Purpose: Resisted sled sprinting (RSS) is an effective tool for improving sprint performance over short distances, but the effect on change-of-direction (COD) performance is largely unknown. The present study investigated the effect of heavy RSS training during the competitive season on sprint and COD performance in professional soccer players. Methods: Over 6 wk in-season, an RSS training group (n = 6) performed RSS at a sled load of 30% body mass for a total program running distance of 800 m, whereas an unresisted sprint (URS) training group (n = 7) performed the same distance of unresisted sprinting. A 20-m maximal sprint with split times measured at 5, 10, and 20 m and the sprint 9-3-6-3-9 m with 180° turns COD test were performed before and after the intervention. Results: Sprint performance (mean, 95% confidence limits, qualitative inference) was improved in both groups over 5 m (URS, 5.1%, −2.4 to 12.7, likely moderate; RSS, 5.4%, 0.5–10.4, likely moderate), 10 m (URS, 3.9%, −0.3 to 8.1, very likely moderate; RSS, 5.0%, 1.8–8.0, very likely large), and 20 m (URS, 2.0%, −0.6 to 4.5, likely moderate; RSS, 3.0%, 1.7–4.4, very likely moderate). COD was improved in both groups (URS, 3.7%, 2.2–5.2, most likely large; RSS, 3.3%, 1.6–5.0, most likely moderate). Between-groups differences were unclear. Conclusion: Heavy RSS and URS training matched for running distance were similarly effective at improving sprint and COD performance in professional soccer players when performed in the competitive phase of the season.
Brian J. McMorrow, Massimiliano Ditroilo and Brendan Egan
Hunter S. Waldman, Brandon D. Shepherd, Brendan Egan and Matthew J. McAllister
In the present study, our team aimed to investigate the effects of acute ingestion of a ketone salt (KS) supplement on the cognitive performance in healthy college-aged males during a dual-stress challenge (DSC). Following a peak oxygen uptake test and DSC familiarization, 16 males completed a DSC while cycling at 60% of their respective peak oxygen uptake after ingesting either a commercially available racemic (D- and L-)β-hydroxybutyrate (β-OHB) KS (0.38 g/kg body mass) or a placebo, using a triple-blinded, crossover, and counterbalanced design. The participants consumed the KS or placebo at −60 and −15 min prior to the start of the DSC. Heart rate, rating of perceived exertion, and blood β-OHB and glucose were sampled throughout. The DSC consisted of a mental arithmetic challenge and a modified Stroop Color Word, which alternated every 2 min for 20 min. Upon completion of the DSC, responses for correct, incorrect, and no responses were recorded for the mental arithmetic challenge and Stroop Color Word. Blood β-OHB was elevated with KS by −15 min and remained so throughout (p < .001), peaking at 0.76 ± 0.32 mM. Blood glucose was lower with KS compared with the placebo at −15 and 10 min by 9% and 5%, respectively (both ps < .05). There were no differences between the treatments for heart rate, rating of perceived exertion, mental arithmetic challenge, or Stroop Color Word. Overall, this study suggests that KSs are not effective aids for enhancing cognitive performance during a DSC, which might partially be explained by the inability of currently available commercial KS supplements to elevate β-OHB blood concentrations above ∼1.0 mM.
Mark Evans, Peter Tierney, Nicola Gray, Greg Hawe, Maria Macken and Brendan Egan
The effects of acute ingestion of caffeine on short-duration high-intensity performance are equivocal, while studies of novel modes of delivery and the efficacy of low doses of caffeine are warranted. The aims of the present study were to investigate the effect of acute ingestion of caffeinated chewing gum on repeated sprint performance (RSP) in team sport athletes, and whether habitual caffeine consumption alters the ergogenic effect, if any, on RSP. A total of 18 male team sport athletes undertook four RSP trials using a 40-m maximum shuttle run test, which incorporates 10 × 40-m sprints with 30 s between the start of each sprint. Each participant completed two familiarization sessions, followed by caffeine (CAF; caffeinated chewing gum; 200 mg caffeine) and placebo (PLA; noncaffeinated chewing gum) trials in a randomized, double-blind manner. RSP, assessed by sprint performance decrement (%), did not differ (p = .209; effect size = 0.16; N = 18) between CAF (5.00 ± 2.84%) and PLA (5.43 ± 2.68%). Secondary analysis revealed that low habitual caffeine consumers (<40 mg/day, n = 10) experienced an attenuation of sprint performance decrement during CAF relative to PLA (5.53 ± 3.12% vs. 6.53 ± 2.91%, respectively; p = .049; effect size =0.33); an effect not observed in moderate/high habitual caffeine consumers (>130 mg/day, n = 6; 3.98 ± 2.57% vs. 3.80 ± 1.79%, respectively; p = .684; effect size = 0.08). The data suggest that a low dose of caffeine in the form of caffeinated chewing gum attenuates the sprint performance decrement during RSP by team sport athletes with low, but not moderate-to-high, habitual consumption of caffeine.