Donderdag 21 juli 2016
The specific skating posture results in blood flow restriction in the legs, which diminishes the relative contribution of the aerobic energy system and increases the contribution of anaerobic energy systems. The purpose of this review was to summarize dietary supplements that might positively affect anaerobic energy metabolism and gross efficiency in speed skating, and to discuss the effects of these supplements on performance. Creatine, β-alanine, and sodium bicarbonate are supplements that might positively affect anaerobic energy metabolism, and dietary nitrate might influence efficiency. Based on the reviewed literature, it can be concluded that the acute effect of creatine seems trivial, but that chronic supplementation seems beneficial. Acute sodium bicarbonate supplementation is expected to result in moderate performance enhancements. Combining chronic β-alanine supplementation with acute sodium bicarbonate supplementation might have additive effects. The effectiveness of chronic β-alanine supplementation, chronic sodium bicarbonate, and acute or chronic dietary nitrate supplementation requires further investigation.
Speed skating performances have improved considerably over the last 50 years. Model calculations showed that about half of this performance improvement could be ascribed to technological innovations and the other half to athletic improvement.1 Athletic improvement can be realized by increasing the total metabolic energy produced or by reducing power losses, as mechanical power output or speed is the result of the dynamic balance between metabolic power production and power losses due to friction.2,3 When the power losses are disregarded, a performance improvement can be realized by an increase in metabolic energy production. There are three main physiological factors that determine metabolic power production: 1) performance VO2, 2) performance O2 deficit (anaerobic capacity), and 3) the gross mechanical efficiency (Figure 1).4
Therefore, dietary supplements that might positively affect energy metabolism, are supplements that affect one or more of these physiological factors. As sport nutrition knowledge and the dietary supplement industry have evolved enormously over the last 50 years, it seems reasonable that sports nutrition (including dietary supplements) nowadays has a larger contribution to performance than 50 years ago, which may explain a small part of the athletic improvement.
Races of elite senior long-track speed skaters over 500 to 10,000 m result in finish times between 34.03 s (current world record 500 m men) and about 14 min.5 To perform these exercise tasks, the body continually needs chemical energy, which is derived from high-energy phosphate compounds, predominantly phosphocreatine and adenosine triphosphate. To continuously resynthesize high-energy phosphate compounds both anaerobic and aerobic energy systems are important.
The specific speed skating technique is characterized by a deeply crouched position (Figure 2). ISU World Cup contestants showed an average pre-extension knee angle of 105.9 ± 5.2 and 111.4 ± 5.3° and an average trunk angle of 14.1 ± 4.8 and 15.2 ± 3.4° during the first complete lap of a 1500 and 5000 m, respectively.6 The small knee angle and low trunk position, shown by elite speed skaters, results in a reduced cardiac output and lower peak oxygen consumption (VO2peak) than during cycling7 and running.8 Besides, skating in the characteristic low position compared to skating in a more upright position resulted in a greater level of muscle desaturation and the level of muscle desaturation is associated with the increase in blood lactate accumulation.7 So, these results support the general notion that speed skating exercise results in blood flow restriction, which diminishes the contribution of the aerobic energy system and increases the relative contribution of the anaerobic energy systems. Foster and de Koning9 concluded correctly that “the skater is left with the problem of balancing the biomechanical advantage of skating low (longer push, reduced frontal area) with the physiological disadvantage of restricted blood flow to the muscles providing propulsion.” Speed skating performance might therefore benefit from dietary supplements that affect anaerobic energy metabolism, but also gross mechanical efficiency. Hence, the main goal of this review is to summarize dietary supplements that might positively affect anaerobic energy metabolism and gross mechanical efficiency, and to discuss the effects of these dietary supplements on performance.
Today, there are no published experimental studies conducted on the effect of dietary supplements on speed skating performance. Reviewing the literature using the search terms “dietary supplements” and “speed skating” resulted in 1 paper (Web of Knowledge, September 2014), the study of Snyder et al.,10 in which the voluntary consumption of a carbohydrate supplement was quantified, but the effect on performance was not assessed. Consequently, the results of studies that have used other exercise models are extrapolated to long-track speed skating.
