Effect of repeated caffeine ingestion on repeated exhaustive exercise endurance.
OBJECTIVE
The purpose of this study was to examine the effect of repeated doses of caffeine on repeated exercise endurance. METHODS Nine male caffeine users performed exercise rides (ER) to exhaustion at 80% VO(2max) after ingesting a placebo, 5 mg x kg-1 of caffeine, or 2.5 mg x kg-1 of caffeine 1 h before the ER. Two ER were performed weekly on the same day once in the morning (AM) and 5 h later in the afternoon (PM). There were four treatments containing either caffeine or placebo, i.e., trial A representing 5-mg x kg-1 caffeine in the AM and 2.5-mg x kg-1 caffeine in the PM; trial B, which was placebo in both AM and PM; trial C representing 5-mg x kg-1 caffeine in the AM and placebo in the PM; and trial D representing a placebo in the AM and 5-mg x kg-1 caffeine in the PM. The order of the treatment trials was double blind and randomized.


RESULTS
Caffeine ingestion significantly increased exercise time to exhaustion in the AM (trial A 24.9 +/- 10.2 min and trial C 21.8 +/- 4.9 vs trial B 18.0 +/- 6.4 min and D 17.7 +/- 4.3 min). This effect was maintained in the PM and greater than placebo (B 18.3 +/- 4.8 min) regardless of whether redosing (trial A 21.5 +/- 8.6 min) or placebo (trial C 21.0 +/- 6.8) followed the initial morning dose. Caffeine dosing in the PM (trial D 22.4 +/- 7.2 min) also increased ER after placebo trial D in the AM.


CONCLUSIONS
It was concluded that redosing with caffeine after exhaustive exercise in the AM was not necessary to maintain the ergogenic effect of the drug during subsequent exercise 6 h later.
Bell
Douglas G
DG
Operational Medicine Section, Defence R&D Canada-Toronto, Ontario, Canada. doug.bell@drdc-rddc.gc.ca
McLellan
Tom M
TM
D000284:Administration, Oral; D000328:Adult; D001786:Blood Glucose / Q000032:analysis / Q000187:drug effects; D002110:Caffeine / Q000008:administration & dosage* / Q000097:blood; D000697:Central Nervous System Stimulants / Q000008:administration & dosage*; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects; D010807:Physical Endurance / Q000187:drug effects*; D005082:Physical Exertion / Q000187:drug effects; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D013997:Time Factors
D001786:Blood Glucose; D000697:Central Nervous System Stimulants; D005230:Fatty Acids, Nonesterified; D019344:Lactic Acid; D002110:Caffeine