Caffeine and Endurance Exercise

[Guest guest]

Many of us know that caffeine is fairly widely used by strength athletes and

footballers in attempts to enhnace performance, but the strength community

doesn't pay much attention to its use in more endurance-oriented sports.

Here is a small selection of studies which examine the effect of caffeine on

endurance athletes. Any other offerings are welcome.

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Experimental Physiol 2001 Jan;86(1):137-44

Effect of caffeine co-ingested with carbohydrate or fat on metabolism and

performance in endurance-trained men.

son TL, Febbraio MA, Arkinstall MJ, Hawley JA.

We examined the effect of caffeine co-ingested with either carbohydrate or

fat on metabolism and performance in eight endurance-trained subjects who

performed a random order of four experimental trials consisting of 120 min of

steady-state ergometer cycling at 70 % of maximal O(2) uptake (SS) followed

by a time trial in which subjects completed a set amount of work (7 kJ kg-1)

as quickly as possible. One hour before SS subjects ingested either 2.6 g per

kg carbohydrate (CHO); 2.6 g kg-1 CHO + 6 mgper kg caffeine (CHO + CAF); 1.2

g kg-1 fat with 2000 U I.V. heparin (FAT); or 1.2 g kg-1 fat with 2000 U I.V.

heparin + 6 mg kg-1 caffeine (FAT + CAF).

The rate of carbohydrate oxidation was higher (micromol per kg min-1: CHO,

243 ± 39 and CHO + CAF, 239 ± 30 vs. FAT, 196 ± 48 and FAT + CAF, 191 ± 55,

values are means +/- S.D.) and the rate of fat oxidation lower (micromol per

kg min-1: CHO, 19 ± 8 and CHO + CAF, 22 ± 7 vs. FAT, 35 +/- 19 and FAT + CAF,

37 ± 17) with carbohydrate than fat ingestion. Yet despite lower carbohydrate

use with fat feeding, the time taken to complete the time trial was less

after carbohydrate than after fat ingestion (min: CHO, 30.37 ± 7.42 and CHO +

CAF, 29.12 ± 5.62 vs. FAT, 33.02 ± 8.50 and FAT + CAF, 32.78 ±7.70).

We conclude that

(1) caffeine co-ingested with either carbohydrate or fat meals has no

additive effect on substrate utilization or exercise performance and

(2) carbohydrate ingestion before exercise improves subsequent time trial

performance compared with fat ingestion.

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J Appl Physiol 1991 Dec;71(6):2292-8

Performance and metabolic responses to a high caffeine dose during prolonged

exercise.

Graham TE, Spriet LL.

The present study examined whether a high caffeine dose improved running and

cycling performance and altered substrate metabolism in well-trained runners.

Seven trained competitive runners [maximal O2 uptake (VO2max) 72.6 ± 1.5

ml.per kg per.min] completed four randomized and double-blind exercise trials

at approximately 85% VO2max; two trials running to exhaustion and two trials

cycling to exhaustion. Subjects ingested either placebo (PL, 9 mg/kg

dextrose) or caffeine (CAF, 9 mg/kg) 1 h before exercise. Endurance times

were increased after CAF ingestion during running (PL 49.2 ± 7.2 min, CAF

71.0 ± 11.0 min) and cycling (PL 39.2 ± 6.5 min, CAF 59.3 ± 9.9 min).

Plasma epinephrine concentration [EPI] was increased with CAF before running

(0.22 ± 0.02 vs. 0.44 ± 0.08 nM) and cycling (0.31 ± 0.06 vs. 0.45 ± 0.06

nM). CAF ingestion also increased [EPI] during exercise; PL and CAF values at

15 min were 1.23 ± 0.13 and 2.51 ± 0.33 nM for running and 1.24 ± 0.24 and

2.53 ± 0.32 nM for cycling. Similar results were obtained at exhaustion.

