died 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 tion, 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 ly larger improvement in bench press lifting volume,32 peated sprint performance,32 but also in a significantreSo, chronic not only resulted in a significantly larger gain in fat free mass compared to placebo supplementation combined with resistance training,31–33 jump squat peak power output attained during the fourth set of 10 repetitions,31 and countermovement vertical jump height.33 and found that muscle total creatine concentration increased with 20-30% in responders and 5-7% in nonresponders. 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 found after acute supplementation,24 also because a 1.2 ± 0.3% increase in body mass due to water retencreatine 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. β-alanine 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 nummer 3 | november 2015 | Sport & Geneeskunde 9 Pagina 8
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