Overzichtsartikel ning status, the dose of nitrate supplementation,58 rences in loading protocol (acute vs. chronic),59 diffethe 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 longtrack speed skaters indeed results in improved exercise performance in normoxic and hypoxic environments. Practical guidelines 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 14 Sport & Geneeskunde | november 2015 | nummer 3 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. Conclusions 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 longtrack speed skaters on skating events performed in nor Pagina 13
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