The Effects of Acute Caffeine Supplementation on Performance in Trained CrossFit Athletes - MDPI
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sports Article The Effects of Acute Caffeine Supplementation on Performance in Trained CrossFit Athletes Jesse A. Stein * , Melitza Ramirez and Katie M. Heinrich Department of Kinesiology, College of Human Ecology, Kansas State University, Manhattan, KS 66506, USA; melitzar@ksu.edu (M.R.); kmhphd@ksu.edu (K.M.H.) * Correspondence: jastein@ksu.edu; Tel.: +1-218-469-1837 Received: 20 March 2019; Accepted: 24 April 2019; Published: 25 April 2019 Abstract: Caffeine’s ergogenic effects persist during various exercise modalities; however, information establishing its efficacy during CrossFit protocols is limited. Our study aimed to determine the effects of caffeine supplementation on CrossFit performance. Thirteen CrossFit-trained men (age = 28.5 ± 6.6 years, experience = 49.2 ± 36.3 months) were randomized in a double-blind, crossover design. Participants completed two sessions separated by a seven-day washout period, 60 min after consuming 5 mg/kg body mass of caffeine or a placebo. In each session, participants completed as many rounds as possible in 20 min of 5 pull-ups, 10 push-ups, and 15 air squats. CrossFit performance was the total number of repetitions completed in 20 min. Paired samples t-tests were used to compare CrossFit performance between caffeine and placebo conditions and to test for a potential learning effect between the first and second sessions. CrossFit performance was significantly higher during the caffeine condition compared to the placebo (461.4 ± 103 vs. 425.0 ± 93.5 repetitions, p < 0.05). No significant learning effect was identified between the first and second sessions (445.6 ± 95.0 vs. 440.8 ± 105.0 repetitions, p = 0.73) nor was there a significant treatment order effect (p = 0.40). Caffeine’s ergogenic effect is present during CrossFit; however, future investigations should establish caffeine’s efficacy during other CrossFit protocols and among female athletes. Keywords: high intensity functional training; exercise; males; muscular endurance; ergogenic aids; sports nutrition 1. Introduction Caffeine supplementation is pervasive in sporting disciplines with 74% of elite athletes consuming caffeine prior to competition for its ergogenic effects [1]. Support for this strategy is recognized by the International Olympic Committee and the International Society of Sports Nutrition who both acknowledge caffeine as a dietary supplement with ‘good evidence’ for its ergogenic effects, benefiting endurance and strength/power in athletes [2–5]. A majority of this evidence has been established utilizing singular exercise modalities when assessing muscle function (muscular strength and endurance) or exhaustive protocols (time-to-exhaustion and repeated-sprint ability) [3,4,6–9]. However, some athletes are not easily classified into physical demands that are strictly endurance or strength/power in nature and require multiple facets of health- (e.g., aerobic capacity, muscular strength) and skill-related (e.g., agility, speed, power) physical fitness [10]. Recently, Mielgo-Ayuso addressed this concern within soccer players; however, a majority of the reviewed investigations evaluated aspects of physical performance (i.e., speed, power, agility, time-to-exhaustion) with limited data reported regarding simulated performance [11]. Reasonably, instructing athletes with diverse physical demands to consume caffeine for performance benefits has limited evidence to support its efficacy [11,12]. Since preserving muscle function during competition is important for preventing Sports 2019, 7, 95; doi:10.3390/sports7040095 www.mdpi.com/journal/sports
Sports 2019, 7, 95 2 of 9 premature fatigue, investigating the role of acute caffeine supplementation during combined exercise modalities is warranted. In the most recent meta-analysis of the effects of caffeine supplementation on muscle function, the authors reported significant improvements (+6–7%) in muscular endurance after caffeine supplementation [13]. A majority of the 17 investigations cited in the review assessed large muscle group(s) muscular endurance via repetitions to failure over the course of multiple weightlifting sets separated by recovery periods [14–17]. These investigations utilized isotonic exercise machines and reported relatively low repetitions (
