CREATINE AFFECTS PERFORMANCE ONLY WHEN REST INTERVALS ARE LONG
Carl, D. L., Alperin, N., Kochendorfer, K., Stieger, J., Andres, F., & Broadley, D. (1999). Effect of oral creatine and caffeine on muscle phosphocreatine resynthesis in competitive swimmers. Medicine and Science in Sports and Exercise, 31(5), Supplement abstract 1283.
The purpose of this investigation was to examine the effects of creatine versus creatine plus caffeine on the resynthesis of muscle phosphocreatine and swimming performance. Highly trained female swimmers (N = 6) were tested before supplementation. Ss consumed creatine (0.4 g/kg/d) for 5 days, with an added gelatin placebo (200 mg/d) for the final 3 days. Following a brief washout period, Ss consumed creatine (0.4 g/kg/d) for 5 days, with added caffeine (200 mg/d) for the final 3 days. Treatments were randomized and double-blind.
31P NMRs of the forearm flexors and a maximal intermittent exercise fatigue test of a wrist curl were performed. The exercise test consisted of 3 x 30-s maximal wrist curls on a 3-minute-rest interval. The two swimming tests were 1) 6 x 8-s tethered resistance swim to measure the amount of force generated and, 2) 6 x 50 y on a 3-minute interval for performance time.
Muscle Pcr concentration or resynthesis did not change across treatment conditions. Total force increased significantly under creatine plus caffeine, but not under creatine alone. Performance time was significantly faster after creatine, but was not as fast for creatine plus caffeine.
Creatine supplementation markedly improved swim performance time when 3-min recovery was provided between repeats. This ergogenic effect was not seen when the exercise recovery was approximately 30 s. Conversely, creatine plus caffeine significantly improved force generation with 30-s recovery. This effect was not seen when the exercise recovery was about three minutes. The 31P NMRs was not found appropriate for measuring Pcr resynthesis. These results await further confirmation in a subsequent study using a larger number of Ss.
Implication. Creatine affects swimming performance when inter-repeat rest intervals are long (> 3 minutes), but not when the rest intervals are short (> 30 seconds).
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