Introduction:
Caffeine increases heart rate by increasing sympathetic activity and it may also delay post-exercise cardiac recovery.

Aim of the study:
The present study investigates the effect of different caffeine doses on autonomic control and fatigue indexes after high-intensity endurance exercise.

Material and methods:
Twelve trained males (20.7 ± 1.9 years; 72.4 ± 4.8 kg; height 1.7 ± 0.0 m; body fat 14.6 ± 2.2%; VO2max 50.9 ± 3.3 ml/ kg/min) were assigned to three trials of 6 or 9 mg/kg caffeine dose or placebo. The protocol included running on a treadmill for 12 minutes at 75% VO2max, followed by 60 minutes of recovery. Heart rate variability (HRV) indexes such as root mean square of successive differences (RMSSD), low frequency (LF), high frequency (HF), and LF/HF were recorded initially, 30 minutes after supplementation, and 0-5, 15-20, 35-40, and 55-60 minutes post-exercise. Systolic and diastolic blood pressure (SBP and DBP) and rate pressure product (RPP), rating of perceived exertion, and perceived pain index were measured during recovery.

Results:
RMSSD was significantly lower during the 0-5 minutes of recovery interval in the placebo condition compared to the 6 mg/kg caffeine dose (P = 0.017). LF, HF, and LF/HF showed no significant changes compared to the placebo trial. A significant decrease in SBP was observed up to 20 minutes of the recovery period in placebo compared to two caffeine doses (P < 0.003). RPP was significantly lower up to 20 minutes of recovery in placebo compared to the 9 mg/kg caffeine dose (P < 0.002).

Conclusions:
It is shown that the acute effect of caffeine can delay blood pressure recovery after endurance activity but does not affect the HRV frequency domain, fatigue, and RPP indexes.