The short-term enhancement of physical performance known as post-activation potentiation could be exploited in the design of sport-specific training sessions. The purpose of this study was to compare the potentiation of softball throwing velocity following two kinds of resistance-training session: a control session consisting of traditional heavy-load sets, and an experimental "Pmax" session consisting of sets of loads selected to maximise the mean power output during explosive bench presses. Both sessions included plyometric medicine ball chest passes. Eight male softball players of premier grade, with at least 2 yr experience of resistance training, performed the two sessions in a crossover fashion, with 30 min recovery between sessions. Softball throwing velocity was measured with a radar gun immediately before and at 2-min intervals 4-10 min after each session. Percent effects on throwing speed were analyzed via log transformation, and t statistics were used to make magnitude-based inferences with respect to the smallest important change of 2%. The average throwing velocity increased between pre and post tests for both treatments; the average increase was a substantial 2.3% (0.5 to 4.1%). Throwing velocity after Pmax training was a trivial 0.4% slower relative to that after heavy-load training (90% confidence limits -1.2 to 1.9%). There was a greater change in throwing velocity by 10 min post treatment than by 4 min post treatment; the change by 10 min was 5.0% (3.2 to 6.7%) for the Pmax training session and 5.3% (2.1 to 8.6%) for the heavy-load session. These effects were almost certainly beneficial for throwing speed, but the difference between them was unclear (-0.3%; -3.7 to 3.1%). The mean change between 4 and 10 min for both treatments combined was 5.1% (90% confidence limits 3.6 to 6.7%). The short-term enhancement of throwing performance following heavy-load and Pmax training sets has implications for the design of softball warm-up routines. There is also the potential for softball players to use such training to improve their throwing velocity during games.