Plasma norepinephrine was unaffected by CAF at rest and during exercise. CAF

ingestion also had no effect on respiratory exchange ratio or plasma free

fatty acid data at rest or during exercise. Plasma glycerol was elevated by

CAF before exercise and at 15 min and exhaustion during running but only at

exhaustion during cycling. Urinary [CAF] increased to 8.7 ± 1.2 and 10.0 ±

0.8 micrograms/ml after the running and cycling trials.

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J Appl Physiol 1998 Oct;85(4):1502-8

Caffeine, performance, and metabolism during repeated Wingate exercise tests.

Greer F, McLean C, Graham TE.

Investigations examining the ergogenic and metabolic influence of caffeine

during short-term high-intensity exercise are few in number and have produced

inconsistent results. This study examined the effects of caffeine on repeated

bouts of high-intensity exercise in recreationally active men.

Subjects (n = 9) completed four 30-s Wingate (WG) sprints with 4 min of rest

between each exercise bout on two separate occasions. One hour before

exercise, either placebo (P1; dextrose) or caffeine (Caf; 6 mg/kg) capsules

were ingested. Caf ingestion did not have any effect on power output (peak or

average) in the first two WG tests and had a negative effect in the latter

two exercise bouts. Plasma epinephrine concentration was significantly

increased 60 min after Caf ingestion compared with P1; however, this

treatment effect disappeared once exercise began. Caf ingestion had no

significant effect on blood lactate, O2 consumption, or aerobic contribution

at any time during the protocol. After the second Wingate test, plasma NH3

concentration increased significantly from the previous WG test and was

significantly higher in the Caf trial compared with P1.

These data demonstrate no ergogenic effect of caffeine on power output during

repeated bouts of short-term, intense exercise. Furthermore, there was no

indication of increased anaerobic metabolism after Caf ingestion with the

exception of an increase in NH3 concentration.

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Braz J Med Biol Res 1998 Apr;31(4):581-5

Effects of caffeine on time to exhaustion in exercise performed below and

above the anaerobic threshold.

Denadai BS, Denadai ML.

Dept de Educacao Fisica, Universidade Estadual ista, Rio Claro, Brazil.

Controversy still exists concerning the potential ergogenic benefit of

caffeine (CAF) for exercise performance. The purpose of this study was to

compare the effects of CAF ingestion on endurance performance during exercise

on a bicycle ergometer at two different intensities, i.e., approximately 10%

below and 10% above the anaerobic threshold (AT).

Eight untrained males, non-regular consumers of CAF, participated in this

study. AT, defined as the intensity (watts) corresponding to a lactate

concentration of 4 mM, was determined during an incremental exercise test

from rest to exhaustion on an electrically braked cycle ergometer. On the

basis of these measurements, the subjects were asked to cycle until

exhaustion at two different intensities, i.e., approximately 10% below and

10% above AT. Each intensity was performed twice in a double-blind randomized

order by ingesting either CAF (5 mg/kg) or a placebo (PLA) 60 min prior to

the test. Venous blood was analyzed for free fatty acid, glucose, and

lactate, before, during, and immediately after exercise. Rating of perceived

exertion and time to exhaustion were also measured during each trial.

There were no differences in free fatty acids or lactate levels between CAF

and PLA during and immediately after exercise for either intensity.

Immediately after exercise glucose increased in the CAF trial at both

intensities. Rating of perceived exertion was significantly lower (CAF = 14.1

± 2.5 vs PLA = 16.6 +/- 2.4) and time to exhaustion was significantly higher

(CAF = 46.54 ±8.05) min vs PLA = 32.42 ± 14.81 min) during exercise below AT

with CAF. However, there was no effect of CAF treatment on rating of

perceived exertion (CAF = 18.0 ± 2.7 vs PLA = 17.6 ± 2.3) and time to

exhaustion (CAF = 18.45 +/- 7.28 min vs PLA = 19.17 ± 4.37 min) during

exercise above AT.

