A German study has shown that using 7mg of caffeine per kilo of body weight, increases the mind to muscle activation of muscle.
Caffeine was shown to increase the activation of muscle at the start of the contraction but does not increase strength nor absolute activation.
This is more important in reaction sports (such as a goalkeeper in football) as it allows them to move more explosively rather than move a given weight around.
Whilst less important in the gym, caffeine can therefore be said to be useful for those where speed of reaction is important.
Taken from Scandinavian Journal Medicine Science in Sports, May 2014.