Here is an exercise I do in the gym to help cultivate muscle stiffness. The downswing only takes about 0.3 seconds, so long big slow jumps won’t transfer as well to golf. The idea here is to create muscle stiffness as you hit the ground and explode up as quickly as possible. Muscle stiffness is not tightness. It is the ability to purposefully create rigidity when needed. In this example the force of stepping off, does not buckle you. Remember that you are trying to hit back against the ground as you hit it. You don’t step off, let the ground hit you, then jump. You are anticipating the ground and hitting back. This is a great exercise not only to help with those fast twitch muscles but also works on Neuro Muscular speed which is the ability for the brain to send a message to the muscles faster. If you don’t have access to a gym, you could use a sturdy table or a step to jump off. This is an advanced exercise for people who already have a good base of strength and training experie...