Caffeine and endurance
exercise performance
Early studies
The interest in caffeine as an ergogenic aid
during endurance exercise was initially stimu-
lated by work from Costill’s laboratory in the late
1970s. Trained cyclists improved their cycle time
to exhaustion at 80% of maximal oxygen con-
sumption (V
.
o2max.) from 75 min in the placebo
condition to 96 min following caffeine (330 mg)
ingestion (Costill et al. 1978). A second study
demonstrated a 20% increase in the amount of
work performed in 2 h following 250 mg caffeine
(Ivyet al. 1979). These studies reported increased
venous free fatty acid (FFA) concentrations,
decreased respiratory exchange ratios (RER) and
increased fat oxidation (ª30%) in the caffeine
trials. A third study reported that ingestion of
5 mg caffeine · kg–1body mass spared muscle
glycogen and increased muscle triacylglycerol
(TG) use (Essig et al. 1980). In the 1980s, most
investigators examined only the effects of caf-
feine on metabolism and not on endurance per-
formance. Furthermore, conclusions regarding
the metabolic effects of caffeine were equivocal
and based on changes in plasma FFA and
RER. This work has been extensively reviewed
(Wilcox 1990; Graham et al. 1994; Tarnopolsky
1994; Spriet 1995).
Recent endurance performance and
metabolic studies
Several well-controlled studies in the 1990s
examined the performance and metabolism
effects of caffeine in well-trained athletes, accus-
tomed to exhaustive exercise and race condi-
tions. These experiments examined the effects of
9 mg caffeine · kg–1body mass (in capsule form)
on running and cycling time to exhaustion at
80–85%V
.
o2max.(Graham & Spriet 1991; Spriet
et al. 1992), the effects of varying doses
(3–13 mg · kg–1) of caffeine on cycling perfor-
mance (Graham & Spriet 1995; Pasman et al.
1995) and the effects of a moderate caffeine dose
380 nutrition and exercise
(5 mg · kg–1) on performance of repeated 30-min
bouts of cycling (5 min rest between bouts) at
85–90%V.
o2max.(Trice & Haymes 1995).
Collectively, this work produced or confirmed
several important findings. Endurance perfor-
mance was improved by approximately 20–50%
compared with the placebo trial (40–77 min) fol-
lowing ingestion of varying caffeine doses (3–13
mg · kg–1) in elite and recreationally trained ath-
letes while running or cycling at approximately
80–90%V.
o2max.(Figs 28.1, 28.2). Without excep-
tion, the 3, 5 and 6 mg · kg–1doses produced an
ergogenic effect with urinary caffeine levels
below the IOC acceptable limit (Fig. 28.3). Three
of four experiments using a 9 mg · kg–1 dose
reported performance increases, while 6/22
athletes tested in these studies had urinary
caffeine at or above 12mg·ml–1. Performance was
enhanced with a 13 mg · kg–1dose, but 6/9 ath-
letes had urinary caffeine well above 12mg·ml–1
(Fig. 28.3). The side-effects of caffeine ingestion
(dizziness, headache, insomnia and gastroin-
testinal distress) were rare with doses at or below
6mg·kg–1, but prevalent at higher doses (9–13
mg · kg–1) and associated with decreased perfor-8006040Bike20
Mean performance time (min)Treadmill151% 144%Fig. 28.1Performance times for subjects running
and cycling to exhaustion at approximately 85%
V
.
o2max.after placebo () or caffeine ( ) ingestion.
Performance was significantly improved by 51%
during running and 44% while cycling. From Graham
and Spriet (1991), with permission.