Guner, R., Turnagol, H., Bayar, C., Ceterman, M., & Ergen, E. (1998). Effects of coffee on isokinetic strength, Wingate test and post exercise urine caffeine metabolites' concentrations. Medicine and Science in Sports and Exercise, 30(5), Supplement abstract 1381.

The effects of regular (5 mg/kg caffeine) and decaffeinated coffee on short-term high-intensity performance and strength were evaluated. Male soccer players (N = 14) were tested under each coffee condition as well as a control no-coffee condition. An isokinetic knee-strength test and a Wingate test were performed one hour after coffee ingestion.

Isokinetic strength was not affected by caffeine. The Wingate test results were significantly better for the caffeine condition than either the decaffeinated or control conditions. Two Ss showed urinary concentrations of caffeine above the limit of 12 ug/ml.

Implications. Caffeine ingestion improved short-term high-intensity exercise but not single bout isokinetic strength. There is considerable individual variation in how the caffeine is metabolized with some Ss exceeding the allowable level.

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