As far as the ergodicity of caffeine is concerned, a recent study which was part of Jared Coburns dissertation at the California State University (Coburn. 2010) suggests that these must be more of a systemic nature. Comparing the effects of a preworkout drink with either 0, 5 or 10 mg/kg caffeine Coburn found
no significant differences for maximal strength, RTD [rate of torque development], EMG [electromyographic] amplitude and frequency, MMG [mechanomyographic] amplitude, EMD [electromechanical delay] and PMD [phonomechanical delay]in his 14 male volunteers. So, while related studies, such as the one done by Pontifex et al. (Pontifex. 2010), where athletes had to perform several consecutive bouts of sprinting, provide evidence for the ergogenic effect of caffeine, it does not appear to benefit isometric muscle actions of the elbow flexors within a single set - in how far the results would have been different, if, for example, the subjects had had to perform dropsets is another kettle of fish.