Ryan, A. K., Dawson, M. L., Zabik, R. M., & Frye, P. A. (1999). The effect of caffeine on reaction time, hand steadiness and specific physiological variables. Medicine and Science in Sports and Exercise, 31(5), Supplement abstract 450.

High- and low-caffeine users were evaluated for heart rate, blood pressure, reaction time, and hand steadiness after consuming 345 mg of caffeine in a 5-min period. Measures were taken at 30, 60, and 90 minutes after ingestion.

It was found that caffeine did not increase heart rate, increased systolic blood pressure at 60 minutes, increased diastolic blood pressure at 30 and 60 minutes, decreased reaction time in the high-caffeine group, and had not effect on hand steadiness.

Implication. Caffeine primarily affects blood pressure measures.

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