The purpose of this study was to investigate the effect of a six-week creatine-electrolyte supplementation intervention on overall and repeated peak and mean power output during repeated short duration sprint cycling. Results of the present study support the hypothesis that creatine-electrolyte supplementation would lead to significant increases in overall and repeated peak and mean power output during repeated short duration sprint cycling performance when the sprints were interspersed with 2 min of passive recovery. We hypothesized that supplementation with the creatine-electrolyte material would lead to improved repeated sprint cycling performance, as the literature generally supports the effectiveness of creatine supplementation at improving such performance [1–4]. Supplementation with creatine increases one’s intramuscular creatine and phosphocreatine contents [6–11], which has been implicated as a contributing factor for the ergogenic effect of creatine supplementation [1–4]. Increased intramuscular phosphocreatine increases the rate and duration that the phosphagen system is able to contribute rapid energy turnover; thus, increasing peak and mean power outputs during sprint cycling [1–4]. Furthermore, the increase in intramuscular creatine content increases the rate of phosphocreatine resynthesis during recovery; thus, improving subsequent sprint performances [7, 9, 10]. Supplementation with creatine also typically increases one’s body mass [7–10, 13, 18, 19, 21, 27, 28, 35, 36, 60–63], presumably due to increased intramuscular total creatine content and the associated increases in water retention and/or lean body mass [28, 36, 62, 63]. Therefore, considering the significant improvements in overall and repeated peak and mean power outputs, and significant increase in body mass, it is reasonable to expect that the creatine-electrolyte supplement increased the intramuscular creatine and phosphocreatine concentrations of the subjects following that treatment.
Improvements in sprint cycling performance observed in our study demonstrate the expected ergogenic effect of creatine-electrolyte supplementation. These outcomes were expected because creatine monohydrate supplementation improves peak and mean power output during sprint cycling [6, 10, 12, 16, 24–26]. Electrolytes further improve creatine uptake [30–33] and the ergogenic effect . Creatine transport into cells is mediated via transporter proteins, which operate in an electrogenic fashion, requiring sodium and chlorine ions. Dai et al.  and Peral et al.  reported that the rate and magnitude of creatine uptake were increased when the extracellular solution contained these electrolytes, compared to when these electrolytes were absent. With creatine monohydrate supplementation, the greatest increase in intramuscular total creatine content occurs during the initial 6–28 days of supplementation, depending on the supplementation protocol . After this, intramuscular total creatine content typically levels off, demonstrating a cellular creatine saturation effect [11, 65, 66]. To the authors’ knowledge, the effect of electrolytes on muscle creatine saturation is unknown. Although cellular creatine saturation likely occurs early in the intervention, sustained supplementation with creatine results in further increases in body mass and fat free mass . Stout et al.  contrasted the effects of creatine-electrolyte versus creatine monohydrate on anaerobic power in NCAA division II athletes. For the creatine-electrolyte group, they found significantly greater improvement in anaerobic power (i.e. bench press 1RM, vertical jump height, and 100-yard dash time) compared to the creatine monohydrate group. Taken together, these results suggest that sustained supplementation with a creatine-electrolyte material may yield greater effect than supplementing with creatine monohydrate alone. However, when Finn et al.  and Kreider et al.  investigated the ergogenic effect of creatine electrolyte supplementation, they did not observe an increase in peak power output across any of their cycling sprints. Our study is the first to demonstrate an improvement in overall and repeated peak power output across cycling sprints, post creatine-electrolyte supplementation.
In the present study, peak power output was almost always (~ 97% of trials) observed during the first sprint effort, and systematically decreased from there. Similar to the present study, peak power output demonstrated a systematic decline during subsequent sprint performances in the study by Finn et al. . In the present study, overall peak power output was increased by ~ 4% in the CE group from pre- to post-supplementation testing. For sprints 1–3, peak power output was increased by 4%, 3%, and 3%, respectively (Fig. 3). Presumably due to lack of significant results, neither Finn et al.  nor Kreider et al.  report both pre- and post-supplementation peak power output values. Therefore, it is not possible to compare post-creatine-electrolyte supplementation changes in peak power output in the present study with those by Finn et al.  and Kreider et al. .
The overall mean power output sustained across all five 15-s sprints interspersed with 2 min of passive recovery by subjects in this study, regardless of group identification and testing time, was 620 ± 79 watts. Across four 20-s sprints interspersed with 20 s of passive recovery, subjects in the study by Finn et al.  maintained an overall mean power output of about 600 watts. Across 12 six-second sprints interspersed with 30 s of passive recovery, subjects in the study by Kreider et al.  sustained an overall mean power output of about 900 watts. However, due to numerous methodological factors that affect peak and mean power output, researchers must exercise caution when comparing data across supplementation and sprint cycling studies. Some of the methodological factors affecting power outputs include: cycle ergometer type [47, 48]; the subjects’ training status [26, 67], sex , and age ; and aspects of the sprint cycling protocol (i.e. resistive load applied [68, 69], starting technique [49, 70], sprint and recovery durations [39, 40], and sprint cycling posture [71, 72]).