Sports 2019, 7, 95 3 of 9 body fat were determined using a bioelectrical impedance analysis in standard mode (TBF-300A; Tanita, Japan). Following anthropometric measures, participants (n = 13, age = 28.5 ± 6.6 years; height = 178.9 ± 5.1 cm; mass = 84.3 ± 9.9 kg; percent body fat = 20.1 ± 2.9%; experience = 49.2 ± 36.3 months) were randomized to consume either caffeine or the placebo. To determine treatment order (placebo then caffeine vs. caffeine then placebo), participants were randomized using a random number generator (0–99) with odd numbers being placed into the placebo condition and even numbers being placed into the caffeine condition for the first visit (placebo then caffeine: n = 7; caffeine then placebo: n = 6). The caffeine pill(s) (Prolab) were provided at 5 mg·kg−1 body mass [28]. A 300 µg biotin pill(s) was used as a placebo to match for color and texture of caffeine pills. The same amount of pill(s) of biotin were administered as caffeine pills to ensure blinding. Participants began a self-selected warm-up 50-min after consumption of the pill(s). Participants began the CrossFit workout—‘Cindy’—60-min after consumption of the pill(s). The workout was performed indoors in a gym with the temperature set to 22 ◦ C. Each participant performed the workout alone with no clock or timing device visible to them and without music. ‘Cindy’ was chosen since it is a standardized CrossFit workout, and it has been previously described in the literature [21,22,29]. Briefly, participants completed as many rounds as possible of 5 pull-ups, 10 push-ups, and 15 air squats in 20 min. CrossFit movement standards were followed; kipping was allowed for the pull-ups; push-ups were performed on the toes, with the subject lowering himself with a straight body until his chest touched the floor; and air squats required subjects to reach full knee and hip extension at the top of each repetition and have their hip crease below their knee at the bottom of each repetition [29]. Judges, with CrossFit Level 1 or 2 Certificates, verbally counted repetitions. Repetitions that did not meet movement standards were not counted, and participants were provided feedback to meet the movement standards. CrossFit performance was the total number of repetitions completed in 20 min. Participants were given a post-exercise survey to determine their rate of perceived exertion (RPE) achieved during the workout on a scale of 1–10 [30]. Participants returned to the laboratory after a 7-day washout period, consumed the opposite pill(s) from their first visit (placebo n = 6; caffeine n = 7), and identical procedures were followed for the workout and post-workout survey. For each participant, the testing sessions were scheduled within a 2 h window. Percent change in the performance (i.e., repetitions completed) was calculated to assess the individual effects of caffeine supplementation [(caffeine − placebo)/(placebo) × 100)]. Individuals were classified as ‘non-responders’ if the percent change was
Sports 2019, 7, 95 4 of 9 Sports Sports 2019, 2019, 7, 7, xx FOR FOR PEER PEER REVIEW REVIEW 44 of of 99 exercise responses (i.e., RPE) between the caffeine (8.5 ± 1.3) and the placebo conditions (8.3 ± 1.3), (8.3=± −0.562, t(12) p= 1.3), t(12) 0.584 (Figure = −0.562, p = 0.5842).(Figure No significant learning effect 2). No significant learningwas identified effect betweenbetween was identified the firstthe and second sessions first and second(445.6 ± 95.0(445.6 sessions vs. 440.8 ± 105.0 ± 95.0 vs. 440.8 ± 105.0t(12) repetitions, = 0.348, t(12) repetitions, p = 0.73). After = 0.348, p =controlling 0.73). Afterfor the total number controlling of repetitions for the total number performed during of repetitions the placebo performed condition, during no significant the placebo condition,treatment order no significant effect was observed treatment for the order effect wastotal number observed forof repetitions the performed total number duringperformed of repetitions the caffeineduring condition between the caffeine treatment conditionorder groups between treatment = 0.760, (F(1,13)order p = 0.40). groups Figure (F(1,13) 3 shows = 0.760, the percent p = 0.40). Figurechange 3 showsin performance the percent change (i.e., total in performance repetitions) (i.e., total [(caffeine repetitions) [(caffeine − placebo)/(placebo) − placebo)/(placebo) × 100)] performed across×all 100)] performed subjects (8.9%, across 95% CI all subjects (8.9%, 95% CI (4.0–13.7%)), three of whom were (4.0–13.7%)), three of whom were ‘non-responders’ (−0.5%, −0.4%, 0.27%). ‘non-responders’ (−0.5%, −0.4%, 0.27%). * Figure Figure 1. 