I am by no means a "Ma Long copy" nor can I "loop like him" but I don't believe in the magic of the stroke, and anyone can learn it as long as they can perform the mechanics with their body.
The easiest way to start is to first have Ma Long's body proportions to 98% or closer. The best coaches in the world showing you your faults also help.
Joking aside, I am very, very, very close in proportions, but still not exact, obviously. So the first thing is to consider if the stroke is even smart to learn for your body mechanics! Bear in mind you also need to be in quite good shape and be able to control your muscle firing orders and amounts subconsciously to really get everything out of the stroke.
Assuming you're 190cm, weak and lanky and still want to learn it, good. Proper mechanics are always good. You will need to develop your own unique technique later, though. Hate to break it to you. The basic mechanics are still very sound.
I will go over my findings step by step and give my own reasoning for why something is done. I do not have footage and pictures, nor can I provide any in any good quality to be considered valid, so just go and film yourself and compare it to Ma Long with frame by frame analysis.
This is assumed for a right handed player. Switch leg and arm positions accordingly.
Assumed to be looping a block, drive or long push. You must perfect that first, and you will learn to do loop backspin and counterloop etc. naturally by comparing.
Backswing - Lower body - Feet
The stance is wide, with the left foot rotated anywhere from a bit "outwards" from the direction of the knee, to slightly inwards. Ideally it is exactly at 0 degrees forward. The right leg is far back, farther than you think, and the feet form a nearly 90 degree angle. It is slightly under 90 degrees usually. The angle between the left foot and right foot's facing is NOT 45 degrees. It is far more.
Backswing - Lower body - Legs
This is a hard one and it will probably be too physically demanding for most people until they get used to it. It's also difficult to consistently do right at first. This is where the power comes from.
The easiest way to do this, keeping in mind it's dynamic, is to place your feet in the right position, then bend your knees until you legs form 45 degree angles behind the knee. You MUST also place your weight on your soles, and lift your heels very slightly.
A common mistake is to have the right angle, but be standing on your heels. This will result in a straight back and no power due to it.
You know when your feet and legs are in the correct position when it feels quite physically demanding and maybe strange to be in this position at first. You should feel it in your thighs and ankles.
The best way is to really just do what I say, then take a picture from the same angle as a picture/video of Ma Long and copy the angles to make it correct. Obviously, longer or shorter legs or proportion of upper leg to lower leg WILL change the angles and it cannot be absolutely set in stone.
Backswing - Upper body - Trunk and hips
Your back should be bent until you feel considerable load on your right sole. Your chin will be approximately in the same line as your right knee. Then, curl your body to the right, so your upper body forms a roughly 45 degree angle viewed from the front. Your hips are also slightly curled to the right, but don't twist excessively.
Don't lean too much forward, don't keep your back straight and don't rest all your weight on the bones of your right leg.
Best way to get this right is picture comparison.
Backswing - Upper body - Racket arm
Once you're in the backswing position, place your right arm so that your shoulder is slightly lowered, your elbow is tucked into your body but without touching your side, and your forearm is at the same angle and "hovering" over your right thigh in the same axis. The wrist is naturally bent so that you get a whipping motion on the swing. Look at pictures.
This varies greatly, but that's the generic backswing that I've seen. The arm is quite bent, definitely not 180deg. Of course, it depends. That is why you must compare pictures and find it out yourself via experience. The generic starting position with the same angles is a good start.
People tend to extend the arm too much, opposed to not enough. The elbow is usually also not tucked in. The arm needs to be bent just right for timing and speed, and the elbow needs to be tucked in for faster movement and a more economic stroke.
Nail the basics, then adjust based on the ball you're hitting.
Backswing - Upper body - Supporting arm
You might have noticed Ma Long doesn't just keep the arm idle. The arm is brought along the body so that the angle is roughly 45 degrees or so and the elbow is over the crotch, and the wrist is over the right knee. Roughly. Your racket arm, supporting hand and shoulders should form closer to a triangle shape from above, opposed to a box.
You want to keep the arm close to your body, and not reach out with it. It's also not at all set in stone exactly how the arm is positioned. Generally, make sure you're bringing the arm across your body and your hand isn't hovering at your stomach like in a drive.
Backswing - Head and shoulders
The head is looking quite to the side. You want to be looking more to your side than where your torso is pointing, for the right timing. Your shoulders should be relaxed and at a 45 degree angle or so from the playing direction.