In each of these studies, including our study, similar to peak power output, mean power output maintained per sprint systematically declined with successive sprints. In the present study, mean power output of the first sprint was 678 ± 88 watts, and decreased to 570 ± 91 watts. Finn et al.  reported that their subjects maintained a mean power output of about 700 watts during their first 20-s cycling sprint. Thereafter, mean power output decreased steadily to about 500 watts during the fourth 20-s sprint effort. Mean power output results (reported as total work) of the study by Kreider et al.  demonstrate the same decreasing pattern. In that study, subjects maintained a mean power output of about 1200 watts during the first of 12 six-second sprints interspersed with 30 s of passive recovery. During the final sprint in that study, mean power output decreased to about 800 watts.
In the present study, mean power output maintained per sprint was significantly increased by about 3–7% across all five sprints following creatine-electrolyte supplementation (Fig. 3). Finn et al.  did not observe pre- to post-supplementation changes in mean power output during any sprint. Kreider et al.  report significant pre- to post-supplementation improvements in mean power output of about 10–15% per sprint during the first five of 12 sprints for their creatine-electrolyte group. However, from sprints 6–12, the differences in pre- to post-supplementation mean power output were not significantly different between the creatine-electrolyte and placebo groups. Interestingly, in the study by Kreider et al.  the placebo group also demonstrated a 5–10% improvement in mean power output per sprint across all 12 sprints. Therefore, in the study by Kreider et al.  the performance improvements following creatine-electrolyte supplementation were about 5–10% greater than the changes shown by the placebo group. While the post-supplementation improvements in mean power output for the creatine-electrolyte and placebo groups in the study by Kreider et al.  appear to be large, it is important to note the study’s subject demographics. The subjects in the study by Kreider et al.  were NCAA division IA football players who participated in a structured exercise program consisting of 5 h per week of heavy resistance training and 3 h per week of agility and sprint training during their four-week supplementation intervention.
Results of the present study and those by Finn et al.  and Kreider et al.  emphasize the importance of the sprint and recovery durations when assessing the efficacy of creatine-electrolyte supplementation at improving repeated sprint cycling performance. However, since overall peak power output is typically recorded during the first sprint, it is unlikely that the either the sprint or recovery duration influenced overall peak power output in this study and those by researchers Finn et al.  and Kreider et al. . Therefore, it remains unknown why subjects in the studies by Finn et al.  and Kreider et al.  did not demonstrate significantly increased peak power output when supplemented with creatine and electrolytes. For mean power output, however, the sprint and recovery durations are crucial aspects to consider for the sprint cycling protocol. When the sprint duration is equal to the duration of the recovery (1:1 work to recovery), ample resynthesis of phosphocreatine does not occur during the inter-sprint recovery [7, 9]. Thus, post-supplementation improvements in sprint performance during subsequent sprints are unlikely. Results of Finn et al.  demonstrate this scenario, as the duration of their sprint and recovery interval were both 20 s (1:1). Conversely, when Kreider et al.  utilized a shorter sprint interval (6 s) and longer recovery duration (30 s), a 1:5 work to recovery ratio, they found improved mean power output during the first five of 12 sprints. The inter-sprint recovery interval utilized in the study by Kreider et al.  allowed for enough phosphocreatine resynthesis to detect post-supplementation improvements in mean power output during the initial five sprints. In the present study, the inter-sprint recovery interval was longer in relation to the sprint duration (i.e. 15-s sprint and 120 s of recovery, or a 1:8 work to recovery ratio). Perhaps, this longer recovery interval allowed for greater phosphocreatine resynthesis, resulting in improved peak and mean power outputs during subsequent sprint performances.
We observed an overall 3–7% improvement in sprint cycling performance following creatine-electrolyte supplementation. These improvements are similar to improvements observed during sprint cycling testing following supplementation with creatine monohydrate alone, typically ranging between 2 and 9% [6, 10, 12, 16, 18, 24–27, 43]. On face value, there appears to be no added benefit of supplementing with a creatine-electrolyte versus creatine monohydrate material. However, due to the numerous methodological factors that influence power output during sprint cycling, it is not possible to determine if creatine-electrolyte supplementation enhances the ergogenic effect of creatine supplementation. Future research should address this by conducting a similar experiment while assessing the differences in sprint cycling performance post-supplementation with creatine-electrolytes compared to creatine monohydrate alone. Furthermore, future studies should investigate the underlying mechanisms of action for the significant post-supplementation increase in body mass, and assess the contribution of the increased body mass on the subjects’ power generating abilities.