Time Course and Magnitude of Tolerance to the Ergogenic Effect of Caffeine on the Second Ventilatory Threshold.
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2020
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Life
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Abstract
Pre‐exercise caffeine ingestion has been shown to increase the workload at ventilatory
threshold, suggesting an ergogenic effect of this stimulant on submaximal aerobic exercise.
However, the time course of tolerance to the effect of caffeine on ventilatory threshold is unknown.
This study aimed to determine the evolution of tolerance to the ergogenic effect of caffeine on the
ventilatory threshold. Methods: Eleven participants (age 32.3 ± 4.9 yrs, height 171 ± 8 cm, body mass
66.6 ± 13.6 kg, VO2max = 48.0 ± 3.8 mL/kg/min) took part in a longitudinal, double‐blind, placebocontrolled,
randomized, crossover experimental design. Each participant took part in two identical
treatments: in one treatment, participants ingested a capsule containing 3 mg of caffeine per kg of
body mass per day (mg/kg/day) for twenty consecutive days; in the other treatment, participants
ingested a capsule filled with a placebo for the same duration and frequency. During these
treatments, participants performed a maximal ramp test on a cycle ergometer three times per week
and the second ventilatory threshold (VT2) was assessed by using the ventilatory equivalents for
oxygen and carbon dioxide. Results: A two‐way ANOVA with repeated measures (substance x time)
revealed statistically significant main effects of caffeine (p < 0.01) and time (p = 0.04) on the wattage
obtained at VT2, although there was no interaction (p = 0.09). In comparison to the placebo, caffeine
increased the workload at VT2 on days 1, 4, 6 and 15 of ingestion (p < 0.05). The size of the ergogenic
effect of caffeine over the placebo on the workload at VT2 was progressively reduced with the
duration of the treatment. In addition, there were main effects of caffeine (p = 0.03) and time (p =
0.16) on VO2 obtained at VT2, with no interaction (p = 0.49). Specifically, caffeine increased oxygen
uptake at VT2 on days 1 and 4 (p < 0.05), with no other caffeine–placebo differences afterwards. For
heart rate obtained at VT2, there was a main effect of substance (p < 0.01), while the overall effect of
time (p = 0.13) and the interaction (p = 0.22) did not reach statistical significance. Heart rate at VT2
was higher with caffeine than with the placebo on days 1 and 4 (p < 0.05). The size of the effect of
caffeine on VO2 and heart at VT2 tended to decline over time. Conclusion: Pre‐exercise intake of 3
mg/kg/day of caffeine for twenty days enhanced the wattage obtained at VT2 during cycling ramp
tests for ~15 days of ingestion, while there was a progressive attenuation of the size of the ergogenic
effect of caffeine on this performance variable. Therefore, habituation to caffeine through daily
ingestion may reduce the ergogenic effect of this stimulant on aerobic exercise of submaximal
intensity.
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Keywords
Exercise performance, Sport performance, Endurance performance, Nutrition, Endurance athlete