Substrate level phosphorylation from phosphocreatine hydrolysis is the primary mechanism by which ATP is resynthesized during the first seconds of a high-intensity exercise bout. Thereafter, the contribution of phosphocreatine hydrolysis diminishes, as phosphocreatine stores become depleted.11 Depleted phosphocreatine stores has been shown to be related to fatigue.12 An increase in muscle creatine and phosphocreatine content, as has been found after creatine supplementation,13 might therefore have an ergogenic effect on relatively short performances. So, creatine could potentially be an ergogenic supplement for long-track speed skaters.
The byproducts of phosphocreatine hydrolysis stimulate glycolysis.11 Anaerobic or fast glycolysis results in the production of lactate anions and hydrogen cations (H+).14 The high rate of lactate and H+ production, as seen during speed skating, can eventually result in a decrement in muscle pH, from resting values of ~7.1 to ~6.4 at exhaustion.15 A decrement in pH has been shown to limit the resynthesis of high energy phosphates, to inhibit glycolysis, and to disrupt the muscle contraction process.16 Although exercise training can increase buffering capacity, the extent of this adaptation seems to be limited.17 Accordingly, supplements that enhance our innate intracellular and extracellular buffering capacity might improve performance. Therefore, supplements that could potentially improve speed skating performances are carnosine, an intracellular buffer, or bicarbonate, an extracellular buffer.18
The synthesis of the intracellular buffer, canonise from the amino acids histidine and β-alanine,18 is suggested to be limited by the intracellular availability of β-alanine.19 Subsequently, it has been shown that the contribution of muscle carnosine to the total muscle buffering capacity was about 9% before supplementation and increased to about 14% (with an ~53% increase in muscle carnosine content) after a 4-week supplementation period with β-alanine.19
A recently published meta-analysis showed that sodium bicarbonate supplementation resulted in an overall clear increase in blood bicarbonate concentration of 3.9 mmol·L-1 (± 90% confidence interval (CI), 0.9 mmol·L-1) and a corresponding increase in blood pH of 0.069 (± 0.018).20 The increase in blood bicarbonate concentration and pH result in an increased efflux of H+ from the muscle.21 It is therefore expected that these changes will enhance the extracellular buffering capacity. Therefore, β-alanine supplementation and/or sodium bicarbonate supplementation are believed to have an ergogenic effect on athletic performances limited by metabolic acidosis.
In addition to dietary supplements related to anaerobic energy metabolism, there are also supplements related to gross mechanical efficiency that might potentially benefit speed skating performances. An increase in gross mechanical efficiency implies that with the same metabolic energy produced (aerobically and anaerobically) more mechanical power output can be generated. A supplement that might influence gross mechanical efficiency is dietary nitrate.22
Nitric oxide (NO) is known to regulate multiple physiological processes,23 especially the effect of NO on mitochondrial respiration and tissue blood flow might be important for sport performance. NO can be synthesized endogenously from L-arginine and molecular oxygen, catalysed by NO synthases (NOS), or through the nitrate-nitrite-NO pathway. The latter pathway can be influenced by increasing dietary nitrate intake from among other green leafy vegetables or beetroot.23 Both pathways have been suggested to work in parallel. However, when oxygen availability is low, as is the case during strenuous exercise, for example during speed skating in the low position, NOS becomes less active and the nitrate-nitrite-NO pathway becomes more important.23 It has been shown that increased plasma nitrate and nitrite levels result in a significant reduction in oxygen cost during submaximal exercise, i.e. in an improved economy or efficiency.22 Thus, the final dietary supplement that might potentially benefit long-track speed-skating performances, by influencing metabolic energy production, is dietary nitrate.