1. Figure 1. Performance Performance Performance (i.e.,(i.e., (i.e., repetitions repetitions repetitions performed) in thein performed) performed) in the the caffeine caffeine caffeine and and placebo and placebo placebo condition. condition. condition. Data Data Data represent represent mean ± SD.mean represent mean ±± SD. SD. ** Significantly * SignificantlySignificantly different different different from from from performance performance performance during theduring during the placebo placebo condition thecondition placebo p < 0.05.pp
Sports 2019, 7, 95 5 of 9 Sports 2019, 7, x FOR PEER REVIEW 5 of 9 Figure 3. Figure 3. Percent Percent change change in in performance performance [(repetitions completed with [(repetitions completed with caffeine caffeine − − repetitions repetitions completed completed with placebo)/(repetitions with placebo)/(repetitions completed completed with with placebo) placebo) ×× 100)] 100)] in in the the caffeine and placebo caffeine and placebo condition condition for for each participant. each participant. 4. Discussion The purpose of our investigation was to determine the effects of acute caffeine supplementation on CrossFit performance performance and and perceptual perceptualresponses responsestotoexercise exerciseininCrossFit-trained CrossFit-trainedmales. males. Because Because of of the well-documented ergogenic effects of caffeine that are likely due to central the well-documented ergogenic effects of caffeine that are likely due to central mechanisms [2–5], we mechanisms [2–5], we hypothesized hypothesized thatthat caffeine caffeine supplementationwould supplementation wouldimprove improveCrossFit CrossFitperformance. performance. OurOur hypothesis was partially supported with significant improvements in CrossFit performance with no changes in perceptual responses after caffeine supplementation. Additionally, we supplementation. Additionally, we tested tested for a learning effect between the thefirst firstand andsecond second session session of of ‘Cindy’ ‘Cindy’ andandfound found no significant no significant differences. differences. Lastly,Lastly, our our study study aimed to provide a novel contribution to the literature regarding aimed to provide a novel contribution to the literature regarding caffeine supplementation caffeine supplementation and muscular muscular endurance endurance by providing a unique high-volume muscular endurance challenge. On average, average, participants participants ininthethecurrent current investigation investigation performed performed overover400 repetitions 400 repetitionsfor thefor 20the min20 workout during min workout the caffeine and placebo conditions, which we believe adequately addressed during the caffeine and placebo conditions, which we believe adequately addressed this challenge. this challenge. To the best To theof our bestknowledge, this is the first of our knowledge, this study is theto first determine study theto effects determineof caffeine supplementation the effects of caffeine on performance during supplementation any CrossFit on performance workout, during which taxed any CrossFit multiple workout, whichmuscle groups for taxed multiple an extended muscle groups period of time with minimal rest. for an extended period of time with minimal rest. In the current current study, study,caffeine caffeinesupplementation supplementation(5 mg·kg−1 (5mg·kg −1 body mass) increased mean CrossFit performance by by 8.9%. 8.9%.Caffeine’s Caffeine’sergogenic ergogenic effect has been effect has been reported reported to improve to improve performance performance by by 5.5– 5.5–8.5% 8.5% during during other other repeated-high-intensity repeated-high-intensity efforts efforts in in teamsports team sportsathletes, athletes,andand by by 6–7% during muscular endurance exercise [6,13,32]. Previous Previous investigations investigations determining determining the the effects of caffeine supplementation on muscular endurance had participants perform a comparatively low number of repetitions (