We conclude that in untrained subjects caffeine can improve endurance

performance during prolonged exercise performed below AT and that the

decrease of perceived exertion can be involved in this process.

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J Appl Physiol 2002 Dec 13; [epub ahead of print] Related Articles, Links

The effect of a divided caffeine dose on endurance cycling performance,

post-exercise urinary caffeine concentration, and plasma paraxanthine.

Conway KJ, Orr R, Stannard SR.

This study compared the effects of a single and divided dose of caffeine on

endurance performance, post-exercise urinary caffeine and plasma paraxanthine

concentrations.

Nine male cyclists and triathletes, cycled for 90-min at 68%VO2max, followed

by a self-paced time-trial (work equivalent to 80%VO2max workload over

30-min) with three randomised, balanced, and double-blind interventions: 1)

placebo 60-min prior to, and 45-min into exercise (PP); 2) single caffeine

dose (6 mg per kg) 60 min prior to exercise and placebo 45-min into exercise

(CP); and 3) divided caffeine dose (3 mg.per kg) 60 min prior to, and 45 mins

into exercise (CC).

Time-trial performance was unchanged with caffeine ingestion , but tended to

be faster in the caffeine trials (CP: 24.2 min and CC: 23.4 min) compared

with placebo (PP: 28.3-min). Post-exercise urinary caffeine concentration was

significantly lower in CC (3.8 microgram per ml) compared with CP (6.8

microgram per ml).

Plasma paraxanthine increased in a dose-dependent fashion and did not peak

during exercise. In conclusion, dividing a caffeine dose provides no

ergogenic effect over a bolus dose, but reduces post-exercise urinary

concentration.

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Am J Physiol 1992 Jun;262(6 Pt 1):E891-8 Related Articles, Links

Caffeine ingestion and muscle metabolism during prolonged exercise in humans.

Spriet LL, MacLean DA, Dyck DJ, Hultman E, Cederblad G, Graham TE.

We examined the effects of a high-caffeine dose on endurance performance and

muscle acetyl group metabolism during prolonged exercise.

Eight subjects cycled to exhaustion at approximately 80% maximal oxygen

uptake (VO2max) 1 h after ingestion of 9 mg/kg body wt dextrose (Pl) or

caffeine (Caf). In the Pl trial, muscle biopsies were taken at rest (1 h

postingestion) and at 15 min and exhaustion during exercise. The Caf trial

followed the same protocol 1 wk later, with an additional biopsy at the time

corresponding to Pl exhaustion.

The subjects cycled significantly longer during the Caf trial (96.2 ± 8.8

min) than in the Pl trial (75.8 ± 4.8 min). Net glycogenolysis during the

initial 15 min of cycling was reduced in the Caf vs. Pl trial (4.7 ± 1.5 vs.

10.6 ±1.3 mmol per kg of dry muscle per min).

Muscle citrate concentration was increased at rest with Caf (0.59 ± 0.07 vs.

0.37 ± 0.05 mmol per kg dry muscle) but increased to similar values in both

trials during cycling. Caf elevated the acetyl-CoA/CoA-SH ratio at rest

(0.316 ± 0.046 vs. 0.201 ± 0.023;) but had no effect on the increases in

muscle acetyl-CoA and acetylcarnitine during exercise.

The results indicate that Caf before exercise decreased muscle glycogenolysis

by approximately 55% over the first 15 min of exercise at approximately 80%

VO2max. This " spared glycogen " was available late in exercise and coincided

with a prolonged time to exhaustion. Increased utilization of intramuscular

triacylglycerol and/or extramuscular free fatty acids after caffeine

ingestion may inhibit carbohydrate use at rest and early during exercise via

elevations in muscle citrate and the acetyl-CoA/CoA-SH ratio. Muscle

acetyl-CoA and acetylcarnitine were maintained above resting contents even

at exhaustion when muscle glycogen was depleted.

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Dr Mel C Siff

Denver, USA

http://groups.yahoo.com/group/Supertraining/