The effect of creatine supplementation on exercise capacity and performance has been extensively studied. Branch24 included 96 papers in a meta-analysis, with at least a single-blind, randomized, placebo-controlled study design. The acute effect of creatine supplementation is mostly studied using a creatine loading phase of 19.7 ± 0.5 g/day for 9 ± 1 days.24 Branch24 summarized that “this meta-analysis lends additional support to the effectiveness of creatine in increasing total and lean body mass, and performance in high-intensity, short-duration, repetitive tasks”. A small, but significant effect size of short-term creatine loading (mean ± SD, 0.22 ± 0.02) was found for all performance variables. As the effect size of single-bout or first-bout exercise was significantly smaller than the effect size of repetitive exercise bouts and the effect size of field-based performances (running, swimming etc.) was significantly smaller than of laboratory-based performances (isokinetic, isometric, isotonic tasks, and simulating rowing etc.), a possible acute effect of short-term creatine loading on long-track speed skating performance seems to be trivial.24,25
The existence of studies reporting a significant positive and studies reporting a non-significant effect of creatine supplementation on high-intensity, short-duration, exercise performances seems to be influenced by the existence of responders and non-responders. Greenhaff et al.26 determined the change in muscle phosphocreatine and free creatine concentrations before and after 5 days of 20 g·d-1 creatine supplementation, the most commonly used dose,24,27 and found that muscle total creatine concentration increased with 20-30% in responders and 5-7% in non-responders. The non-responders had an initial total creatine concentration of 130.4 ± 4.7 mmol/kg dry matter, compared to 119.4 ± 3.5 mmol/kg dry matter in responders. So, the increase in muscle total creatine concentration after supplementation is the largest in individuals with the lowest baseline muscle total creatine concentration. Unfortunately, Greenhaff et al.26 did not investigate the effect of the increase in muscle total creatine concentration on performance, but Casey et al.28 showed that the increase in muscle total creatine concentration after 5 days of supplementation was positively correlated with the cumulative change in peak work production (r = 0.71) and total work production (r = 0.71) during two consecutive 30-s supramaximal cycling bouts. Coingestion of creatine supplements with large amounts of carbohydrates resulted in a significantly augmented increase in muscle total creatine concentration.29,30 So, co-ingestion of large amounts of carbohydrates might minimize individual differences in the effectiveness of a creatine supplementation regimen.30
Although an acute effect of short-term creatine loading on long-track speed skating performance seems to be trivial,24,25 also because a 1.2 ± 0.3% increase in body mass found after acute supplementation,24 due to water retention, is likely to be detrimental for a weight-bearing sport like speed skating, chronic creatine supplementation might be beneficial, as several studies showed that creatine supplementation together with resistance training, a training modality that is part of the training program of long-track speed skaters, positively influences training adaptations.31–33 Combining chronic creatine supplementation with resistance training (in combination with sprint/agility training)32,33 not only resulted in a significantly larger gain in fat free mass compared to placebo supplementation combined with resistance training,31–33 but also in a significantly larger improvement in bench press lifting volume,32 repeated sprint performance,32 jump squat peak power output attained during the fourth set of 10 repetitions,31and countermovement vertical jump height.33 So, chronic creatine supplementation combined with resistance and sprint training, at least 3 times per week, seems to be beneficial for sprint- and possibly middle-distance long-track speed skaters.
As most studies investigated the effect of creatine supplementation in untrained or recreationally active subjects, future research is necessary to study the effect of creatine supplementation on total muscle creatine concentration and performance in elite athletes. Currently, it is expected that there are large interindividual differences in the effect of creatine supplementation on total muscle creatine concentration and therefore on exercise performance. In summary, it is expected that the acute effect on long-track speed skating performances will be trivial. However, chronic creatine supplementation combined with resistance and sprint training might benefit sprint- and possibly middle-distance long-track speed skaters.
Studies investigating the chronic effect of β-alanine supplementation on power-based exercise performance are summarized in Table 1. As can be seen from the results column, several studies used the magnitude based inferences approach.34 Batterham and Hopkins34 mentioned that: “the p-value alone provides us with no information about the direction or size of the effect or, given sampling variability, the range of feasible values”, after which they introduced the magnitude based inferences approach, a statistical method that provides “qualitatively the likelihood that the true value will have the observed magnitude (e.g., very likely beneficial).” This relatively new approach seems to be useful for among others sports science, as a small sample size, as is often the case in sport science, or large variability can prevent important effects from being statistically significant.
The effect of chronic β-alanine supplementation on middle-distance power-based events, namely 400-m and 800-m running races, was investigated by Derave et al.35 and Ducker et al.36 These 400-m and 800-m races resulted in finish times ranging from ~49 s to ~2.5 min, which corresponds best with 1000-m and 1500-m speed-skating events. β-alanine supplementation did not significantly improve 400-m running performance,35 but did result in a significantly larger performance enhancement than placebo ingestion before a 800-m race (Table 1).36 In addition, de Salles Painelli et al.37 studied the effect of β-alanine supplementation on 100-m and 200-m swimming events, also similar in duration to 1000-m and 1500-m speed-skating events. The authors concluded that β-alanine supplementation resulted in a non-significant improvement of the 100 m and a significant improvement of 200-m swimming performance. The cause of the non-significant effect of β-alanine supplementation on 100-m swimming and 400-m running performances might be due to the short duration of these events. Hobson et al.38 concluded, based on a meta-analysis that exercise of a duration < 60 s, like a 500 m skating, is not improved by β-alanine supplementation.
