Overzichtsartikel 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. Supplements that might promote energy metabolism during 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 shown to be related to fatigue.12 atine 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 duction of lactate anions and hydrogen cations (H+ high rate of lactate and H+ Anaerobic or fast glycolysis results in the pro).14 The 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 limited by the intracellular availability of β-alanine.19 is suggested to be 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) 8 Sport & Geneeskunde | november 2015 | nummer 3 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 ponding increase in blood pH of 0.069 (± 0.018).20 from the muscle.21 ) and a corresThe increase in blood bicarbonate concentration and pH result in an increased efflux of H+ It is therefore Depleted phosphocreatine stores has been An increase in muscle creexpected 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. Creatine 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 stu Pagina 7
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