Sports 2019, 7, 95 6 of 9 results [3]. Thus, researchers might consider additional measurements of during-workout exertion since RPE is usually taken after the exercise bout given the nature of resistance exercise [35]. Our study assessed CrossFit performance via ‘Cindy’, which has been the most studied CrossFit workout to date [21,22,29]. Butcher and colleagues reported ‘Cindy’ performance between competitive, experienced, and novice CrossFit athletes completing 698, 469, 389 repetitions, respectively [21,23]. The current study, which aimed to recruit CrossFit-trained (i.e., experienced) participants, seems to follow those trends. Moreover, Crawford [24] measured work capacity derived from performance during a similar CrossFit workout and reported ~16% increase in work capacity after 6 weeks of a high-intensity functional training intervention which followed a CrossFit template for novice healthy adult participants. This is promising for researchers and practitioners alike as the use of benchmark workouts, such as ‘Cindy’, may be sensitive enough to detect changes in CrossFit performance from ergogenic aids (e.g., exercise training interventions, nutrient modification) [21]. Strengths of the current investigation include a robust study design with subjects serving as their own controls, the recruitment of trained male CrossFit participants who were able to complete ‘Cindy’ as prescribed as a high-volume muscular endurance workout, and it is the first study to document an ergogenic effect during a CrossFit workout. However, our study does not go without limitation. Although 13 CrossFit-trained men completed our study, our sample size is reasonably small. However, the average sample size reported in a recently published systematic review on the effects of caffeine in trained soccer players was 15 participants; therefore, our investigation reflects similar sample sizes compared to other studies regarding caffeine’s ergogenic effect in trained populations [11]. Participant training volume was not reported leading up or during the investigation. Although participants were instructed not to exercise vigorously for 24 h prior to each testing session or change their training regimen during the study period, fatigue and/or delayed onset muscle soreness from other training sessions could impact our results. Additionally, our study lacked more invasive measures to determine blood caffeine concentration and caffeine metabolism. Recently identified, caffeine supplementation may have a ‘responder’ vs. ‘non-responder’ nature, which limits the translation of our investigation to ‘non-responder’ populations [27]. In our investigation, we had three participants (−0.5%, −0.4%, 0.27%) who were ‘non-responders’ to caffeine supplementation (Figure 2). The inter-individual differences in the ergogenicity of caffeine are thought to be related to genetic polymorphisms associated with the CYP1A2 and ADORA2A genes, which discern fast and slow caffeine metabolism/clearance [36]. Although the current investigation did not characterize the genetic differences among our participants, these differences may explain the ‘responder’ vs. ‘non-responder’ nature of our findings and present an avenue for future investigations. However, to truly elucidate ‘responders’ vs. ‘non-responders’, a baseline control condition where no supplements are provided to the participants prior to the exercise bout is necessary. Additionally, our study investigated the effects of caffeine supplementation on CrossFit performance for males and may not be generalizable to female participants. Caffeine supplementation in females is complicated by the effects of estrogen and oral contraceptive steroids on caffeine metabolism, both of which appear to prolong the effects of caffeine in the body [3,37]. To increase internal validity, participants performed the workout alone, with no clock visible, and no music was playing. Results may differ when ‘Cindy’ is performed in a group setting with a visible clock and music playing [38–40]. Lastly, our investigation utilized a 10-point Likert scale for RPE and may not be sensitive enough to capture perceptual changes during CrossFit protocols. Although mixed results exist for 10-point and 15-point scales for RPE during caffeine supplementation utilizing resistance- and endurance-based protocols, a recent publication by Crawford and colleagues highlight that a 15-point scale may be more appropriate in CrossFit athletes [3,34,35]. 5. Conclusions In conclusion, we have provided evidence that caffeine supplementation at 5 mg·kg−1 body mass ingested 60 min prior to the CrossFit workout ‘Cindy’ increased the number of repetitions performed in male CrossFit-trained individuals. However, despite the central effects of caffeine, we found no
