title: Acute effects of caffeine-containing energy drinks on physical performance: a systematic review and meta-analysis.
abstract: OBJECTIVE
  Caffeine-containing energy drinks (EDs) are currently used as ergogenic aids to improve physical performance in a wide variety of sport disciplines. However, the outcomes of previous investigations on this topic are inconclusive due to methodological differences, especially, in the dosage of the active ingredients and the test used to assess performance.
  
  
  METHODS
  We performed a systematic review and meta-analysis of published studies to evaluate the effects of acute ED intake on physical performance. The search for references was conducted in the databases PubMed, ISI Web of Knowledge and SPORTDiscus until December 2015.
  
  
  RESULTS
  Thirty-four studies published between 1998 and 2015 were included in the analysis. Using a random-effects model, effect sizes (ES) were calculated as the standardized mean difference. Overall, ED ingestion improved physical performance in muscle strength and endurance (ES = 0.49; p < 0.001), endurance exercise tests (ES = 0.53; p < 0.001), jumping (ES = 0.29; p = 0.01) and sport-specific actions (ES = 0.51; p < 0.001), but not in sprinting (ES = 0.14; p = 0.06). The meta-regression demonstrated a significant association between taurine dosage (mg) and performance (slope = 0.0001; p = 0.04), but not between caffeine dosage (mg) and performance (slope = 0.0009; p = 0.21).
  
  
  CONCLUSIONS
  ED ingestion improved performance in muscle strength and endurance, endurance exercise tests, jumping and sport-specific actions. However, the improvement in performance was associated with taurine dosage.
authors.affiliation: Department of Physical Education, Londrina State University, Londrina, Brazil.
authors.forename: Diego B
authors.initials: DB
authors.lastname: Souza
authors.affiliation: Exercise Physiology Laboratory, Camilo José Cela University, Madrid, Spain.
authors.forename: Juan
authors.initials: J
authors.lastname: Del Coso
authors.affiliation: Center of Life Sciences and Health, University of North Paraná, Londrina, Brazil.
authors.forename: Juliano
authors.initials: J
authors.lastname: Casonatto
authors.affiliation: Department of Physical Education, Londrina State University, Londrina, Brazil. marcospolito@uel.br.|Universidade Estadual de Londrina, Rod. Celso Garcia Cid, km 380, Londrina, PR, 86050-520, Brazil. marcospolito@uel.br.
authors.forename: Marcos D
authors.initials: MD
authors.lastname: Polito
mesh_terms: D054874:Athletic Performance; D002110:Caffeine / Q000008:administration & dosage*; D061215:Energy Drinks; D015444:Exercise; D006801:Humans; D053580:Muscle Strength / Q000187:drug effects; D010807:Physical Endurance / Q000187:drug effects*; D064133:Sports Nutritional Physiological Phenomena
chemical_list: D002110:Caffeine
keywords: Caffeine; Performance-enhancing substances; Sports; Taurine