidation of a triacylglycerol that is representative of human adipose tissue. However, in many exercise conditions, glycogen and not glucose is the predominant carbohydrate substrate. Therefore we propose slightly modified equations for the calculation of carbohydrate and fat oxidation for use during low to high intensity exercise. Studies that investigated fat oxidation over a wide range of intensities and that determined the exercise intensity at which fat oxidation is maximal have provided useful insights in the variation in fat oxidation between individuals and in the factors that affect fat oxidation. Fat oxidation during exercise can be influenced by exercise intensity and duration, diet, exercise training, exercise mode and gender. Although a number of important factors regulating fat oxidation have been identified, it is apparent that a considerable degree of inter-subject variability in substrate utilization persists and cannot be explained by the aforementioned factors. Future research should investigate the causes of the large inter-individual differences in fat metabolism between individuals and their links with various disease states.

Performance testing is one of the most common and important measures used in sports science and physiology. Performance tests allow for a controlled simulation of sports and exercise performance for research or applied science purposes. There are three factors that contribute to a good performance test: (i) validity; (ii) reliability; and (iii) sensitivity. A valid protocol is one that resembles the performance that is being simulated as closely as possible. When investigating race-type events, the two most common protocols are time to exhaustion and time trials. Time trials have greater validity than time to exhaustion because they provide a good physiological simulation of actual performance and correlate with actual performance. Sports such as soccer are more difficult to simulate. While shuttle-running protocols such as the Loughborough Intermittent Shuttle Test may simulate physiology of soccer using time to exhaustion or distance covered, it is not a valid measure of soccer performance. There is a need to include measures of skill in such protocols. Reliability is the variation of a protocol. Research has shown that time-to-exhaustion protocols have a coefficient of variation (CV) of >10%, whereas time trials are more reliable as they have been shown to have a CV of <5%. A sensitive protocol is one that is able to detect small, but important, changes in performance. The difference between finishing first and second in a sporting event is <1%. Therefore, it is important to be able to detect small changes with performance protocols. A quantitative value of sensitivity may be accomplished through the signal : noise ratio, where the signal is the percentage improvement in performance and the noise is the CV.

It is concluded that a protocol with 3-min stages and 35-W increments in work rate can be used to determine Fat(max). Fat oxidation rates are high over a large range of intensities; however, at exercise intensities above Fat(max), fat oxidation rates drop markedly.

Ϫ ] increased in a dose-dependent manner, with the peak changes occurring at approximately 2-3 h. Compared with PL, 70 ml BR did not alter the physiological responses to exercise. However, 140 and 280 ml BR reduced the steady-state oxygen (O2) uptake during moderateintensity exercise by 1.7% (P ϭ 0.06) and 3.0% (P Ͻ 0.05), whereas time-to-task failure was extended by 14% and 12% (both P Ͻ 0.05), respectively, compared with PL. The results indicate that whereas plasma [NO 2 Ϫ ] and the O2 cost of moderate-intensity exercise are altered dose dependently with NO 3 Ϫ -rich BR, there is no additional improvement in exercise tolerance after ingesting BR containing 16.8 compared with 8.4 mmol NO 3 Ϫ . These findings have important implications for the use of BR to enhance cardiovascular health and exercise performance in young adults.nitrate; nitrite; nitric oxide; blood pressure; exercise economy; O2 uptake; exercise tolerance NITRIC OXIDE (NO) IS A GASEOUS signaling molecule that modulates human physiological function via its role in, for example, the regulation of blood flow, neurotransmission, immune function, glucose and calcium homeostasis, muscle contractility, and mitochondrial respiration (9, 36). 1 NO is generated through the oxidation of the amino acid L-arginine Ϫ ] peaked 3 h postingestion, remained close to peak values until 5 h postingestion, and returned to baseline after 24 h (39). The systolic and diastolic BP and the mean arterial pressure (MAP) were reduced significantly, by ϳ10, ϳ8, and ϳ8 mmHg, respectively, at 2.5-3 h after BR intake. The same research group later reported a dose-dependent increase in plasma [ ] was accompanied by significant reductions in both systolic BP (of ϳ2, ϳ6, and ϳ9 mmHg, respectively) and diastolic BP (of ϳ4, ϳ4, and ϳ6 mmHg, respectively). However, since BR contains polyphenols and antioxidants, which can facilitate the synthesis of NO from NO 2 Ϫ in the stomach (30), it is unclear whether BP is similarly impacted when different doses of BR are ingested compared with equivalent doses of NO 3 Ϫ salts. Given the growing interest in dietary NO 3 Ϫ supplementation in the form of BR amongst athletes and the general population, it is important to determine the pharmacokinetic-pharmacodynamic relationship between different volumes of BR consumption and changes in plasma [NO 2 Ϫ ] and BP to establish an optimal dose for beneficial effects.Recent investigations suggest that dietary NO 3 Ϫ supplementation has the potential to influence human physiology beyond 1 This article is the topic of an Invited Editorial by L. Burke (5a).

