CAFFEINE EFFECTS ARE MODIFIED BY STATE OF FATIGUE OF MUSCLES
Lewis, S. F., Soares, R., Lammi, E., Baker-Fulco, C., Lieberman, H. R., & Fulco, C. S. (2001). Knee extensor muscle endurance and caffeine dose before and after exhaustive dynamic exercise. Medicine and Science in Sports and Exercise, 33(5), Supplement abstract 927.
The effects of caffeine dosage on endurance of both non-fatigued and previously exhausted muscles were studied in soldiers (M = 7; F = 2). Ss performed four pairs of 2-leg constant work-rate tests isolated to the knee extensor muscles of each leg. One pair of tests was performed each week for four weeks. The first test was with fresh muscles and the second was conducted one hour later from the point of exhaustion of the first. Work rate was identical for all tests. Test pairs were as follows: placebo - placebo; low caffeine (2.5 mg/kg) - placebo; high caffeine (5 mg/kg) - placebo; and placebo - high caffeine.
With fresh muscles, low and high caffeine conditions produced 40-50% longer endurance times than placebo. After exhaustion, endurance was 75% longer for placebo after high caffeine than after placebo. Endurance time for low caffeine was significantly shorter after fatigue than in the fresh condition. Endurance time for placebo following high caffeine was similar for both fresh and fatigued states. Thus, for fresh conditions, low and high caffeine doses produced the same performance effects. After exhaustion, the high caffeine dose produced significantly greater performances than low.
Implication. In non-fatigued states, low doses of caffeine are as effective as high doses for producing an ergogenic effect. After fatiguing exercise, higher doses of caffeine are more effective than low doses for performance improvement.
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