A 4-min cycling time trial can also be regarded as a power-based sporting event and the duration corresponds best with a 3000-m speed-skating event. β-alanine supplementation resulted in a 3239 to 44% possible chance of benefit on average power output,40 compared to a placebo (Table 1). Both studies reported that the likelihood of a negative effect was 1%, which results in a 67 and 55% chance on a trivial effect.
Finally, rowing can just as middle-distance running, track cycling, and speed skating be regarded as a power-based sport.15 The 2000-m rowing event, lasting about 5-8 min is similar in terms of duration to a 5000-m speed-skating event. The effect of β-alanine supplementation on 2000-m rowing performance ranged from a non-significant difference between the β-alanine and placebo group41,42 to a very likely chance of benefit43 (Table 1).
What strikes when looking at the results summarized in Table 1, is that the studies reporting a significant effect and a very likely chance of benefit are the two studies which included club-level athletes instead of highly-trained athletes or athletes of national and/or international level. However, as not all studies reported the training background of their subjects, it remains doubtful to conclude that the subjects in the studies of Ducker et al.36 and Hobson et al.43 were indeed less well trained than the subjects in the other studies summarized in Table 1. Besides, in the study of de Salles Painelli et al.,44 in which the influence of training status on the efficacy of β-alanine supplementation on repeated Wingate performances was determined, a significant ergogenic effect of β-alanine was found, regardless of training status (non-trained or trained). It therefore seems that the effect of training status on the efficacy of β-alanine supplementation is negligible.
So, in general the effect of β-alanine supplementation on power-based sports ranges from no significant effect to a very likely chance of benefit (Table 1). It must be mentioned that 6 out of 8 studies described in Table 1, used a double-blind, randomized, placebo-controlled design, which is preferable over a single-blind design. Unfortunately, the effect of β-alanine supplementation on performance in these studies is also inconclusive. The inconclusive results might be partly due to the high interindividual variation in the increase in carnosine content with β-alanine supplementation.35,42 The increase in muscle carnosine content with supplementation was independent of the initial carnosine content in a group of well-trained sprinters,35 but the increase in muscle carnosine content is positively correlated (r = 0.50, p = 0.042) to performance improvement.42 Thus, the effect of β-alanine supplementation on performance might vary substantially between individuals and seems to depend on the increase in muscle carnosine content. Further research is necessary to find the cause of the high interindividual variation and to study the effect of β-alanine supplementation in elite athletes on long-track speed-skating events. When athletes want to experiment with β-alanine supplementation, they should be careful when choosing a certain dose. Supplementing β-alanine in acute doses above 10 mg·kg-1 body mass (or 800 mg) results in an increased incidence of paraesthesia.19 These adverse effects can be minimized or avoided by limiting the amount of β-alanine ingested per dose (increasing the frequency of intake over the day)19 or by choosing a slow-release β-alanine formula.45
Based on 38 studies, using mainly a double-blind design, Carr et al.20 found that sodium bicarbonate supplementation by male athletes, using a dosage of 3.5 mmol·kg-1 body mass (~0.3 g·kg-1 body mass) ingested prior to a 1-min sprint, enhanced performance by 1.7% (± 90% CI, 2.0%), which can be regarded as a moderate performance enhancement. A 1-min sprint corresponds in duration best to a 1000-m speed-skating race, with a current world record of 1:06.42 and 1:12.58 in men and women, respectively.5 The percentage performance enhancement, due to sodium bicarbonate supplementation, increases by 0.5% when the dosage increases by 1.0 mmol·kg-1 body mass and reduces by 0.6% when the duration of the event increases to 10 min or longer.20
It is hypothesized that combining an increase in intracellular and extracellular buffering capacity results in an augmented ergogenic effect, compared to increasing only one of the two. Recently, there are a few studies published on the effect of combining chronic β-alanine supplementation with acute sodium bicarbonate supplementation on performance (Table 2). The results of these studies showed that the additive effect of acute sodium bicarbonate supplementation to chronic β-alanine supplementation ranged from minimal 40 to a 64% possible chance of benefit.43 Although there are only a few studies that investigated the effect of combining β-alanine with sodium bicarbonate supplementation on performance in trained and highly-trained athletes and more research is necessary, it seems that there might be an additive effect of combining these supplements in power-based sport events. Like β-alanine supplementation sodium bicarbonate supplementation might result in side effects.40,46 Three of the 14 subjects that participated in the study of Bellinger et al.40 experienced mild gastrointestinal symptoms related to sodium bicarbonate supplementation.
