In previous research we have shown that an acute caffeine dose of 5 mg/kg body mass reduces heart rate at rest and during low intensity exercise, with the effect dissipating as exercise intensity increases. If, as suspected, the effect at rest and at low intensities is due to an effect of caffeine on parasympathetic activity, this is likely to be reflected in an increase in heart rate variability (the beat-to-beat fluctuation in heart rate). The aim of this study is therefore to investigate the effect of caffeine on heart rate and heart rate variability at rest and during submaximal exercise.

Inclusion Criteria:

• Trained cyclists

Exclusion Criteria:

• Injured or a contraindicative medical condition