Effect of caffeine on motor performance by caffeine-naive and -familiar subjects.

The purpose of this investigation was to assess the effect of caffeine on selected manipulation skills by caffeine-naive and caffeine-familiar subjects. The subjects were 20 caffeine-naive (less than 90 mg/d) and 20 caffeine-familiar (greater than 750 mg/d) college-age (21 +/- 1.7 yr.) women. Measurements included steadiness error time and frequency, duration of tracing, error time and frequency, and dexterity. Doses of 2.5, 5.0 mg.kg-1 body weight caffeine or a placebo (200 mg. methylcellulose) were administered randomly to all subjects on three separate occasions. A 2 x 3 repeated-measures analysis of variance yielded a significant group difference for steadiness error time between the 5 mg.kg-1 and 2.5 mg.kg-1 dose and between 5 mg.kg-1 and the placebo. For frequency of steadiness errors, the nonuser group posted significant gains for both 5.0 and 2.5 mg.kg-1 over the placebo control. On tracing error time and error frequency, 5.0 mg.kg-1 resulted in significant increases from both 2.5 mg.kg-1 and the placebo group. In the caffeine-naive group, both doses of caffeine led to significant increases in dexterity time from the placebo, and the 5.0 mg.kg-1 dose was significantly different from the 2.5 mg.kg-1 trial. It was concluded that caffeine had detrimental effects on selected performance skills of caffeine-naive women but not in caffeine-familiar women.