Effect of habitual caffeine consumption on individual responses to acute caffeine supplementation

Abstract

Caffeine is one of most consumed psychostimulant substances in the world and in many sports it is used as an ergogenic aid by athletes and non-athletes. There is substantial evidence showing increased muscular resistance, strength, anaerobic power and aerobic resistance across many sports. We can definitely say that caffeine ingestion is inherent in modern society, and athletes are the biggest users of this substance on regular bases through several sources. However, it has been suggested that regular intake of caffeine could lead to habituation and a possible decrease of the physiological effects from acute supplementation. There is current fierce debate regarding the variation in response to acute caffeine supplementation between habitual and non-habitual caffeine consumers. There is a complex and unclear relationship between caffeine habituation, acute supplementation, the ideal dosage and sports performance. To better understand this relationship, in this study we will recruit 20 male volunteers that are young, healthy and moderately trained in cycling. The research will have a randomized, double blind, cross over and placebo-controlled design. The subjects will be allocated in one of three groups, according to their habitual intake of caffeine: I) <0.3 g·kg-1·day-1; II) >0.3 g·kg-1·day-1, <0.6 g·kg-1·day-1; III) >0.6 g·kg-1·day-1. I) <0.3 g·kg-1·day-1; II) >0.3 g·kg-1·day-1, <0.6 g·kg-1·day-1; III) >0.6 g·kg-1·day-1. All individuals will perform a 4-km time trial on three separate occasions, receiving a) 3mg/kg of caffeine b) 6mg/kg of caffeine and c) placebo, in order to investigate if the regular use of caffeine interferes with the possible ergogenic effects of acute caffeine supplementation.