The transition, bio mechanically speaking, is probably the most important phase of the baseball/softball swing. The transition starts when the first segment of your body changes its direction of rotation, and ends when the last segment of your body reverses its motion. It is the shortest space of time leading up to the load, the point at which the barrel changes direction. It is the sequence where the hitter transitions from the load to the launch of the swing.
A bio mechanically efficient transition starts at the bottom and works its way up, going from the hips to the chest, the lead arm, and finally the bat.
The swing progresses in time from the left to the right. Negative rotational speed indicates the load. Positive rotational speed indicates movement towards the ball in the swing.
From the graph, you can see that the hips change direction first, then the chest, then the lead arm, and finally the bat.
The transition sequence shown in the graph above, is bio mechanically correct as far as the order is concerned. A good transition order is hips, chest, lead arm, and then the bat. In the first half of the transition, the hips are rotating towards the baseball, while the chest, arms and bat are still loading.
The hips should rotate towards the baseball faster than any other part of the body from the beginning of the transition, until just before the bat changes direction. The rotation of the hips towards the target, while the chest is still rotating back, and the fact that the hips keep moving faster than the chest for sometime after, creates the transitional spine stretch. The longer the hip curve stays above the chest curve, the more the spine stretch is increasing, and thus the more power the hitter is able to generate with the large muscles of his core.
Next, we can see that halfway through the transition, the chest starts turning back towards the baseball, while the lead arm is still loading. The turn of the chest ahead of the lead arm causes the shoulder to stretch, as the shoulder angle closes.
Finally, we see that the lead arm works towards the baseball while the bat is still loading. The longer that the arm moves faster than the bat, the more the wrist is stretching, and the more bat lag is generated. Each body segment in the chain lags behind the one inside it. The bat lags behind the lead arm, which lags behind the chest, which lags behind the hips.
As we see, the hips get a good head start. They load first, well before the chest, and then lead the way throughout the transition. This is important because you need time to stretch the big muscles in your core for maximum power.
Understand that this process happens very quickly and the transition can’t be rushed, but if the hitter takes too long, he will be losing the full benefit of the muscle stretches generated during this phase.