While acute supplementation with sodium bicarbontate has been studied most extensively, a recent study of Mc Naughton and Thompson47 showed that chronic supplementation might be preferable. One day after acute supplementation with sodium bicarbonate the ergogenic effect on performance was already absent, but one and two days after chronic (6 days) supplementation the ergogenic effect was still present. Thus, subjects using the chronic protocol can eliminate the chance on side effects during competition by stopping supplementation on the day(s) of competition. Another possibility to minimize the chance on gastrointestinal discomfort after sodium bicarbonate ingestion is to co-ingest a small carbohydrate-rich meal.46 Supplementation with sodium bicarbonate might not only result in gastrointestinal discomfort but might also result in a 1-2% increase in body mass.15 However, weight bearing sports, like running were included in the meta-analysis of Carr et al.20 and still a performance enhancement of 1.7% was found.
Mc Naughton and Thompson47 studied the direct effect of chronic supplementation on performance. However, there are also a few studies48,49 that evaluated the indirect effect of chronic sodium bicarbonate supplementation on performance. Driller et al.49 showed, using a double-blind placebo-controlled trial, that during a four-week training period, including two high-intensity interval-training sessions per week, sodium bicarbonate supplementation did not result in significant additional benefits to 2000-m rowing performance in highly trained rowers. This in contrast to the finding of Edge et al.,48 they showed significant greater improvements in time-to-fatigue tests after an eight-week period of combined high-intensity interval training and sodium bicarbonate supplementation in recreationally trained subjects. This discrepancy might be due to difference in training status of the subjects, the duration of the training period or the difference in ‘performance’ test. Future research is necessary to elucidate the indirect effect of chronic sodium bicarbonate supplementation on performance.
To summarize, the reviewed literature showed that acute sodium bicarbonate supplementation results in a moderate performance enhancement for exercise bouts lasting between 1 and 10 min. In addition, there might be additive effect of combining chronic β-alanine and acute sodium bicarbonate supplementation on performance. Future research is necessary to elucidate the indirect effect of chronic sodium bicarbonate supplementation on long-track speed-skating performance.
The first study investigating the effect of acute dietary nitrate supplementation on exercise performance showed that cycling time trial performance (4 to 16.1 km) improved by 2.7 to 2.8% in trained50 cyclists.51 However, recent investigations in well-trained and professional athletes showed no significant effect of 6-8 days of dietary nitrate supplementation on performance bouts lasting ~4 to 19 min.52,53 These conflicting findings might be caused by an interaction between training status and the possible beneficial effect of dietary nitrate supplementation.54,55 It seems that the ergogenic effect of dietary nitrate supplementation is less in well-trained or highly-trained subjects and professional athletes, compared to untrained and moderately-trained or recreationally active subjects.55
When looking at the individual effects instead of the group mean effects, Wilkerson et al.56 noted that within a group of trained and well-trained cyclists there seem to be responders and non-responders to nitrate supplementation. In their study, dietary nitrate supplementation resulted in a non-significant group mean performance improvement of 0.8%. However, the responders (defined as subjects with a plasma nitrite, a biomarker of NO availability, increase exceeding 30% following nitrate supplementation; n = 5) improved their performance with 2.0% (p < 0.05) and two out of the three non-responders did not improve their performance.56 The existence of responders and non-responders to nitrate supplementation is supported by the findings of Christensen et al.53 A positive group mean effect of nitrate supplementation on plasma nitrate + nitrite concentration was found (p < 0.01), without a significant group mean effect on time trial performance in well-trained subjects and professional athletes. However, two subjects that were classified as responders by Christensen et al.53 showed a 2.5 and 8% improvement in time trial performance. Future research is necessary to elucidate the reasons for the existence of responders (~20-25%)57 and non-responders and the reduced ergogenic effect of nitrate supplementation in well-trained subjects and professional athletes.