Sports 2019, 7, 95 7 of 9 significant changes in perceptual responses during the exercise bout. Caffeine’s ergogenic effects are well documented in the literature and further supported by our investigation, yet practitioners and athletes should be aware that some ‘non-responders’ may exist; thus, evaluating caffeine’s effectiveness prior to competition for a specific athlete is encouraged. Author Contributions: Conceptualization, J.A.S. and M.R.; methodology, J.A.S. and K.M.H.; software, J.A.S.; formal analysis, J.A.S.; investigation, J.A.S., M.R. and K.M.H.; resources, J.A.S. and M.R.; data curation, M.R. and J.A.S.; writing—original draft preparation, J.A.S.; writing—review and editing, J.A.S., M.R. and K.M.H.; visualization, J.A.S.; supervision, K.M.H.; project administration, J.A.S. and M.R.; funding acquisition, M.R. Funding: This research was funded by the Kansas State University Office of Undergraduate Research and Creative Inquiry awarded to M.R. Time spent preparing the manuscript was funded by the National Institutes of Diabetes and Digestive and Kidney Diseases (R01DK099516) awarded to K.M.H. Acknowledgments: We would like to acknowledge the lab assistants from the Kansas State University Functional Intensity Training lab Timothy C. Hepler, Brady K. Kurtz, Bryan S. Heinrich, Jason Sartor, and Victor Andrews during data collection. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. References 1. Del Coso, J.; Muñoz, G.; Muñoz-Guerra, J. Prevalence of caffeine use in elite athletes following its removal from the World Anti-Doping Agency list of banned substances. Appl. Physiol. Nutr. Metab. 2011, 36, 555–561. [CrossRef] 2. Maughan, R.J.; Burke, L.M.; Dvorak, J.; Larson-Meyer, D.E.; Peeling, P.; Phillips, S.M. IOC consensus statement: Dietary supplements and the high-performance athlete. Int. J. Sport Nutr. Exerc. Metab. 2018, 28, 104–125. [CrossRef] 3. Grgic, J.; Mikulic, P.; Schoenfeld, B.J.; Bishop, D.J.; Pedisic, Z. The Influence of Caffeine Supplementation on Resistance Exercise: A Review. Sport Med. 2018, 49, 17–30. [CrossRef] [PubMed] 4. Warren, G.L.; Park, N.D.; Maresca, R.D.; McKibans, K.I.; Millard-Stafford, M.L. Effect of Caffeine Ingestion on Muscular Strength and Endurance: A Meta-Analysis. Med. Sci. Sport Exerc. 2010, 42, 1375–1387. [CrossRef] 5. Kerksick, C.M.; Wilborn, C.D.; Roberts, M.D.; Smith-Ryan, A.; Kleiner, S.M.; Jäger, R.; Greenwood, M. ISSN exercise & sports nutrition review update: research & recommendations. J. Int. Soc. Sports Nutr. 2018, 15, 38. 6. Evans, M.; Tierney, P.; Gray, N.; Hawe, G.; Macken, M.; Egan, B. Acute Ingestion of Caffeinated Chewing Gum Improves Repeated Sprint Performance of Team Sport Athletes with Low Habitual Caffeine Consumption. Int. J. Sport Nutr. Exerc. Metab. 2018, 28, 221–227. [CrossRef] 7. Peyer, K.L.; Pivarnik, J.M.; Eisenmann, J.C.; Vorkapich, M. Physiological Characteristics of National Collegiate Athletic Association Division I Ice Hockey Players and Their Relation to Game Performance. J. Strength Cond. Res. 2011, 25, 1183–1192. [CrossRef] [PubMed] 8. Graham, T.E. Caffeine and Exercise Metabolism, Endurance and Performance. Sport Med. 2001, 31, 785–807. [CrossRef] 9. Todd, A.; Daniel, W. Efficacy of caffeine ingestion for short-term high-intensity performance: A systematic review. J. Strength Cond. Res. 2010, 24, 257–265. 10. Bishop, D.J.; Girard, O. Determinants of team-sport performance: implications for altitude training by team-sport athletes. Br J. Sports Med. 2013, 47, 17–21. [CrossRef] [PubMed] 11. Mielgo-Ayuso, J.; Calleja-Gonzalez, J.; Del Coso, J.; Urdampilleta, A.; León-Guereño, P.; Fernández-Lázaro, D. Caffeine Supplementation and Physical Performance, Muscle Damage and Perception of Fatigue in Soccer Players: A Systematic Review. Nutrients 2019, 11, 440. [CrossRef] [PubMed] 12. Salinero, J.J.; Lara, B.; Del Coso, J. Effects of acute ingestion of caffeine on team sports performance: A systematic review and meta-analysis. Res. Sport Med. 2018, 27, 1–19. [CrossRef] 13. Polito, M.D.; Souza, D.B.; Casonatto, J.; Farinatti, P. Acute effect of caffeine consumption on isotonic muscular strength and endurance: A systematic review and meta-analysis. Sci. Sports 2016, 31, 119–128. [CrossRef] 14. Astorino, T.A.; Rohmann, R.L.; Firth, K. Effect of caffeine ingestion on one-repetition maximum muscular strength. Eur. J. Appl. Physiol. 2008, 102, 127–132. [CrossRef]
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