First of all the term “trail side” simply refers to the side of your body furthest away from the target, so for a golfer setting up in a right handed position the trail side is the right hand side of the body.
In all sports that use a rotational sequence to generate power one of the key moves is to shift weight off the trail side. This weight shift in some sports is more natural because there is natural linear step towards the target. If you can picture a baseball hitter, there is a little step forward with the left foot that then initiates the rotational movements. Another example is a cricket batsman playing a powerful shot, they will often move forward with the front foot and then initiate rotational movement with the hips.
In the golf swing it’s easy to get over focused on the rotation so that the lateral weight shift doesn’t happen and as a result we lose effectiveness. One of the things that can help some golfers is to focus on releasing the trail side of your body all the way through.
Another image from another sport that may be useful is of a boxer throwing a powerful punch with their trail hand. Notice how even though the body has turned the weight has come all the way off the right side allowing the full force to be delivered at the target. The other important thing to point out and although it is just an image, is the balance the picture portrays.
If we look at the image of the golfer we can see a lot of similar characteristics in the finish position
I recently saw a video of Tiger Woods talking about the development of his golf game and swing in his early years. One of the things he referred to was the power in his swing and he mentioned that his dad had encouraged him to hit the ball hard off the tee but only he could achieve two things.
That he hit the ball from the center of the club
That he finished his swing in balance
Something you can try the next time you get an opportunity is to take a practice swing and hold the top of your backswing for a second or so to make sure you are in balance at this point. Then take your forward swing through to follow through and hold it. Focus on where your weight is, make a point to observe if your trail side has been fully released or whether you are hanging back. When you are happy with the finish try it with a ball and see if you can achieve the same feeling of a fully released, balanced follow through.