Do muscle fibres get "faster" when you perform a strength exercise explosively?

Contrary to popular belief, "explosive" training makes the muscle fibres slower at the level of their molecular motors (a switch from muscle fibre type 2X to 2A). Inactivity (voluntary or forced) makes the muscle fibres "faster" (a switch from 2A to 2X). It's assumed that, in humans, crossing the boundary between type 2 and type 1 is unlikely under normal circumstances. Endurance training therefore, contrary to popular belief, does not on average lead to an increase in type 1 fibres.
Summary of muscle fibre type changes

Figure 1: Image reproduced with kind permission from Dr. sc. nat. Marco Toigo

We therefore also recommend that competitive athletes perform the exercise slowly, in a controlled way and through the greatest possible joint range of motion. On the one hand, having many sarcomeres in series is certainly beneficial for being fast at the muscle level (see the blog post Force-Length Relationship). It also takes an adequate muscle mass (parallel sarcomeres) relative to the mass being moved, or relative to the external torques to be overcome. In addition, muscle force decreases as shortening velocity increases (see the blog post Velocity-Force Relation).

It is indeed likely that, with appropriate training, the RFD (rate of force development, i.e. the increase in force per unit of time) can be increased on a machine. Unfortunately, however, it remains completely unclear what physiological significance this might have for everyday movements. What sport-specific training actually achieves has barely been studied, because measurement methods in the field are often problematic.

Sources: Zurich Forum for Applied Sport Sciences Discussion 2011, Force Theory, Scientifics AG