Force-Stretch the Pumped Muscle
Your normal calf training workout should leave you with a massive pump throughout the entire lower leg. But don't stop there or you'll be missing an opportunity for growth.
Directly after your last set of calf exercises, force your calves into a hard, heavy stretch with an extended knee and terminally dorsiflexed ankle joint. You must literally force your calf to stretch with as much tension and force as you can generate.
Here are two methods to accentuate this stretch:
Forced Single-Leg Bodyweight Calf Stretch
This stretch uses a single-leg setup. Alternate between stretches for each side.
Machine Loaded Forced-Calf Stretch
The one is a machine-loaded stretch through both legs at once. Be sure that the setup allows you to reach terminal dorsiflexion at the ankle and your feet are symmetrical in stance.
How Long Do I Stretch?
For each of these forced stretching techniques, you're going to force the stretch for as long as humanly possible to maximize time under tension. Again, setup is huge on these, as a poor setup will leave you vulnerable to injury. The knee always needs to be in perfect alignment with the ankle and hip.
Go through as many rounds as you can tolerate. Usually 2-4 rounds is about all people can take. Many times, forced stretches will span something like 90 seconds on the first round, 60 seconds on the second round, and 30-45 seconds on the last round before the lifter mentally breaks down. You can use those numbers as a starting point.
The harder you push it, the more you'll grow. Keep that in mind when the pain from these forced stretches make you want to quit.