The aim of the present study was to establish fat oxidation rates over a range of exercise intensities in a large group of healthy men and women. It was hypothesised that exercise intensity is of primary importance to the regulation of fat oxidation and that gender, body composition, physical activity level, and training status are secondary and can explain part of the observed interindividual variation. For this purpose, 300 healthy men and women (157 men and 143 women) performed an incremental exercise test to exhaustion on a treadmill [adapted from a previous protocol (Achten J, Venables MC, and Jeukendrup AE. Metabolism 52: 747-752, 2003)]. Substrate oxidation was determined using indirect calorimetry. For each individual, maximal fat oxidation (MFO) and the intensity at which MFO occurred (Fat(max)) were determined. On average, MFO was 7.8 +/- 0.13 mg.kg fat-free mass (FFM)(-1).min(-1) and occurred at 48.3 +/- 0.9% maximal oxygen uptake (Vo(2 max)), equivalent to 61.5 +/- 0.6% maximal heart rate. MFO (7.4 +/- 0.2 vs. 8.3 +/- 0.2 mg.kg.FFM(-1).min(-1); P < 0.01) and Fat(max) (45 +/- 1 vs. 52 +/- 1% Vo(2 max); P < 0.01) were significantly lower in men compared with women. When corrected for FFM, MFO was predicted by physical activity (self-reported physical activity level), Vo(2 max), and gender (R(2) = 0.12) but not with fat mass. Men compared with women had lower rates of fat oxidation and an earlier shift to using carbohydrate as the dominant fuel. Physical activity, Vo(2 max), and gender explained only 12% of the interindividual variation in MFO during exercise, whereas body fatness was not a predictor. The interindividual variation in fat oxidation remains largely unexplained.

No abstract

27 The present study aimed to investigate the influence of timing of pre-exercise carbohydrate 28 feeding (Part A), and carbohydrate concentration (Part B), on short-duration high-intensity 29 exercise capacity. In Part A, seventeen males, and in Part B ten males, performed a peak 30 power output (PPO) test, two familiarisation trials at 90% of PPO, and 4 (for Part A) or 3 (for 31 Part B) experimental trials involving exercise capacity tests at 90% PPO. In Part A, the 4 trials 32 were conducted following ingestion of a 6.4% carbohydrate/electrolyte sports drink ingested 30 33 (C30) or 120 (C120) minutes before exercise, or a flavour-matched placebo administered either 34 30 (P30) or 120 (P120) minutes before exercise. In Part B, the 3 trials were performed 30 35 minutes after ingestion of 0%, 2% or 12% carbohydrate solutions. All trials were performed in a 36 double blind cross-over design following and overnight fast. Dietary intake and activity in the two 37 days before trials was recorded and replicated on each visit. Glucose, lactate, heart rate and 38 mood/arousal were recorded at intervals during the trials. In Part A, C30 produced the greatest 39 exercise capacity (mean±SD; 9.0±1.9 min, P<0.01) compared with all other trials (7.7±1.5 min 40 P30, 8.0±1.7 min P120, 7.9±1.9 min C120). In Part B, exercise capacity (min) following 41 ingestion of the 2% solution (9.2±2.1) compared with 0% (8.2±0.7) and 12% (8.0±1.3) solutions 42 approached significance (p=0.09). This study provides new evidence to suggest that timing of 43 carbohydrate intake is important in short duration high-intensity exercise tasks, but a 44 concentration effect requires further exploration. 45 46 47 48 The majority of studies examining the effects of carbohydrate feeding on exercise performance 49 and exercise capacity have focused on carbohydrate ingestion during prolonged exercise, or on 50 pre-exercise carbohydrate feeding in the few hours or minutes before prolonged endurance 51 activities (for reviews see Cermak & Van Loon, 2013; Temesi et al., 2011; Karelis et al., 2010; 52 Jeukendrup & Killer, 2010). There has been limited focus on carbohydrate feeding prior to short 53 duration (<10 min), high-intensity (>85% max), exercise tasks, presumably because it is 54 acknowledged that muscle glycogen depletion will not be limiting during exercise of this nature. 55 As a result, guidelines for pre-event fuelling focus on providing information about carbohydrate 56 intake before endurance exercise tasks lasting longer than 60 minutes (Burke et al., 2011). 57 Current guidelines specify that there is no requirement for ingestion of carbohydrate before 58 events lasting less than 45 minutes. Furthermore, it is recognized that ingestion of carbohydrate 59 in the immediate pre-exercise period (30-60 minutes before exercise) can reduce liver glucose 60 output, stimulate glucose uptake and oxidation and induce a rebound hypoglycaemia in 61 susceptible individuals (Williams and Lamb, 2008; Jeukendrup & Killer, 2010). Interestingly, 62 these known me...