Here's a video (3:56) of all-time great Ma Long looping forehand, including slow motion. (It starts with one backhand loop - which you should also study! - and then goes to forehands.)
Note in the video how he basically rotates his body around an imaginary vertical rod going through the top of his head, with his head only moving slightly forward, and how he contacts the ball almost directly to the side of his body? Many players violate one of these principles, either moving the body forward too much as they do the shot, or (even more common) contacting the ball too far in front.
There are times when you should move the body more forward on a shot, such as against an easy high ball or when you are rushed in stepping around the backhand corner, but normally you should go more in a circle. This both gives you great centripetal force as you rotate around, but also leaves you in position for the next shot, balanced and ready, which is how top players can play power shots over and over in quick succession.
But as noted above, the more common problem is that players tend to contact the ball too far in front. This either keeps them from rotating backwards fully (and so losing power), or forces them to reach for the ball (thereby dissipating power and putting you off balance).
Also note how the legs (and especially the knees) are used to rotate into the shot. The legs aren't just for standing; they are the primary start to every shot, and give you the pivot into your shots.
Here's a 13-second video of Japanese sensation Tomokazu Harimoto as a kid, knocking balls off a table. (He's now world #5, and the best in the world outside China, circa March 2020.) Note the same principle - he rotates in a circle and contacts the ball directly to the side of that imaginary rod going through his head. You can see the same principles in this 46-second video of 3-time World Men's Singles Champion Wang Liqin (2001, 2005, 2007), demonstrating "The shot that owned a decade."