Swing geometry and mechanics up to contact
Here is where it gets hard, of course. Seriously, just take a slowmotion video and pause it at spots and place yourself in them to see how it feels. Then remember that feeling and try to stroke the stroke, and keep being super anal and analytical with it until it's your default stroke. It'll take very long to really get it right.
For me to explain the exact angles at the exact timings is completely useless. It changes as soon as the spin and placement on the ball changes.
So let me just try to explain the feeling.
After backswing, the racket arm raises a bit, closes the angle automatically and starts swinging forward like a whip. The arm is kept relatively straight compared to where it was on the backswing, you're NOT bending from your elbow to stroke, you're whipping with your shoulder and the forearm follows. The wrist will do the whipping itself if you're not tense.
The geometry is slightly concave and the angle is generally the same when viewed from the side. It's whipping, NOT throwing a ball underhand. Also, don't raise your shoulders. It's a bad habit, and Ma Long doesn't do it because it doesn't add anything except neck injuries. I know from experience.
Your left shoulder does not go up on the stroke, it goes to the left and you must actively pull with the left side of your body while pushing. The elbow is close to the body and pulls to the left.
This will come with time and comparing videos until you get the feel. Make your hand into an aerodynamic shape and tense it very slightly on contact so that the blood doesn't pile up into your fingertips when you pull to avoid tingling and numbness and you have less resistance from the air when pulling it back. (I can pull very hard and the blood piling and drag is a real issue.)
Your fingers should point to the side on swing, and up on the follow through, then go back to the starting position in an oval motion.
With your legs, you transfer load forward and your legs naturally bend around the axis. Your feet shouldn't shuffle around, changing angles too much in the basic relaxed stroke. Your feet do point more to the left when swinging and revert back more to the right after the stroke.
You rotate on your soles, you don't keep your feet completely glued to the floor. Load transfers forward and from the right leg to the left, and your leg angles change.
Again, use videos. It changes on every variation of stroke and to compensate for being slightly out of position.
The trunk is rotated, and follows with the legs. I don't have this as good as I like, myself, so I can only instruct you to refer to Ma Long himself to see what's too much and what's not enough. It's very easy to extend too much and actually risk hurting your lower back.
Just as your start swinging, tense your abs fully, then relax them exactly as you make contact. Snap your elbow rapidly at contact, this brings the power.
Directly after contact
Your body will be higher, but you will still be leaning forward with legs bent. Your torso will be facing more forward.
The balance arm is pointing up and tucked to your side, and the racket arm is bent 90 degrees or so and roughly vertical. It is extremely important for stroke mechanics and to avoid neck and shoulder injury to NOT raise your shoulders.
I can't say much about contact and follow through because it's such a subconscious thing that you really just need to learn the correct starting position first, then tie it all in from there, comparing videos and pictures from videos with you performing the stroke slowly and at full speed.
Don't expect your stroke to look anything like his in even a week, but you should see and feel a little bit improvement every day. The key is to be very analytical and a good physics understanding also helps.
If your stroke is not any good before, then this will feel quite weird at first, but it's actually quite relaxing once your form is better.
Whatever you do, don't just film yourself and go on feel based on how it looks. Actually make reasonably accurate comparison pictures of you and him both doing drills and playing and really look at the details. Things like how much you raise your shoulders, the geometry of your swing, angles of your legs, angle of your back etc.
You can't fully copy his technique unless you have the exact same composition down to the last muscle fiber, but many aspects should be common between your good stroke and his good stroke.
Also know that you're not going to be looping like Ma Long even if your form is like his, so don't try to copy everything down to the last radian and expect to hit through professionals immediately. It's a very subconscious stroke based on exquisite timing and muscle firing in the right sequence and amount.
You may now proceed to discredit everything I just typed.
I did my best to include everything I know that isn't too advanced and redundant for it's own good. You'll figure everything out if you have a good physics knowledge and can perform a reasonable stroke.
You also don't need a pro grade tuned Chinese rubber to do this stroke, you can do it with pretty much anything standard inverted, even rubbish premades. So if the ball slams into the net, please don't change your rubber. Change your mechanics. Practice with a slower wooden bat.
EDIT: Oh, I forgot to mention, but you need to
really be in good shape. Shoulder injuries and neck injuries are very common, especially when you're starting out and you're trying to muscle it too much. Take it slow first and go to the gym regularly.