It must be mentioned that in addition to differences in training status, the dose of nitrate supplementation,58 differences in loading protocol (acute vs. chronic),59 the exercise bouts performed, and differences in the statistical approach used, all influence the results found and the conclusions drawn. For example, Vanhatalo et al.59 found that acute (2.5 h before exercise) and chronic (5 or 15 d) nitrate supplementation in physically active subjects had distinct effects. Both supplementation protocols resulted in a significantly reduced oxygen cost of submaximal exercise, but only chronic supplementation (15 d) resulted a significantly higher peak power output and work rate at the gas exchange threshold attained during a maximal incremental test. These different variables, namely training status, dose, loading protocol, and exercise protocol, which all influence the effect of nitrate supplementation on performance, make it difficult to draw any firm conclusions.
An interesting study for speed skating is the study of Kelly et al.,60 they showed that nitrate supplementation increased exercise capacity in hypoxia (p < 0.05), but not in normoxia. So, as nitrate supplementation might be more beneficial in ischemic or hypoxic conditions,23,57,60 the possible ergogenic effect might be larger in speed skating exercise than in running or cycling exercise, as speed skating in the characteristic low position results in significantly higher levels of muscle desaturation than skating in a more upright position or cycling.7 Besides ISU World Cup events are held several times per season at ~1000-1500 m above sea level, which might also enlarge the possible ergogenic effect of nitrate supplementation. Future research should reveal if acute and/or chronic nitrate supplementation in elite long-track speed skaters indeed results in improved exercise performance in normoxic and hypoxic environments.
Based on the reviewed literature, chronic creatine monohydrate supplementation combined with resistance and sprint training might be beneficial for sprint- and possibly middle-distance long-track speed skaters. In addition, chronic β-alanine supplementation might be beneficial for all long-track speed skating events, except the 500 m. Chronic β-alanine supplementation can be combined with acute sodium bicarbonate supplementation, however for the 10,000 m an ergogenic effect might not be expected. It is difficult to give practical guidelines regarding the use of dietary nitrate, as more research is necessary.
Athletes who wish to experience the possible ergogenic effects of supplements discussed in this review are referred to Table 3. These practical guidelines are extrapolated from results of studies investigating other power-based sports than long-track speed skating. Therefore, no firm conclusions on the effect of these supplements on speed skating performance can be drawn. Besides, most studies included only male athletes, which complicates the generalization to female athletes. Therefore, future research is necessary to investigate the effect of the ingestion of these dietary supplements by male and female elite skaters on multiple skating events. In this review we only described studies in which β-alanine and sodium bicarbonate supplementation were combined. Therefore, athletes must be careful when combining other supplements. Finally, dietary supplements might be contaminated with prohibited substances and could cause an athlete to fail a doping test,61 so caution is necessary.
The goal of the current review was to summarize dietary supplements that might positively affect anaerobic energy metabolism and gross mechanical efficiency, and to discuss the effects of these dietary supplements on performance. Creatine, β-alanine, and sodium bicarbonate are dietary supplements that might positively affect anaerobic energy metabolism and therefore speed skating performance. A dietary supplement that might affect gross mechanical efficiency is dietary nitrate. Based on the reviewed literature, it can be concluded that the acute effect of creatine supplementation seems trivial, however chronic creatine monohydrate supplementation combined with resistance and sprinting exercise seems to augment training adaptations and might therefore benefit long-track speed-skating performance. The effect of chronic β-alanine supplementation varies substantially between individuals, therefore future research is necessary to study the cause of the high interindividual variation and to the study the effect on performance in elite long-track speed skaters. Moderate performance enhancements for exercise bouts lasting between 1 and 10 min are expected with acute sodium bicarbonate supplementation. Besides, combining chronic β-alanine supplementation with acute sodium bicarbonate supplementation might have additive effects on performance. Future research is necessary to elucidate the effect of chronic sodium bicarbonate supplementation on training outcomes and indirectly on performance. Finally, currently the effect of acute and chronic dietary nitrate supplementation in well-trained athletes seems inconclusive. Therefore, further research is necessary to study the effect of acute and chronic dietary nitrate supplementation in elite long-track speed skaters on skating events performed in normoxic and hypoxic environments. Athletes wanting to explore the possible ergogenic effects of these supplements should test the efficacy, under supervision of qualified personal, in training situations or minor competitions.